Re: Topband: The WD8DSB mini-flag antenna
Correction to my previous comment. I didn't realize that the mini-flag impedance is close to 50 ohms resistive at all frequencies of interest. Therefore, the 50 NF of any amplifier is also the NF that applies when connected to the loop. The 50 ohm source impedance is a due to a physical resistor with a physical temperature of 300K, therefore the noise temperature of the system will never be less than 300K. It is easy to find an amplifier that gives a sensitivity within a few dB of a hypothetical noiseless amplifier. Rick N6RK On 2/24/2021 4:53 PM, Richard (Rick) Karlquist wrote: > 6. NF is source impedance dependent. Measuring the NF with a 50 ohm source doesn't tell you anything about the effective NF when terminated with the loop impedance (which is no where near 50 ohms resistive.) _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna (LONG!)
main lobe. This calculation assumes the atmospheric noise has a uniform distribution over all of space, which is probably not exactly true but we’ll make that assumption to get a ballpark result. Note that an ideal lossless antenna would have an average gain of exactly 0 dBi, which, by definition, is the gain of an isoptropic radiator. That results falls out from the concept of antenna gain averaged over all of space. One caveat: the assumption of uniformly distributed noise is definitely not true for local man-made noise, which comes from specific directions and propagates via groundwave at essentially zero elevation angle. The EZNEC average gain calculation uses a far-field antenna gain pattern and does not take groundwave into account. Next I created an EZNEC model of the DXE mini-flag and found it has an average gain of about -72 dBi on 1.8 MHz. Because this is 65 dB lower than the average gain of my transmit vertical, the mini-flag should theoretically deliver 65 dB less atmospheric noise, or -185 dBm/Hz, to the receiver. I make no claim these are super-accurate numbers but it’s the best I can come up with, at least at my location. It does give an idea of the magnitude of the problem we’re dealing with when it comes to noise limits. Because I already calculated/measured the thermal noise floor of my system as -171 dBm/Hz, the atmospheric noise floor level from the mini-flag at my QTH will be about 14 dB below thermal noise. That means the atmospheric noise will be swamped by thermal noise in my electronics and not vice versa. The higher atmospheric noise at night will be somewhat closer to thermal noise but probably not enough to change the conclusion here. Thermal noise will limit one’s ability to hear very weak signals with this antenna. This might be improved marginally with a preamp with a lower noise figure but 2.3 dB is already getting close to the limits of what can be achieved practically. More preamp gain, without an improvement in noise figure, will not improve weak signal reception. This finding confirms what others have stated about very low gain receiving antennas being limited by thermal noise. If you have an antenna with a different gain than the mini-flag, you can substitute its average gain into the calculation I just did. EZNEC says the gain of the mini-flag increases about 10 dB for each doubling in frequency above 1.8 MHz. This means you start to have a chance of beating the thermal noise limit with this antenna at higher frequencies, maybe 7 MHz or above, depending on the ambient external noise environment. For direction-finding purposes, you generally don’t need the ultimate in low-noise reception. You only need the DF antenna to be good enough to hear the signal or interfering noise source well above whatever noise is in your receiver. For this purpose, the WD8DSB mini-flag should work great in most situations. I welcome any comments about this analysis and these results. 73, John W1FV From: Don Kirk [mailto:wd8...@gmail.com] Sent: Wednesday, February 24, 2021 3:33 PM To: john.kaufm...@verizon.net Cc: TopBand List Subject: Re: Topband: The WD8DSB mini-flag antenna Hi John, You started this mess (or maybe I did), and finally here is my response to a few of the questions you had and thanks so much for waiting in line for my response. 1) As I have mentioned in a few other responses I suspect having the short 10 foot feedline helps to negate common mode noise and direct signal ingress into the feedline that often haunts us. I do have one recommendation about pattern distortion as follows. Check to make sure the peak and the null of the antenna are in agreement on the signal you are direction finding. If you notice a slight skew (where they don't agree with each other), then move away from existing objects and this will correct that problem. I sometimes notice a slight skew when in my backyard near my house (looks like the null shifts slightly from where it should be), and when I get out away from my house (I move to the sidewalk in front of my house) the slight pattern skew goes away. 2) I don't know what the DX Engineering preamp noise figure is, and there definitely is no expectation from the designers standpoint that it's spectacular. Even though I did most of the field testing of this preamp I have no idea what the amplifier part of the circuit is as DX Engineering tightly controls their designs. 3) My antenna does not have a long mast, and it easily fits in the back seat of my very small 1996 Saturn Station Wagon. It fits widthwise in my backseat, and I have to imagine it will do the same in almost any car since my car is about as small as they come. Looks like the DX Engineering version of my antenna has a longer mast, and that can easily be shortened if it helps you fit the antenna into other areas of your vehicle. I only use
Re: Topband: The WD8DSB mini-flag antenna
>> 1. I am specifically talking about "small" loops. The antenna in question is not a "loop" it is a terminated loop, the diagram is a cardioid, it is very broadband 1-10, like 1 MHz to 10 MHz or 3 o 30 MHz with the same irradiation diagram. The behavior is comparable a two dipoles in phase. Thermal noise is low as the resistor. >> 2. In small loops, the ohmic dissipation of the conductor vastly overwhelms >> the tiny radiation resistance. Yes , but loads loop is based on reflected wave and the one direction current dissipate on a 1K resistor ( gives you the front back and the other direction the current see a 9:1 Balun. Again it is not a loop the Q is very very low because it is broadband, >> 3. This is unlike a vertical antenna or a dipole, which can be considered >> non-dissipative. Again it is not a loop with high current and high Q or a tunned loop, it is very broad band the BW is over 10 MHz. >> 4. Therefore, if the conductor is at a physical temperature of 300K, its >> Johnson noise will correspond to that temperature. The voltage is not over the wire in on the termination due the high SWR, one side is dissipated, the one you don’t use and the other is a transformer. >> 7. It is extremely easy to get a 50 ohm NF of 0.5 dB with a BF981 at 88 MHz >> as specified by its data sheet. All you have to do is transform the 50 ohm >> source so that it loads the FET with about 1,000 ohms. I did this 40 years >> ago. Unfortunately, at 1.8 MHz, the flicker noise of the BF981 dominates, >> so you can't get the low NF down there. >> 8. I did this same experiment with the multiple paralleled BF981's over 15 years ago and was limited by flicker noise, which is unspecified, YMMV. Maybe you had better devices than I did. > pair of phase loops. A/B tests with NORTON preamps show not possible > to copy the weak signals I did copy with my 6xBF981. Here I agree, I was luck , I was not expecting 43 db gain. I was looking for a good input filter and I used a T240-6 with litz wire for a Q over 500. The impedance of a 3T to 11T inductor and a very high Q provide a voltage gain at eh input , the transconductance of the gates doe the work and I got a 43 db gain single stage preamplifier with a very high IP3, the BW just enough for 40 Khz, but the extra gain make the preamp usable for 1.8 to 1.9 mHz. >> Considering that the input of the preamp is deliberately connected to the >> antenna, it is hard to imagine what signal the shield is shielding the >> amplifier from. Large BCB signals out of band coming up the feedline? Is >> the shield still needed for QTHs that have no nearby BCB stations? Not at all, the amp is very well protected below my desk, inside a galvanized steel box, inside an aluminum box and the preamp inside a tinplate box. My HWF a phase pair or loaded loops, reject vertical noise with a 50 db null at the direction of the maximum horizontal gain. Adding a negative gain over 40 db, the rejection of any vertical signal is over 90 db, no manmade noise or BCB in below the MDS of my system. All my cables run inside metal conduit too. The transmit vertical is a folded UNIPOLE and I use the skirt to detune the TX antenna during RX. You can find all information on WWROF webinar archive. 73's JC N4IS _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
On 2/24/2021 12:26 PM, n...@comcast.net wrote: Hi Rich " The problem here is that any loop antenna inherently has a noise temperature of 300K, because it is lossy, and because it "sees" the earth" Would you elaborate on that? Small loop 1/10 of wave length works very different from a loop or large loop. I experimented with a large number of Local noise is the most misunderstood figure. On top-band during a winter Sunday morning the noise can be low as 70K. On topband the only source of nom mam made noise atmospheric noise. No atmospheric activity means no noise. Yes it is that low. I am using horizontal phased loops for almost 15 1. I am specifically talking about "small" loops. 2. In small loops, the ohmic dissipation of the conductor vastly overwhelms the tiny radiation resistance. 3. This is unlike a vertical antenna or a dipole, which can be considered non-dissipative. 4. Therefore, if the conductor is at a physical temperature of 300K, its Johnson noise will correspond to that temperature. (-173 dBm/Hz). IOW, the antenna's noise temperature will never be less than 300K. 5. If we were to put a loop in "free space", meaning outer space, where there is no noise besides the 3K cosmic background noise, it would still have a noise temperature of 300K, assuming that the physical temperature were somehow maintained at 300K. 6. NF is source impedance dependent. Measuring the NF with a 50 ohm source doesn't tell you anything about the effective NF when terminated with the loop impedance (which is no where near 50 ohms resistive.) still in use here, using 6 BF981 and large Q input filter. It measured .7 db NF including the input tuning filter loss. It does make a difference on signals at noise level. I built one for NX4D and Doug still use it. Making 7. It is extremely easy to get a 50 ohm NF of 0.5 dB with a BF981 at 88 MHz as specified by its data sheet. All you have to do is transform the 50 ohm source so that it loads the FET with about 1,000 ohms. I did this 40 years ago. Unfortunately, at 1.8 MHz, the flicker noise of the BF981 dominates, so you can't get the low NF down there. 8. I did this same experiment with the multiple paralleled BF981's over 15 years ago and was limited by flicker noise, which is unspecified, YMMV. Maybe you had better devices than I did. pair of phase loops. A/B tests with NORTON preamps show not possible to copy the weak signals I did copy with my 6xBF981. Norton amps are not noted for low NF, so this is a straw man. Maybe they are picking up BCB QRM (see below). Implementation is a different ball game. The .7 db NF preamp needs 3 level of shield including a magnetic shield with steel, just aluminum is not enough, and no open shield at all, a 1 mm gap will ruin your system. You can find information about my preamp on google or WWROF archives. Considering that the input of the preamp is deliberately connected to the antenna, it is hard to imagine what signal the shield is shielding the amplifier from. Large BCB signals out of band coming up the feedline? Is the shield still needed for QTHs that have no nearby BCB stations? 73's N4IS JC 73 Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
