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Re: Preamp for a Mobile Application



Jeff,

You are partly correct, but the main job of the preamp is to lower 
the noise figure of the overall receiving system.  The gain in the 
preamp is primarly to provide a strong enough signal for the 
following receiver that its noise figure is not significant.  Having 
enough gain is important so that there is enough extra too overcome 
coax line loss and still have sufficient gain left over at the 
receiver (approx. 15-dB is needed).

So, a preamp can help a mobile satellite station if there is a way to 
install it.  If your radio only has one antenna connector for both 2m 
and 70cm, then it will not be possible to use a preamp for a full 
duplex radio.  If it is not able to operate duplex then a switching 
preamp would work OK.

73 Ed - KL7UW

At 09:52 AM 3/31/2008, Jeff Mock wrote:
>It's not clear that a preamp will improve your reception.  The 2720H has
>a pretty sensitive receiver.  The preamp will help you if the noise
>figure of the preamp is better than the noise figure of your radio.
>It's not clear to me that you can make much of an improvement here.
>
>I have a preamp on the masthead at home, but I have a long feedline from
>my receiver to the antenna, I have about 7db of loss from the antenna to
>the radio at 70cm and I get a noticeable improvement with a preamp.  The
>main job of my preamp is to overcome the loss of the feedline, otherwise
>the preamp is not that much better than the radio.
>
>jeff
>AD6EO
>
>Kent R. Frazier wrote:
> > Hi all,
> >
> > I am really enjoying the satellite aspect of the hobby and have enjoyed the
> > contacts I have made with my Icom IC-2720H with a 19" whip antenna from my
> > vehicle. I have seen talk recently of using a preamp to improve the
> > reception. From what I've read and understand, it appears that a 
> "switching"
> > preamp is needed for a setup using only one antenna for Tx and Rx such as
> > mine. Is this correct?
> >
> > It also appears that most of the preamps are mast mounted. Since this would
> > not be an option for me can the preamp be put near the transceiver? Are
> > there any issues that result of doing so?
> >
> > Lastly, what preamp(s) would you recommend for an application such as mine?
> >
> >
> > Thanks,
> >
> > Kent
> >
>
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