[DSP-10] AA1YN email address

[Liljeqvist W7SZ]

Hi Lee..Have tried to contact you directly on several occasions
but comes back as undeliverable. Please let me know your
current email address. Thanks and 73,  Larry W7SZ



At 09:51 PM 3/23/2002 -0500, you wrote:
>After much thinking about the wave of noise, I've come to a conclusion. I 
>may be so far off with my thoughts that I need someone like W7PUA to set 
>me straight. - Anyway, here goes....
>
>The audio window is just under 5khz wide and we are moving that window 
>5khz for a total of about 10khz.  We are asking the crystal filter to be 
>flat for that 10khz.  If we adjust the filter coils L12 and L13 only for 
>max signal, we may indeed be peaking that filter with a flat top width of 
>about 2khz.  If we start measuring the noise at a frequency just above the 
>5khz step and then slowly move up in frequency, you will see the peak of 
>the noise at the high end of the audio window and it will look like a wave 
>as we move up in frequency until this wave is at the low end of the audio 
>window.  Once we reach that 5khz step point, the noise wave will then move 
>back up to the top of the window.
>
>Unless I am wrong, we really need a procedure for adjusting the crystal 
>coils L12 and L13 so the crystal filter is as flat as possible for the 
>full 10khz and not just centered in the 10khz window with it's 3db points 
>at +/- 5khz.  What I tried was to set the frequency to the low end of the 
>5khz step and adjust L12, set the frequency to the high end of the 5khz 
>step and adjust L13.  By doing so, I was able to see 2 noise waves which 
>kind of backs up what I've been describing. At least in my mind.
>
>If the local osc was continuously variable and we weren't moving an audio 
>window, you would never see this phenomenon and we could happily set up 
>the crystal filter for a 3khz bandwidth and be pretty much flat across it.
>
>Anyone else have any thoughts on this???
>
>As to the 5khz birdie I have, I have ran heavy grounding straps from the 
>board to the chassis, from the board to the DSP box, I drilled 6 small 
>holes in the top of the DSP box and soldered 14awg wire to tie the top and 
>bottom foils together next to each screw. I have double checked all 
>grounding wires and touched up any which might be less than perfect.  I 
>think I've reduced this birdie about 1db so it is now only 4db in 
>height.  I did manage to lower the overall noise of the receiver from 
>-149dbm to -152dbm with a 50 ohm termination on the antenna so there was 
>an improvement there.  The birdie still moves up in the audio frequency 
>when you move up in receiver frequency.  Since there are no actual 
>frequency changes within the 5khz step, I still feel this has to be 
>internal to the DSP program.
>
>One other ground point which eliminated my digital noise was to run a 
>ground strap from pin 5 of the serial jack to its chassis mtg screw.  I 
>had only grounded one end shields before at the DSP box.
>
>Hope my ramblings aren't too far afield.
>
>Lee Scott - AA1YN
>
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