Re: [Elecraft] The use of a doublet
I use mine with a 2 x 88ft doublet fed straight in and it works on all bands. David G3UNA - Original Message - From: THOMAS BRERETON w2...@msn.com To: Elecraft Reflector Elecraft@mailman.qth.net Sent: Wednesday, July 15, 2009 11:44 PM Subject: [Elecraft] The use of a doublet I have long been an advocate of the center fed doublet. I have put them up in numerous state and even in Germany. Of course I have used different tuners. Folks here in this write about of all kinds of external tuners. May I make a radical suggestion? Use the internal K3 antenna tuner! Now I know that most transceivers have internal tuners that will operate well only up to 3:1 swr. The K3 tuner is rated much higher than that. Indeed, I was very surprised how well it works here in my station with my 135' foot dipole with 450 ohm ladder line and a balun. I highly recommend that one should consider the K3 tuner. It's a winner. Tom Brereton, W0TOM __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
Joe, Thank you for thst wonderful reference. Steve, W2MY -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net]on Behalf Of Joe Planisky Sent: Wednesday, July 15, 2009 9:29 PM To: Elecraft Reflector Subject: Re: [Elecraft] The use of a doublet For those who might be a little mystified by this discussion of feedlines and antennas, I can recommend the series of articles titled Another Look at Reflections by M. Walter Maxwell (W2DU/W8HKK) published in QST between 1973 and 1976. The whole series is available as a single PDF file at http://www.arrl.org/members-only/tis/info/pdf/Reflect.pdf (for ARRL members only, sorry.) 73 -- Joe KB8AP __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
I use the K3 internal tuner then to a BL2. Most bands are good with the 1:1 ratio. That little switch is handy to go to 4:1 for some bands. I have a 85 m loop and have worked 160 to 6 meters with good results. On 160 I do have to tie the 450 Ohm line wires together and feed it against ground. A DPDT knife switch does that for me. 73, Ty, W1TF, K3 #696 __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
Tom, W0TOM wrote: May I make a radical suggestion? Use the internal K3 antenna tuner! Now I know that most transceivers have internal tuners that will operate well only up to 3:1 swr. The K3 tuner is rated much higher than that. Indeed, I was very surprised how well it works here in my station with my 135' foot dipole with 450 ohm ladder line and a balun. I highly recommend that one should consider the K3 tuner. It's a winner. -- That's true of all the Elecraft tuners, AFAIK except the KX1's optional internal ATU. Perhaps it speaks to Wayne's roots as a QRP enthusiast who loves operating portable that the Elecraft tuners all have a very good matching range. The KX1 has a slightly smaller range simply because he ran out of room to squeeze any more toriods into the tiny space allotted to the tuner. Even so, it'll load up most ad-hoc random wires and doublets. That said, the limitation on all tuners is what maximum currents (when feeding very low impedance loads) and what maximum voltages(when feeding high impedance loads) they can handle without parts failing. The smaller the physical size of the tuner, the greater these limits, especially on voltages. Anyone who has messed with a Tesla coil can attest to how high voltage RF behaves. Nothing can replace lots of physical separation between components, and that's not possible in a physically small tuner. A little attention to avoiding a voltage loop at the rig end of the feeder will avoid that extreme condition. Although baluns can be very unpredictable (and sometimes lossy) at extreme impedances, many Hams have successfully used a 4:1 balun, like the Elecraft BL2, to reduce the impedance at the rig to something the ATU can more easily handle. That has the same effect as adding or subtracting feed line or adjusting the length of the antenna, and it's obviously easier to do. Ron AC7AC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
Can anyone point to why the single coil Z match wasn't commercialised rather than the T match? (Perhaps it's a historical thing and manufacturers just copy each other, notwithstanding the Johnson Matchbox of course, which is no longer produced.) I'm in process of building one to cover 160 to 10 from VK2BR (?). I'm hoping that the link coupling will help with balanced feeders and antennas, though one side is bound to have more capacitance to earth than the other, so balanced is fairly relative. David G3UNA __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
