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Re: ARR in-shack preamps



John,

The preamp will likely help your overall system NF in either location as
most radios have NF > 10-dB.
But you will not get as much increase in sensitivity if you put in the
shack.  

The loss of the cable from the antenna adds directly to the NF (i.e if you
have 6-dB cable loss your NF = 6 + NFpreamp = 6.5, assuming the preamp
NF=0.5 dB).

If you place the preamp at the antenna, then your NF ~ 0.5 dB.  You will
find that is a very noticeable difference.

If you would like to analyze it yourself, go to my website eme pathloss
excel spreadsheet and plug your own numbers in.  The first section deals
with receiver NF and sensitivity (MDS).  it may take some time to download,
but you can save it on your computer for future use:
http://www.qsl.net/al7eb/emelink.xls

if that does not work you can go to 
http://www.qsl.net/al7eb/eme144.htm 
and click the "system NF" link.

I ran the numbers: 
at antenna NFsys = 1.06 dB, Pn = -140.1 dBm = MDS
in the shack NFsys = 6.64 dB, Pn = -134.2 dBm  
you loose 6-dB of sensitivity or about one s-unit.

Hope that helps!

73's Ed - AL7EB


At 10:17 PM 2/9/2005 -0800, John Geiger wrote:
>I am looking to get a 70cm preamp to help with Mode J
>on receive, and have found a couple of good deals on
>the Advanced Receiver Research (ARR) 432 in shack
>preamps.  I have used these before for weak signal
>work, but not on the satellites.  Do these in shack
>preamps really help on the downlink signal, especially
>for SO50 and AO27, or would a mast mounted preamp be
>the only think that would help?
>
>73s John NE0P
>Tired of spam?  Yahoo! Mail has the best spam protection around 
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