[Moon-Net] RFI from laptop via USB cable

James Morris jmorris at namei.org
Fri Apr 23 01:54:59 CEST 2021


Yep, I'm using Spectravue, via a Rigblaster, but will try a direct audio 
cable. AGC is off.

I'm building a dedicated moon noise meter (VK3NX / DB6NT) but haven't 
completed it yet. This should be much more useful as it uses a much wider 
bandwidth.

Thanks for all the tips!



On Thu, 22 Apr 2021, Edward R Cole wrote:

> 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
> >http://www.nlsa.com/nets/moon-net-help.html
> 
> 73, Ed - KL7UW
>   http://www.kl7uw.com
> Dubus-NA Business mail:
>   dubususa at gmail.com  

-- 
James Morris
<jmorris at namei.org>



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