[DSP-10] 5khz birdies and noise

Gary Lauterbach [email protected]
Fri, 22 Mar 2002 15:51:36 -0800 

Lee -

    If you get any insight into this 5khz wave problem please let me know.
    I have the same problem and it only appeared after I added grounding
    to the second mixer case.  Thanks.

- gary ad6fp


----- Original Message ----- 
From: "Lee Scott" <[email protected]>
To: <[email protected]>
Sent: Thursday, March 21, 2002 7:28 AM
Subject: [DSP-10] 5khz birdies and noise


> I am in the process of eliminating the small noises in the DSP-10.  I have 
> at least eliminated any detectable digital noises and am now working on 
> other noise sources.
> 
> Here's what I now have.
> 
> There is a 2kc wide wave of noise approx 3 dB in amplitude every 5khz. This 
> noise wave decreases in frequency when you increase the receiver 
> frequency.  It is controllable via the RF gain and it appears across the 
> 144 to 148mhz band much like rolling waves on the ocean. A 50 ohm 
> termination is on the antenna input. The first mixer is on top of the board 
> with 4 grounding straps.  The second mixer is on the bottom of the board 
> and the case is well grounded.
> 
> The best way to display this noise on the waterfall is to start at 144mhz 
> in cw mode and increase the frequency 100hz every 10 seconds. When you get 
> to the top of the 5khz step with the 124mhz lo, the next frequency step 
> will place the noise at the high end of the audio spectrum.
> 
> Second, I have a very narrow 5db birdie - but it's frequency increases in 
> the audio spectrum as you increase the receiver frequency and is 
> independent of the RF gain. I suspect it has to do with the software BFO. 
> Changing RIT frequency offset will change the frequency of the birdie.
> 
> I am running V2.0 of the software.
> 
> Anyone have any ideas?? - would it help if I were to solder some shielding 
> on the top of the board where the ground straps are?
> 
> Lee Scott - AA1YN
> 
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