[Skimmertalk] Dynamic Range of SDR

[Dave Pascoe]

I have seen momentary SNR's like this if I happened to be transmitting,
even at 100W. Even with receiver protection in-line there is a surge in
received signal power that affects the SKimmer Server/CW Skimmer SNR
measurement.

Dave KM3T

On Tue, Nov 28, 2017 at 5:12 AM, <dd5xx at web.de> wrote:

> I had a weird S/N report during CQWWCW contest on 40m. I was running 100W
> with a very low performance ANT in the center of a city between huge
> buildings. Of course I know the S/N reports I got from US stations, usual
> lower than 10dB in best times <20dB. W3LPL reported 73dB, I was shocked
> -HI- of course this never can be a real S/N report but who knows what
> happened at that particular time when he spotted me. I never saw such spots
> before, I even wasn't aware that it can go up so high. However, it was
> funny to see this on the RBN.
>
> 73
> Saki, DD5XX
>
>
> Gesendet: Montag, 27. November 2017 um 23:44 Uhr
> Von: "Lee Sawkins" <ve7cc at shaw.ca>
> An: skimmertalk at contesting.com
> Betreff: [Skimmertalk] Dynamic Range of SDR
> It appears to me there is a simple way to determine the dynamic range of
> any SDR. The lowest s/n you will see reported is zero. So is the dynamic
> range not simply the highest reported s/n reported by your SDR, as long as
> it doesn't go crazy when hit by huge signals.
> During the CQ WW I was single band 160 and had my SDR offline during times
> I was operating. I turned it on when I was not on 160.
> I was turning around on 20 while 160 was dead and heard VE7NY. He was
> operating from VE7SZ's QTH. His signal was extremely strong as I am 5 miles
> away, 600 ft higher in elevation and directly in line towards Europe. I was
> curious what the reported s/n was. Surprisingly, my Red Pitaya 14 bit was
> not reporting him on 20 on the frequency he was using. He was being
> reported on his second harmonic on 10 with a s/n of 14 dB or so and
> occasionally on slight offsets from his 20 meter frequency at low s/n. None
> of these "bad" frequencies should have made it through any dx cluster's bad
> spot filtering. Looking at the HDSDR using the same Red Pitaya he was S9+25
> dB. I removed the power from the pre-amp I was using, leaving the input and
> output connected. The signal dropped to S5 and the Red Pitaya then reported
> him on the right frequency with a s/n of 74 dB, which is the highest report
> I have ever seen. I never run my skimmer like this normally. I just did
> this as a test. No
> rmally the highest s/n I see reported is in the mid 60s. I believe this is
> the dynamic range of my setup. Am I wrong? Of course there may be different
> numbers on different bands, but I believe that at least for 20 meters I am
> in the ball park believing my dynamic range is about 65 dB. Theoretically a
> 14 bit ADC should have a dynamic range of 85.8 dB plus whatever can be
> gained by decimation. http://www.qsl.net/z33t/dynamic_range_eng.htmlWhat
> I believe happens with VE7SZ's main signal is that it gets clipped by the
> ADC and is ignored. I do not see any problems created by this. If I
> decrease the gain of my system to stop the clipping, I am going to lose all
> the weak signals. Lee VE7CC
> _______________________________________________
> Skimmertalk mailing list
> Skimmertalk at contesting.com
> http://dayton.contesting.com/mailman/listinfo/skimmertalk[
> http://dayton.contesting.com/mailman/listinfo/skimmertalk]
> _______________________________________________
> Skimmertalk mailing list
> Skimmertalk at contesting.com
> http://dayton.contesting.com/mailman/listinfo/skimmertalk
>