[NLRS] DEMI 5760 lp factory built xverter wanted

[tosca005 at umn.edu]

On Aug 5 2009, Paul Beckmann wrote:

>I'm looking for a used 5760lp unit in good condition. Anyone?
>
>73
>-Paul, wa0rse

Paul:

Since you've asked this question a couple of times, it sounds like you 
REALLY want one of these guys. Well, I have one. As far as I know, it was 
factory built, but I couldn't swear to that right now. I bought it used 
from Lenny, K0SHF. I've only used it a couple of times so far, and I'm not 
ready to abandon the 5.7 GHz band, so I hadn't planned on selling it, but 
if your need is great enough, I might be convinced to part with it...

One of the things that bugs me about this transverter is one of the 
features you are looking for, namely the low power output. I've been 
planning to boost the power output on mine, by hook or by crook. I'm 
guessing that you already have the PA to do this, and that's why you're 
looking for a low power model. Is that the case? If not, are you interested 
in boosting the power later on?

I bought one of the DEMI "cut-off boards", which is basically the pre-amp 
and power amp section of the standard (1-2 watt) transverter, along with 
the complete set of components to build it. I planned to get that 
assembled, and bring the transverter up to the 1-2 watt output level and 
also improve the noise figure a bit. And it seemed like a good option 
because I could mount just that board and a T/R relay near the feed, and 
then run a little bit of coax without so much guilt to enable me to mount 
the transverter itself a short distance away, e.g. on the rear of the dish 
instead of on the offset feed arm, for better system mechanical balance. 
But assembly of the cut-off board does not look to be a simple thing, with 
the surface mount parts and the need for a lot of heat and good dexterity 
to attach the pipe caps, and some care needed in fabricating the heat sink 
to not short out other traces on the back side of the board. So, when I saw 
an Avantek AWP-64100 amplifier at Aurora for sale at a good price, I 
snapped it up. (It is supposedly capable of up to 10 watts of output, but 
this one was reportedly only able to make something like 4-6 watts, which 
is still easier to hear than 10 mW or 1-2 W). I haven't put that on the air 
either, because it needs some funky voltages to operate. I guess it was 
designed as a solid-state drop-in replacement for a TWT. But apparently if 
I was to disassemble the power supply side of it, I could replace most of 
the circuitry in there with a +12v to -12v DC-DC converter (less than 1 
amp) for the bias voltage, and either a simple regulator or DC-DC converter 
to drop the +13.8v supply to +10.5v (at 3 or 4 amps) for the main power. 
These tasks are not insurmountable, but as always, my chronic lack of 
"round tuits" gets in the way. (You know, I'll work on that when I get 
"around to it".)

So, I'm curious about your needs and plans. Maybe we can help one another, 
or maybe not. No promises, mostly questions...

73 de W0JT