That should be VK5BR Lloyd Butler http://users.tpg.com.au/users/ldbutler/SingleCoilZMatch.htm David G3UNA d.cut...@ntlworld.com wrote: Can anyone point to why the single coil Z match wasn't commercialised rather than the T match? (Perhaps it's a historical thing and manufacturers just copy each other, notwithstanding the Johnson Matchbox of course, which is no longer produced.) I'm in process of building one to cover 160 to 10 from VK2BR (?). I'm hoping that the link coupling will help with balanced feeders and antennas, though one side is bound to have more capacitance to earth than the other, so balanced is fairly relative. David G3UNA __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
For years I've used a a Z-match tuner I built using very husky components - big transmitting variables, salvaged 3 diameter silver plated tank coil and a 9:1 gear reduction drive for the main tuning cap. It works very well tuning a doublet fed with 450 ohm window line -- but even with the 9:1 reduction tuning can be very sharp. It's also more sensitive to slight variations caused by antenna movement etc. since you're tuning for near resonance. Those may be reasons it wasn't commercialised (much). In comparison, the Palstar BT1500A balanced L tuner I acquired a while back is less fussy - tuning isn't nearly as fast or critical. It also has the virtue of highly repeatable settings - it's quicker and easier to hop from band to band. Bob NW8L On Wed, Jul 15, 2009 at 3:44 AM, d.cut...@ntlworld.com wrote: Can anyone point to why the single coil Z match wasn't commercialised rather than the T match? (Perhaps it's a historical thing and manufacturers just copy each other, notwithstanding the Johnson Matchbox of course, which is no longer produced.) I'm in process of building one to cover 160 to 10 from VK2BR (?). I'm hoping that the link coupling will help with balanced feeders and antennas, though one side is bound to have more capacitance to earth than the other, so balanced is fairly relative. David G3UNA __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
Can anyone point to why the single coil Z match wasn't commercialised rather than the T match? (Perhaps it's a historical thing and manufacturers just copy each other, notwithstanding the Johnson Matchbox of course, which is no longer produced.) I'm in process of building one to cover 160 to 10 from VK2BR (?). I'm hoping that the link coupling will help with balanced feeders and antennas, though one side is bound to have more capacitance to earth than the other, so balanced is fairly relative. David G3UNA I believe it comes back to addressing the largest possible market with the simplest product, David. Relatively inexpensive Shunt-L T-network commercial tuners (e.g. MFJ) appeared in great quantity as no tune solid state transceivers became popular. These transceivers are really not no tune but, instead, are pre tuned for specific load impedance. The user is required to provide a pre tuned load that shows the proper impedance, indicated by a low SWR at the transmitter output. Unfortunately, many antennas in common use as the no-tune rigs came on the market - trap dipoles, multiple paralleled dipoles, trap verticals or, frequently, an end-fed random wires - provided the required match across the bands. The external tuner solved the problem, providing the low SWR the modern rigs required when feeding these antennas and able to handle an impedance range similar to the popular Pi-network used in older transmitter outputs that previously fed these antennas. In short, no tune rigs just moved the output tuning from the transmitter or transceiver itself to an external box: the antenna tuner. Although the Shunt-L, T-network can be very lossy, it can be very efficient too when used properly. The key is to adjust it for lowest Q where the circulating currents in the coil are lowest. Just like feed lines, With the Shunt-L T-network the lowest Q and lowest loss occur with the *least* inductance in the circuit that can provide a match to the rig. Again, keeping things simple to address the basic needs of the