"Owen Duffy" wrote in message
...
Dave Oldridge wrote in
:

...
I used to have an FT-221 tricked out with a hot front end. Solar
noise would run the S meter up to well over the S9 mark and you could
even see the galactic plane passing through the antenna pattern.
Needless to say, it heard well on terrestrial 2m SSB.

That is no mean feat!

I think ambient noise temperature at 144MHz for an antenna pointed at
cold sky is somewhere around 200K to 250K, when you add a pretty good
receiver at say 30K, you are talking 230K to 280K total system noise, and
the sun is probably around 800K with a low end 4 bay EME antenna setup
(Gain~22dBi), for a noise rise of 10*log((800+255)/255) or 16dB.

A single yagi of gain around 15dBi is much poorer, not only is the sun
noise reduced proportionately to the gain reduction, but the ambient
noise increases with higher gain in the side and back area of the
antenna, but it still should be possible to reliably 'see' the sun with a
very good receiver.

Ambient noise temperature for a beam at zero elevation here in suburbia
varies from 1000K to 6000K depending on the day and time... so a very low
temperature receiver is wasted for terrestrial contacts.

Owen

Owen

I would like to see what mods are made to the 221 to do that and also what
kind of antenna system. I have a 221 I am using with a gasfet preamp in
the shack that should be less than 1 db of noise fugure and about 20 db of
gain. The antenna is a klm 22c and 75 feet of 9913 type of coax. I can
just see some sun noise with the antenna aimed at the sun. It sure does not
deflect the smeter several sunits. The antenna is on an azel mount. I am
sure the system is working as I compaired it to an Icom 706 and another
antenna that is mounted on a tower and I am getting about the differance in
signal levels I would expect at the horizon.

I would like to see what mods are made to the 221 to do that and also what
kind of antenna system. I have a 221 I am using with a gasfet preamp in
the shack that should be less than 1 db of noise fugure and about 20 db
of gain. The antenna is a klm 22c and 75 feet of 9913 type of coax. I
can just see some sun noise with the antenna aimed at the sun. It sure
does not deflect the smeter several sunits. The antenna is on an azel
mount. I am sure the system is working as I compaired it to an Icom 706
and another antenna that is mounted on a tower and I am getting about the
differance in signal levels I would expect at the horizon.

The 75 feet of coax is your problem!!! What is the point of a 1dB NF preamp
with all that loss ahead of it? To see the benefit of the low noise figure
the amp must be before all that cable loss!!

73
Jeff
G8HUL

"Jeff" wrote in message
. com...
I would like to see what mods are made to the 221 to do that and also
what kind of antenna system. I have a 221 I am using with a gasfet
preamp in the shack that should be less than 1 db of noise fugure and
about 20 db of gain. The antenna is a klm 22c and 75 feet of 9913 type
of coax. I can just see some sun noise with the antenna aimed at the
sun. It sure does not deflect the smeter several sunits. The antenna is
on an azel mount. I am sure the system is working as I compaired it to
an Icom 706 and another antenna that is mounted on a tower and I am
getting about the differance in signal levels I would expect at the
horizon.

The 75 feet of coax is your problem!!! What is the point of a 1dB NF
preamp with all that loss ahead of it? To see the benefit of the low noise
figure the amp must be before all that cable loss!!

73
Jeff
G8HUL

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.

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.


Agreed. Your 1 dB preamp just became a 2 dB preamp and the visible ground
temperature likely overrode either figure and by a good margin. I suspect
the original poster with his S9 sun noise and "seeing" the Galactic plane
was being a bit optimistic.

W4ZCB

" 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

"Ralph Mowery" wrote in
:


"Jeff" wrote in message
. com...
I would like to see what mods are made to the 221 to do that and
also what kind of antenna system. I have a 221 I am using with a
gasfet preamp in the shack that should be less than 1 db of noise
fugure and about 20 db of gain. The antenna is a klm 22c and 75
feet of 9913 type of coax. I can just see some sun noise with the
antenna aimed at the sun. It sure does not deflect the smeter
several sunits. The antenna is on an azel mount. I am sure the
system is working as I compaired it to an Icom 706 and another
antenna that is mounted on a tower and I am getting about the
differance in signal levels I would expect at the horizon.

The 75 feet of coax is your problem!!! What is the point of a 1dB NF
preamp with all that loss ahead of it? To see the benefit of the low
noise figure the amp must be before all that cable loss!!

73
Jeff
G8HUL

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

Out of the box, the 221 had a noise figure somewhat north of 12db. I've
seen vacuum tube radios that were not much worse.


--
Dave Oldridge+
ICQ 1800667

Out of the box, the 221 had a noise figure somewhat north of 12db. I've
seen vacuum tube radios that were not much worse.


I have never seen an FT221 with a NF anywhere near that. They normally cone
in at about 5-6dB as standard and about 1.5 with the Mutek front-end board
fitted.

73
Jeff