[TenTec] Pegasus, magnetic interference & solution

[n4lq@iglou.com]

If you really want to have some fun with that thing, Listen to the 
carrier of the first oscillator at 70mhz. This is where the trouble 
usually begins. The area around that part of the circuit board is so 
sensitive that I was able to modulate it by tapping anywhere on the 
cabinet. I used my IC-706 tuned to 70mhz and a short wire from the 706's 
antenna jack to near the Pegasus's board for a pickup. This is where the 
fuzzy sounding cw carrier originates and no doubt the cause of the raspy 
carrier in from the Jupiters. Almost any field will couple into and 
modulate this oscillator. 

N4LQ Steve

-----Original Message-----
From: Darrel Emerson <74010.2230@compuserve.com>
To: tentec@contesting.com
Date: Fri, 15 Nov 2002 06:47:45 -0700
Subject: [TenTec] Pegasus, magnetic interference & solution

> I found I was getting slight 60 Hz and 120 Hz modulation of signals
> received with the Pegasus. This was not noticeable by ear, but
> using the Waterfall display of a PSK31 program it was very
> obvious on strong signals, with spurious images of the main signal
> at +/-60 Hz and +/-120 Hz, each about 20 dB down on the main signal. 
> This only appeared as MODULATION of incoming signals; there was 
> no obvious 60 Hz or 120 Hz component in the absence of signal.  
> This occurred with an Astron RS-20A on the floor next to 
> the Pegasus, with the RS-20A on the right side of the Pegasus, 
> separated from it by about an inch.
>   By placing the RS-20A on the LEFT side of the Pegasus, even 
> touching it, the modulation disappeared. Using a search coil
> to probe the magnetic field around the RS-20A, I found that
> at the left side of this power supply, presumably closer to the
> transformer, the 60 Hz and 120 Hz magnetic field was at least
> 10 dB stronger than at the right side of the power supply.
> 
>   Maybe this potential magnetic cross-modulation within the Pegasus
> (and probably most other receivers) is well known, but I'm
> posting this in case the information is useful to anyone else.
> 
>       73
>         Darrel Emerson, aa7fv.
> 
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>