Re: Topband: K9AY Loop Questions
Thank you Jose, Here's an earlier Ref.. R. Keen; Wireless Direction Finding and Directional Reception 1927 Page 75. Describes Heart-Shape Circuit (Societe Francaise Radio Electrique) using a two turn loop with a connexion to ground via a variable resistor. It is very much like the K9AY. A two turn K9AY with the a 1m separation at the horizontal ends of the triangle or diamond shape with give approx. 3dB gain increase providing that the loops total length doesn't exceed approx. Lambda/4. Great for MW and LF work. Size for size this antenna has the highest gain of all the terminate cardioid loops. J. A. Lambert G3FNZ RadCom Nov. 82 Describes the C & S Antennas Ltd Directional active loop receiving antenna system. The article describes how cardioid pattern is created from the loops figure of 8 pattern ( H field ) and the monpole mode ( E field ). 73 Andrew Hi Andrew In this case it is very important to consider that both antennas are close to the ground. It means the reflection from the ground is different for vertical vectors, that see a image below the ground in the same phase and the horizontal vector that see a 180 degree image that cancel the horizontal components in opposite phase. The vertical components adds because they are in phase. There are very few books about loaded loop receiver antennas, most because the WWII use. https://wwrof.org/webinar-archive/high-performance-rx-antennas-for-a-small-lot/ See the slides download. You will find a reference of the first loaded loop patent. 1938 Horizontal polarized. Harold Beverage patents 1938 1941 ( 80 years ago) •US 2138134 A Phasing antennas •US 2247743 A Broad Band RX Antenna • https://patentimages.storage.googleapis.com/73/83/00/14943032331cef/US2247743.pdf and 1940 vertical polarized 1940. Nearly all the newly re-invented compact receive antennas derive from the terminated loop, the earliest reference was in an appallingly mimeographed prewar training manual of W3EEE Dad‘s 1973 COMMUNICATIONS 74 CONFERENCE BRIGHTON Wednesday, June 5 1974 — Session 5 Equipment Design Paper 5.3: Loop Antennas for HF Reception Contributed by: B.S.Collins, C & S Antennas Ltd., 73’s JC N4IS _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: K9AY Loop Questions
Hi Jose, I think that we are going to agree to disagree as to how these type of cardioid antennas work. Yes you are correct that there is a vertical antenna mode, but you can't ignore that the induce current from the H field has to be managed. Lets say that the induced currents from the E and H fields differ by 90 degrees or put it another way the currents are -45 and +45 degrees. These cannot be added to generate a cardioid. However, as these currents flow though the termination resistor, then the phase difference diminishes because the resistor tends to be the dominant reactance in the antenna. At a certain resistor value the induce currents can be equalise so that they can be added in a similar manner like a sense antenna in a loop DF system. As the relationship of the E and H field is constant over a wide bandwidth and so is cardioid. If you phase 2 verticals you will find that the rear pattern does shows a good high angle FB. This is not the case with a Flag. Now phase a loop with a vertical and you will see the opposite is true. Just like a simple Flag. 73 Andrew Hi Andrew He concept is very simple, you can phase 2 verticals. 3 verticals or 4 vertical. See you got, two verticals in phase give you a cardioid pattern, only one deep null on the back. Moving to 3 or 4 verticals gives you two deep side nulls plus some front back. The SAL does not have side lobe nulls. The feed system does no change the fact that you have only two vertical wires as antenna, the inclined wire can be describe as two vectors one vertical and another horizontal. The two vertical vector and the center of the inclined wire define the pattern. See the case of a DHDL, invented by George AA7JV, the vertical wires are far apart and the two inclined wires vertical vectors are half way each other. The DHDL has 4 verticals as the Waller Flag with two independent loops making 4 verticals as well, but the gain of the DHDL is 1-2 db below the WF. Why? the reflection between the two loops and the proximity of the two vertical vectors impact the DHDL pattern, as well the two verticals wires on the SAL. The SAL and the DHDL does not have side lobe nulls. One Loaded loop or EWE, K9AY RDF is close to 9 db, the SAL and DHDL are slighted better RDF 10 db on EZENEC, but again on practice, measuring the diagram of irradiation the SAL never achieved the extra 1 db in RDF. Two loaded loops has side lobe nulls and RDF is close to 12 db, very similar to 3 element yagi azimuth diagram. Both antennas, the SAL and the K9AY have impressive deep null on the back, giving you a good front back. It is a null on the back , very different than front rear, that take the 180 degree energy between the front and the back. You can find several stations using two DHDL in phase and it does work, but you wont find any array of two SAL because the phase is so critical that became impractical. 73's JC N4IS 73 Andrew Ikin G8LUG _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: K9AY Loop Questions
