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Re: S-band receiving requirements



You should figure in .5 Db per N connector if they are of good quality !!!

Jerry Pixton wrote:

> 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.
> >To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>
> ------------------------------------------
> Dr. Jerry R. Pixton, PIXOS Designs LLC
> http://www.pixos.com/designs/
> jpixton@shentel.net
> ------------------------------------------
>
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