[amsat-bb] Re: Preamp Distance from Antenna

i8cvs domenico.i8cvs at tin.it
Wed Mar 30 15:02:36 PDT 2011

Hi Zack, KD8KSN

The loss in dB of the coax cable from the antenna to your preamplifier adds
directly to the Noise Figure NF of your preamplifier. As an example if the
loss of the coax cable is say 0.7 dB and the Noise Figure of the
preamplifier is 0.55 dB as specified by the manufacturer then the overall
Noise Figure of the system antenna plus preamplifier is  0.7+0.55=1.25 dB

This is why to reduce the overall Noise Figure of any receiving system it is
necessary to install the preamplifier as close as possible to the antenna

By the way the gain of a ARR SP432VDG preamplifier is 16 dB and as
connected in front of your 70 cm receiver you will see an increase of noise
level of about 3  S-units in your S meter but the overall Noise Figure of
your receiving system will be much lover than the Noise Figure of the 70 cm
receiver alone.

In this condition using a preamplifier the 70 cm receiving system will be
more sensitive but it will be more susceptible to intermodulation and
overloading when you transmit to a satellite in  the 2 meters band.

If you suffer with intermod the only cure is to add a 6 dB attenuator from
the preamplifier output to the 70 cm receiver input but if you use a 70 cm
tranceiver don't forget to remove the attenuator before to transmit in 70 cm

I hope this helps.

73" de

i8CVS Domenico

----- Original Message -----
From: "Zachary Beougher" <zack.kd8ksn at hotmail.com>
To: <amsat-bb at amsat.org>
Sent: Wednesday, March 30, 2011 4:24 PM
Subject: [amsat-bb] Preamp Distance from Antenna

> Hi,
> I am in the process of getting the ARR SP432VDG preamp for my mobile setup
(and just to have around), and I have read that the closer to antenna you
mount the preamp, the lower noise figure you will have.  My question is,
what is close to the antenna – 1ft., 5ft., 10ft.?  Ideally, I would probably
mount it about 5-6ft. from the antenna (1/4 wave) – would this be
> Any additional advice would be appreciated!
> Zack
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