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Re: Icom 820H/ UT-50/AG25+35

Hello Emily,

You are absolutely correct.  Do not provide a dc ground for any 
transceiver RF output center conductor.

Some filters may provide a DC short to ground and different antenna 
matching systems may  be DC grounded.

My practice is to externally inject DC power onto a coaxial line with RF,
for power needs at the antenna, like a preamplifier.

With external ( to the transceiver) DC injection, I can easily measure 
DC current, and have a beefier DC injection than
from any transceiver.

Similarly, some lightning suppression devices may be a a DC short to 
ground, and others have a DC passthrough capability.

Stan, WA1ECF       Patiently waiting for ECHO

Emily Clarke wrote:

> Hi Stan,
> At 07:33 PM 4/20/2004 +0000, Stan wrote:
>> Try adding a good band pass filter between the transceiver and the 
>> antenna feed line,
>> is there an improvement in hearing a distant station ?    If there is 
>> improvement,
>> add the good band pass filter between the antenna and the mast 
>> mounted preamplifier and check again.
>> If preamplifier performance is better with the band pass filter, 
>> weather proof it and leave in line.
> Since the AG-25/35 are fed through the coax, it's probably best to 
> mount the band pass filter only between the preamp and receive 
> antenna, otherwise nasty things can happen.  I don't know for certain, 
> but I have heard that you can blow out the preamp power supply (in the 
> rig).  That doesn't seem to happen on the 910H as it detects this and 
> turns the power supply off, but I don't know about the 820H.
> I used a Diamond MX-72N duplexer as a Mode J filter, and it worked 
> just fine. I connected the input of the 72N to the antenna and 70cm 
> output side to the preamp.  I then fed the 2m side into a 50 ohm load  
> (You can find some diagrams on the back of the 72N package.)
> 73,
> Emily
> ---------------------------------
> W0EEC - CM87tm
> AMSAT Area Coordinator - San Francisco Bay Area
> http://www.projectoscar.net   http://www.PlanetEmily.com 
> http://www.experthams.net/ao7
> Help Launch Echo - http://www.amsat.org/amsat/sats/echo/index.html
> --------------------------------- 

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