N4IS, Wrote on Jan. 7. " I’m afraid your information is not accurate, SAL is the same as a K9AY, the two wires close to each other can be removed because they cancel each other. The remain wires works like two vertical in phase, as the same in any flag, loaded loop or pennant. The cardioid pattern is the same." Jose, The SAL is a very close spaced phased array of two loop antennas, hence, it has high rejection of the Electric Field in the antennas near field at MF. The K9AY is a combination of a H and E field antenna, that generates its cardioid pattern by combining the two fields using the termination resistor to reduce the phase and amplitude difference between these fields. Hence, the K9AY and other similar antennas like the FLAG are prone to pattern distortion if nearby objects are within the antennas near-field. The SAL has different pattern compared to the K9AY. Early editions of Keens Wireless Direction Finding describe and two turn cardioid loop with a ground connexion in a similar fashion to the K9AY. 73 Andrew Ikin G8LUG _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground loop isolator that passes DC
Chuck Hutton, Wrote on Dec. 3. I guess what Chuck means, is a Ground loop due to the antenna end of the coax. screen being connected to Earth thus causing the feeder shield to become a loop antenna with the ground RF return path to Rx. Hence, resulting in excess noise pick-up. Normally common mode choke will be of benefit. But I would guess that Chuck has already tried this. One option could be fit a 1:1 isolation transformer at the Rx input or into the Bias T. Then use a floating power supply to the drive antenna pre-amp.. A bias T that already has a common mode choke on the DC input would help too. The Antenna Interfaces manufactures by Wellbrook have this choke feature. 73 Andrew Ikin G8LUG _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: Test message only
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Re: Topband: MFJ Receive Loop
Bill, I Bought one of these loops to evaluate. Without going into an in-depth critique. There are a few things that are worth noting. The loop amp. has an input z of 140 Ohms. Hence, there is loop/amp. miss-match at 1.8MHz i.e. the amp. input z should be approx. 20 Ohms. The amp. gain is low at just 19dB. Notwithstanding MFJ claims that MMIC amplifiers afford low noise. The reality is that the measured noise is approx. 6dB higher than thermal noise at 290 K. Thus we are looking at amp. + the loop NF of approx. 7dB. At 1.8MHz there is also a 4dB, loss due to the loop/amp/ miss-match. Therefore, the MFJ loop is only really suitable where the local noise is high. The W6LVP loop has a similar high noise figure at MF, but it does reduce to approx. 3dB above 4MHz. Also it provides a better loop/amp. match at MF compared to the MFJ. However, there maybe potential issue with IMD. The W6LVP amplifier third order OIP3 is low at +25dBm. The OIP2 is a respectable; +70/80dBm. The Low OIP3 may not seem a problem at first sight. But what it does; it reduces the overall power bandwidth of the amp. i.e. lets say you have 2 AM stations at about –10dBm output, the IMD will be –80dBm. This is still too high. If there are other lower level signals these will be affected because of the amp. is being driven into non-linearity. The Wellbrook ALA1530LN has an OIP3 of +50dBm. Therefore, with the same signal level compared to the W6LVP, the 3rd order IMD will 50dB lower compared to the W6LVP Loop. What is also interesting; neither MFJ or W6LVP provide any loop/amp. performance data. 1m dia. loops manufactured by Wellbrook and Pixel/Dx engineering have low IMD and much lower amp. noise figures; ranging from 0.2dB to 2dB respectively; thus making these antennas much more suitable for Dxing. 73 Andrew Ikin -Original Message- From: Bill Gillenwater Sent: Tuesday, September 25, 2018 5:31 PM To: topband@contesting.com Subject: Topband: MFJ Receive Loop Anyone have the MFJ 1886 receive loop? Any reviews on 160? Thanks, Bill K3SV _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: The band sans noise
Mike Waters wrote on April 22. snip< 1. What does the Pixel Loop do better than these and other loops? 2. What does the Pixel Loop's preamp do to improve the S/N ratio??? 3. And what IS its RDF?> The Pixel loop is balanced, so it will reject locally radiated E-Field noise providing this noise is within the near -field of the loop. This feature is not available with Vertical and terminated loop antennas. Plus the 20dB nulls previously mentioned. Also balanced loops afford very high rejection of conducted power-line noise. The Pixel loop pre-amp. doesn't improve the S/N ratio except that the IMD noise floor will be much lower compared to single ended amps. Generally speaking the amp. noise of the Pixel loop is on the high side compared to Wellbrook Loops. The RDF is about 5dB. End -fire phasing will improve the RDF whilst still providing rejection of near E-Field noise. However, one requires very low noise loops or larger loops to maintain a good S/N to compensate for phasing signal loss. 73 Andrew Ikin G8LUG _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low noise preamp suggestions?
