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-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
Behalf Of TheComputerDoctor
Sent: Thursday, January 29, 2009 2:10 PM
To: amps@contesting.com
Subject: [Amps] Amplifier Question
This is for anyone that might own and RF Concepts, Mirage, or similar 2m Amp
that can help answer this..
I got a hold of a used RF Concepts 2-417, dirt cheap as it needed some work,
my intent was to use it on 2m FM with my FT-8800R. Question is, i want it
to also be able to pass UHF when its OFF. The radio seems deaf on UHF
receive with the amp and preamp turned off, this should flip the relays
internally to effectively put the amp out of the circuit. Upon further
inspection of the schematic located here..
http://www.radioamateur.eu/schemi/ACC_PA/RFConcepts_2-315_2-417_sch.pdf
If you look to the right hand side about the middle of the page you will see
the antenna connection, there is a couple caps and a couple coils, matching
network? Not really familiar with these units, whats the actual purpose of
these components and can they be bypassed?
::Not if you want the amp to work properly on two meters, they cannot. They
are both Z-matching and also a third harmonic filter (FL1). If you remove FL1,
you'll have harmonics galore from the amp on 2m. However, its presence is why
the amp won't receive anything through it on 70cm!
I assume that these components
filters the output of the amp? If so that would be why my UHF receive is
deaf now. VHF receive is perfect by the way, so its not another problem,
and if i remove the amp and put a barrel in place of it the UHF works fine
again.
I thought about buying a couple diplexers, one to split the radio, and the
other to combine the UHF and the output of the amp back to the antenna. But
its a lot of extra expense, and a lot of extra connections inline as well!
Not to mention the fact that i only have a couple UHF repeaters around here
that i even use, so its not worth all the effort for two repeaters. But at
the same time i don't need suggestions like "get a different radio", "use
two antennas" etc.. Let's focus on the amp and what can be done with it to
pass UHF.
::You could use a double pole bypass relay or coaxial switch to simply fully
switch the amp out of the circuit on 70cm. In fact, that's what I do at home!
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