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

Interesting numbers, Dave.

W8PIL and I published a paper in QST in the 60s that dealt with the noise
into a receiver from extraterrestrial sources. For those numbers to be
limiting, one needs to be well away from people and one needs an antenna
that has a very large directivity. In the other hand, if your receiver is
in space, its antenna is not pointed at earth, and you have an antenna with
a moderate directivity, then the numbers we presented will limit SNR.

I was involved in the early measurements of the temperature of the moon with
a two-frequency feed using an 85 foot dish. Two-frequency = resonate at two
frequencies separated by 2 times the IF frequency so more "signal" could be
acquired. VT front end using every scheme in the book. Today, with almost
no design, an FET off-the-shelf would be much better.


What huge improvements I have seen in the NF of VHF and UHF amplifiers.
However, the techniques for achieving low NF have not changed from the ideas
contained in v18 of the MIT Radiation Lab series.

73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"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

"Ralph Mowery" wrote in
:


"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.

Firstly, this was actually Howard's statement.


That is no mean feat!

And my comment.


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.



So, lets take some guesses about things here. FT221 native NF ~8dB, line
loss 0.2dB, preamp 1dB NF, 20dB gain, 9913 loss 1.2dB (75', load end VSWR
1.5). On my reckoning, Teq at antenna connector is 200K. The antenna is I
understand a 22 element crossed Yagi, let's assign it 15dBi for the
purposes of discussion.

Looking back at the earlier scenario, ambient (cold sky and earth) of
225K (ignoring the prospect of worse spillover with the smaller antenna)
and sun noise of 160K, sun noise rise would be (225+200+160)/(225+200) or
1.4dB. That is not going to be very noticeable on an S meter.

O&OE!!!

At higher points in the solar cycle or if the sun is disturbed, the rise
will be greater, but genuine quiet sun measurements should not capture
disturbed sun, should they? Antennas more sensitive off the back / sides
will be worse.

In that scenario, moving the preamp to the antenna would improve G/T from
-11.3dB to -10.1, yielding a 1.2dB improvement in S/N ratio. At zero
elevation, the ambient noise is typically much higher and the improvement
would be much less.

Ambient noise is pretty easy to measure on 144MHz in a simple station. If
you know the noise figure of your receiver and loss to the antenna, and
providing ambient noise is not sufficient to cause AGC, note the audio
power output change between antenna and a dummy load, you can calculate
the ambient noise, see http://www.vk1od.net/sc/anc.htm for more
information. In fact, with this tool, I can measure the change in audio
output on my TS2000 by switching the internal 12.1dB attenuator in, and
calculate Ta (try Example 3).

I hear sun noise rise bragged about, but the bragger often cannot quote
the solar flux prevailing at the time, in which case it is rather
meaningless, especially when their method is to capture the largest rise
rather than largest minimum rise whithout artificial compression.

The reason I wrote the online calculator is that a number of people I
have discussed sun noise rise with were using solar flux figures that
were old and / or the wrong frequency.

Owen

"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

Owen Duffy wrote in
:

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.

This was a VERY quiet location. The only VHF stuff around was a bit of
156mhz and 161mhz stuff on a tower about 5 miles away. I could JUST see
the big tower downtown that most of the FM broadcast stations used, but
it was about 12 miles away and partially obscured by trees and a hill.
But to the south and west was mostly ocean. VERY quiet VHF location. One
time I worked a guy in a plane flying from St. Johns, Newfoundland to
Montreal, on 146.49 simplex FM. He just had a handheld in the cockpit
window and we stayed in contact (from my suburban Halifax location) from
the time he reached cruising altitude (30-some thousand) until he began
his descent into Montreal. The distance at the end of the QSO was
approaching 800 miles.

I did not notice any particular propagation that day, this was just plain
simplex FM. Now I was running about 600 watts at my end of the pipe, but
I could hear his handheld just fine.

Near as I could measure it, the NF of the receiver after my mod was
1.2db. I had to resort to boiling and freezing water and a tiny dummy
load to measure it at all.


--
Dave Oldridge+
ICQ 1800667

"Harold E. Johnson" wrote in
news:ci5Ai.58746$Xa3.26736@attbi_s22:


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!

You better believe no mean feat! I worked off the moon on 432 MHz back
in the late 70's. Sixteen 16 element Yagis (calculated gain ~26 dB)
and an STA from the FCC to use 5 KW as long as the antennas were
pointed above 25 degrees elevation. (Protecting Eglin radars some 200
plus miles away.)

I could consistently manage some 4, 4-1/2 dB of sun noise off a quiet
sun and not one smidge more even with a mast mounted GaAs Fet preamp
supposedly with some 0.8 dB NF.

I DID however, at around the same time, own a 2 meter Jap all-mode
transceiver that I happened to measure the "S" meter accuracy with an
HP signal generator. It turned out that 2 uVolts was "S"-1. THREE
uVolts was "S"-9.

Yeah, and that just gets worse when you put a decent preamp in front of
it.


--
Dave Oldridge+
ICQ 1800667