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PA BOARD MODS
RCVR/LNA BOARD MODS
XVTR AC/DC POWER SUPPLY
COAX-WAVEGUIDE TRANSITION
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 GHz 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 don'ts 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.
Do:
- Use low-voltage grounded soldering iron & work in a static free area.
- Check for negative bias on all 3 stages prior to connecting Vcc voltage.
- Check current on Vcc line - should be approximately 34 mA.
- Solder the UT-085 shield to the board ground as close to the end of the UT-085 as possible.
- Use good quality (ATC) 50 mil, 1 to 2 pF chip caps - in and out
- Remove all voltages prior to soldering on board.
- Use a low-input level to avoid saturation. -30 dBm (0.001 mW) works very well.
- Occasionally 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.
Don't:
- 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 grounded.
- Apply Vcc to any stage lacking gate bias voltage.
- Shoot for 45 dB gain - you won't get it! Be happy with 25 to 30 dB.