AM reception problem

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NO6B
Posts: 53
Joined: Wed Aug 19, 2020 7:06 am

AM reception problem

#1

Unread post by NO6B »

Having problems with AM & SSB reception with an RSP-1a whenever I reduce the RF gain below 6: very distorted or no audio. It sounds just like a biasing problem with an op amp when the DC bias point shifts toward one of the supply rails. Everything looks normal to me in the screen shot. I have the same problem with the RX-888, though kind of backwards: if I set the HF attn. to -20 dB reception is OK, at -10 it's very distorted & at 0 the audio fades away after a couple seconds of severe distortion. The RSP-1a works perfectly in SDRuno at all RF/IF gain combos. The problem is in the MW band I have to turn the RF gain in SDRC way down to avoid overload, & at those RF gains the demoded audio goes away.

Also attaching a short video that shows what happens as the RF gain is changed.

Bob NO6B
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KA1GJU
Posts: 263
Joined: Tue Aug 11, 2020 2:16 pm

Re: AM reception problem

#2

Unread post by KA1GJU »

Turn on the AGC!
The one in the DSP panel.
You don’t use your ‘old school’ HF rig with he AGC off? If you did, the strong signals would be distorted too.

Typically I use RF gain of 5 to 7, -30 or -35 of Manual (not automatic) IF gain an 10 to 15 dab visual gain.
With IF gain in automatic, the AGC pumps wildly if a strong pulsing signal i.e. CW is in the operating bandwidth.

73 Kriss KA1GJU
73 Kriss KA1GJU Home of the KA1GJU Super Station SDRC Servers in NH, USA (FN42mw & FN43na)

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NO6B
Posts: 53
Joined: Wed Aug 19, 2020 7:06 am

Re: AM reception problem

#3

Unread post by NO6B »

Thanks Kriss. I knew it had to be something simple but I couldn't find it, maybe because I use FM 98% of the time. I also missed the manual gain slider that's present when AGC is off; adjusting that fixes it too.

Bob NO6B

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Simon G4ELI
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Joined: Thu Aug 06, 2020 7:27 am
Location: Mawnan Smith
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Re: AM reception problem

#4

Unread post by Simon G4ELI »

I also suggest using the RSP's AGC gains rather than setting the RF/IF but that's really just me being lazy :)
Simon Brown :shock:
www.sdr-radio.com

Do not send me direct e-mail, thank-you!

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