[TenTec] DRM IF vs. AF

[Duane Grotophorst]

Don't forget thst the 12KHz IF out is before any DSP
filtering in the RX-320, so the PBT of the control
software will have no effect. The RX-320 with IF out
is effectively a 2.5KHz tuning step RX with only a
relatively wide roofing filter in the IF chain.

The RX-340 tunes in 1KHz steps (if I recall correctly)
and the instructions on the TT website are a way to
get its 14KHz (nominal) IF effectively down to 12KHz.

My guess is that DRM folks chose 12KHz because it
easily accomodated by most sound cards but is still
well above the highest frequency of the recovered
audio.

Duane
N9DG


--- Mark Erbaugh <mark at microenh.com> wrote:
> Recently, TenTec announced a new version of the
> RX320 that has a 12 kHz IF
> output suitable for use with DRM software.  A couple
> of days later, there
> was an article on the TT website of how to use the
> RX340 with DRM.
> Basically, they say to use USB, adjust the filter to
> 16 kHz, set the PBT to
> 2 kHz and use the audio output.  I don't have the
> DRM software yet, but
> followed their instructions and using a audio
> spectrum analyzer, I was able
> to see what looks like the DRM data.
> 
> I guess I don't understand the difference between IF
> and AF, especially when
> the IF is relatively low (12 kHz). Is the reason the
> DRM software wants the
> IF output just that most receiver audio stages don't
> pass 12 kHz of audio
> bandwidth?
> 
> Also, while receiving (but not decoding) the DRM
> broadcast on the RX320, I
> adjusted the PBT and saw no difference in the
> received signal using the
> SpectroGram audio spectrum program. Is the PBT
> adjustment really needed for
> DRM reception?
> 
> 73,
> Mark
> 
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec


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