Flex5000/PSDR AM Detection

Lionel

I sometimes use my Flex5000 to listen to SW broadcast and 75m AM and it seems like the detected audio while listening on AM or SAM is low. Always has been. At S9+ carrier levels it is pretty good but below that level audio recovery and intelligibility drop off quickly.  On 75m perhaps the modulation levels are low though it would seem odd that all of the AM stations are operated in this manner. The audio is lower on SAM than in AM mode. 

It does not seem to be a function of AGC-T. NB, NR off.  It is better if I use USB or LSB to demodulate one sideband. 

My old analog receiver (R4C)  seems to do a better job of delivering AM station audio to the speakers.
Yep, this is qualitative but I wonder if this is expected in AM/SAM mode for the 5000 or PSDR design. 
Has any other 5000 user noticed this?
Just a question about SDR, not a problem.  On SSB/CW/Digital all is FB.

John

I found that if I reduce the bandwidth from say 10khz downwards on my 3k to say 6k, it helps to bring out the audio on weaker signals on AM

k0eoo

Try putting the AGC recovery to FAST when in AM...

Lionel

I do both, narrowing BW and FAST AGC and still I find both the volume of detected audio low and the intelligibility low.    I suppose they could both be related to the hearing issue my wife points out when talking to me.  
I'll try some more setting changes in different combinations and see what I get.   It is interesting that it improves if I use SSB on AM reception, louder "sounding" and more intelligible.
Why would SAM seem to be worse than AM mode?  Sadly I don't know enough about how AM is demodulated in an SDR; not like the old diode in the BA. 
tnx for the feedback.

John

I think the main problem is twofold our hearing ability and also the type of AM modern radio's produce. The earlier transceivers were more AM oreintated, while for modern rigs, its an add on or an after thought and not enough thought put into what AM modulation should be. Some rigs are leaning towards more like dsb then am. Have you tried dsb ?
I also found that by placing a TNF filter to one or both sides of the am carrier can help at times. But then we also get am signals which have an extra carrier thrown in, this I believe is because of these audio mixer craze thats doing its round. These same carriers can be seen on ssb stations. A typical example is HB9ASQ

Lionel

I just tried DSB and it is better.  From the old days I tend to think in terms of high level plate modulation and I guess it isn't used much.  I've a SW station on right now running about S8-9 and it sounds okay in SAM and the stations BW seems to be ~6 or 7 kHz wide and with the Flex at 6 it okay. 

John

I am on a AM top band net right now and one station's carrier is 20 over the 9, but his audio is weak and it does help to lower the bandwidth. I have also on occasion used the filters such as NR and NB and other by slowly adjusting them for the best audio quality on weak audio signals.
I guess its a lot of playing around to get the best out of it. HB9ASQ on 40m ..note the carrier, while other station have no carrier.
I guess even something like a FL3 multimode filter on the audio line would help to some extent with the noise.

W7NGA

that isn't AM ...

John

No, its not AM, but an example of a ssb signal with a carrier, caused by the addition of audio mixers and other such like equipment.

Bob Zanotti

The cause of the carrier on my SSB signal has nothing to do with audio processing. It is caused by a carrier suppression alignment fault that I need to fix. That's all it is. I do not use a "rack", but one, signal commercial BC processor: the Orban Optimiod 9105A, designed for SW broadcasting. As for the carrier, few notice it and hardly anyone complains. 73, Bob HB9ASQ