most customers, manufacturers like MFJ use an inexpensive switch-tapped inductor in their original tuners. The taps, inductance and capacitor ranges were established to provide a match from a few tens of ohms to 600 ohms or so. They'd match much wider ranges of impedances, but it was not unusual to discover that the tap settings weren't optimal. In some cases that led to situations where high circulating currents and losses occurred because the taps were too far apart. And of course, some tuners are used by Hams who have never carefully studied the manual that came with it, so they ended up using the wrong settings with the mistaken belief that all was well if the SWR on the link to the rig was low. Some years ago, Kevin Schmidt, W9CF, wrote a neat little Shunt-L T-Match tuner simulator in Java that's available to play with on line at many sites. One is here: http://fermi.la.asu.edu/w9cf/tuner/tuner.html You can download the program or run it on the WEB page, twirling the knobs with your mouse. It gives you the input/output impedances with the inductance and capacitance needed and the loss as a percentage of power and in dB for a given setting. I'm not sure what all the assumptions about conductor losses, etc., were for this simulator, but playing with it provides an intuitive feel for how the T-match works. I ignored one type of antenna that was quite popular about the time the no tune rigs appeared. That was the folded dipole. It was cheap and easy to make from 300 ohm twin-lead or home-made open wire line, avoiding the expense of coax for a very efficient and relatively broad band antenna, covering much if not all of the 80 meter band with a decently low SWR. But it needed a balanced feed. So MFJ and others provided a 4:1 toroidal balun in their tuners specifically to provide for these types of antennas (including the variant of the Windom fed with twin lead that was becoming popular too). Those baluns work well when feeding an impedance somewhere around 300 to 600 ohms, transforming it to about 50 or 100 ohms, right in the middle target range for the T-network to match most efficiently. Of course, many Hams immediately attached those baluns to their open-wire fed multiband doublets. That works fine where the antenna and feed line combine to provide a low impedance at the rig. Where the impedance is very high it doesn't. Again, the manuals with most Shunt-L T-network tuners I've seen say to avoid situations where the feed point impedance is high. MFJ, for example, goes so far as to give owners combinations of feed line lengths and antenna lengths to avoid with a doublet and cautions about using them with Windom antennas under certain situations to avoid these impedance extremes. That's why I have a wide-range link-coupled tuner for use with a doublet. That sort of
Re: [Elecraft] The use of a doublet
I'm using a 66' doublet fed with homebrew ladder line for portable operations in my yard. I have it flat top up in a tree about 35' up. I made a small adapter to go from the ANT1 connector from my KAT3 to a couple of banana sockets. I then bring the ladder line straight into that adapter. I wound up with a feedline length of around 55' and the KAT3 tunes up on this arrangement 80m-10m FB. It is obviously very short for 80m and I don't use it on that band, but the KAT3 did tune up on it (I'm sure not very efficiently). I've been running 5 watts out there and worked a number of states. I worked Italy on 5 watts last summer on 20m. I hooked the doublet directly to the KAT3 at the urging of Ron (AC7AC) and Don (W3FPR) here on the list and have been very happy with it. 73, Dave W8FGU THOMAS BRERETON wrote: I have long been an advocate of the center fed doublet. I have put them up in numerous state and even in Germany. Of course I have used different tuners. Folks here in this write about of all kinds of external tuners. May I make a radical suggestion? Use the internal K3 antenna tuner! Now I know that most transceivers have internal tuners that will operate well only up to 3:1 swr. The K3 tuner is rated much higher than that. Indeed, I was very surprised how well it works here in my station with my 135' foot dipole with 450 ohm ladder line and a balun. I highly recommend that one should consider the K3 tuner. It's a winner. Tom Brereton, W0TOM __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
