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Re: masthead preamp question



It won't make a difference at 144 MHz where the sky temperature is over 600
K.

At 432 MHz there will be at least another 0.1 dB loss in the connectors so
the loss of 1 dB is about 75 K. Sky temperature is also about 75 K at that
frequency. A 1 dB NF preamp adds 75 K so the system noise temperature will
be about 150 K with the preamp at the antenna or about 225 K with the preamp
at the receiver. You get 1 dB extra SNR by mounting an inexpensive preamp at
the antenna. The very best preamps are 0.4 dB NF or 30 K so you could get a
2 dB improvement.

73,

John
KD6OZH

----- Original Message -----
From: "Jack" <vk2trf@bigpond.net.au>
To: <amsat-bb@amsat.org>
Sent: Tuesday, May 03, 2005 20:48 UTC
Subject: [amsat-bb] masthead preamp question


> Hi All,
>
> I am constructing a sat array for my QTH.
>
> Q:
> If I have 50ft of LMR600 low loss coax from the antenna to the receiver,
is
> there an advantage in mounting the preamp at the antenna or will it
perform
> as well at the receiver end of the cable.
>
> The losses in the 50ft of cable are 0.5 dB at 144Mhz and 0.9dB at 432Mhz
>
>
> --
> 73
>
> Jack Swart
> VK2TRF
> QF56oe
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
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----
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