[Moon-Net] RFI from laptop via USB cable

Edward R Cole kl7uw at acsalaska.net
Fri Apr 23 01:06:37 CEST 2021


James,

I noted from your earlier post that your receiver is a FT-817.  To 
get accurate sun noise vs cold sky noise you need to defeat AGC in 
the system.  Not sure the FT-817 has that ability so running with RF 
Gain greatly turned down does help minimizing gain changes by the AGC.

You do not tell us how you are measuring RF power?  S-meter is 
worthless as an indicator as most are fed off the AGC detector.

Using receiver audio and measuring with a well calibrated audio meter 
is one of the old standby methods.  Using a step attenuator to return 
meter reading of the Sun back to what you see form cold sky may give 
a better measurement (maybe within 1/2 dB if you have 1-dB steps in 
attenuation).

I use a SDR-IQ on output of my transverter for sun and cold sky 
measurements.  Running Spectravue sw (which was designed for the 
SDR-IQ) in the "Continuum Mode" presents amplitude vs time 
with  adjustable detail of gain (I set the display for 0.2 dB/DIV so 
get about that resolution of gain measurement).  Another nice feature 
is pointing antenna ahead of the Sun and letting it drift through 
dish boresight.  This paints a nice display of my dish beamwidth 
pattern and show first sidelobes.

Spectravue will work with most computer soundcards so you may be able 
to use it with audio output of  the FT-817.  Spectravue is available 
from www.RFSpace.com for free.

73, Ed - KL7UW

At 01:51 PM 4/22/2021, James Morris via Moon-net wrote:
>On Thu, 22 Apr 2021, Charles wrote:
>
> > Hi James
> >
> > On 10GHz, and really any EME application on the higher bands, dynamic range
> > isn't an issue.
>
>Btw, by dynamic range, I was talking about getting the maximum Sun noise
>out of the system. I'd found that reducing the rx gain of the transverter
>and then putting a 6dB attenuator before it gave me the highest figure, by
>several dB.
>
>
>--
>James Morris
><jmorris at namei.org>
>
>_______________________________________________
>Moon-Net posting and subscription instructions are at 
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73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
   dubususa at gmail.com  



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