Tom (and all others who have commented), Please pass along the length and type of your feedline when making statements of the effectiveness and ease of tuning for your antenna. With a resonant halfwave dipole fed with coax (or any line matched to the antenna impedance), the feedline length is not important, but most multiband antennas are not like that and the feedline length is a very important parameter. The feedline is a part of the antenna system, and when not matched to the antenna feedpoint impedance, it will act as an impedance transformer. Your particular antenna and feedline may work just fine, but the same antenna with a different feedline length may not work out well. So for others to duplicate your experiences (or attempt to), please add the length and type of feedline. 73, Don W3FPR THOMAS BRERETON wrote: I have long been an advocate of the center fed doublet. I have put them up in numerous state and even in Germany. Of course I have used different tuners. Folks here in this write about of all kinds of external tuners. May I make a radical suggestion? Use the internal K3 antenna tuner! Now I know that most transceivers have internal tuners that will operate well only up to 3:1 swr. The K3 tuner is rated much higher than that. Indeed, I was very surprised how well it works here in my station with my 135' foot dipole with 450 ohm ladder line and a balun. I highly recommend that one should consider the K3 tuner. It's a winner. Tom Brereton, W0TOM __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
For those who might be a little mystified by this discussion of feedlines and antennas, I can recommend the series of articles titled Another Look at Reflections by M. Walter Maxwell (W2DU/W8HKK) published in QST between 1973 and 1976. The whole series is available as a single PDF file at http://www.arrl.org/members-only/tis/info/pdf/Reflect.pdf (for ARRL members only, sorry.) It's a very thorough treatment of the subject of transmission lines and impedance matching. Easy reading in some places and a bit tougher in others, it's well worth close and careful study if you want to understand transmission lines and matching. 73 -- Joe KB8AP On Jul 15, 2009, at 4:34 PM, Don Wilhelm wrote: ... The feedline is a part of the antenna system, and when not matched to the antenna feedpoint impedance, it will act as an impedance transformer. Your particular antenna and feedline may work just fine, but the same antenna with a different feedline length may not work out well. ... __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
DX Engineering shared an antenna with me that I put up and it works
wonderful on all bands with a tuner. 120 ft and fed with 90 ft of 300 ohm
line into a 1:1 balun of theirs and into the tuner with RE 213. Tuner is a
Palstar AT2K. The feed line length must be 90 feet. YES, it really works.
Phil
Philip LaMarche
LaMarche Enterprises, Inc.
www.instantgourmetspices.com
www.w9dvm.com
800-395-7795 pin 02
727-944-3226
FAX 727-937-8834
NASFT 30210
K3 #1605
CCA 98 00827
CRA 1701
W9DVM
-Original Message-
From: elecraft-boun...@mailman.qth.net
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of dw
Sent: Tuesday, July 14, 2009 12:26 PM
To: Elecraft_List
Subject: [Elecraft] The use of a doublet
Great post Rick!
Yes, the doublet has been over the years for me the easiest and best
performing all band single antenna I've ever had.
I feed mine with 450 also, but the top is only 135' long.
I use the more robust SGC auto-tuner in external config.
40 feet of good quality coax and a high quality balun feed the tuner.
With 20 watts applied, it finds best match in 3 seconds.
It makes me feel like I'm cheating!! ;^D
Duane
N1BBR
Hello Jim,
I saw two of those tape measures once and they were actually part of a
military dipole antenna system. The original antenna had 2 of them and you
just pulled them ou to the coresponding frequency measurements on each side
and you had a resonant dipole for that frequency. So if your friend used
that to measue the wire with, then its most likely somewhere around 33 feet
on each side. Being fed with 300 ohm balanced feedline makes your antenna a
doublet - and a doublet is a very good all band antenna ! I use a doublet
here that is 178 feet long - 89 feet per side and fed with 450 ohm feedline
and it works 10 thru 160 meters via the tuner.
