Let's never forget that ANY loss between the antenna and the receiver will degrade the rx's noise figure. That means feedline, duplexer, cavities, connectors, Polyphasers, etc.
Noise figure degradation means less sensitivity, period. There's no way to make up for that EXCEPT with a preamp at the antenna. If that preamp's gain just equals the losses downstream from it, you've got a wash. However, you will lose on strong signal performance, IM, 3rd order intercept, etc., i.e. the preamp may be prone to overload by strong sigs. depending on its design. --John --- On Fri, 8/21/09, ka1jfy <[email protected]> wrote: From: ka1jfy <[email protected]> Subject: [Repeater-Builder] Re: Sinclair UHF Receive Antenna Multicoupler Question To: [email protected] Date: Friday, August 21, 2009, 5:31 PM Not quite the whole story Eric. If the original poster is trying to use this in the ham 440 band, then the preselector will most definitely need tuning before use. Sinclair says their standard preselector is +/- 5 MHz. And it should be mentioned that the gain of the amp is set to make up for the losses in the resistive dividers and nothing more. To get 'gain', you'll have to bypass one or more stages of the divider network. 2x divider gives you 3dB loss, and a 4x gives you 6dB. Remove one of those for corresponding 'gain'. Lastly, all unused outputs should have 50 ohm terminations. WalterH --- In Repeater-Builder@ yahoogroups. com, "Eric Lemmon" <wb6...@...> wrote: > > Tony, > > Those Sinclair multicouplers are intended to serve as many as 12 separate > receivers from one antenna. Ideally, all receivers should be for > frequencies that are clustered within a few MHz of each other, and the > preselector will be tuned to pass a band that is perhaps 2-4 MHz wide. The > splitter that follows the amplifier will provide sufficient isolation > between receivers. No additional cavities are needed. > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: Repeater-Builder@ yahoogroups. com > [mailto:Repeater-Builder@ yahoogroups. com] On Behalf Of kt...@... > Sent: Friday, August 21, 2009 7:27 AM > To: Repeater-Builder@ yahoogroups. com > Subject: [Repeater-Builder] Sinclair UHF Receive Antenna Multicoupler > Question > > > > Good Day everyone, > Does anyone have experience or tuning info for a Sinclair UHF Antenna > Multicoupler? The model on the rack panel is "CR4-302CF" and contains a > power supply, pre-amp (or preselector) and BNC distribution box (1 to 12 > outputs). Looks like 450-470 range. > > I haven't hooked this up yet, but wanted to see what to expect from it.. Can > such a device be used directly to receivers, or do you still need to add > band-pass cavities between it and the receiver? > > Thanks for any information! > > Tony >
