Noise cancelling techniques - Your advice needed

[ON4KHG]

Dears,



Even in a rural environment where I live, It’s increasingly difficult do make terrestrial “weak signals” traffic (at least on 2m), due to solar panels, LED’s, etc. EME is even more difficult of course !

So, I’m gaining interest in “noise cancelling” techniques to (try to) get rid of these interfering noise sources.
My main 2 m antenna for terrestrial or EME is 2x9 el side by side. In between, I have installed a small 4 el as “noise pick-up” antenna.

The goal of the technique (which is not new) is to adjust the respective noise powers received on the main and on the pick-up antennas so that the amplitudes are of the same magnitude order and the phase so that they are 180° out of phase to cancel each other. Except installing the noise pick-up antenna, I haven’t made experiments yet so far.

To point is that on the 4 el noise pick-up antenna the interfering noise has a lower magnitude than on the main 2x9el (which is normal of course !)
In that condition, I fear the noise cancellation ratio will be far from optimal ?

The noise cancelling can be done thanks to analogue or software means. I prefer software ones, Linrad allows it. SDR Uno and SDR Play also (diversity mode), and probably others too.

I think the best way to achieve noise cancelling is to use HV or Xpol antennas, assuming the interfering noise is not polarized (does that assumption makes sense or is it a bit silly ?). This way, the noise power magnitude will be the same on the 2 polarizations and the noise cancelling radio should be optimal I think.
My question here : does somebody here has experience in that domain ? If yes, I’m taker of any advice (and I think I’m not the only one !)

Thanks in advance for your support.
73,

Gaëtan, ON4KHG
http://on4khg.be

[Earl Shaffer]

Gaëtan

Your noise will nearly always be polarized.  It will usually not be in the same general direction as the moon.

I suggest an independent  installation of your noise antenna such as your 4 element yagi probably vertically polarized.

Much of the time you may be able to null your noise by choosing  the opposite polarization of the noise.

You can start by identifying noise source directions and polarization by using your EME array. Armed with that information,

I would spend some time using that 4 element yagi held in your hand with a portable 2 meter SSB receiver to see what sources of noise are significant. In some cases you might fix them at their source. Armed with information about location and polarity you will be able to decide the best way to null it out. Perhaps there is only one bad noise source and you can dedicate a fixed yagi pointed at it in an optimal location. You will need the best possible S/N on the noise source so the addition of the output from the 4 element yagi does not degrade the lower noise EME RX antenna. If you find that there are many sources of noise at various polarities, it might be a better plan to install a low side-lobe EME array. A 4 yagi box array will get quiet at a lower elevation. One trick I have often used was to add some extra elevation to the array reducing noise.

Your EME array should have elevation control. Noise is much lower at higher elevations.

Your EME array should be as low as practical and still have a decent moon window.

I have done EME with a 4 element yagi just 3 feet off the ground in my urban location.

A low EME array no more than 15 to 25 feet high will be line of site to fewer sources of noise than an array 60 to 90 feet high.

It is better to have a separate EME and tropo array. I had a long yagi at 90 feet and NEVER heard any EME signals on it.

It was not until I tried a small array about 10 feet off the ground that I heard my first EME signals.

BTW, your 4 element yagi between the two 9 element yagis can spoil the pattern of your two 9 element yagis.

WB9UWA.

--
There is an excellent Linrad User Guide by Gaetan, ON4KHG, at:
http://w3sz.com/Linrad%20Installation%20&%20Configuration%20User%20Guide%20-%20V1-0.pdf
---
You received this message because you are subscribed to the Google Groups "Linrad" group.
To unsubscribe from this group and stop receiving emails from it, send an email to linrad+un...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/linrad/009501d6084b%24e59401e0%24b0bc05a0%24%40voo.be.

--

Earl Shaffer,  WB9UWA

 

My EME array photos

http://www.gm4jjj.co.uk/WB9UWA/array_files/page33-1001-full.html

Detailed array photos

http://www.gm4jjj.co.uk/WB9UWA/

Facebook

http://www.facebook.com/earl.shaffer

Linkedin
http://www.linkedin.com/pub/earl-shaffer/12/881/735

[Leif Asbrink]

Hello Gaëtan,

Noise cancelling on 144 MHz is difficult.

With two antennas, one pointing to the interference and
the other pointing to the desired signal you must have
a good S/N for the interference in the subtraction antenna
because when you add its signal (in antiphase) to the signal
from the antenna pointing to the DX you will add the noise
from the antenna pointing to the interference.

You would also need a stable amplitude and phase ratio. Difficult
with 144 MHz directional antennas if there is some wind outside.

If the source is near your QTH and you can pick up a strong signal
from it, there is a chance you can do something useful in calm weather.

If the source is wideband pulses you can remove the problem
with a wideband noise blanker. With a large number of uncorrelated
switch power supplies pulses would arrive very often and could not
be resolved in a "normal" bandwidth.

Signals from a single source have a defined polarization and by
use of a cross yagi you can tune to the orthogonal polarization
which is likely to be elliptic because the radiation would not
come from a "proper antenna" but from various wires with
different orientations and phases as seen from your antenna.

Make a wideband recording. Minimum 1 MHz bandwidth - preferrably
more - and make it available to me. There is a chance that
the Linrad noise blanker could be helpful.

73

Leif

[ON4KHG]

Hi Leif,



Thanks for your feed-back. Actually, I have 3 different noise sources. 2 From nearby solar panels and a third one 1km away or so but from an unknown origin.
May I please ask you to remind me how to make a wideband recording ? I can send it via We Transfer.
Thanks in advance.

73,

Gaëtan, ON4KHG

_______________________________________________
Moon-Net posting and subscription instructions are at http://www.nlsa.com/nets/moon-net-help.html

[ON4KHG]

Hi Earl,

 

 

 

Thanks for your feed-back. I can hardly have separate antenna arrays and if too low, an EME array may have a too limited moon window, due to the trees and buildings around.

Indeed, with elevation I can of course still work EME. What is the most annoying to me is the impact of the noise on the terrestrial traffic. One thing I need to do indeed is to better assess the characteristics (polarization) of the interfering noise sources.

 

As you mentioned, I feared the 4 el would disturb the pattern of the 2x9el and I was about to simulate it but practically I didn’t notice an impact on the stations heard/worked off the moon.

73,

 

Gaëtan

To view this discussion on the web visit https://groups.google.com/d/msgid/linrad/CABipsT0orCUR9HNbWBuYxbZhzUht9bY8KuRTDwhadS0fGi%2BdDQ%40mail.gmail.com.

[Earl Shaffer]

Hi Gaëtan

A friend of mine suffers noise from the power inverters on his own solar panels.

Fortunately they are quiet at night when he is not making solar power.

The leads on these things probably need ferrite.

To view this discussion on the web visit https://groups.google.com/d/msgid/linrad/005501d609b5%24c31fa590%24495ef0b0%24%40voo.be.