73 - Rick McKee, KC8AON
Southern Ohio - EM88sn
www.angelfire.com/electronic2/qrp
With God all things are possible ~ ((' ~
--
bw...@fastmail.net
__
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Re: [Elecraft] The use of a doublet
How do you establish that, it really works? --- On Tue, 7/14/09, Phil LaMarche plama...@verizon.net wrote: DX Engineering shared an antenna with me that I put up and it works wonderful on all bands with a tuner. 120 ft and fed with 90 ft of 300 ohm line into a 1:1 balun of theirs and into the tuner with RE 213. Tuner is a Palstar AT2K. The feed line length must be 90 feet. YES, it really works. Phil __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
The beauty of a doublet is that the length of the radiator and the length of the feed line is completely unimportant if you have a wide-range tuner and the radiator is at least 1/2 wave end-to-end. With modern tuners -especially most automatic types - the feeder can present an impedance outside their matching range. That requires adjusting the feed line length to find something that will provide a match on all bands. Such an antenna should work as well or better than a dipole at equivalent height all frequencies at which it is at least 1/2 wavelength long. If good open wire line with a moderate impedance in the 450-600 ohm range is used, the line losses are very low thanks to the moderate SWR. Typically the SWR on any frequency will be less than 10:1, which won't result in significant losses if the conductors are of a decent size. Extremely high currents can flow at some points along the line, and large conductors help minimize the ohmic losses in the line. For that reason, 300 ohm twinlead or 450 ohm ladder line works, but has larger-than-necessary losses because of the small diameter conductors those lines use. Whenever possible, I use a #12 or larger wire for my open wire lines. At frequencies where the antenna is considerably longer than 1/2 wavelength, it shows some gain over a dipole with narrower but stronger lobes. It will work well down to where the antenna is only 1/4 wavelength end-to-end, showing only a small loss compared to a full size dipole. The problem there is that the SWR on the feeder jumps up as the impedance drops quickly at that size. Ron AC7AC -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Phil LaMarche Sent: Tuesday, July 14, 2009 9:32 AM To: 'dw'; 'Elecraft_List' Subject: Re: [Elecraft] The use of a doublet DX Engineering shared an antenna with me that I put up and it works wonderful on all bands with a tuner. 120 ft and fed with 90 ft of 300 ohm line into a 1:1 balun of theirs and into the tuner with RE 213. Tuner is a Palstar AT2K. The feed line length must be 90 feet. YES, it really works. Phil __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
The ladder line I purchased from DX Engineering is rated at full legal limit and 18 gage conductors with 19 strands of copper clad steel wire, resulting in a velocity factor of .88. Should it be larger? Phil Philip LaMarche LaMarche Enterprises, Inc. www.instantgourmetspices.com www.w9dvm.com 800-395-7795 pin 02 727-944-3226 FAX 727-937-8834 NASFT 30210 K3 #1605 CCA 98 00827 CRA 1701 W9DVM -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Ron D'Eau Claire Sent: Tuesday, July 14, 2009 1:16 PM To: 'Elecraft_List' Subject: Re: [Elecraft] The use of a doublet The beauty of a doublet is that the length of the radiator and the length of the feed line is completely unimportant if you have a wide-range tuner and the radiator is at least 1/2 wave end-to-end. With modern tuners -especially most automatic types - the feeder can present an impedance outside their matching range. That requires adjusting the feed line length to find something that will provide a match on all bands. Such an antenna should work as well or better than a dipole at equivalent height all frequencies at which it is at least 1/2 wavelength long. If good open wire line with a moderate impedance in the 450-600 ohm range is used, the line losses are very low thanks to the moderate SWR. Typically the SWR on any frequency will be less than 10:1, which won't result in significant losses if the conductors are of a decent size. Extremely high currents can flow at some points along the line, and large conductors help minimize the ohmic losses in the line. For that reason, 300 ohm twinlead or 450 ohm ladder line works, but has larger-than-necessary losses because of the small diameter conductors those lines use. Whenever possible, I use a #12 or larger wire for my open wire lines. At frequencies where the antenna is considerably longer than 1/2 wavelength, it shows some gain over a dipole with narrower but stronger lobes. It will work well down to where the antenna is only 1/4 wavelength end-to-end, showing only a small loss compared to a full size dipole. The problem there is that the SWR on the feeder jumps up as the impedance drops quickly at that size. Ron AC7AC -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Phil LaMarche Sent: Tuesday, July 14, 2009 9:32 AM To: 'dw'; 'Elecraft_List' Subject: Re: [Elecraft] The use of a doublet DX Engineering shared an antenna with me that I put up and it works wonderful on all bands with a tuner. 120 ft and fed with 90 ft of 300 ohm line into a 1:1 balun of theirs and into the tuner with RE 213. Tuner is a Palstar AT2K. The feed line length must be 90 feet. YES, it really works. Phil __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT:The use of a doublet
