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Re: Preamp for a Mobile Application



Ed:

If you use a Comet Diplexer such as the CF160 that I have, it can split 
things out to two antennas and then you can use a preamp on the receive 
side.  I have used that approach when I have worked sats low to the 
horizon or when I had time to find a good parked position with a clear 
view of the sky.

Ron
KA4KYI

Edward Cole wrote:
> 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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