Re: [amsat-bb] Adding Preamp to 2.4 Gig

["John P. Toscano" <tosca005@xxxxxxxxxx>]

Jesse Morris (W4MVB) wrote:
 
> I have a plan (well maybe a half hatched idea would be more like it) to
> get one of the Down East Microwave PCB kits, make my own enclosure from
> PCB material and include 2 "F" connectors and a "drop" for the preamp
> power.  Of course you could buy the whole preamp and install connectors
> in the housing provided but I really want to install a chassis mounted
> male type "N" connector  in the preamp so it can be connected directly to
> the antenna.

1) Are you sure such an enclosure will be fully weatherproof?  The
   assembled or complete kit from DEM will be.  Also, you can buy
   the weatherproof enclosure from Down East Microwave with no holes
   pre-drilled, so that you can make any arrangement you want.  On
   their catalog page, scroll down to enclosures and you should be
   able to find the weatherproof ones in several sized without any
   difficulty.

2) While I agree it would be nice if the preamp had a Male N connectors
   instead of a Female N connectors, a Male-Male N Barrel Connector
   is cheap and fixes the problem easily.  I suppose that at 2400 MHz
   there might be a measurable loss, but I doubt it is high enough to
   be of concern, especially compared to a short run of coax.  That's
   how I plan to mount mine directly to the antenna, and the preamp to
   the Drake 2880.  Then coax the rest of the way down, where some
   degree of loss is actually a good thing.

3) The DEM unit will accept DC power on EITHER the coax (output end)
   or on a feedthrough capacitor on the side of the box.  If you are
   feeding DC power up the coax through a bias T in the shack to the
   downconverter, you could add a second bias T at the output of the
   downconverter, and instead of using it to feed DC into the down-
   converter, use it to feed DC out to the preamp's feedthrough cap.

Also, keep in mind that the DEM preamp and a Drake 2880 will be
happy with 13.8 vdc minus line drop, but other downconverters such
as the AIDC and CalAmp units need a higher DC voltage.  I'd have
to check, but I *think* that 15 or 16 volts would make any of these
devices happy, so that might be the ideal if you are using only one
source of power for both a preamp and downconverter.

73 de KB0ZEV
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