My turn...
Hi Paul,
We are currently applying for a 7.6Mhz split UHF repeater here which
means we will be able to do away with the old and lossy large cavity
filters for our old 1.6Mhz split repeater and use a commercial unit.
Wow, kind of hard for some of us to imagine anything but the
standard 5MHz UHF Repeater Offsets found used in the US 440
to 470 MHz range. No big deal really but I/we often wonder if
the Amateur Radios you folks purchase easily program these splits
as standard or if you have to program them in as what we call an
odd split?
We've already tried a loaned Procom duplexer and the results
are most promising with no TX desense or noise noted on the
RX and minimal loss of TX power.
... which is what a duplexer is hopefully supposed to do for you.
As we now need to purchase a filter for ourselves I've
come across these on Ebay, has anyone any experience of them?
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItemitem=160192454185
What I'm seeing is a picture of a common vhf flat-pack duplexer
(also known as a mobile duplexer by many) set up as an auction to
offer you to be able to select a UHF or VHF duplexer selection
once you make high bidder at the auction close. In other words it's
a rather generic auction listing.
Looking through the archives I can see some groups use pre amps on
70cm repeaters, this isn't something we've considered before but
presuming they fit between the RX and the duplexer how effective are
they?
A preamplifier can make a night and day difference in repeater
coverage only if it's properly engineered (and installed) into
a repeater system. The issue with adding an external preamplifier
is properly protecting it from unwanted energy, which includes
the transmitter, external (outside) signals and lightning.
Yes, on a repeater the preamplifier normally installs in front of
the receiver and the filter network in front of it, which may be
a duplexer or pre-selector assembly.
If they are worth considering what make and model is favourite?
The question that always makes the repeater preamplifier people
offer an answer regarding their one favorite manufacture.
A number of people make pre-amplifiers and pre-amplifiers with
built in/on integrated filters of various sizes. Brand names
include Angle Linear, ARR, SSB Electronics, Hamtronics, Spectrum,
Ramsey... yadda, yadda.
The most popular repeater pre-amplifiers are probably sold by
ARR and Angle Linear. I use many of both brands in various commercial
and Amateur Radio systems around my end of California.
http://www.advancedreceiver.com/page5.html
or
http://www.anglelinear.com/
Like everything else the addition of a pre-amplifier should be
well thought out else or you'll cause yourself more grief than you
thought possible... hence the reason asking for opinions here on
the group is a good thing.
Under the pre-amp description there are at least four major types
available... so again more questions to the group will help you
sort out a viable option for your system.
Making a full circle we arrive back at the flat pack duplexer
you see in that Ebay auction. Normally that type of duplexer
is not used stand-alone with an additional receiver pre-amplifier.
There is simply not enough protection provided by that type duplexer
operation. You would need to obtain a more conventional band-pass,
band-reject type duplexer or include some type of quality band-pass
filter in front of any added external pre-amplifier when using
a flat-pack unit.
OK, my fingers hurt...
chow
skipp
