Hello to the group, this is my first post here.? I have a PIXEL PRO-1B (DXE-PRO-1B) that is mounted on a tripod, about 10' above ground and in the open.? The loop is being fed with 75 ohm quad shield coax.? No issues.

I've been using the loop with my FTDX-101D for diversity reception. While doing careful A/B comparisons between the loop and other wire antennas, I find that the strongest signal received varies based on time of day, frequency, distance to the target station, etc. It would be very interesting if there were guidelines one when the loop may have it's best performance? For example, on 75m, the loop seems pretty good during morning greyline propagation, but not at other times of the day.? My wire antennas generally outperform the loop (stronger signals, lower noise) as they are 40-65' above ground, but not always.

Are there any guidelines on when a loop may provide its best performance?

Regards,
Tom Kruczek
W1TXT?

I am sure someone will chine in and give a detailed explanation, but as very busy fixing car will just say..

If using a decent loop preamp on a small rx loop ( say 1m dia) the loop should give you a better sn ratio than say a low dipole..the dipole will give stronger readings on your S meter, but that is not important…

If say on 80m your dipole is up at 40m in a rural location then you probably won’t be needing a rx loop..but then again ..

Expect one antenna to be better than the other one day, then next day maybe not..

As many rx antennas as you can fit is always good..ask any low band dxer..

Simon G0zen

Thanks Simon.? The Pixel loop is 100% original and operating as it should.??

I'm very interested in comments to what I'm observing and if there is any science behind it.? As I type this, I'm listening to the AM broadcast band and the loop (RX1) at 10' is generally stronger, but noisier than my ZS6BKW (RX2) at 60'.? However, I expect the ZS6BKW to outperform the loop as propagation shifts from daytime to nighttime skip.? All parameters between the receivers are the same.? I've looked around the web and haven't found anything that discusses the science behind what I've been observing.

Also, and FYI, I live in what is considered a rural area with homes separated by at least a couple hundred feet and 2-acre zoning.?

Regards,
Tom Kruczek?
W1TXT

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Yes. Makes sense. You’re approaching the area where the pixel amplified loop starts to fall off. ?It should be better on LF and MW though.?

Many factors at play here...

• Polarization of antenna
• Polarization of received signal
  • Signal level is reduced considerably when signal and antenna polarization is orthogonal
  • With HF the ionosphere rotates polarization? -? can be slow or fast depending on conditions

• Man-made noise (local and distant) picked up by antenna and affecting SNR
  
  • Local noise can be horizontally or vertically polarized
  • Distant made made noise is vertically polarized
• Gain of antenna vs elevation and azimuth
  • gain varies considerably with frequency especially with loops
  • Height plays a significant factor here for all antennas
  • Loops work well a short distance above the ground
• Angle of arrival of signal - horizontally and vertical
  • HF DX often at low vertical angle

A good article about loop reception with links to references :
?

Roger

On Sun, Apr 3, 2022 at 10:53 PM, Roger Need wrote:

Many factors at play here...

• Polarization of antenna
• Polarization of received signal
  • Signal level is reduced considerably when signal and antenna polarization is orthogonal
  • With HF the ionosphere rotates polarization? -? can be slow or fast depending on conditions

• Man-made noise (local and distant) picked up by antenna and affecting SNR
  
  • Local noise can be horizontally or vertically polarized
  • Distant made made noise is vertically polarized
• Gain of antenna vs elevation and azimuth
  • gain varies considerably with frequency especially with loops
  • Height plays a significant factor here for all antennas
  • Loops work well a short distance above the ground
• Angle of arrival of signal - horizontally and vertical
  • HF DX often at low vertical angle

That's a very good summary, I was thinking along the same lines, but you beat me to it.

For me, Polarisation and Directivity would be the biggest factors.

Regards,

Martin

Great info and when taken in as a whole, it does indeed confirm what I'm seeing.?
Excellent links, too....thanks.
Tom Kruczek / W1TXT

Is anyone aware of a reference that describes the fading improvements that might be had by using an elliptically polarized antenna instead of a linearly polarized antenna to receive low-angle skywave transmissions on HF? ?Most literature I read seems to focus on linear receive antennas.?

?

Dave

On Wed, Apr 6, 2022 at 06:57 PM, <groups@...> wrote:

Is anyone aware of a reference that describes the fading improvements that might be had by using an elliptically polarized antenna instead of a linearly polarized antenna to receive low-angle skywave transmissions on HF? ?Most literature I read seems to focus on linear receive antennas.?

Most research / experiments of this nature have been focused on X and O wave propagation, typically using NVIS propagation on bands around 5MHz.

Some notes here



Some interesting notes on X & O wave propagation.



And also DSP applied to diversity reception and noise cancelling.



I think as an experiment, it would be fairly easy to put up a pair of crossed dipoles for 60m as inverted Vee's around a central support pole, and then with a phased 90 degree length of coax and some relay switching to swap between E-W / N-S / Clockwise / Anti-clockwise.

Regards,

Martin

I forgot to add this link, to what I think is pretty much the most ambitious amateur receive loop project I think I've seen (so far).



Regards,

Martin

Martin,

Thank you for those links, that 24 loop array is interesting. ?It seems like many HF users are leaving 3-6 dB of receive SNR on the table by not using circularly polarized antennas, and possibly more if the channel impulse response distribution is more favorable.

Dave

On Sat, Apr 9, 2022 at 10:48 PM, <groups@...> wrote:

It seems like many HF users are leaving 3-6 dB of receive SNR on the table by not using circularly polarized antennas, and possibly more if the channel impulse response distribution is more favorable.

Hi Dave,

Maybe, maybe not.

Like you I, think a lot depends upon how the noise component is distributed.

SNR is usually improved by greater directivity of the receive antenna, and omni coverage may be worse than the directional response of a single loop (RDF factor). However, circular polarisation may improve fading that could be present due to cross polarisation when using a linearly polarised antenna, so there are a number of factors that need to be taken into account.

One of my longer term projects is to refurbish two ex-military CSA crossed loop antennas that were once part of a Racal HF DF system. The antenna consists of a pair of loops mounted at right angles along a common axis, with separate loop amplifiers that are combined via a switched 90 degree hybrid, which can be used to select linear, clockwise and anti-clockwise circular polarisation.

I don't have the control unit and the loop amplifiers are a bit poor by modern standards, so my plan is to replace the two loop amplifiers, add a vertical active whip to the top of the loops and build a new combining unit. This should allow me to produce a cardioid pattern, so that I can electronically 'steer' the direction of the receive lobes and change between various types of polarisation, including omni and both types of circular. Hopefully the one antenna can then be used in place of my current 'farm' of active antennas.

Regards,

Martin