On 2/24/2021 12:54 PM, kol...@rcn.com wrote: But I can recommend this: LAN-IQ SDR (Stand-alone SDR) (afedri-sdr.com) Studying the fine print, the stand-alone unit needs either USB power or 7.5-10VDC. I've got a couple of 3 Ah Motorola-branded outboard cell phone battery packs that look like they could work with the right adapter cable. I bought them as back-up batteries for my phone. A google search found a lot of options. 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
The link takes me to a page showing a unit with no display and no tuning knob, needing a computer to run it. I needed to follow a link on that page to find the self-contained unit. http://afedri-sdr.com/index.php/lan-iq-sdr http://afedri-sdr.com/index.php/ordering-information I agree that the LAN-IQ-SDR looks really slick for DF work. Thanks for posting! 73, Jim K9YC On 2/24/2021 12:54 PM, kol...@rcn.com wrote: I have read some negative info on the Malahit (the EBAY clones especially, the Russian originals seem better) but it might be OK for RFI investigations. N9EWO Review : Russian Malachite / Malahit DSP SDR (qsl.net) But I can recommend this: LAN-IQ SDR (Stand-alone SDR) (afedri-sdr.com) This is about $400 with tuning knob encoder but is a small, slick and fairly serious receiver with a 12 bit Direct Sampling receiver on HF (the Icom 7300 is a 14 bit Direct Sampler) and covers from 30 kHz to 1700 gHz with built in Spectrum Display and Waterfall. It runs on USB power (I use a Power Bank that folks use to recharge up their phones). It probably is overkill for just occasional RFI expeditions, but if you like the idea of having a portable wide range RX when not on the RFI hunt), it is well worth it. No connection to the seller (4Z5LB in Israel). He shipped mine promptly, I was surprised how soon it arrived! 73, Kevin K3OX - Original Message - From: Don Kirk To: David Raymond Cc: topband Sent: Wed, 24 Feb 2021 14:23:17 -0500 (EST) Subject: Re: Topband: The WD8DSB mini-flag antenna Hi Dave, I hate to recommend anything and others have given you some good recommendations, nevertheless I will make a few comments. My workhorse radio for direction finding is the good old Realistic DX-440 (also sold as a Sangen ATS-803A) and you can still find nice clean used ones on E-Bay for less than $100 (I suspect I drove the price of them up). It is a very old and large radio, but I love this radio for numerous reasons. It has an external antenna jack as well as an excellent continuously adjustable RF gain control that really comes in handy. It also has a BFO for receiving CW which sometimes is very helpful depending on the signal you are tracking. It uses 6 D cells and has excellent battery life. I use the radio in AM mode for tracking down power line noise, but sometimes I need to use the BFO for signals that are just a carrier as it helps to hear the signal (no need to look at a meter, etc). I also use a laptop based SDR receiver which is just a cheap RTL-SDR dongle along with a ham it up converter (both from NooElec) and I have both of these stuck to the back of my laptop screen so I can go portable with it, and this is a very handy tool especially if the signal is wandering all over the place or if I am in a heavily populated area with lots of different sources of RFI present. If you go this route make sure you pay the few extra bucks for a TCXO in both of them. The IC-705 is also a radio that likely would work well, especially since it has waterfall displays for both the RF and Audio Spectrum, and it also has an Audio Oscilloscope and I'm anxious to see how helpful that might be. I see there is now a very small handheld HF SDR receiver called the Malahit (looks like the size of nanoVNAs), but I don't know how good they really work. If they become a trusted device I certainly will be interested in using one for DFing. 73 my friend, Don (wd8dsb) On Tue, Feb 23, 2021 at 9:18 PM David Raymond wrote: Don. . .thank you for the very nice loop article in QST. And, thank you for your generosity of not taking compensation to help make it affordable. The loop antenna would be a very useful tool to have in the arsenal for DFing interference sources of all kinds which continue to proliferate (even out in the country where I live). I am currently experiencing an interference problem on 160m that is about 10-15 KHz broad with a couple of modest peaks. It often parks in the 1825-1835 KHz window on 160m. The frequency range it occupies wanders some and varies inversely with the outside temperature. I have DFd it fairly close with the HI-Z 8 circle array and know the direction of the source but need something portable to home in on it. Do you or anyone here any suggestions for a reasonably good portable receiver with an external antenna jack (might be hard to find?) that will cover the 160m band . . .and maybe up to 30 MHz? Thanks and 73. . . Dave, W0FLS On 2/23/2021 5:37 PM, John Kaufmann via Topband wrote: As a follow-up to my original post, here are a few additional comments. Don, you mention that you designed the mini-flag for a deep null off the back at low elevation angles, which is entirely understandable. As I said in my earlier post, the null is very pronounced in the AM BCB on local groundwave signals. However, I also see pretty significant nulls on higher-angle signals, too. Just a short time ago, I was listening to W1AW on the low end of 160. They are located only ~100
Re: Topband: The WD8DSB mini-flag antenna
Hi Tim, Thanks, and I have gain vs frequency plot on my website for the DX Engineering preamp and my measurements agree with yours. The DX Engineering preamp designed for use my my portable flag is definitely my favorite preamp to use with my portable flag. Will be interesting to see what noise figure you guys measure. Thanks and 73, Don (wd8dsb) On Wed, Feb 24, 2021 at 4:55 PM Tim Duffy wrote: > Hello Don and John: > > DXE has not measured the noise figure of the loop preamp yet, but we will > soon and it will be posted on the part detail for the loop amplifier. > https://www.dxengineering.com/parts/dxe-nl-pre-att-1 > > I suspect the noise figure is about 3 dB. > > I am using the WD8DSB noise loop and the handheld preamp here at K3LR to > find several noise sources. I measured the pre amp gain at 32 dB on 160 and > 10 meters. > > 73 > Tim K3LR > > > -Original Message- > From: Topband [mailto:topband-bounces+k3lr=k3lr@contesting.com] On > Behalf Of Don Kirk > Sent: Wednesday, February 24, 2021 3:33 PM > To: john.kaufm...@verizon.net > Cc: TopBand List > Subject: Re: Topband: The WD8DSB mini-flag antenna > > Hi John, > > You started this mess (or maybe I did), and finally here is my response to > a few of the questions you had and thanks so much for waiting in line for > my response. > > 1) As I have mentioned in a few other responses I suspect having the short > 10 foot feedline helps to negate common mode noise and direct signal > ingress into the feedline that often haunts us. I do have one > recommendation about pattern distortion as follows. Check to make sure the > peak and the null of the antenna are in agreement on the signal you are > direction finding. If you notice a slight skew (where they don't agree > with each other), then move away from existing objects and this will > correct that problem. I sometimes notice a slight skew when in my backyard > near my house (looks like the null shifts slightly from where it should > be), and when I get out away from my house (I move to the sidewalk in front > of my house) the slight pattern skew goes away. > > 2) I don't know what the DX Engineering preamp noise figure is, and there > definitely is no expectation from the designers standpoint that it's > spectacular. Even though I did most of the field testing of this preamp I > have no idea what the amplifier part of the circuit is as DX Engineering > tightly controls their designs. > > 3) My antenna does not have a long mast, and it easily fits in the back > seat of my very small 1996 Saturn Station Wagon. It fits widthwise in my > backseat, and I have to imagine it will do the same in almost any car since > my car is about as small as they come. Looks like the DX Engineering > version of my antenna has a longer mast, and that can easily be shortened > if it helps you fit the antenna into other areas of your vehicle. I only > use the extension on my antenna if I'm doing some stationary tests in my > backyard, otherwise I use it as shown on the cover of QST. > > I Really appreciate you jumping in so quickly on the antenna build and > reporting some of your results. Sometimes when I have a few minutes I will > go outside and just play with the antenna and marvel on how simple it is, > but how well it works. > > I hope I have now covered the majority of everyones questions and > comments. If there are other comments or questions we probably should move > this discussion over to the RFI Reflector or e-mail me direct. > > 73, > Don (wd8sb) > > On Tue, Feb 23, 2021 at 1:26 PM John Kaufmann via Topband < > topband@contesting.com> wrote: > > > Some of you may have seen the article by WD8DSB in the latest issue of > QST. > > I believe WD8DSB is on this reflector. His article describes a mini-flag > > antenna that can be used for direction-finding. The neat thing about > this > > antenna, besides its compact size, is that it is unidirectional and is > very > > broadband. It works from the AM BCB through 10m. It produces a sharp > null > > off the back which allows you to determine signal direction without the > > direction ambiguity you get with a conventional unterminated loop. > > > > > > > > DX Engineering is producing this antenna as a kit, along with a companion > > preamp. (Disclaimer: I have no affiliation or commercial interest in DX > > Engineering). See: https://www.dxengineering.com/parts/dxe-noiseloop. > I > > just bought the flag kit last week and finished assembling it this past > > weekend. I see today that the kit is now back-ordered until April so it > > was > > good that I ordered it as soon as I saw the QST article. >
