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More AIDC 3373 mods: Change osc freq



I took my low freq signal generator and ran it up and down around the 8.898
normal frequency to see where the loop would lock.
Its a fluke 6010a synthesized 0.01 - 11 mhz generator.
Using a 10x scope probe to feed the generator into the crystal socket pin at
50 mv. I provide a stable reference signal I can vary to watch where the vco
lock will hold.

This turns out to be 2200-2300 mhz. By adding small metal squares to the
oscillator I found it possible to move it to 2178 but to big a change to go
much farther. I had a crystal for 2178  (Flo / 256) = 8.5 mhz.
(actually the crystal was a 25.5 third overtone)
which it turns out will run at 8.5 in this circuit. I added a .05" x .1" tab
to the collector of the oscillator transistor and got it to run at 2178 and
relock quickly when the power was cycled. Dont know how the
thermal will do on it but drift is a few khz as the unit warms up. Thats
a lot better then I had on the DRO converter.

When I check it my test signals are there and strong and a freq counter
reads it correctly, and it is very low phase noise on an icom r3 reciever
(0.5-2.45 ghz fm am tv) when checking 2178.
The LO leaks out the antenna pretty strong, it is hard to tell what the
second filter is set to but looks like an LO filter or maybe its a second
preselector filter.

Having the LO here puts the image out of band above 100 mhz so I can
use the 2300 and 2400 parts of the bands without touching the filter
in the converter, but can still pick up image free reception above 2270 mhz.
Should get 3db more noise below 2270 which is somewhat acceptable.
I thought it was really easy to unsolder the notch filter stub mentioned in
other messages.

The new range is shown in a table below.
If you move it to 2meter band 2255 LO it will go no problem, but
you will have image noise up to an IF of 175 mhz so you will
be 3db noisier unless the 2109 mhz band is filtered out.
Tomorrow I will measure the response of the modified unit.

With image noise:
rf      if       rfimage
2080 -98 2276 double sideband    this band is pretty quiet, space to earth
band.
2105 -73 2251
2130 -48 2226
2155 -23 2201 no if
2180 +02 2176
2205 27 2151 no if
2230 52 2126
2255 77 2101 double sideband
2280 102 2076 above here there should be no image noise or signals
2305 127 2051<right column is filtered out below this line
2330 152 2026
2355 177 2001
2380 202 1976
2405 227 1951
2430 252 1926
2455 277 1901
2480 302 1876
2505 327 1851
2530 352 1826
2555 377 1801
2580 402 1776
2605 427 1751
2630 452 1726
2655 477 1701
2680 502 1676
2705 527 1651

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