[amsat-bb] Re: Preamp Distance from Antenna
matthias.bopp at gmx.de
Sat Apr 2 03:22:20 PDT 2011
Hi Zack and Domenico,
I would like to add, that the negative effect of the added losses in front
of the preamplifier and thus reduced sensitivity of your system is also a
function of the noise level: in terrestrial systems where your antenna
typically sees a noise temperature equal to the ambient temperature all
written below is reflecting the negative effect quite well.
However in a satellite system where your antenna sees the noise of the sky
the "Noise temperature" is a function of frequency and at VHF/UHF/SHF the
sky is "quite cold" and thus the "noise temperature" is much lower than the
Therefore the negative effect of the degraded noise figure is much higher.
Please keep this in mind.
Von: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] Im
Auftrag von i8cvs
Gesendet: Donnerstag, 31. März 2011 00:03
An: Zachary Beougher; Amsat - BBs
Betreff: [amsat-bb] Re: Preamp Distance from Antenna
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
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.
----- 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
> 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!
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
More information about the AMSAT-BB