Re: Topband: The WD8DSB mini-flag antenna
On 2/24/2021 12:33 PM, Don Kirk wrote: As I have mentioned in a few other responses I suspect having the short 10 foot feedline helps to negate common mode noise YES! and direct signal ingress into the feedline that often haunts us. I do have one recommendation about pattern distortion as follows. Check to make sure the peak and the null of the antenna are in agreement on the signal you are direction finding. If you notice a slight skew (where they don't agree with each other), then move away from existing objects and this will correct that problem. I sometimes notice a slight skew when in my backyard near my house (looks like the null shifts slightly from where it should be), and when I get out away from my house (I move to the sidewalk in front of my house) the slight pattern skew goes away. Yes again! Rudy, N6LF, has shown that even relatively short towers that are nowhere near resonance can skew the pattern of a nearby vertical. My 120 ft tower with the small 3-el straight SteppIR and a long-boom 6M Yagi acts as a passive reflector to my Tee vertical that's 200 ft from it. Before I added chokes top and bottom to the feedlines of my high dipoles, they degraded that Tee. In general, the most sensitive parts of an antenna's pattern are its null(s), because they are the result of the cancellation of two nearly equal complex numbers that must be equal in both magnitude and phase. 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
Hello Don and John: DXE has not measured the noise figure of the loop preamp yet, but we will soon and it will be posted on the part detail for the loop amplifier. https://www.dxengineering.com/parts/dxe-nl-pre-att-1 I suspect the noise figure is about 3 dB. I am using the WD8DSB noise loop and the handheld preamp here at K3LR to find several noise sources. I measured the pre amp gain at 32 dB on 160 and 10 meters. 73 Tim K3LR -Original Message- From: Topband [mailto:topband-bounces+k3lr=k3lr@contesting.com] On Behalf Of Don Kirk Sent: Wednesday, February 24, 2021 3:33 PM To: john.kaufm...@verizon.net Cc: TopBand List Subject: Re: Topband: The WD8DSB mini-flag antenna Hi John, You started this mess (or maybe I did), and finally here is my response to a few of the questions you had and thanks so much for waiting in line for my response. 1) As I have mentioned in a few other responses I suspect having the short 10 foot feedline helps to negate common mode noise and direct signal ingress into the feedline that often haunts us. I do have one recommendation about pattern distortion as follows. Check to make sure the peak and the null of the antenna are in agreement on the signal you are direction finding. If you notice a slight skew (where they don't agree with each other), then move away from existing objects and this will correct that problem. I sometimes notice a slight skew when in my backyard near my house (looks like the null shifts slightly from where it should be), and when I get out away from my house (I move to the sidewalk in front of my house) the slight pattern skew goes away. 2) I don't know what the DX Engineering preamp noise figure is, and there definitely is no expectation from the designers standpoint that it's spectacular. Even though I did most of the field testing of this preamp I have no idea what the amplifier part of the circuit is as DX Engineering tightly controls their designs. 3) My antenna does not have a long mast, and it easily fits in the back seat of my very small 1996 Saturn Station Wagon. It fits widthwise in my backseat, and I have to imagine it will do the same in almost any car since my car is about as small as they come. Looks like the DX Engineering version of my antenna has a longer mast, and that can easily be shortened if it helps you fit the antenna into other areas of your vehicle. I only use the extension on my antenna if I'm doing some stationary tests in my backyard, otherwise I use it as shown on the cover of QST. I Really appreciate you jumping in so quickly on the antenna build and reporting some of your results. Sometimes when I have a few minutes I will go outside and just play with the antenna and marvel on how simple it is, but how well it works. I hope I have now covered the majority of everyones questions and comments. If there are other comments or questions we probably should move this discussion over to the RFI Reflector or e-mail me direct. 73, Don (wd8sb) On Tue, Feb 23, 2021 at 1:26 PM John Kaufmann via Topband < topband@contesting.com> wrote: > Some of you may have seen the article by WD8DSB in the latest issue of QST. > I believe WD8DSB is on this reflector. His article describes a mini-flag > antenna that can be used for direction-finding. The neat thing about this > antenna, besides its compact size, is that it is unidirectional and is very > broadband. It works from the AM BCB through 10m. It produces a sharp null > off the back which allows you to determine signal direction without the > direction ambiguity you get with a conventional unterminated loop. > > > > DX Engineering is producing this antenna as a kit, along with a companion > preamp. (Disclaimer: I have no affiliation or commercial interest in DX > Engineering). See: https://www.dxengineering.com/parts/dxe-noiseloop. I > just bought the flag kit last week and finished assembling it this past > weekend. I see today that the kit is now back-ordered until April so it > was > good that I ordered it as soon as I saw the QST article. > > > > It took me about 3 hours to assemble the mini-flag even though the DXE Web > site says it can be done in 1-2 hours. There is a bit of fussy mechanical > assembly involved in getting the symmetry and dimensions just right, > although it's not hard work. The flag is 42 inches wide and 21 inches > tall. > The DXE version of the antenna has slightly smaller dimensions than those > given in the QST article, which results in a small reduction in gain, which > doesn't really matter, but the pattern is the same. > > > > I did some testing of the mini-flag in the AM BCB. The gain is very > low--about -65 dBi on 160m--so it needs a good preamp. I used a homebrew > preamp made up of a couple of MMIC's that produce about 35 dB of gain. The > DXE preamp for this antenna won't be available unti
Re: Topband: The WD8DSB mini-flag antenna
I have read some negative info on the Malahit (the EBAY clones especially, the Russian originals seem better) but it might be OK for RFI investigations. N9EWO Review : Russian Malachite / Malahit DSP SDR (qsl.net) But I can recommend this: LAN-IQ SDR (Stand-alone SDR) (afedri-sdr.com) This is about $400 with tuning knob encoder but is a small, slick and fairly serious receiver with a 12 bit Direct Sampling receiver on HF (the Icom 7300 is a 14 bit Direct Sampler) and covers from 30 kHz to 1700 gHz with built in Spectrum Display and Waterfall. It runs on USB power (I use a Power Bank that folks use to recharge up their phones). It probably is overkill for just occasional RFI expeditions, but if you like the idea of having a portable wide range RX when not on the RFI hunt), it is well worth it. No connection to the seller (4Z5LB in Israel). He shipped mine promptly, I was surprised how soon it arrived! 73, Kevin K3OX - Original Message - From: Don Kirk To: David Raymond Cc: topband Sent: Wed, 24 Feb 2021 14:23:17 -0500 (EST) Subject: Re: Topband: The WD8DSB mini-flag antenna Hi Dave, I hate to recommend anything and others have given you some good recommendations, nevertheless I will make a few comments. My workhorse radio for direction finding is the good old Realistic DX-440 (also sold as a Sangen ATS-803A) and you can still find nice clean used ones on E-Bay for less than $100 (I suspect I drove the price of them up). It is a very old and large radio, but I love this radio for numerous reasons. It has an external antenna jack as well as an excellent continuously adjustable RF gain control that really comes in handy. It also has a BFO for receiving CW which sometimes is very helpful depending on the signal you are tracking. It uses 6 D cells and has excellent battery life. I use the radio in AM mode for tracking down power line noise, but sometimes I need to use the BFO for signals that are just a carrier as it helps to hear the signal (no need to look at a meter, etc). I also use a laptop based SDR receiver which is just a cheap RTL-SDR dongle along with a ham it up converter (both from NooElec) and I have both of these stuck to the back of my laptop screen so I can go portable with it, and this is a very handy tool especially if the signal is wandering all over the place or if I am in a heavily populated area with lots of different sources of RFI present. If you go this route make sure you pay the few extra bucks for a TCXO in both of them. The IC-705 is also a radio that likely would work well, especially since it has waterfall displays for both the RF and Audio Spectrum, and it also has an Audio Oscilloscope and I'm anxious to see how helpful that might be. I see there is now a very small handheld HF SDR receiver called the Malahit (looks like the size of nanoVNAs), but I don't know how good they really work. If they become a trusted device I certainly will be interested in using one for DFing. 73 my friend, Don (wd8dsb) On Tue, Feb 23, 2021 at 9:18 PM David Raymond wrote: > Don. . .thank you for the very nice loop article in QST. And, thank > you for your generosity of not taking compensation to help make it > affordable. The loop antenna would be a very useful tool to have in the > arsenal for DFing interference sources of all kinds which continue to > proliferate (even out in the country where I live). I am currently > experiencing an interference problem on 160m that is about 10-15 KHz > broad with a couple of modest peaks. It often parks in the 1825-1835 KHz > window on 160m. The frequency range it occupies wanders some and varies > inversely with the outside temperature. I have DFd it fairly close with > the HI-Z 8 circle array and know the direction of the source but need > something portable to home in on it. Do you or anyone here any > suggestions for a reasonably good portable receiver with an external > antenna jack (might be hard to find?) that will cover the 160m band . . > .and maybe up to 30 MHz? > > Thanks and 73. . . Dave, W0FLS > > On 2/23/2021 5:37 PM, John Kaufmann via Topband wrote: > > As a follow-up to my original post, here are a few additional comments. > > > > Don, you mention that you designed the mini-flag for a deep null off the > > back at low elevation angles, which is entirely understandable. As I > said > > in my earlier post, the null is very pronounced in the AM BCB on local > > groundwave signals. However, I also see pretty significant nulls on > > higher-angle signals, too. Just a short time ago, I was listening to > W1AW > > on the low end of 160. They are located only ~100 miles from me. Their > > signal has to be arriving at a pretty high angle, but the null is still > > quite pronounced. > > > > My homebrew preamp, that I mentioned in my post, uses a cascade of UTO > 511 > > and UT
