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Re: Pacific Monolithics PM 3192i



Bob,
Printed filters can sometimes be re-tuned with a layer of dielectric
material over it as you suggested.  I modified a Cal Amp downconverter that
has a hefty S-Band filter by putting a layer of PTFE adhesive-backed  tape
over the printed filter.  The tape is 0.015 inch thick.  The filter response
was down 20 dB at 2400 MHz with a 3 dB cutoff at 2500 MHz before this mod.

I'm not sure about the silicon glue in the unit you are working with.  That
may interfere with placing the tape across the filter.  I wonder if that was
their way of tuning the filter?

The tape mod can be seen with test results on the Cal Amp 31732 page at
http://communities.msn.com/wc0y

73,
Ward - WC0Y

----- Original Message -----
From: <BobsImsai8800@aol.com>
To: <amsat-bb@AMSAT.Org>
Sent: Saturday, April 07, 2001 10:26 AM
Subject: [amsat-bb] Pacific Monolithics PM 3192i


> 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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