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Re: Preamp recommendations



Mark West wrote:

> Question 1: Will a preamp help at all? One book says I MUST have preamps,
> another says I don't need them. Lots of opinions. Does anyone have yet
more
> opinions, if so I would like to hear them.
>

Mark, my experience with both analog and digital sats is that a pre-amp at
the
antenna will make your operations much more successful. Sure, you can do
without them, but you will not enjoy it as much, and you will not hear the
weak
ones. Also, on PACSATS, preamps will improve your thruput, and you will be
able
to follow the birds down to lower elevations.

> Question 2: Is there a preamp FAQ out there?

I don't know...???

> Question 3: If you are using preamps, what is your favorite brand/model?

I have had good service from both ARR and Landwear.  I have no experience
with others (except at 2.4 Ghz, where I use Down East Microwave dual MMIC)

> So far it looks like the SSB SP-7000 is the one to beat. It claims 10-20dB
> with a maximum Noise figure of 0.9db. Others are publishing better noise
> numbers
> but do not provide curves like SSB does. Also SSB is using single gate
> GaAsFets,
> which I undestand are quieter than dual gate GaAsFets, and MUCH quieter
than
> bipolars (which realy are'nt under consideration anyway).
>

Extreamly good noise figure is not really that important at 144 Mhz for the
type work we do.  The sky noise at 144 Mhz is so high, you will probably not
benefit from an extreamly low noise figure preamp.  The situation is
different at 432 Mhz, as the sky is pretty quiet there... so extreamly low
noise preamps would make some difference, but only with very weak signal
work.

A preamp with a modest noise figure will help you almost as much as a very
quiet one.  The loss in your feedline between the antenna and first
amplifier is added directly to your system noise figure.  If you place your
first amplifier in front of as much of your feedline as possible you can
remove the feedline's loss from your total system noise figure.   The
differences in the noise added by various brands of preamps are usually
small compaired to
the overall system noise figure.  I personally would not get too hung up on
small differences in noise figures, especially at 144 Mhz. I'd focus more on
quality construction and dependability

73,

Dennis - N4NR



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