Re: Signal strength puzzle

Allan Isaacs

Hi Tom

I tried removing the switch in my workshop and feeding the SDR directly to the incoming CAT5 cable from my office (about 80 feet)

The office computer gave me the same results as before with the workshop switch in place


198KHz          -63dBm

252KHz          --84dBm

234KHz          -90dBm

60KHz            -107dBm


I then connected the SDR directly to the workshop computer, results the same as before

198KHz          -49dBm

252KHz          -71dBm

234KHz          -74dBm

60KHz            -95dBm


I then put back the workshop switch and used a second Windows 10 computer in the workshop.

Results exactly the same as the first 198KHz -49dBm etc


I haven’t tried bypassing the office switch yet because it’s in a rats nest of cabling, and a router plus the switch (the latter is brand new and carries two network cameras as well as a printer, the workshop CAT5 cable and a couple other cables not being used).


I’m a bit puzzled. I imagine the CAT5 cable from the SDR carries digital signals to the SDR program so should get decoded exactly the same in two computers. The only difference is I’m using Win 10 in the workshop and Win 7 in the office.

I’ll dig out a Win 7 laptop next and try that. Surely something must account for over 20dB difference in signals??


All signals are solid and changing AGC has no effect on the readings

I have 4 gain settings. On 60KHz the -30dB gain gives -113dBm, -24dB gain gives -107dBm, -12dB shifts the base line down about 10dB with the signal still -107dBm and 0dB gain shifts the baseline down another 10dB with the signal at -108dBm.

Allan G3PIY



From: [] On Behalf Of Tom Crosbie G6PZZ
Sent: 03 November 2020 15:11
Subject: Re: [SDR-Radio] Signal strength puzzle



I’m not familiar with the Andrus. My only thought might be latency in the network, but that’s probably clutching at straws. Can you bypass the second switch and see if it makes a difference?

I can’t think why it should but I’ve seen latency problems but only on much bigger networks operating at the limit of several CAT5 cable lengths with switches in between. Perhaps you have a rogue peripheral on the network?

I wondered if one computer is measuring the incoming signal at a slightly different point in the signal strength variation, e.g. is AGC making a difference? Although 198 is normally rock solid.

Have you tried looking at other stations and on other bands to see if the same phenomenon exists?

I can’t think what else could be causing this.

Good luck!




From: <> On Behalf Of Allan Isaacs
Sent: 03 November 2020 14:19
Subject: [SDR-Radio] Signal strength puzzle


I've been using my SDR which is an Andrus on my Windows 7 x 64 office computer and have recently used it on my Windows 10 x64 workshop computer.
The Andrus (powered by an adjacent 6 volt PSU)  is in my workshop and is fed with an 80m dipole which receives reasonably well over most bands.
Connection to the Andrus is via a local network switch to the workshop computer and via that switch to a second switch to my office computer.
Receiving Radio 4 on 198KHz on my office computer records S9 + 12dB or -62/-63dBm but on the workshop computer it recorded as S9 +24dB and -49/-50dBm.
The software is identical, Sept 2020 on both and all the settings are the same.
Why the difference in signal strength??
Allan G3PIY

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