[hpsdr] Digital Voice and HPSDR

[Glenn Thomas]

Hi John.

I've been on DV with an AOR box, though not recently, and not via an SDR 
or any sort. I would think that the AOR DV analog ODFM signals in and 
out would work as well with an SDR as with an analog radio because the 
HF SSB channel is pretty much the same when viewed from the 
microphone/speaker jack interface...

My experience with the AOR system (on 40m) is that it requires more 
precise frequency control and higher SNR (maybe 10db more?) than analog 
SSB on the same channel. PSDR provides more precise carrier frequency 
control than the typical analog radio (Kenweed TS-50 in my case). The 
SNR is a function of band conditions, good luck on doing much about 
that! With a good HF channel, DV provides an audio voice-channel that 
(unsurprisingly) rivals FM in SNR but is not even as good as SSB in 
voice quality.

73 de Glenn WB6W

PS. (only slightly off topic) In thinking about "additional modulation 
schemes", perhaps an interesting PSDR add-on would be software to do 
generalized ODFM (possibly defined by a selectable configuration file), 
going from audio to digital I&Q with no intermediate Dig-An-Dig step as 
happens with the AOR dongle. An open software vocoder is also required 
because the vocoder that AOR uses is (I think) closed. Has anyone tried 
to build a Huffman vocoder.

Another useful function that might be provided via a general ODFM 
capability is rapid digital data transfers via HF. The 300 baud limit in 
the US (FCC 97.305(f)(3)) can be maintained while providing an effective 
data rate of up to 600 Kbyte/sec (limited in the US by FCC 
97.305(f)(2)). That's with no data compression of any type.The AOR box 
provides something like this, but with an SDR we'd still have the 
dig-analog-dig process. Besides, an HFftp-type system should be able to 
directly access the file on both ends of the link.

The generalized ODFM system can also provide traditional FSK/PSK RTTY, 
PSKnn, packet etc by simply setting the above mentioned configuration to 
use a single carrier with the appropriate modulation scheme 
(FSK/BPSK/4PSK etc) and baud rate. Thus generalized digital modulation 
could provide the SDR with whatever HF digital modulation scheme is 
desired. An additional layer over this could manage an adaptive channel 
that responds to band conditions, something that has been done before 
but not in open source.

I don't have the time or the skill to implement this generalized ODFM 
system. I've only sketched it here. If anyone is interested in a more 
detailed description, drop me a note...


On 10/31/2010 10:13 AM, John Petrich wrote:
> All,
>
> Are any of you experienced with Digital Voice (DV) and it's 
> implementation with HPSDR?  My HPSDR rig is running so well, that I am 
> dying to try additional modulation modes.  Am I doomed to 
> frustration?  I have a general familiarity with the commercial AOR9800 
> product.  But do not know if that system will work thru the PowerSDR 
> DSP that we use.  Does anyone know?
>
> Also, I'd appreciate general reports, on or off line, on people's DV 
> experience.  Is there anyone actually out there to talk to on DV?  
> Know there are WE nets on 14.236 USB.  Is the AOR system the dominant 
> DV system for now and the near future?
>
> All thoughts would be appreciated.
>
> John Petrich, W7FU



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