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Re: How to connect DC to ARR preamp or dc injector?



OK, Here is some answers...but you may not like them.

At 01:26 PM 1/7/2005 -0500, Ka8syx2003@aol.com wrote:
>Hi, Jeff,
>
><<MAYBE YOU COULD HELP ME, I HAVE UHV/VHF/FM TV PREAMP. RADIO SHACK MODEL
15 1113B. I WANT TO HOOK IT UP TO MY UHF KLM ANT AND SEE IT HELPS BRING IN
AO-51 DATA/TLM. IT HAS A INPUT AND OUTPUT. ANT. END GOES IN THE INPUT?
OUTPUT GOES TO THE RIG? YES I KNOW I CANT XMIT WHILE ITS HOOKEDUP.>>
===============================================
I believe nearly all TV preamps are powered thru the coax coming up from
the TV.  The antenna is connected to "input" and the TV to "output".  In
addtion to the preamp that is installed on the antenna, there is a power
inserter which used to be a box with two F-connectors (TV coax connectors)
and an ac cord.  Newer units now have a wall cube with cord to the power
insertor.  The insertor has two coax connectors and is usually marked "ant"
and "TV", also.  To use one on a ham antenna you will need a coax adapter
to go from F-connector to whatever style connector the antenna uses
(probably a SO-239 or "female UHF" coax connector).

If all you have is the preamp and no power insertor, you can get them at
Radio Shack.

=============================================

>I was just looking for advice on specifically how others connect the (+)
and (-) leads from their respective power supplies to their preamps, or in
my case, their bias-tees.  Directly soldering the lead ends to the
feed-through and ground lug, or via some type of removable/unpluggable
affair?  What about a fuse?  Does ARR put one in their preamps or
bias-tees, or do I need to fuse the DC line from my battery/PS on my own?
>
>I have this bare nubbin-like bit of thick wire coming out, to which I'm
supposed to attached +Vdc; how do I form a good electrical AND mechanical
connection to it?  The lug on the gnd side looks pretty academic, so I
don't anticipate problems.  Why didn't ARR just build these things with a
coax DC input jack?  Does a design like that not lend itself well to the
inclusion of a DC feedthrough cap?
>
>BTW, in response to at least one reply to my initially-posted query, the
preamp in question is a P432VDG, good for 420 - 450, has a .5Nf, advertised
as offering 17dB gain, +12 dBm 1dB comp and a 1db BW of 40MHz.
=============================================
Ray, you have a very good UHF preamp.  But it is not designed for use with
a Bias-T (what I called a power insertor, above).  Normally most VHF/UHF
hams do not power their preamps by feeding dc-voltage up the coax.  It is
because having a voltage on the coax can cause trouble in the connections
over the long-term.  So we just run some two-conductor cable to the preamp
and connect the +12v side to the feed-thru cap pin and -12v to the ground
tab.  It is bad form to use the coax shield for the -12v return.

Since you got a bias-T with your preamp, you have two ways to go
1) modify your preamp using a RF Choke to bring voltage from the output
coax connector, or
2) buy a second bias-T and put on the output of the preamp and use a short
pair of wires to the feed thru pin and ground tab.  (hint try one for TV
from RS)

73's and GL
Ed - AL7EB
----
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