Re: Topband: The WD8DSB mini-flag antenna
Hi John, You started this mess (or maybe I did), and finally here is my response to a few of the questions you had and thanks so much for waiting in line for my response. 1) As I have mentioned in a few other responses I suspect having the short 10 foot feedline helps to negate common mode noise and direct signal ingress into the feedline that often haunts us. I do have one recommendation about pattern distortion as follows. Check to make sure the peak and the null of the antenna are in agreement on the signal you are direction finding. If you notice a slight skew (where they don't agree with each other), then move away from existing objects and this will correct that problem. I sometimes notice a slight skew when in my backyard near my house (looks like the null shifts slightly from where it should be), and when I get out away from my house (I move to the sidewalk in front of my house) the slight pattern skew goes away. 2) I don't know what the DX Engineering preamp noise figure is, and there definitely is no expectation from the designers standpoint that it's spectacular. Even though I did most of the field testing of this preamp I have no idea what the amplifier part of the circuit is as DX Engineering tightly controls their designs. 3) My antenna does not have a long mast, and it easily fits in the back seat of my very small 1996 Saturn Station Wagon. It fits widthwise in my backseat, and I have to imagine it will do the same in almost any car since my car is about as small as they come. Looks like the DX Engineering version of my antenna has a longer mast, and that can easily be shortened if it helps you fit the antenna into other areas of your vehicle. I only use the extension on my antenna if I'm doing some stationary tests in my backyard, otherwise I use it as shown on the cover of QST. I Really appreciate you jumping in so quickly on the antenna build and reporting some of your results. Sometimes when I have a few minutes I will go outside and just play with the antenna and marvel on how simple it is, but how well it works. I hope I have now covered the majority of everyones questions and comments. If there are other comments or questions we probably should move this discussion over to the RFI Reflector or e-mail me direct. 73, Don (wd8sb) On Tue, Feb 23, 2021 at 1:26 PM John Kaufmann via Topband < topband@contesting.com> wrote: > Some of you may have seen the article by WD8DSB in the latest issue of QST. > I believe WD8DSB is on this reflector. His article describes a mini-flag > antenna that can be used for direction-finding. The neat thing about this > antenna, besides its compact size, is that it is unidirectional and is very > broadband. It works from the AM BCB through 10m. It produces a sharp null > off the back which allows you to determine signal direction without the > direction ambiguity you get with a conventional unterminated loop. > > > > DX Engineering is producing this antenna as a kit, along with a companion > preamp. (Disclaimer: I have no affiliation or commercial interest in DX > Engineering). See: https://www.dxengineering.com/parts/dxe-noiseloop. I > just bought the flag kit last week and finished assembling it this past > weekend. I see today that the kit is now back-ordered until April so it > was > good that I ordered it as soon as I saw the QST article. > > > > It took me about 3 hours to assemble the mini-flag even though the DXE Web > site says it can be done in 1-2 hours. There is a bit of fussy mechanical > assembly involved in getting the symmetry and dimensions just right, > although it's not hard work. The flag is 42 inches wide and 21 inches > tall. > The DXE version of the antenna has slightly smaller dimensions than those > given in the QST article, which results in a small reduction in gain, which > doesn't really matter, but the pattern is the same. > > > > I did some testing of the mini-flag in the AM BCB. The gain is very > low--about -65 dBi on 160m--so it needs a good preamp. I used a homebrew > preamp made up of a couple of MMIC's that produce about 35 dB of gain. The > DXE preamp for this antenna won't be available until April. On the higher > frequencies, less preamp gain is needed because the gain of the mini-flag > increases with frequency. > > > > My initial tests indicate this antenna clearly works. By rotating the flag > for the deepest null, I could nail the heading an AM BCB station to a few > degrees. > > > > This antenna could also be used as directional receiving antenna on its > own. > Although it is not hugely directive, it can be rotated easily to peak or > null signals or noise, and it is better than a conventional unterminated > loop. It has essentially the same RDF as other larger flag or pennant > antennas but is obviously far more compact. > > > > This is a nice contribution by WD8DSB. Now I have to go off with the > mini-flag and chase some local noise sources that have been plaguing me > this
Re: Topband: The WD8DSB mini-flag antenna
Hi Rich " The problem here is that any loop antenna inherently has a noise temperature of 300K, because it is lossy, and because it "sees" the earth" Would you elaborate on that? Small loop 1/10 of wave length works very different from a loop or large loop. I experimented with a large number of small loops in phase on 1.8 MHz. The frequency is very important because almost everything we know is different around 1.8 Mhz. Local noise is the most misunderstood figure. On top-band during a winter Sunday morning the noise can be low as 70K. On topband the only source of nom mam made noise atmospheric noise. No atmospheric activity means no noise. Yes it is that low. I am using horizontal phased loops for almost 15 years. It needs to be high for 160m, my is at 120 FT, it is large 50 Ft boom and loops are 24 x 12, all fiberglass. The gain is around -53db. The preamplifier required a minimum sensitivity is near 1 db NF, for that winter Sunday morning on 160m. I tested almost all available preamplifier, and the NF at 1.8 MHz is very different from NF measured at 10 MHz. The best I found was the NORTON with 1.5 to 2 db NF. I developed my own preamplifier , the same I build in 2010 still in use here, using 6 BF981 and large Q input filter. It measured .7 db NF including the input tuning filter loss. It does make a difference on signals at noise level. I built one for NX4D and Doug still use it. Making it short, I heard 316 countries (CW) and worked 305 since I built my N4IS preamp on 0ct 2010 (city lot). Doug worked 311 from a 1/5 acre lot using a pair of phase loops. A/B tests with NORTON preamps show not possible to copy the weak signals I did copy with my 6xBF981. Implementation is a different ball game. The .7 db NF preamp needs 3 level of shield including a magnetic shield with steel, just aluminum is not enough, and no open shield at all, a 1 mm gap will ruin your system. You can find information about my preamp on google or WWROF archives. A friend told my 2010 seems to be a very long time ago. Sure It does. 73's N4IS JC -Original Message- From: Topband On Behalf Of Richard (Rick) Karlquist Sent: Wednesday, February 24, 2021 12:50 PM To: GEORGE WALLNER ; Don Kirk ; topband@contesting.com Subject: Re: Topband: The WD8DSB mini-flag antenna On 2/24/2021 6:32 AM, GEORGE WALLNER wrote: > Don, > I put that note out because friends were asking if with a > "ultra-low-noise" pre-amp they could use it for DX. Unfortunately, > that's not the case. (I have tried.) George, AA7JV/C6AGU > The problem here is that any loop antenna inherently has a noise temperature of 300K, because it is lossy, and because it "sees" the earth. Therefore, a 0.5 dB NF amplifier adds 0.5 dB of noise, etc. As opposed to the 0.5 dB NF amplifier on an EME array that is something like 10 dB better than a 3 dB NF amplifier because of how noise temperature works. Also, for NF's below 3 dB or so, the source impedance is very critical in order to actually achieve the specified NF. This is impossible in an untuned wide band loop antenna. So in practice, a NF of around 3 dB is the best you can do, and even that may be optimistic. BTW, the multiple turns on the loop do not increase the available received power or SNR in any way. They simply increase the source impedance. It is analogous to a folded dipole. There are two tools that will reliably increase sensitivity: 1. Make the loop area larger. 2. Change to a tuned loop. 73 Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
K9AY loop or > > other similar pennant/flag antennas. For use as a receiving antenna, the > > important thing is the noise figure of the preamp. The DX Engineering > Web > > site does not give the noise figure of their preamp. Don, perhaps you > know? > > > > The other thing that might degrade the antenna is common-mode signal > pickup, > > which can be a problem for very low gain antennas where you are working > with > > very small signals. However, based on what I observe in terms of antenna > > pattern for this mini-flag, I can't say that I see any pattern effects > that > > might be attributable to common mode degradation. Don, maybe you can > > comment here as well on this aspect of the antenna. > > > > As I also mentioned in my earlier post, the dimensions of the DXE > > implementation are somewhat smaller than what's given in the QST article. > > For me, that works out well because the width of the DXE mini-flag just > > manages to fit inside the trunk of my mid-size sedan. A wider flag would > > not fit. > > > > 73, John W1FV > > > > -Original Message- > > From: Topband > > [mailto:topband-bounces+john.kaufmann=verizon@contesting.com] On > Behalf > > Of Don Kirk > > Sent: Tuesday, February 23, 2021 5:22 PM > > To: wb6r...