Ron D'Eau Claire wrote: Extremely high currents can flow at some points along the line, and large conductors help minimize the ohmic losses in the line. For that reason, 300 ohm twinlead or 450 ohm ladder line works, but has larger-than-necessary losses because of the small diameter conductors those lines use. Whenever possible, I use a #12 or larger wire for my open wire lines. It will work well down to where the antenna is only 1/4 wavelength end-to-end, showing only a small loss compared to a full size dipole. The problem there is that the SWR on the feeder jumps up as the impedance drops quickly at that size. I noticed an improvement with my DJ4VM quad, which is a balanced 2 el design for 20M, but works with gain on the other HF bands. No problem on 20 and above, but I found that feeding it with 450 ohm twin on 30M where the impedance is low was a problem. I got round it by putting a 9:1 balun between the element and the line. Now, having beefed up the guage of the element itself, it tunes 30m without the balun and I can get 599 reports from the East Coast USA on my 10 watt K3. Good f/b also. It would seem from what you say Ron, that increasing the feeder guage may be make it even better. Another not unexpected result was experienced when using a G4LNA quad loop, a vertical square about 25 feet each side for 160M http://www.qsl.net/g4lna/pages/myant.html This is fed with 50ohm coax to a step down transformer on a ferrite ring. The secondary goes to a series variable C then on to the loop. Mounted only anout 2 feet above group, this radiates a big signal on topband for its size and was only a couple of s points down on my half wave doublet. I thought I'd be clever and ditch the transformer and slap the 450 ohm line straight on to the loop and let the balanced tuner handle it. Guess what. The SWR was perfect - but everything was being lost in the line / and or the tuner. The G5RV is another story. Everyone misuses these antennas. They should be fed balanced all the way and they become - a doublet. As most folk use them, with a balnced transformer into, hopefully, a balun, then coax into a tuner. This is a definate no no. The transformer can only be right for a given frequency and that will change with height above ground, whether the elements are horizontal or inverted V etc. Nothing wrong with a 5RV if fed directly with balanced line - but you would be better cutting it as an extended double zepp for 20 and get 3DBd gain. 73 John Petters www.traditional-jazz.com Amateur Radio Station G3YPZ -- John Petters www.traditional-jazz.com Amateur Radio Station G3YPZ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
I've used the less expensive flat 300 ohm TV twinlead at the legal limit (unknown velocity factor, unknown quality, etc) and it worked very well and never melted any of it! But if you're willing to pay for the bigger better feedline, I am very sure that although it will work much the same, it will look incredibly better! And WorldRadio will publish the pictures to prove it. 73HankK8DD Phil LaMarche wrote: The ladder line I purchased from DX Engineering is rated at full legal limit and 18 gage conductors with 19 strands of copper clad steel wire, resulting in a velocity factor of .88. Should it be larger? Phil Philip LaMarche LaMarche Enterprises, Inc. www.instantgourmetspices.com www.w9dvm.com 800-395-7795 pin 02 727-944-3226 FAX 727-937-8834 NASFT 30210 K3 #1605 CCA 98 00827 CRA 1701 W9DVM __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
