Thanks for your input Steve. I'm actually changing my duplexer setup to the Motorola T1500 series 4 can setup when the weather allows. I believe they're BpBR. I know that when the line was swept a few months ago that I have the noise figures. I have to get them again. Maybe that would be a good indicator of what I need. Regardless of needing a preamp or not I'm still planning on adding a filter or bandpass cavities in the receive side. I just don't know exactly which way to go cavity or filter? Do you have any suggestions? What kind of filter would you use? I'm also thinking about putting a circulator on the transmit side. Any thoughts? Thanks again.
Dino
"Steve S. Bosshard (NU5D)" <[EMAIL PROTECTED]> wrote:
"Steve S. Bosshard (NU5D)" <[EMAIL PROTECTED]> wrote:
Before you fix a receive problem be sure there is a problem. I have used
ARR GasFet preamps for some time with excellent results. Be sure you have
a filter or cavity ahead of the preamp, and that you do not have so much
out of band energy getting to the preamp that it goes into overload and
becomes a non-linear mixer. I have used GasFets in tower top systems (one
at 600 ft for over 15 years) with PolyPhaser's ahead of the amp.
I also built a relay tree to bypass the preamp when power was removed. The
relays (GE Pro antenna relays) caused more trouble than they solved because
there was no wiping action in the contacts.
Aside from the obvious gain of the preamp, the very low noise figure ahead
of a not so good front end amp can make a substantial improvement. Be the
3rd order intercept point is as high as possible for intermodulation
mixture products. Also test for receiver desentization with an isolated
tee incase there is not enough receiver protection from the transmitter.
What worked before preamp now needs to be at least 15 db better with the
preamp. That is, if you had a little desensitization before adding the
preamp, it will probably get worse - double shielded cable and ground is a
must.
73,
steve
nu5d
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