Robert wrote on Nov. 3. <I’ve have built another TX3A.com DHDL antenna and am in search of a wide band low-noise preamp. My current custom built preamp has a 23db gain figure , as well as built in RX signal limiter , but I am unable to purchase a second unit from the manufacturer. Any recommendations for a high quality, low noise, broadband unit?> Rob, You may wish to have a look at the http://www.loop-antennas.com/Loop_Antennas/FLG100LN-2The Antenna Interface for the FLG100LN has a Rx signal limiter. 73 Andrew Ikin G8LUG _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low noise preamp suggestions?
Bill wrote on Nov. 3. AGC is an automatic variable gain function of a receiver to compensate for fluctuations in signal strength, a signal limiter, limits or clamps excess signal that could overload the receiver input circuits. The signal limiter could be a diode clamp or a saturated transformer. 73 Andrew _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: HMC580 instead of W7IUV preamp
Rick N6RK Wrote Sept 9. Snip<I've characterized this device and can tell you that the 1/f corner is well below 2 MHz, because it is based on HBT technology. The devices that are good at VHF and noisy at 2 MHz use MOSFET, GaAsFET, or ephemt technology. JFET devices are also low noise at 2 MHz if they have a sufficiently low channel resistance.> Both amps, being single ended are likely to be susceptible to second order IMD from BC AM band Tx. Whether one would notice much difference with a amp. with a less than 1dB NF versus the above mentioned types with higher NFs is debatable. The reason I say this is; is that the Flag has a high NF due to its termination resistance. With other antenna types the noise due to the loss resistance is a minute fraction of the antenna impedance. Hence, this noise resistance is mismatch to amp. input z. For example a very low noise JFet amp. (Wellbrook ALA100LN) when terminated with a loop antenna will provide a 6-8dB lower noise floor compared to the amp. being terminated with a resistance equal to its input z. 73 Andrew Ikin G8LUG _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Waller Flag Question
Bruce wrote on Sept 6. Snip < Check it out http://www.qsl.net/k4fk/presentations/WF-receiver-antennas-SFDXAs.pdf > Bruce, ref to the link above there is a gap in the "History of the Flag Antenna" The earliest fef. to the Terminate loop I have found is in Keen’s Wireless Direction Finding 1927 Ed. Page 75. Keen describes a two turn resistance terminated loop used by Societe Francaicse Radio-Electrique. It resembles the K9AY and uses a similar operation to create a cardiode. 73 Andrew Ikin G8LUG _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Waller Flag Question
Art Delibert wrote on Set. 6 snip would need about 40 dB of gain to boost the signal to a usable level. One of the postings says that cascading two preamps of 20 dB each seems to add extra noise, and they talk about developmental work being done on a single preamp of 40 dB. Is there now such a 40 dB preamp? Is it made commercially? Alternatively, are there plans on-line somewhere? Has someone actually used it in a high-RF urban/suburban area, with multiple 50 kW AM BC stations? With what results?> Art, The Wellbrook FLG100LN Flag Head amplifier may offer a partial solution to the gain and IMD issue with multiple 50kW AM Tx. The amp. has a 23dB gain and a near to zero NF. The current production has an OIP3 of +49dBm and OIP2 of +90dBm. Additional 17dB gain in the shack could be afforded with a Dxeng RPA-1. Unfortunately, the Website details for the FLG100LN have not been updated to reflect the new design. Basically the new FLG100LN is the ALA100LN Loop amplifier with an 800 Ohm input matching/ Isolation transformer. 73 Andrew Ikin G8LUG _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Test message ignore
The quick brown fox jumps over the lazy dog Andrew Ikin _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Preamplifiers
Andy, The Clifton Labs Norton and the RPA-1 are both Push-pull designs and thus have high +80dBm second order intercepts. This is essential to avoid BCB mixing products affecting TB. Single ended amplifiers like the W7IUV may need some pre BCB filtering. 73 Andrew Ikin G8LUG _ Topband Reflector Archives - http://www.contesting.com/_topband
