# [amsat-bb] Re: AMSAT Broadband Preamp Specs

i8cvs domenico.i8cvs at tin.it
Thu Oct 3 20:06:46 PDT 2013

```----- Original Message -----
From: "Paul Stoetzer" <n8hm at arrl.net>
To: <APBIDDLE at MAILAPS.ORG>
Cc: "Alan" <wa4sca at gmail.com>; <amsat-bb at amsat.org>
Sent: Thursday, October 03, 2013 6:02 PM
Subject: [amsat-bb] Re: AMSAT Broadband Preamp Specs

> Alan,
>
> Thanks for the "real world" example. My receiver is an Icom IC-R10,
> which the specifications say has a 0.25 uV sensitivity on 144 MHz and
> 0.32 uV on 435. I operate portable, so I'm not using the preamp for the
> high gain to overcome cable loss, but to overcome the relatively high
> noise figure of the receiver. The preamp works great for FO-29. When I
> have a clear horizon, I can hear it down to 1 degree or so with an Arrow
> antenna. My problem is the horizon (and a military spread spectrum
> radiolocation system that causes "clicking" noises all over the 70cm
> band here in Washington).
>
> 73,
>
> Paul, N8HM

Hi Paul, N8HM

Just for your information the sensitivity of the ICOM IC-R10 in CW
and SSB is :

144 MHz: 0.25 uV for a S/N ratio of 10 dB
435 MHz: 0.32 uV for a S/N ratio of 10 dB

To convert the above sensitivity in Noise Figure (NF) you can use the
folloving formula:
-6   2
( Vi x 10    )   x 20
NF    = 10 log     [ ------------------------ ] +174
dB              10          BW  x  S/N

where:

Vi = input signal in uV applied over the 50 ohm RX input
BW = Band Wide in Hz (2400 Hz for SSB)
S/N = Signal to Noise ratio in power ratio = 10

Back to arithmetic and using a scientific pocket calculator you
get the following results:

144 MHz  NF = 11.2 dB
435MHz   NF = 13.3 dB

The above NF are very high and to overcome only part of
requires sharp notch filtering you need front end preamplifiers
with at least the following characteristic:

144 MHz : NF= 0.6 dB and gain G = 20 dB with a very high
third order intercept point IP3 and very high 1 dB compression
point like a  preamplifiers of the Norton type circuit.

435 MHz : NF = 0.5 dB and gain G 20 dB possibly with
cavity input circuit like that described in my article publisched
recently into the AMSAT Journal March/April 2013

I hope this helps.

73" de i8CVS Domenico

```