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Re: Another interesting preamp story



 Hi John,

     Yes I agree with you  in that particular use where you have a wideband
antenna and you are going to hook your 2m rig to the LO port and your 70cm
rig to the HI port and the common port is going to a wideband antenna,in that
instance you will filter a 3rd harmonic on the LO side

    I guess I should have specified in the context of a sat op where you
have your sat antennas and you have a 2m yagi and a 70cm yagi and your getting
desense,  the usage has been to hook your 70cm antenna to the common
port and the HI port to your 70cm preamp to act as a filter, in this case
no 2M 3rd harmonic rejection is going to happen, but attenuation of a overloading
2M signal will.

   Expanding on your idea you could use two diplexers and one coax run and
still use a 2m and 70cm antenna and get complete filtering, but since  many times we
are also running 12volts up a coax to feed a preamp that would be hard to do.

  But the example I was disagreeing with  was the use of a diplexer on the 70cm side
only to attenuate 2M harmonics.

 73
Kevin WA6FWF



----- Original Message ----- 
From: "jmfranke" <jmfranke@cox.net>
To: <wa6fwf@amsat.org>; "AMSAT-BB" <amsat-bb@amsat.org>
Sent: Wednesday, March 29, 2006 7:10 PM
Subject: Re: [amsat-bb] Another interesting preamp story


> Yes, the diplexer does pass 1.3-170 MHz and 350-540 MHz but to separate ports.  The two-meter rig is connected to the 1.3-170 MHz 
> filter and hence does not see or pass 432 energy but receives and transmitts the 144 MHz energy with little attenuation.  Hence, 
> the 144 MHz third harmonic is blocked at the source.  Similarly, the 432 rig is connected to the 350-540 MHz port and is not 
> subjected to the 144 MHz transmitter output.  Remember the 144 MHz third harmonic was blocked by the 1.3-170 MHz band pass filter.
>
> John  WA4WDL
----
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