Hi Modern distribution amp chips are likely to be sub 2 db NF. Gain is generally just a bit more than the loss through any post filtering and the passive power splitter after it.
Bob > On Sep 2, 2017, at 7:02 PM, Wes <w...@triconet.org> wrote: > > This is just a cascaded noise figure situation. > > The first stage is the antenna (preamp) which has 26 dB gain (assumed) and an > unknown noise figure. Assume it's a dB or so. Let the second stage gain be a > negative value equal to the cable loss and the second stage noise figure be > equal to the cable loss in dB. Assume a lousy 10 dB NF and 10 dB gain for > the distribution amp. > > If the cable loss is 5 dB then the cascaded noise figure and gain are: 1.26 > dB, 31 dB gain. > > If the cable loss is 2 dB then the cascaded noise figure and gain are: 1.13 > dB, 33 dB gain. > > I would use RG-6. > > See: https://www.pasternack.com/t-calculator-noise-figure.aspx > > The secret here is the 26 dB gain. > > > Wes N7WS > > On 9/2/2017 11:57 AM, Clay Autery wrote: >> Having decision-making problems for the materials for my GPS main >> feedline. Going to use a TM LMR stock, just can't decide how big to go >> with it... >> >> 26 dB 5vdc antenna on top of a 38 foot mast. Feed will come down the >> inside/center of mast and exit near the bottom, thence routed through a >> window and to the GPS distro amp. Antenna will feed GPSDO, NTP Server, >> Blitzortung System Blue station, and one other device TBD. >> >> Just cannot decide how big to go with the antenna to distro amp feed... >> Assuming 50 feet total (38' mast + 12 feet to amp in shack) @ 1800 MHz >> (closest to 1725 MHz), here are the losses from just this piece >> (ignoring the amp to device jumpers): >> >> -240 = 5.45 dB XXX - too much loss? >> -400 = 2.85 dB >> -500 = 2.30 dB XXX - too hard to find >> -600 = 1.85 dB >> -900 = 1.25 dB >> >> Money not necessarily a consideration as this is a short run for a >> permanent installation. Don't anticipate ever moving the GPS antenna to >> the tower. >> For 900 and likely 600, likely would not be able to do it in one piece >> as routing it out of the mast and into the shack would get complicated. >> Would likely bring it out of the mast at the bottom with a right angle >> connector, and then use a smaller diameter jumper for the last 12 feet. >> 500 is pretty uncommon stock wise and it and connectors are harder to find. >> >> I already have the tooling for both 240 and 400... but I definitely >> don't want to challenge ANY of the devices for signal gain. >> >> So it mostly boils down to easy vs. more effort ($$ aside).... Is it >> worth the additional trouble to move from -400 to -600 or -900? To NOT >> lose the 1-1.6 dB additional? >> >> I'd appreciate your recommendation and reasoning. Thanks in advance! >> >> 73, >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.