I thought the wire gauge was of little importance with parallel feeder, since the energy flow is between the wires not in them. The insulation is of more importance. You might want something stronger for mechanical reasons. I used that pink tv twin many years ago and learnt that the terminations need to be well sealed to prevent water ingress. It is lightweight and thus adds little to drag the feedpoint down (catenary), however, I had to take a lot of care at the joints to relieve wind stress which otherwise causes breakages. David G3UNA Subject: Re: [Elecraft] The use of a doublet I've used the less expensive flat 300 ohm TV twinlead at the legal limit (unknown velocity factor, unknown quality, etc) and it worked very well and never melted any of it! But if you're willing to pay for the bigger better feedline, I am very sure that although it will work much the same, it will look incredibly better! And WorldRadio will publish the pictures to prove it. 73HankK8DD Phil LaMarche wrote: The ladder line I purchased from DX Engineering is rated at full legal limit and 18 gage conductors with 19 strands of copper clad steel wire, resulting in a velocity factor of .88. Should it be larger? Phil __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
Quite true, David, but that energy flowing along the feed line induces currents in the feeder wires as the currents produce the field. Those currents can be considerable at the current loops, even at low RF power levels and, considering that the current is flowing along the surface of the wire, the resistance of the wire at RF is much greater than at dc. It's my understanding that it's that resistance that cause feeder losses you see on the loss vs. frequency curves as the SWR rises above 1:1. That's why the curves are straight lines. They represent simple resistance. Of course, what makes open wire feeders superior to coax is that the practical impedance of coax is limited to fairly low levels, meaning much higher SWRs when terminated at a voltage loop on the radiator. In practical antennas that voltage loop may show as much as 4,000 ohms, resulting in a very high SWR on a 50 or 75 ohm line but a rather modest SWR on 450 or 600 ohm line. Of course that holds down the current maxima. I have not done a numerical analysis of the loss of open wire line using small vs. large conductors. Obviously, large conductors offer lower resistive losses but I, too, have used small diameter feed line conductors for light weight when I had to let the antenna carry the weight of the feedline. I'd not panic over using 450 ohm or, in a pinch, even 300 ohm twinlead if that was what was fit the situation. But when I can, I use larger wire. Even so, in my overflowing notebook of experiments I'd like to do is to set up, say, 100 feet of open wire line and terminate it in an impedance that produces an SWR of, say 10:1, then measure the loss with different diameter conductors. Antennas are like any other part of our gear: if we stick with what the manufacturers offer us, it's pretty simple. But manufacturers are trying to address the biggest audience with the most fool-proof designs. They can be good performers too, but that's not their most important criteria. Us O.T.s learned that with the Gotham vertical decades ago and the newer Hams are seeing it in the absurd claims of gadgets like the magic antenna. In both cases performance' is a distant concern to the manufacturer compared to a broad appeal based on the idea that they are very easy to set up and use. At the other extreme are a very few options requiring specific installations and environments for proper performance. If we have the room and money for a tower or some really high poles, we're in luck. If not, we're pretty much on our own designing the best antenna for our individual situations. I find that part of the fun -- and part of the frustration when I'm convinced I did it wrong, Hi! I generally install my doublets inverted V style if I have only one support and run the open wire feeder up the support. If it's metal I keep it several line spacings from the support, of course. That way the weight of the feeder is unimportant and it's easy to install it so it's stable and free from twisting. I can use rather large wire easily. 73, Ron AC7AC -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of David Cutter Sent: Tuesday, July 14, 2009 3:01 PM To: .hank.; Phil LaMarche Cc: 'Elecraft_List' Subject: Re: [Elecraft] The use of a doublet I thought the wire gauge was of little importance with parallel feeder, since the energy flow is between the wires not in them. The insulation is of more importance. You might want something stronger for mechanical reasons. I used that pink tv twin many years ago and learnt that the terminations need to be well sealed to prevent water ingress. It is lightweight and thus adds little to drag the feedpoint down (catenary), however, I had to take a lot of care at the joints to relieve wind stress which otherwise causes breakages. David G3UNA Subject: Re: [Elecraft] The use of a doublet __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