@mac.com > > Cc: Top Band List List > > Subject: Re: Topband: The WD8DSB mini-flag antenna > > > > HI Steve, > > > > Thanks for the nice implementation comment. > > > > The portable flag front to back ratio is highly related to the elevation > > angle and frequency of operation (just like any terminated loop), and > > therefore I did not want to overstate the front to back ratio in my > > portable flag article. I designed the portable flag for direction > finding > > local RFI (ground wave based signals) and therefore made sure I selected > an > > appropriate termination resistor to provide a very deep null at low > > elevation angles on 160, 80 and 40 meters where I often deal with RFI > (the > > portable flag has a very high front to back ratio at low elevation > angles), > > and because of this it also has exceptional front to back ratio at low > > elevation angles down in the AM Broadcast Band. Very small flags have > just > > as good front to back ratio and RDF as a full size flag as long as the > > appropriate termination resistor is used. The problem is when the flag > > becomes too large for the frequency of operation which causes the > > directional properties to degrade. You can see some front to back ratio > > vs. elevation plots for my portable flag on my simple portable flag > website > > and here is the URL to that site: > > https://sites.google.com/site/portableflagantenna/home > > > > Problem with very small flags is that the noise figure of the preamp > > becomes a critical parameter, and because of this I don't recommend > > attenuators be placed before the preamp as this causes degradation in the > > signal to noise ratio. I stumbled upon this issue when doing field tests > > on one of the DX Engineering prototype preamps, and had them change the > > design so the attenuators now come after the actual amplifier stage which > > solved the problem. > > > > Everything I said above about the performance of very small terminated > > loops assumes no interaction with surrounding objects, and ignores issues > > related with feedlines since the feedline is very short on the portable > > flag. > > > > P.S. I make no money from DX Engineering as I agreed to not be paid in > > order to keep the price of the portable flag as low as possible. > > > > 73, > > Don (wd8dsb) > > _ > > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > > > > _ > > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
15 -0500 > > Don Kirk wrote: > > Hi George, > > > > Thanks for mentioning that antenna system thermal noise eventually > > establishes the limiting factor where additional preamp gain will not > > provide any additional improvement in performance. > > Earlier today I was > > looking for a previous discussion by Tom (W8JI) that explained this very > > well and I believe he provided some examples but I have not yet located it > > (but still looking). > > > > 73, > > Don (wd8dsb) > > > > On Tue, Feb 23, 2021 at 8:20 PM GEORGE WALLNER > wrote: > > The smaller the flag the lower its gain and its signal output. The limit > > of > > usefulness is reached when a weak signal is below the thermal (Johnson) > > noise of the system (~ loading resistor). Below this point a pre-amp will > > no > > longer help. That limits the usefulness of small flags for weak signals, > > regardless of RDF. > > > > 73, > > George > > AA7JV/C6AGU > > > > > > On Tue, 23 Feb 2021 18:37:03 -0500 > > John Kaufmann via Topband wrote: > > > As a follow-up to my original post, here are a few additional comments. > > > > > > Don, you mention that you designed the mini-flag for a deep null off the > > > back at low elevation angles, which is entirely understandable. As I > > said > > > in my earlier post, the null is very pronounced in the AM BCB on local > > > groundwave signals. However, I also see pretty significant nulls on > > > higher-angle signals, too. Just a short time ago, I was listening to > > W1AW > > > on the low end of 160. They are located only ~100 miles from me. Their > > > signal has to be arriving at a pretty high angle, but the null is still > > > quite pronounced. > > > > > > My homebrew preamp, that I mentioned in my post, uses a cascade of UTO > > 511 > > > and UTO 533 mini-amplifier modules. I used this preamp, not necessarily > > > because it's optimal, but because I already happened to have it on hand. > > > The gain of the 511 is given as 16 dB typical while the 533 is 17 dB, > > which > > > should yield a net gain of ~33 dB for the cascade of the two. The noise > > > figure on the 511 that serves as the input amplifier is specified as 2.3 > > dB, > > > but its spec sheet gives an operational frequency range of 5-500 MHz, so > > I > > > can't be sure the noise figure (or the gain) holds up at lower > > frequencies. > > > Nonetheless I can hear the ambient noise in my receiver increase on 160m > > > when I connect the mini-flag to the preamp, which suggests the noise > > figure > > > for this preamp is at least adequate at my location. > > I use a Yaesu > > FT-817ND > > > "backpack" radio as a portable radio with this antenna. > > > > > > In EZNEC I calculate the RDF of this mini-flag as 7.4 dB on 160m at a 20 > > > degree elevation angle. That's essentially the same as the K9AY loop or > > > other similar pennant/flag antennas. For use as a receiving antenna, the > > > important thing is the noise figure of the preamp. > > The DX Engineering > > Web > > > site does not give the noise figure of their preamp. > > > Don, perhaps you know? > > > > > > The other thing that might degrade the antenna is common-mode signal > > pickup, > > > which can be a problem for very low gain antennas where you are working > > with > > > very small signals. However, based on what I observe in terms of antenna > > > pattern for this mini-flag, I can't say that I see any pattern effects > > that > > > might be attributable to common mode degradation. > > Don, maybe you can > > > comment here as well on this aspect of the antenna. > > > > > > As I also mentioned in my earlier post, the dimensions of the DXE > > > implementation are somewhat smaller than what's given in the QST article. > > >For me, that works out well because the width of the DXE mini-flag just > > > manages to fit inside the trunk of my mid-size sedan. > > A wider flag would > > > not fit. > > > > > > 73, John W1FV > > > > > > -Original Message- > > >From: Topband > > > [mailto:topband-bounces+john.kaufmann=verizon@contesting.com] On > > Behalf > > > Of Don Kirk > > > Sent: Tuesday, February 23, 2021 5:22 PM > > > To: wb6r...@mac.com > > > Cc: Top Band List List > > > Subject: Re:
Re: Topband: The WD8DSB mini-flag antenna
On 2/24/2021 6:32 AM, GEORGE WALLNER wrote: Don, I put that note out because friends were asking if with a "ultra-low-noise" pre-amp they could use it for DX. Unfortunately, that's not the case. (I have tried.) George, AA7JV/C6AGU The problem here is that any loop antenna inherently has a noise temperature of 300K, because it is lossy, and because it "sees" the earth. Therefore, a 0.5 dB NF amplifier adds 0.5 dB of noise, etc. As opposed to the 0.5 dB NF amplifier on an EME array that is something like 10 dB better than a 3 dB NF amplifier because of how noise temperature works. Also, for NF's below 3 dB or so, the source impedance is very critical in order to actually achieve the specified NF. This is impossible in an untuned wide band loop antenna. So in practice, a NF of around 3 dB is the best you can do, and even that may be optimistic. BTW, the multiple turns on the loop do not increase the available received power or SNR in any way. They simply increase the source impedance. It is analogous to a folded dipole. There are two tools that will reliably increase sensitivity: 1. Make the loop area larger. 2. Change to a tuned loop. 73 Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
Don's directional loop should significantly reduce my tracking time for most common switching noise in the neighboring area. I currently use a National RF loop + preamp with an SDR-IQ receiver strapped with Velcro to a notebook PC. The SDR-IQ is powered from the PC's USB port. It's very helpful to watch the signature of a switch-mode noise pattern to ensure you're not tracking other noise sources when roving on foot. It's important to stay focused on one noise source before embarking on another. For this reason, I recommend using an SDR receiver of some type rather than a conventional portable receiver. Next, my plan is to acquire an Expert Electronics ColibriNano SDR dongle together with a Microsoft Surface tablet PC. That will reduce some of the baggage and weight while roaming. Paul, W9AC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
On 2/23/2021 6:18 PM, David Raymond wrote: Don. . .thank you for the very nice loop article in QST. And, thank something portable to home in on it. Do you or anyone here any suggestions for a reasonably good portable receiver with an external antenna jack (might be hard to find?) that will cover the 160m band . . .and maybe up to 30 MHz? Thanks and 73. . . Dave, W0FLS Not hard to find: Icom IC-R6 hand held "scanning receiver", 100 kHz to 1.3 GHz, available at HRO. I've been using one of these for years for doing DF,ing. Works great with a hand held 144/432 MHz ham satellite Yagi. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
Don, I put that note out because friends were asking if with a "ultra-low-noise" pre-amp they could use it for DX. Unfortunately, that's not the case. (I have tried.) Of course, that does not diminish the usefulness of your antenna for DR. Also, a somewhat larger version (1.5 - 2 m per side) could be useful for very noisy locations. TKS for starting this discussion as we still have more to discover with resistor loaded loops. 73, George, AA7JV/C6AGU On Tue, 23 Feb 2021 21:46:15 -0500 Don Kirk wrote: Hi George, Thanks for mentioning that antenna system thermal noise eventually establishes the limiting factor where additional preamp gain will not provide any additional improvement in performance. Earlier today I was looking for a previous discussion by Tom (W8JI) that explained this very well and I believe he provided some examples but I have not yet located it (but still looking). 