" The coax only has a loss of 1 db for the length I am running it. I doubt
that at 2 meters I would see any benift of putting the preamp at the
antenna. It is as easy to get a 1 db or less noise figure at 2 meters as
it is to make any preamp and the 221 does need some help on the receiving
side.
From the articals I have read the beam width of most any single antennas
at 2 meters is wide enough the ground noise will override that ammount of
loss.


I think 1dB is a little optimistic for 75' of 9913 coax, it is in reality, I
suspect, nearer 1.5dB.

Any loss ahead of your preamp adds directly to the noise figure of the
system so the best NF that you could ever have is 2.5dB plus a little form
the 221.
Also 20dB of gain in the preamp sounds like a sure way to produce intermods
in your radio.

Regards
Jeff

I think 1dB is a little optimistic for 75' of 9913 coax, it is in reality,
I
suspect, nearer 1.5dB.

Any loss ahead of your preamp adds directly to the noise figure of the
system so the best NF that you could ever have is 2.5dB plus a little form
the 221.
Also 20dB of gain in the preamp sounds like a sure way to produce
intermods in your radio.

Regards
Jeff

Well of course it is Jeff, but in moonbounce, noise figure is the holy
grail. There weren't as many folks on 432 and moonbounce in particular back
in 1979, but I NEVER was plagued with intermod off the moon, and the
directivity of the array kept me from having any from anywhere else.

W4ZCB

"Harold E. Johnson" wrote in
news:4mkAi.59515$Xa3.5320@attbi_s22:

Well of course it is Jeff, but in moonbounce, noise figure is the holy
grail.

Is it?

Knowing G/T allows you to calculate the S/N ratio for a known incoming
power flux density. Better, improvement in G/T ratio yields exactly the
same improvement in S/N.

You cannot do that with NF alone, so it is not a single metric that
characterises receive performance of a station.

Moonbouncers who focus on NF alone are as blinkered as anyone else who does
that.

Owen

Any loss ahead of your preamp adds directly to the noise figure of the
system so the best NF that you could ever have is 2.5dB plus a little
form the 221.
Also 20dB of gain in the preamp sounds like a sure way to produce
intermods in your radio.



Well of course it is Jeff, but in moonbounce, noise figure is the holy
grail. There weren't as many folks on 432 and moonbounce in particular
back in 1979, but I NEVER was plagued with intermod off the moon, and the
directivity of the array kept me from having any from anywhere else.

W4ZCB

Well that's the first FT221 I heard of working on 432MHz!! If you are
talking about that band rather than 144MHz then the cable loss would have
been far higher and the NF of the system much higher.

Having a preamp with a gain of 20dB right in front of the radio is just
plain silly. Pre-amp gains should be kept as low as possible. They should
have just sufficient gain so that their low noise figure defines the system
noise figure. Any excess gain is wasted and just asking for large signal
problems.

If NF was such a Holy Grail then why throw away a significant improvement by
putting the preamp after the feeder any degrading the system NF by the
feeder loss?

Jeff