[R-390] R390a and SDR

Mon Apr 22 23:10:35 EDT 2019

Alan,

Never have played with 16Khz Bw

If I can remember this weekend, I may bring the equipment home and do some playing and see.

Also, here is an interesting article that you might  take a look at:

http://w1vd.com/R-390ASoftRockdetails.html

David

WB5UOM

Texas USA

From: Alan Victor <amvictor at ncsu.edu> 
Sent: Monday, April 22, 2019 10:05 PM
To: wb5uom at hughes.net
Cc: jm <josemic at gmail.com>; 390 list <R-390 at mailman.qth.net>
Subject: Re: [R-390] R390a and SDR

Hi David, thanks for the input. 

But I really do not see how you can use the SDR to state the sensitivity of
the 390, UNLESS  you 
Have calibrated it (the SDR) with a accurate signal generator.

I agree and certainly did not make that inference, I hope. I believe all of this discussion is based on bench measurements from nice sources and NO ANTENNA. Just box to box calculations. An R390A to a pan adapter and what is possible was my understanding. It would be useful to look at some bench measurements and then correlate those numbers to the performance of the pan adapter. In the end, without modification of the 390A at 16 kHz BW what is the minimum BENCH discernible signal level?  Alan 

On Mon, Apr 22, 2019 at 6:07 PM <wb5uom at hughes.net <mailto:wb5uom at hughes.net> > wrote:

Well, I decided to chime in here, hopefully I will not offend anyone.

I have 3 R-390A's as well as a gathering of other "classic" Hf receivers,
and I have several SDR's as well.

I have played with the R-390 as the 'front end' to the SDR and it is fun to
play with.

But I really do not see how you can use the SDR to state the sensitivity of
the 390, UNLESS  you 
Have calibrated it (the SDR) with a accurate signal generator.

I am lucky enough (on some days) to work in the commercial communications
field, and happen to own a 
AEROFLEX 3920 service monitor that does SSB (and AM too).  

Now I have gotten frowns from others on various lists, but the 3920's
generate function is calibrated down to -138Dbm.
IF  I say IF I use the MDS method (minimum discernable signal) on SSB -
using a 1000khz test tone, I can hear that test tone
All the way to the bottom on the 390's and the Winradio 313i
Does that mean I could copy a SSB station that weak, nope, because the tone
is a steady signal and a voice ssb as we know is not.
(And I am part deaf after all these years of listening to a 1khx test tone,
so I have to wear headphones when I do this)

I have never been a fan of the 12db sinad test, since in the 2way
communications business we use the 20db sinad.

At 20db sinad, my 390's will do around -109Dbm as will my Winradio 313i on
SSB

Now that you all have my mind going on this, I guess I need to bring the
3920 home and see what the SDRplay RSPduo will really do.

Just my 2 cents worth.

David

WB5UOM
Texas USA

-----Original Message-----
From: r-390-bounces at mailman.qth.net <mailto:r-390-bounces at mailman.qth.net>  <r-390-bounces at mailman.qth.net <mailto:r-390-bounces at mailman.qth.net> > On
Behalf Of Alan Victor
Sent: Monday, April 22, 2019 6:54 PM
To: jm <josemic at gmail.com <mailto:josemic at gmail.com> >
Cc: 390 list <R-390 at mailman.qth.net <mailto:R-390 at mailman.qth.net> >
Subject: Re: [R-390] R390a and SDR

Hello again.

I did not imply that the R390A was limited to -100 dbm at its INPUT. I
indicated that its noise power at its output might be as high as -100 dBm.
Most likely higher, Lets consider the sensitivity equation. Its pretty
straight forward.

Sens (dBm) = -174 + 10 log (BW) + NF (dB) + S+N/N ratio in dB for desired
intelligibility.

Lets plug in some typical numbers. BW: 3 kHz, NF: 10 dB, S+N/N: 10 dB

Then SENS is -174+30+10+10 = -124 dBm. Obviously if we reduce the BW by
another order of magnitude then we could achieve -134 dBm and so on. The
noise power OUT would be dictated by the input sensitivity or the NF
multiplied by the total forward gain of the receiver. Additional gain could
be added as required as long as we don't compromise distortion, IMD, etc...
Alan

On Mon, Apr 22, 2019 at 3:45 PM jm <josemic at gmail.com <mailto:josemic at gmail.com> > wrote:

> John
>
> Very clear and educational.
>
> Many thanks
>
> Jose
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