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Re: 12V Tap for Pre-Amp, Best location on a 3731AA



W1PA wrote:

Has any one ever installed a feed thru cap to the outside world on a Transystem 3731AA?

I have one that I removed and bypassed the 12v regulator for direct power from my FT-847, and I want to try a DEM ULNA in front of it. I thought I could install the feed thru cap attached to the 12v line inside the Transystem to feed the DEM pre-amp with a single wire from the Transystem over to the ULNA.


W9AE replies:

I added a feed-thru capacitor to my Transystem 3731AA for the exact same purpose, to power a DEM ULNA preamp.  I bought the feed-thru capacitor at the same time I bought the preamp.  It is identical to the feed-thru capacitor on the preamp.

The preamp only draws about 25 mA, so you should be able to power the downconverter and the preamp via the coax cable from the FT-847 "preamp power" signal.  I use an external power inserter because I have a PTC thermistor in the downconverter that draws a lot of current for the first couple seconds when it's powered up.

According to the Gene Marcus AO40 downlink calculator, my signal to noise ratio improves 1.1 dB when I lower the noise figure from 1.2 dB to 0.7 dB.  That's more than $100 per dB, but it does help.

Wayne Estes W9AE
Mundelein, IL, USA
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