SDRPlay RSPdx DAB Notch filter causing 430Mhz humps

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tomstephens89

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Hi all,

I have noticed that when enabling the DAB notch filter on my RSPdx under SDRUno, there is a wide 'hump' in the 430mhz area of the spectrum. see attached picture.

The 'humps' are wide, a few Mhz and there appears to be a few of them around 430Mhz land. When the DAB notch is disabled, the humps drop right down.

I do seem to be seeing some noise on the 70cm band recently, is the DAB filter just allowing this noise to come through do you think?
 

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KE5MC

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Both the 1.33 manual and release notes only have 3 references when searched using "DAB". Truly underwhelming in content. :-(

DAB = Digital Audio Broadcast, so at 433 MHz it might be an interesting result, but a function to be used at lower frequencies/modes.

Using your screen shots I set my RSPdx and I get a slight rise in noise level across the total spectral display, but no hump like you have. Release notes speak of turning on DAB for a calculation, but really no how to use information. Might be something in the support group or other information.
 

tomstephens89

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Mar 14, 2020
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Both the 1.33 manual and release notes only have 3 references when searched using "DAB". Truly underwhelming in content. :-(

DAB = Digital Audio Broadcast, so at 433 MHz it might be an interesting result, but a function to be used at lower frequencies/modes.

Using your screen shots I set my RSPdx and I get a slight rise in noise level across the total spectral display, but no hump like you have. Release notes speak of turning on DAB for a calculation, but really no how to use information. Might be something in the support group or other information.

Thanks for the reply.

I should add that I live within 1 mile of the 'Hannington transmitter' in the south, UK. It broadcasts FM/DAB radio at 3-5kW as well as digital TV at 50kW.

I did a test with the SDR hooked up to my outdoor Diamon X300 @ 5m height, vs to a cheap indoor whip stood by a window. The signals are only coming in via the big antenna at height, so this leads me to beleive it could well be powerful harmonics/bleed over from that broadcast transmitter.

I guess the only way to really know for sure here is to buy a high quality dual 2m/70cm band-pass filter to put in between the X300 and my receiver/radio.

Heres a video of the issue:


Tom
 

KE5MC

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That 'Hannington transmitter' could likely be the source. Is there a chance the broadcasters have any off-air time to correlate noise gone when they are off-air?. RTL-SDR.com has a 88-108MHz bandstop filter that is inexpensive and knocks the signals down. I'm not familiar Hannington's frequencies so the suggest might not apply. Especially if there are station in that band you want to listen to. Good luck with your efforts. Such bad luck to have an interest in radio not of the broadcast variety and live so close to them.
Mike
P.S. watched video and it played well for me...
 

Ubbe

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Can you do an experiment and monitor a 70cm repeater, preferably a weak one, and switch the DAB filter in and out and keep an eye on the signal level of the 70cm repeater.

It could be that the receiver get desensed by the DAB transmitter and loose sensitivity and you then do not see those bumps, but when filtering out the interference you regain the sensitivity.

Those Diamond amateur antennas are narrow banded so the hump corresponds to where the antenna work at its best and gives you the most signal, even from a high background noise level that you might have when living so close to broadcast transmitters.

/Ubbe
 
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