Hi Guys, Thanks for the replies on this, my curiousity about the pre amp is based on my limited knowledge that you can't improve what you can't already hear so I wasn't too sure how much benefit they actually give. We are lucky in as much as our site has no other users and the nearest UHF site is about 1/2 mile away with 410Mhz Tetra and TV. I had a quick look on the Angle linear site for pre amps and notice they sell complete duplexers as well, the spec looks excellent but I'm sure it comes at a price! On this side of the pond there doesn't seem to be much of a second hand market for commercial kit, for new stuff we've got Procom, their website lists http://www.profilant.net/uk/filter/13061800 which seems to BPBR and has more than adequate power handling, UK repeaters are limited to a measly 25W ERP! I'll make some enquiries about the Procom and meantime our groups technical guy has decided to buy one of those Ebay items to see if it performs as stated with no intention of using it on our repeater :)
Cheers Paul --- In Repeater-Builder@yahoogroups.com, Ken Arck <[EMAIL PROTECTED]> wrote: > <---Hi Paul. First of all, the type of duplexer you're looking at is > a notch only type. Secondly, I find their claim of > 75 dB isolation > and < 1 dB insertion loss pretty comical. I'd go so far as to say > that claim is total BS. Even at your spacing of 7.5 mHz, I don't see > how the performance is anywhere near as good as they claim. "You ca' > not fight the law of physics" as Scotty would say. > > A notch-only type duplexer is usually adequate for lower power > repeaters in a low RF environment. I would certainly NEVER use one at > a radio site where other radios/repeaters reside as they do not offer > adequate out-of-band rejection nor even adequate in-band rejection. > > To further complicate things, adding a preamp would probably be a > complete disaster without adding additional filtering. I do agree > with Jed that AngleLinear makes most excellent preamps with just the > right amount of gain for a repeater preamp, whereas ones such as ARR > have WAAAAY too much gain. The purpose of a preamp in a repeater > (assuming your receiver is worth a damn in the first place) is to > overcome the loss of the duplexer and feedline. Too much gain opens > the door to all sorts of issues, not the least of which are desense > and front-end overloading. And again, using one with the typical > "mobile" duplexer will probably cause problems anyway. > > You can find good deals on used band-pass/band-reject UHF duplexers, > usually quite easily. My advice is to buy one of those and forget > about the "mobile" type. > > Ken