73, Don (wd8dsb) On Tue, Feb 23, 2021 at 8:20 PM GEORGE WALLNER wrote: The smaller the flag the lower its gain and its signal output. The limit of usefulness is reached when a weak signal is below the thermal (Johnson) noise of the system (~ loading resistor). Below this point a pre-amp will no longer help. That limits the usefulness of small flags for weak signals, regardless of RDF. 73, George AA7JV/C6AGU On Tue, 23 Feb 2021 18:37:03 -0500 John Kaufmann via Topband wrote: > As a follow-up to my original post, here are a few additional comments. > > Don, you mention that you designed the mini-flag for a deep null off the > back at low elevation angles, which is entirely understandable. As I said > in my earlier post, the null is very pronounced in the AM BCB on local > groundwave signals. However, I also see pretty significant nulls on > higher-angle signals, too. Just a short time ago, I was listening to W1AW > on the low end of 160. They are located only ~100 miles from me. Their > signal has to be arriving at a pretty high angle, but the null is still > quite pronounced. > > My homebrew preamp, that I mentioned in my post, uses a cascade of UTO 511 > and UTO 533 mini-amplifier modules. I used this preamp, not necessarily > because it's optimal, but because I already happened to have it on hand. > The gain of the 511 is given as 16 dB typical while the 533 is 17 dB, which > should yield a net gain of ~33 dB for the cascade of the two. The noise > figure on the 511 that serves as the input amplifier is specified as 2.3 dB, > but its spec sheet gives an operational frequency range of 5-500 MHz, so I > can't be sure the noise figure (or the gain) holds up at lower frequencies. > Nonetheless I can hear the ambient noise in my receiver increase on 160m > when I connect the mini-flag to the preamp, which suggests the noise figure > for this preamp is at least adequate at my location. I use a Yaesu FT-817ND > "backpack" radio as a portable radio with this antenna. > > In EZNEC I calculate the RDF of this mini-flag as 7.4 dB on 160m at a 20 > degree elevation angle. That's essentially the same as the K9AY loop or > other similar pennant/flag antennas. For use as a receiving antenna, the > important thing is the noise figure of the preamp. The DX Engineering Web > site does not give the noise figure of their preamp. > Don, perhaps you know? > > The other thing that might degrade the antenna is common-mode signal pickup, > which can be a problem for very low gain antennas where you are working with > very small signals. However, based on what I observe in terms of antenna > pattern for this mini-flag, I can't say that I see any pattern effects that > might be attributable to common mode degradation. Don, maybe you can > comment here as well on this aspect of the antenna. > > As I also mentioned in my earlier post, the dimensions of the DXE > implementation are somewhat smaller than what's given in the QST article. >For me, that works out well because the width of the DXE mini-flag just > manages to fit inside the trunk of my mid-size sedan. A wider flag would > not fit. > > 73, John W1FV > > -Original Message- >From: Topband > [mailto:topband-bounces+john.kaufmann=verizon....@contesting.com] On Behalf > Of Don Kirk > Sent: Tuesday, February 23, 2021 5:22 PM > To: wb6r...@mac.com > Cc: Top Band List List > Subject: Re: Topband: The WD8DSB mini-flag antenna > > HI Steve, > > Thanks for the nice implementation comment. > > The portable flag front to back ratio is highly related to the elevation > angle and frequency of operation (just like any terminated loop), and > therefore I did not want to overstate the front to back ratio in my > portable flag article. I designed the portable flag for direction finding > local RFI (ground wave based signals) and therefore made sure I selec
Re: Topband: The WD8DSB mini-flag antenna
Hi Rob, Front to back ratio all depends on the arrival angle of the signal, and the portable flag directional properties are just like full size flag directional properties assuming you select the appropriate termination resistor. On my portable flag website I show front to back ratio vs elevation angle when using a 680 ohm termination resistor versus using a 820 ohm termination resistor and you will see that you can move where the front to back ratio peaks to a higher elevation angle if using a 820 ohm termination resistor compared with using a 680 ohm termination resistor. I use a 680 ohm termination resistor because I wanted best performance for ground wave based signals but if I wanted to reject skywave signals off the back of the antenna versus local noise I would use a 820 ohm resistor as an example. Here is a link to my website where you will see the plots I mention: https://sites.google.com/site/portableflagantenna/ 73, Don (wd8dsb) On Wed, Feb 24, 2021 at 6:31 AM Rob Atkinson wrote: > Bi-directional loops lose their directivity for the most part, when > being applied to skywave signals. Is this mini-flag still > unidirectional on skywave? I would think not, but must ask. > > 73 > Rob > K5UJ > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
Bi-directional loops lose their directivity for the most part, when being applied to skywave signals. Is this mini-flag still unidirectional on skywave? I would think not, but must ask. 73 Rob K5UJ _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
> On 24 Feb 2021, at 02:18, David Raymond wrote: > > anyone here any suggestions for a reasonably good portable receiver with an > external antenna jack (might be hard to find?) that will cover the 160m band > . . .and maybe up to 30 MHz? Hi Dave, How about an SDR (e.g. RSP1A, Funcube dongle or even RTL dongle) and a small laptop or tablet? That way you’d get spectrum and waterfall as well as audio. And you can record everything for analysis / future reference should the interference return. There’s probably an app out there to connect a dongle to your cellphone, but I’ve not investigated that. 73 Chris, G3SVL p.s. can I add my thanks to Don too for the loop design. _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
Hi George, Thanks for mentioning that antenna system thermal noise eventually establishes the limiting factor where additional preamp gain will not provide any additional improvement in performance. Earlier today I was looking for a previous discussion by Tom (W8JI) that explained this very well and I believe he provided some examples but I have not yet located it (but still looking). 73, Don (wd8dsb) On Tue, Feb 23, 2021 at 8:20 PM GEORGE WALLNER wrote: > The smaller the flag the lower its gain and its signal output. The limit > of > usefulness is reached when a weak signal is below the thermal (Johnson) > noise of the system (~ loading resistor). Below this point a pre-amp will > no > longer help. That limits the usefulness of small flags for weak signals, > regardless of RDF. > > 73, > George > AA7JV/C6AGU > > > On Tue, 23 Feb 2021 18:37:03 -0500 > John Kaufmann via Topband wrote: > > As a follow-up to my original post, here are a few additional comments. > > > > Don, you mention that you designed the mini-flag for a deep null off the > > back at low elevation angles, which is entirely understandable. As I > said > > in my earlier post, the null is very pronounced in the AM BCB on local > > groundwave signals. However, I also see pretty significant nulls on > > higher-angle signals, too. Just a short time ago, I was listening to > W1AW > > on the low end of 160. They are located only ~100 miles from me. Their > > signal has to be arriving at a pretty high angle, but the null is still > > quite pronounced. > > > > My homebrew preamp, that I mentioned in my post, uses a cascade of UTO > 511 > > and UTO 533 mini-amplifier modules. I used this preamp, not necessarily > > because it's optimal, but because I already happened to have it on hand. > > The gain of the 511 is given as 16 dB typical while the 533 is 17 dB, > which > > should yield a net gain of ~33 dB for the cascade of the two. The noise > > figure on the 511 that serves as the input amplifier is specified as 2.3 > dB, > > but its spec sheet gives an operational frequency range of 5-500 MHz, so > I > > can't be sure the noise figure (or the gain) holds up at lower > frequencies. > > Nonetheless I can hear the ambient noise in my receiver increase on 160m > > when I connect the mini-flag to the preamp, which suggests the noise > figure > > for this preamp is at least adequate at my location. I use a Yaesu > FT-817ND > > "backpack" radio as a portable radio with this antenna. > > > > In EZNEC I calculate the RDF of this mini-flag as 7.4 dB on 160m at a 20 > > degree elevation angle. That's essentially the same as the K9AY loop or > > other similar pennant/flag antennas. For use as a receiving antenna, the > > important thing is the noise figure of the preamp. The DX Engineering > Web > > site does not give the noise figure of their preamp. > > Don, perhaps you know? > > > > The other thing that might degrade the antenna is common-mode signal > pickup, > > which can be a problem for very low gain antennas where you are working > with > > very small signals. However, based on what I observe in terms of antenna > > pattern for this mini-flag, I can't say that I see any pattern effects > that > > might be attributable to common mode degradation. Don, maybe you can > > comment here as well on this aspect of the antenna. > > > > As I also mentioned in my earlier post, the dimensions of the DXE > > implementation are somewhat smaller than what's given in the QST article. > >For me, that works out well because the width of the DXE mini-flag just > > manages to fit inside the trunk of my mid-size sedan. A wider flag would > > not fit. > > > > 73, John W1FV > > > > -Original Message- > >From: Topband > > [mailto:topband-bounces+john.kaufmann=verizon@contesting.com] On > Behalf > > Of Don Kirk > > Sent: Tuesday, February 23, 2021 5:22 PM > > To: wb6r...@mac.com > > Cc: Top Band List List > > Subject: Re: Topband: The WD8DSB mini-flag antenna > > > > HI Steve, > > > > Thanks for the nice implementation comment. > > > > The portable flag front to back ratio is highly related to the elevation > > angle and frequency of operation (just like any terminated loop), and > > therefore I did not want to overstate the front to back ratio in my > > portable flag article. I designed the portable flag for direction > finding > > local RFI (ground wave based signals) and therefore made sure I selected > an > > appropriate termination resistor to provide a
Re: Topband: The WD8DSB mini-flag antenna
Don. . .thank you for the very nice loop article in QST. And, thank you for your generosity of not taking compensation to help make it affordable. The loop antenna would be a very useful tool to have in the arsenal for DFing interference sources of all kinds which continue to proliferate (even out in the country where I live). I am currently experiencing an interference problem on 160m that is about 10-15 KHz broad with a couple of modest peaks. It often parks in the 1825-1835 KHz window on 160m. The frequency range it occupies wanders some and varies inversely with the outside temperature. I have DFd it fairly close with the HI-Z 8 circle array and know the direction of the source but need something portable to home in on it. Do you or anyone here any suggestions for a reasonably good portable receiver with an external antenna jack (might be hard to find?) that will cover the 160m band . . .and maybe up to 30 MHz? Thanks and 73. . . Dave, W0FLS On 2/23/2021 5:37 PM, John Kaufmann via Topband wrote: As a follow-up to my original post, here are a few additional comments. Don, you mention that you designed the mini-flag for a deep null off the back at low elevation angles, which is entirely understandable. As I said in my earlier post, the null is very pronounced in the AM BCB on local groundwave signals. However, I also see pretty significant nulls on higher-angle signals, too. Just a short time ago, I was listening to W1AW on the low end of 160. They are located only ~100 miles from me. Their signal has to be arriving at a pretty high angle, but the null is still quite pronounced. My homebrew preamp, that I mentioned in my post, uses a cascade of UTO 511 and UTO 533 mini-amplifier modules. I used this preamp, not necessarily because it's optimal, but because I already happened to have it on hand. The gain of the 511 is given as 16 dB typical while