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Re: S-band receiving requirements



Mike and Gene,

Ya, that coax ahead of the preamp/downconverer is all important. What is 
the loss at 2400 Mhz of just a male/male N connector between the antenna 
and converter  I have been using 0.25 db as a wag.

If I have a helix antenna with 17 dBic, does that mean I should enter 14 
into the spread sheet to cover the loss from circular to linear. Or should 
I be entering 20 since my antenna is really 3 db better than a linearly 
polarized antenna?????  The antenna gain seems to be used on the data sheet 
to compute the transponder levels. Is the 3 db polarity loss embedded in 
the "24" factor at the end of the equation?

Jerry W6IHG



At 08:17 AM 5/19/01 -0400, Mike73@aol.com wrote:
>In a message dated 5/18/01 8:40:08 PM Eastern Daylight Time,
>al7eb@ptialaska.net writes:
>
> >  Gene Marcus' spreadsheet is very useful for this process.
>
>I agree!!  A couple of pointers.....
>
>The very first coax loss number before the preamp is very important. This
>really effects overall system noise. I calculated the 3 foot jumper (RG-8) on
>my Meyers dish as -.36 dB at 2400 (yuk). Throw that number in the spreadsheet
>and see what happens.
>
>Also, I asked Gene about the antenna gain. The number you input is dBi
>Linear. So to be accurate, if you're using a Meyers dish you should subtract
>3 dB for the theoretical loss when going from linear to circular. So, for a
>Meyers dish that was advertised as 25 dBi, you would input 22 dBi.
>
>I can see if I were to do any improvements to my system, I'd probably attack
>the antenna. I already have a good low NF preamp. The changes I'd contemplate
>would be to change the feed to circular and reduce the coax loss before the
>preamp. To see the effect of these two changes, input .1 dB for first coax
>loss and 25 dBi antenna gain in the spreadsheet and you'll see the
>improvement.
>
>Now back to cobbling together a 5668 uplink :-}
>
>73,
>Mike, N1JEZ
>AMSAT #29649
>Local Area Coordinator
>"A closed mouth gathers no feet."
>----
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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------------------------------------------
Dr. Jerry R. Pixton, PIXOS Designs LLC
http://www.pixos.com/designs/
jpixton@shentel.net
------------------------------------------

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