Weird Noise Across all frequencies

[Oriol Cortés]

Hello everyone!

I have a dedicated UHF cross yagi antenna in the rooftop with a LNA connected through 40m of coaxial cable to a HackRF One 936 and then to the computer (running on Linux), and whenever I try receiving any signal I get this periodic noise across all UHF frequencies in GQRX (or any other Software). Any idea what it is?

I've tried different GC settings, different softwares, a spare HackRF, deactivating the LNA, changing the sample rate, etc. But I cannot get rid of it. I'm pretty sure it's not a real interference either, there is nothing nearby that works in this frequency range (as far as I know). Any ideas?

[Joseph DiVerdi]

When I experience a situation like the one you describe the first thing I do is confirm that the signals are real. I would do this by disconnecting the antenna from the cable (if it's convenient) and replacing it with the 50 ohm load and either also or alternatively disconnect the antenna cable from the SDR and replace it with a 50 ohm load. Confirm that the signal is really associated with the outside world and not an artifact of your room or workshop or laboratory.

Once you've confirmed that it is associated with the outside world then I suggest the second step based on my experience of turning down the front end preamp gain. At times I have found strong signals in nearby bands can wreak havoc while observing at other frequencies. If you find this to be the case then you may need to insert RF filters in between the antenna and the front end of the SDR. But it's too soon to worry about this until you know if this problem is associated with the outside world. Good luck

Best regards,
Joseph
AF6OY

[Richard Bown]

Far more fundamentally , if you are using a yagi try pointing it in
another direction, yagis are directional antennas, so rotate it ideally
thru 360 degs and see in which direction it peaks, If that fails remove
the power to the LNA with it still connected, which should give you
20dB attenuation, and if its still there at the same level its liable
to be some system generated noise
Richard

--
Best wishes /73
Richard Bown

Email : ric...@g8jvm.com

HTTP : http://www.g8jvm.com

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Ham Call: G8JVM . QRV: 50-432 MHz + Microwave
Maidenhead QRA: IO82SP38, LAT. 52 39.720' N LONG. 2 28.171 W
QRV 6mtrs 200W, 4mtrs 150W, 2mtrs 300W, 70cms 200W,
Microwave 1296MHz 140W, 2320MHz 100W & 10368MHz 5W
OS: Linux Mint 19.1 x86_64 Tessa, on a Dell Inspiron N5030 laptop
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