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Re: question about the DEM 13 ULNA 2.4GHz preamp

Mark:  I'm forwarding this for Don. Message follows:

Art N3OY

To: Mark Hammond  N8MH

From: Don Rees W4VQA


You should see some increase in background noise when LNA is powered up.
Just how much depends on your configuration. Good check here is to use the
SUN noise as reference with & without LNA.
As always Steve at DEM has done an outstanding job in making their units
goof proof. In your case putting the LNA in backwards should not affect
anything long lasting.
The TranSystems unit input (if unmodified) is at DC ground via the comb
filter. The DEM LNA input is also at DC ground via an inductor for "static"
FYI the DEM LNA is configured for DC bias via the output connector. I'm
working on a way to drive it from the TranSystem units without external
jumpers (details to follow).
The DEM LNA without DC power will be a massive pad. You should see no
signals at all without DC power.
Construction/tuning sheets from DEM for "read the voltage here" measurements
will not provide meaningful data for anything other than basic DC
measurements. Real world tests (in my opinion) should be based either on
A0-40 or SUN noise.
I do have the docs on the 13ULNA & would be happy to FAX to you.

Don - W4VQA

----- Original Message -----
From: Mark L. Hammond <hammond@camel.campbell.edu>
To: <amsat-bb@AMSAT.Org>
Sent: Thursday, June 07, 2001 1:18 PM
Subject: [amsat-bb] question about the DEM 13 ULNA 2.4GHz preamp

> The details on this preamp are here:
> http://www.downeastmicrowave.com/PDF/13ulna.PDF
> I have one of these (pre-built) units  in the following configuration:
> helix feed->13ULNA premp->Transystem 3373 downconverter on a BBQ dish.
> My question is this--does an increase in S-meter background noise
> level/floor (compared to without the preamp installed) on my 2M rig
> guarantee that the preamp is working correctly?
> Or is it possible that one of the components has actually failed (like the
> PHEMT), but yet it still causes an increase in the S-meter?
> The reason I ask is this--when I first got the unit, I installed the
> BACKWARDS in between the helix feed and the downconverter, and powered it
> up.  (I'm feeding DC into the preamp through the external feed-through
> NOT via the coax)  And AO-40 signals have been quite poor, and I'm not
> certain that my preamp is actually working....
> Does having the preamp in line WITHOUT powering it allow signals
> through?  I would expect yes, with perhaps a tiny reduction in signal from
> loss through the unpowered preamp.  Yes, I need to and can test a few of
> these things out, but it's a bit challenging to do it based on my current
> configuration/power scheme.
> I know I'm showing my ignorance on how the preamp works, but I hope to
> learn something from constructive replies.
> Perhaps somebody has the construction/tuning sheet(s) for this unit from
> when they built it from the kit.  I'd like that information very much...it
> might have some "read the voltage here" type of troubleshooting/tuning
> information...
> Thanks for any comments.
> Mark L. Hammond  [N8MH]
> ----
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