[amsat-bb] Pacific Monolithics PM 3192i

[BobsImsai8800@xxxxxxx]

>From K5GNA:

I obtained a couple of boxes of the Pacific Monolithics PM 3192i 
downconverters at the same time I purchased my quantity of the AIDC 3733's & 
3033's from the bankrupt MMDS company.  I have broken one open (a knife along 
the edge of the external plastic housing) and have done some measurements on 
them:

The PM 3192i units work well down to 2.5 GHZ, below 2.5 GHZ the loss is 
unacceptable.  They have a built in antenna on the circuit board feeding a 
single transistor (or MMIC?) RF gain stage, feeding an IC mixer (maybe with 
an RF gain stage).  It also has a multipole stripline filter as part of the 
circuit board, after the RF preamp and connected to the mixer chip.  This 
stripline filter has silicone glue on the top, or tuning end, to protect it's 
tuning.  

The filter obviously needs to be retuned to work at 2.4 GHZ.  The problem is 
that it will be hard to make it longer, but possibly insulated foil or very 
thin PC board material can be added to the top (more capacitance) area of the 
filter to bring the frequency down.

The power supplies for the Pacific Monolithics downconverters are quite 
hefty; they are 24 VDC at 525 milliamps.  I was wondering why.  Removing the 
unit from the plastic housing, I found that it is a small diecast device, 
with push on metal covers.  After being powered a while, I found that I could 
not hold the bare metal on the downconverter, as it was too hot.  It appears 
that they have designed the whole unit to get hot.  After a quick look, it 
seems to be the 3 terminal regulator is doing all the heating.  It appears 
that they achieve thermal stability (and frequency stability) by running the 
whole converter quite hot.


TNX & 73,

Bob Seydler
K5GNA
k5gna@aol.com
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