This is simply untrue on all counts. Is wire size unimportant in AC power circuits? Of course not. Larger wire simply has lower resistive loss. Ohm’s law is still in effect at radio frequency. And for a given size, as the frequency increases, the resistance increases due to skin effect. So wire size can be more important at h-f. Also, assuming that the dielectric is mostly air, polyethylene or something comparable, the loss due to the dielectric is immaterial for all practical purposes. --- On Tue, 7/14/09, David Cutter d.cut...@ntlworld.com I thought the wire gauge was of little importance with parallel feeder, since the energy flow is between the wires not in them. The insulation is of more importance. You might want something stronger for mechanical reasons. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] The use of a doublet
Maybe notes 10 and 11 here: http://k6mhe.com/n7ws/ will be helpful. --- On Tue, 7/14/09, Ron D'Eau Claire r...@cobi.biz wrote: From: Ron D'Eau Claire r...@cobi.biz Subject: Re: [Elecraft] The use of a doublet To: 'David Cutter' d.cut...@ntlworld.com, '.hank.' k...@inbox.com, 'Phil LaMarche' plama...@verizon.net Cc: 'Elecraft_List' elecraft@mailman.qth.net Date: Tuesday, July 14, 2009, 5:02 PM Quite true, David, but that energy flowing along the feed line induces currents in the feeder wires as the currents produce the field. Those currents can be considerable at the current loops, even at low RF power levels and, considering that the current is flowing along the surface of the wire, the resistance of the wire at RF is much greater than at dc. It's my understanding that it's that resistance that cause feeder losses you see on the loss vs. frequency curves as the SWR rises above 1:1. That's why the curves are straight lines. They represent simple resistance. Of course, what makes open wire feeders superior to coax is that the practical impedance of coax is limited to fairly low levels, meaning much higher SWRs when terminated at a voltage loop on the radiator. In practical antennas that voltage loop may show as much as 4,000 ohms, resulting in a very high SWR on a 50 or 75 ohm line but a rather modest SWR on 450 or 600 ohm line. Of course that holds down the current maxima. I have not done a numerical analysis of the loss of open wire line using small vs. large conductors. Obviously, large conductors offer lower resistive losses but I, too, have used small diameter feed line conductors for light weight when I had to let the antenna carry the weight of the feedline. I'd not panic over using 450 ohm or, in a pinch, even 300 ohm twinlead if that was what was fit the situation. But when I can, I use larger wire. Even so, in my overflowing notebook of experiments I'd like to do is to set up, say, 100 feet of open wire line and terminate it in an impedance that produces an SWR of, say 10:1, then measure the loss with different diameter conductors. Antennas are like any other part of our gear: if we stick with what the manufacturers offer us, it's pretty simple. But manufacturers are trying to address the biggest audience with the most fool-proof designs. They can be good performers too, but that's not their most important criteria. Us O.T.s learned that with the Gotham vertical decades ago and the newer Hams are seeing it in the absurd claims of gadgets like the magic antenna. In both cases performance' is a distant concern to the manufacturer compared to a broad appeal based on the idea that they are very easy to set up and use. At the other extreme are a very few options requiring specific installations and environments for proper performance. If we have the room and money for a tower or some really high poles, we're in luck. If not, we're pretty much on our own designing the best antenna for our individual situations. I find that part of the fun -- and part of the frustration when I'm convinced I did it wrong, Hi! I generally install my doublets inverted V style if I have only one support and run the open wire feeder up the support. If it's metal I keep it several line spacings from the support, of course. That way the weight of the feeder is unimportant and it's easy to install it so it's stable and free from twisting. I can use rather large wire easily. 73, Ron AC7AC -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of David Cutter Sent: Tuesday, July 14, 2009 3:01 PM To: .hank.; Phil LaMarche Cc: 'Elecraft_List' Subject: Re: [Elecraft] The use of a doublet I thought the wire gauge was of little importance with parallel feeder, since the energy flow is between the wires not in them. The insulation is of more importance. You might want something stronger for mechanical reasons. I used that pink tv twin many years ago and learnt that the terminations need to be well sealed to prevent water ingress. It is lightweight and thus adds little to drag the feedpoint down (catenary), however, I had to take a lot of care at the joints to relieve wind stress which otherwise causes breakages. David G3UNA Subject: Re: [Elecraft] The use of a doublet __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