the 533 is 17 dB, which should yield a net gain of ~33 dB for the cascade of the two. The noise figure on the 511 that serves as the input amplifier is specified as 2.3 dB, but its spec sheet gives an operational frequency range of 5-500 MHz, so I can't be sure the noise figure (or the gain) holds up at lower frequencies. Nonetheless I can hear the ambient noise in my receiver increase on 160m when I connect the mini-flag to the preamp, which suggests the noise figure for this preamp is at least adequate at my location. I use a Yaesu FT-817ND "backpack" radio as a portable radio with this antenna. In EZNEC I calculate the RDF of this mini-flag as 7.4 dB on 160m at a 20 degree elevation angle. That's essentially the same as the K9AY loop or other similar pennant/flag antennas. For use as a receiving antenna, the important thing is the noise figure of the preamp. The DX Engineering Web site does not give the noise figure of their preamp. Don, perhaps you know? The other thing that might degrade the antenna is common-mode signal pickup, which can be a problem for very low gain antennas where you are working with very small signals. However, based on what I observe in terms of antenna pattern for this mini-flag, I can't say that I see any pattern effects that might be attributable to common mode degradation. Don, maybe you can comment here as well on this aspect of the antenna. As I also mentioned in my earlier post, the dimensions of the DXE implementation are somewhat smaller than what's given in the QST article. For me, that works out well because the width of the DXE mini-flag just manages to fit inside the trunk of my mid-size sedan. A wider flag would not fit. 73, John W1FV -Original Message- From: Topband [mailto:topband-bounces+john.kaufmann=verizon@contesting.com] On Behalf Of Don Kirk Sent: Tuesday, February 23, 2021 5:22 PM To: wb6r...@mac.com Cc: Top Band List List Subject: Re: Topband: The WD8DSB mini-flag antenna HI Steve, Thanks for the nice implementation comment. The portable flag front to back ratio is highly related to the elevation angle and frequency of operation (just like any terminated loop), and therefore I did not want to overstate the front to back ratio in my portable flag article. I designed the portable flag for direction finding local RFI (ground wave based signals) and therefore made sure I selected an appropriate termination resistor to provide a very deep null at low elevation angles on 160, 80 and 40 meters where I often deal with RFI (the portable flag has a very high front to back ratio at low elevation angles), and because of this it also has exceptional front to back ratio at low elevation angles down in the AM Broadcast Band. Very small flags have just as good front to back ratio and RDF as a full size flag as long as the appropriate termination resistor is used. The problem is when the flag becomes too large for the frequency of operation which causes the directional properties to degrade. You can see some front to back ratio vs. elevation pl
Re: Topband: The WD8DSB mini-flag antenna
The smaller the flag the lower its gain and its signal output. The limit of usefulness is reached when a weak signal is below the thermal (Johnson) noise of the system (~ loading resistor). Below this point a pre-amp will no longer help. That limits the usefulness of small flags for weak signals, regardless of RDF. 73, George AA7JV/C6AGU On Tue, 23 Feb 2021 18:37:03 -0500 John Kaufmann via Topband wrote: As a follow-up to my original post, here are a few additional comments. Don, you mention that you designed the mini-flag for a deep null off the back at low elevation angles, which is entirely understandable. As I said in my earlier post, the null is very pronounced in the AM BCB on local groundwave signals. However, I also see pretty significant nulls on higher-angle signals, too. Just a short time ago, I was listening to W1AW on the low end of 160. They are located only ~100 miles from me. Their signal has to be arriving at a pretty high angle, but the null is still quite pronounced. My homebrew preamp, that I mentioned in my post, uses a cascade of UTO 511 and UTO 533 mini-amplifier modules. I used this preamp, not necessarily because it's optimal, but because I already happened to have it on hand. The gain of the 511 is given as 16 dB typical while the 533 is 17 dB, which should yield a net gain of ~33 dB for the cascade of the two. The noise figure on the 511 that serves as the input amplifier is specified as 2.3 dB, but its spec sheet gives an operational frequency range of 5-500 MHz, so I can't be sure the noise figure (or the gain) holds up at lower frequencies. Nonetheless I can hear the ambient noise in my receiver increase on 160m when I connect the mini-flag to the preamp, which suggests the noise figure for this preamp is at least adequate at my location. I use a Yaesu FT-817ND "backpack" radio as a portable radio with this antenna. In EZNEC I calculate the RDF of this mini-flag as 7.4 dB on 160m at a 20 degree elevation angle. That's essentially the same as the K9AY loop or other similar pennant/flag antennas. For use as a receiving antenna, the important thing is the noise figure of the preamp. The DX Engineering Web site does not give the noise figure of their preamp. Don, perhaps you know? The other thing that might degrade the antenna is common-mode signal pickup, which can be a problem for very low gain antennas where you are working with very small signals. However, based on what I observe in terms of antenna pattern for this mini-flag, I can't say that I see any pattern effects that might be attributable to common mode degradation. Don, maybe you can comment here as well on this aspect of the antenna. As I also mentioned in my earlier post, the dimensions of the DXE implementation are somewhat smaller than what's given in the QST article. For me, that works out well because the width of the DXE mini-flag just manages to fit inside the trunk of my mid-size sedan. A wider flag would not fit. 73, John W1FV -Original Message- From: Topband [mailto:topband-bounces+john.kaufmann=verizon@contesting.com] On Behalf Of Don Kirk Sent: Tuesday, February 23, 2021 5:22 PM To: wb6r...@mac.com Cc: Top Band List List Subject: Re: Topband: The WD8DSB mini-flag antenna HI Steve, Thanks for the nice implementation comment. The portable flag front to back ratio is highly related to the elevation angle and frequency of operation (just like any terminated loop), and therefore I did not want to overstate the front to back ratio in my portable flag article. I designed the portable flag for direction finding local RFI (ground wave based signals) and therefore made sure I selected an appropriate termination resistor to provide a very deep null at low elevation angles on 160, 80 and 40 meters where I often deal with RFI (the portable flag has a very high front to back ratio at low elevation angles), and because of this it also has exceptional front to back ratio at low elevation angles down in the AM Broadcast Band. Very small flags have just as good front to back ratio and RDF as a full size flag as long as the appropriate termination resistor is used. The problem is when the flag becomes too large for the frequency of operation which causes the directional properties to degrade. You can see some front to back ratio vs. elevation plots for my portable flag on my simple portable flag website and here is the URL to that site: https://sites.google.com/site/portableflagantenna/home Problem with very small flags is that the noise figure of the preamp becomes a critical parameter, and because of this I don't recommend attenuators be placed before the preamp as this causes degradation in the signal to noise ratio. I stumbled upon this issue when doing field tests on one of the DX Engineering prototype preamps, and had them change the design so the attenuators now come after the actual amplifier stage which solved the problem. Everything I said a
Re: Topband: The WD8DSB mini-flag antenna
As a follow-up to my original post, here are a few additional comments. Don, you mention that you designed the mini-flag for a deep null off the back at low elevation angles, which is entirely understandable. As I said in my earlier post, the null is very pronounced in the AM BCB on local groundwave signals. However, I also see pretty significant nulls on higher-angle signals, too. Just a short time ago, I was listening to W1AW on the low end of 160. They are located only ~100 miles from me. Their signal has to be arriving at a pretty high angle, but the null is still quite pronounced. My homebrew preamp, that I mentioned in my post, uses a cascade of UTO 511 and UTO 533 mini-amplifier modules. I used this preamp, not necessarily because it's optimal, but because I already happened to have it on hand. The gain of the 511 is given as 16 dB typical while the 533 is 17 dB, which should yield a net gain of ~33 dB for the cascade of the two. The noise figure on the 511 that serves as the input amplifier is specified as 2.3 dB, but its spec sheet gives an operational frequency range of 5-500 MHz, so I can't be sure the noise figure (or the gain) holds up at lower frequencies. Nonetheless I can hear the ambient noise in my receiver increase on 160m when I connect the mini-flag to the preamp, which suggests the noise figure for this preamp is at least adequate at my location. I use a Yaesu FT-817ND "backpack" radio as a portable radio with this antenna. In EZNEC I calculate the RDF of this mini-flag as 7.4 dB on 160m at a 20 degree elevation angle. That's essentially the same as the K9AY loop or other similar pennant/flag antennas. For use as a receiving antenna, the important thing is the noise figure of the preamp. The DX Engineering Web site does not give the noise figure of their preamp. Don, perhaps you know? The other thing that might degrade the antenna is common-mode signal pickup, which can be a problem for very low gain antennas where you are working with very small signals. However, based on what I observe in terms of antenna pattern for this mini-flag, I can't say that I see any pattern effects that might be attributable to common mode degradation. Don, maybe you can comment here as well on this aspect of the antenna. As I also mentioned in my earlier post, the dimensions of the DXE implementation are somewhat smaller than what's given in the QST article. For me, that works out well because the width of the DXE mini-flag just manages to fit inside the trunk of my mid-size sedan. A wider flag would not fit. 73, John W1FV -Original Message- From: Topband [mailto:topband-bounces+john.kaufmann=verizon@contesting.com] On Behalf Of Don Kirk Sent: Tuesday, February 23, 2021 5:22 PM To: wb6r...