W1RIL's Qualcomm 10 Ghz mods
PA BOARD MODS
RCVR/LNA BOARD MODS
XVTR AC/DC POWER SUPPLY
W1RIL 4/11/95 - Suggestions for modification of Qualcomm boards
for 10 Ghz use - update:
As of this date over a dozen LNA & PA boards have been successfully
retuned for 10 Gig operation.
Gains achieved range from a low of 25.5 dB to a high of 29.4 dB.
Noise figures have not been checked due to lack of measuring
equipment. The one unit that was checked at the Eastern Conference
last Fall came out slightly over 3 dB. Proper tuning on noise figure
equipment should result in a noise figure in the 2 dB range. Keep in
mind that the procedures shown in the drawings are not cast in stone.
No two boards are exactly alike and each will tune a little different
than its apparent twin. The numbered steps in the AFTER drawing will
in many cases get your LNA up into the gain range stated above. You
will find that numbered step 3 to be the most sensitive to gain
increase. Unfortunately it is also one of the "busiest" areas on the
board - BE CAREFUL ! A few do's and dont's are herein presented to
help you bypass some of the many pitfalls that can be encountered -
many are obvious and have been stated before, but bare repeating.
Use low voltage grounded soldering iron & work in a static free area.
Check for negative bias on all 3 stages prior to connecting Vcc
Check current on Vcc line - should be ~ 34 ma.
Solder the UT-085 shield to the board ground as close to the end of
the 085 as possible.
Use good quality 50 mil chip caps - in and out ~ 1 to 2 pf.
Remove all voltages prior to soldering on board.
Use a low input level to avoid saturation. -30 dBm works very well.
Ocassionally check gain with cover in place to avoid "overtuning"
The added capacity caused by the cover will change the tuning, and
with care, in the right direction.
Work on board traces when tired, shaky or after just losing an
argument with the XYL.
Touch device inputs with anything that hasn't been just previously
Apply Vcc to any stage lacking bias voltage.
Shoot for 45 dB gain - you won't get it! Be happy with 25 to 30 dB
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