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 Post subject: Demodulating AM
PostPosted: Thu Aug 09, 2018 6:19 am 

Joined: Thu Nov 17, 2016 6:58 pm
Posts: 32
A few times I've tried using my RS-HFIQ on 'nearby' shortwave broadcast bands (41m, 31m, 19m). What I've found, since there's 0 Hz LO offset in HDSDR, audio is distorted. I haven't played around with HDSDR enough to figure out how to set the offset properly, I thought I'd ask here. Would the same procedure apply if trying to transmit AM phone on the ham bands?



Al Holt

Rigs/Radios: RS-HFIQ, Ultimate 3S, GenesisRadio G3020, SDRplay RSP1, Kenwood R-1000, Halli S-40B
Computer Hardware: Dell Inspiron 570 w/ Xonar DX
Software: HDSDR, OmniRig, com0com, VB-Audio, WSJT-X, FLDigi, SDRuno

 Post subject: Re: Demodulating AM
PostPosted: Fri Aug 10, 2018 5:22 am 

Joined: Mon Jul 23, 2012 6:25 am
Posts: 1143
Hi Al,

Since both sound cards and the RS-HFIQ not no response at DC on TX or RX if the carrier of an AM signal is at the same frequency (+/- 20 Hz) it is eliminated.

So to run any mode that needs a response at the center (AM, FM) you'll need to offset the LO from the carrier by at least half the bandwidth of the signal. For AM, 4 kHz is probably a good value. In HDSDR go into Options > Misc Options > Set LO <-> Tuned Offset and enter 4000.

You can run SSB/CW etc with this offset as well but the soundcard/RS-HFIQ's performance is best at lower IQ frequencies.


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