@mac.com Cc: Top Band List List Subject: Re: Topband: The WD8DSB mini-flag antenna HI Steve, Thanks for the nice implementation comment. The portable flag front to back ratio is highly related to the elevation angle and frequency of operation (just like any terminated loop), and therefore I did not want to overstate the front to back ratio in my portable flag article. I designed the portable flag for direction finding local RFI (ground wave based signals) and therefore made sure I selected an appropriate termination resistor to provide a very deep null at low elevation angles on 160, 80 and 40 meters where I often deal with RFI (the portable flag has a very high front to back ratio at low elevation angles), and because of this it also has exceptional front to back ratio at low elevation angles down in the AM Broadcast Band. Very small flags have just as good front to back ratio and RDF as a full size flag as long as the appropriate termination resistor is used. The problem is when the flag becomes too large for the frequency of operation which causes the directional properties to degrade. You can see some front to back ratio vs. elevation plots for my portable flag on my simple portable flag website and here is the URL to that site: https://sites.google.com/site/portableflagantenna/home Problem with very small flags is that the noise figure of the preamp becomes a critical parameter, and because of this I don't recommend attenuators be placed before the preamp as this causes degradation in the signal to noise ratio. I stumbled upon this issue when doing field tests on one of the DX Engineering prototype preamps, and had them change the design so the attenuators now come after the actual amplifier stage which solved the problem. Everything I said above about the performance of very small terminated loops assumes no interaction with surrounding objects, and ignores issues related with feedlines since the feedline is very short on the portable flag. P.S. I make no money from DX Engineering as I agreed to not be paid in order to keep the price of the portable flag as low as possible. 73, Don (wd8dsb) _ Searchable Archives: http://www.contesting.co
Re: Topband: The WD8DSB mini-flag antenna
HI Steve, Thanks for the nice implementation comment. The portable flag front to back ratio is highly related to the elevation angle and frequency of operation (just like any terminated loop), and therefore I did not want to overstate the front to back ratio in my portable flag article. I designed the portable flag for direction finding local RFI (ground wave based signals) and therefore made sure I selected an appropriate termination resistor to provide a very deep null at low elevation angles on 160, 80 and 40 meters where I often deal with RFI (the portable flag has a very high front to back ratio at low elevation angles), and because of this it also has exceptional front to back ratio at low elevation angles down in the AM Broadcast Band. Very small flags have just as good front to back ratio and RDF as a full size flag as long as the appropriate termination resistor is used. The problem is when the flag becomes too large for the frequency of operation which causes the directional properties to degrade. You can see some front to back ratio vs. elevation plots for my portable flag on my simple portable flag website and here is the URL to that site: https://sites.google.com/site/portableflagantenna/home Problem with very small flags is that the noise figure of the preamp becomes a critical parameter, and because of this I don't recommend attenuators be placed before the preamp as this causes degradation in the signal to noise ratio. I stumbled upon this issue when doing field tests on one of the DX Engineering prototype preamps, and had them change the design so the attenuators now come after the actual amplifier stage which solved the problem. Everything I said above about the performance of very small terminated loops assumes no interaction with surrounding objects, and ignores issues related with feedlines since the feedline is very short on the portable flag. P.S. I make no money from DX Engineering as I agreed to not be paid in order to keep the price of the portable flag as low as possible. 73, Don (wd8dsb) _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
For finding 160 meter noise sources, I use a C-Crane or Sangean pocket AM band radio tuned to 1710 kHz. It also has a very sharp null due to the ferrite loop stick antenna built in. The QST antenna does have the advantage of being unidirectional, but I can often triangulate with the pocket radio by walking around and getting two different null directions. Rick N6RK On 2/23/2021 10:25 AM, John Kaufmann via Topband wrote: Some of you may have seen the article by WD8DSB in the latest issue of QST. I believe WD8DSB is on this reflector. His article describes a mini-flag antenna that can be used for direction-finding. The neat thing about this antenna, besides its compact size, is that it is unidirectional and is very broadband. It works from the AM BCB through 10m. It produces a sharp null off the back which allows you to determine signal direction without the direction ambiguity you get with a conventional unterminated loop. DX Engineering is producing this antenna as a kit, along with a companion preamp. (Disclaimer: I have no affiliation or commercial interest in DX Engineering). See: https://www.dxengineering.com/parts/dxe-noiseloop. I just bought the flag kit last week and finished assembling it this past weekend. I see today that the kit is now back-ordered until April so it was good that I ordered it as soon as I saw the QST article. It took me about 3 hours to assemble the mini-flag even though the DXE Web site says it can be done in 1-2 hours. There is a bit of fussy mechanical assembly involved in getting the symmetry and dimensions just right, although it's not hard work. The flag is 42 inches wide and 21 inches tall. The DXE version of the antenna has slightly smaller dimensions than those given in the QST article, which results in a small reduction in gain, which doesn't really matter, but the pattern is the same. I did some testing of the mini-flag in the AM BCB. The gain is very low--about -65 dBi on 160m--so it needs a good preamp. I used a homebrew preamp made up of a couple of MMIC's that produce about 35 dB of gain. The DXE preamp for this antenna won't be available until April. On the higher frequencies, less preamp gain is needed because the gain of the mini-flag increases with frequency. My initial tests indicate this antenna clearly works. By rotating the flag for the deepest null, I could nail the heading an AM BCB station to a few degrees. This antenna could also be used as directional receiving antenna on its own. Although it is not hugely directive, it can be rotated easily to peak or null signals or noise, and it is better than a conventional unterminated loop. It has essentially the same RDF as other larger flag or pennant antennas but is obviously far more compact. This is a nice contribution by WD8DSB. Now I have to go off with the mini-flag and chase some local noise sources that have been plaguing me this winter on the low bands. 73, John W1FV _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: The WD8DSB mini-flag antenna
Yes very nice article and design by Don. Flags/loops do not exhibit gain but rather directivity. The larger the loop the greater the capture area and the less of a need for a preamp. I routinely use my full size flag without any preamp external to the rig. A correctly designed and built full size flag will exhibit front/back of 25-30 db. If smaller loops (and I've tried many) have "essentially the same RDF as other larger flag or pennant antennas" I could have saved myself a lot of work by never having put up a full size flag. Size matters. For the purpose of direction finding of relatively close noise sources, Don's implementation looks excellent. 73 - Steve WB6RSE > On Feb 23, 2021, at 10:25 AM, John Kaufmann via Topband > wrote: > > This antenna could also be used as directional receiving antenna on its own. > Although it is not hugely directive, it can be rotated easily to peak or > null signals or noise, and it is better than a conventional unterminated > loop. It has essentially the same RDF as other larger flag or pennant > antennas but is obviously far more compact. > > > > This is a nice contribution by WD8DSB. Now I have to go off with the > mini-flag and chase some local noise sources that have been plaguing me this > winter on the low bands. _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: The WD8DSB mini-flag antenna
Some of you may have seen the article by WD8DSB in the latest issue of QST. I believe WD8DSB is on this reflector. His article describes a mini-flag antenna that can be used for direction-finding. The neat thing about this antenna, besides its compact size, is that it is unidirectional and is very broadband. It works from the AM BCB through 10m. It produces a sharp null off the back which allows you to determine signal direction without the direction ambiguity you get with a conventional unterminated loop. DX Engineering is producing this antenna as a kit, along with a companion preamp. (Disclaimer: I have no affiliation or commercial interest in DX Engineering). See: https://www.dxengineering.com/parts/dxe-noiseloop. I just bought the flag kit last week and finished assembling it this past weekend. I see today that the kit is now back-ordered until April so it was good that I ordered it as soon as I saw the QST article. It took me about 3 hours to assemble the mini-flag even though the DXE Web site says it can be done in 1-2 hours. There is a bit of fussy mechanical assembly involved in getting the symmetry and dimensions just right, although it's not hard work. The flag is 42 inches wide and 21 inches tall. The DXE version of the antenna has slightly smaller dimensions than those given in the QST article, which results in a small reduction in gain, which doesn't really matter, but the pattern is the same. I did some testing of the mini-flag in the AM BCB. The gain is very low--about -65 dBi on 160m--so it needs a good preamp. I used a homebrew preamp made up of a couple of MMIC's that produce about 35 dB of gain. The DXE preamp for this antenna won't be available until April. On the higher frequencies, less preamp gain is needed because the gain of the mini-flag increases with frequency. My initial tests indicate this antenna clearly works. By rotating the flag for the deepest null, I could nail the heading an AM BCB station to a few degrees. This antenna could also be used as directional receiving antenna on its own. Although it is not hugely directive, it can be rotated easily to peak or null signals or noise, and it is better than a conventional unterminated loop. It has essentially the same RDF as other larger flag or pennant antennas but is obviously far more compact. This is a nice contribution by WD8DSB. Now I have to go off with the mini-flag and chase some local noise sources that have been plaguing me this winter on the low bands. 73, John W1FV _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
