Too bad everyone does not think that way Kevin.
Vincent N6OA
----- Original Message -----
From: "Kevin Custer" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Sunday, January 01, 2006 8:31 AM
Subject: Re: FW: [Repeater-Builder] Duplexer for sale
> As Eric points out, this duplexer doesn't provide a lot of isolation.
> Usually 90+ dB is required and more is often necessary, depending on
> several factors like the actual receiver sensitivity, using a preamp and
> how good it is, and the actual transmitter power level, spectral purity
> of it, and actual site conditions.
>
> That being said, this duplexer would perform very satisfactorily on a GE
> Mastr II 2 meter repeater (600 kHz) running 100 watts utilizing a PLL
> exciter, and possibly a preamp. The GE PLL exciter exhibits about 22 dB
> less transmitter sideband noise than does a typical multiplier exciter,
> and that 22 dB doesn't need to be made up for in the duplexer. Many
> preamps should not be hit any harder than about -40 to -50 with shear
> power or, with other out of band sources present, will be driven into
> the non-linear region. Considering 100 watts of power into the
> duplexer, about 70 watts would appear at the antenna port, or a level of
> +48 dBm. Now take the 48 dBm and reduce it by 77 dB and -29 dB
> results. At neg 29, the stock GE Mastr II UHS preamp would likely work
> as the measured noise figure & 1 dB output gain compression point are
> 4.6 dB & +1 dBm, respectively. Considering a gain of around 12 dB and
> assuming your VHF preamp performed similarly, you'd get -17 dBm of TX
> signal at the preamp output, 18 dB below the +1 dB GCP. While it would
> work, it won't be able to handle much more signal from any other sources.
>
> This duplexer could work well at a unpopulated site using (the above
> suggested) solid state equipment at typical levels (100 watts); with
> decent receiver sensitivity (-122 dBm for 12 dB sinad).
>
> Kevin Custer
>
>
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