"Owen Duffy" wrote in message
...
"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.

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.

Owen

Thanks for the calculations Owen. That agrees with what I thought I read
many years ago. At 2 meters unless you have an antenna the size of the ham
in Texas ( I think) that has about 20 or 30 yagies in about a 1/2 half acer
field, it is difficult to hear any sun noise rise on 2 meters most of the
time. Certainly not something that would push an smeter to s-9.

As I turn my antenna to the sun (azel mount) when it is high in the sky I
just barley can see the sun noise sometimes.
That is with using an audio voltmeter across the speaker.
I have not tried this too many times, but I don't recall ever seeing the
s-meter jump up an s unit or two due to the sun.

I don't do moon bounce, but did set the system to work the Oscars. Usually
no problem hearing 10 and 13 when they were way out.

"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.

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.

Well, the sun is much quieter nowadays than it was back then. When I had
the station at its peak, I was running a single 19-element boomer at 85
feet, with boudle shielded Belden COAX. The preamp I was using was a
mosfet, which, to the best of my measurement ability (none of the signal
generators at work could come close to measuring it) gave it a 1.2db
noise figure. Now there was probably also a 6db ground reflection gain
from measuring the solar noise at the horizon (sunset or sunrise) and, as
I say, it was a period when solar activity was high (6 meters was open to
Mexico city a lot).

--
Dave Oldridge+
ICQ 1800667

"Jeff" wrote in
. 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!!

Yep...when I moved, I put in hardline and lowered the antenna a bunch.

That's when I started to hear other things besides the sun. And I could
plot it. When the galactic plane was in front of the antenna, the noise
floor would be up an S-unit from base.


--
Dave Oldridge+
ICQ 1800667

"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

Dave Oldridge wrote in
9:

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.

I haven't tried hot/cold tests using ice and boiling water, I didn't
think it was practical.

You finally measured a receiver noise temperature of 50K with hot and
cold loads of 270 and 370.

That means a Y factor of 1.059dB.

If Y were just 0.1dB greater, NF would be 0.78dB, 0.1dB lower and, NF
would be 1.66dB.

With this configuration the sensitivity of NF to changes in Y are
extreme, 0.4dB change in NF per 0.1dB change in Y around that point.

If you made the Y measurements using the audio output of a narrow band
receiver, it is very hard to make high resolution measurements (eg to
0.01dB resolution) with say, a multimeter.

I have done these tests with a liquid nitrogen cooled load and room
temperature load, and that gives more practical Y ratios, 3.7dB for a
1.2dBNF, and the sensitivity in NF is 0.08dB per 0.1dB change in Y. This
still demands high resolution measurement of noise power.

Owen

Dear Owen:
Others too may remember the use of a noise source comprising a gas tube
crossways in a piece of waveguide (with 50 ohm probes) to estimate noise
figure in the VT days. One would fire the gas tube and it was estimated to
have a very large, "known" noise temp. Boiling water, while a known temp.,
would not have been hot enough.

Ice water was critical in the use of the HILLMS receiver used to measure
absolute flux. The antenna was a very long horn antenna resting on the side
of a deep gully. In those days, a horn antenna was one of the few antennas
with a predictable gain. The receiver switched at a low frequency between
the antenna and a load kept in ice water. The gain of the receiver was
stabilized with a huge amount of negative feedback. Once a day, the source
would pass through the antenna's beam and a strip chart recorder would
indicate the difference between ice water and the source's temp.

Today, with much lower NF, and much more EM pollution, different techniques
might be used.
73 Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Owen Duffy" wrote in message


Dave Oldridge wrote in



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.




I haven't tried hot/cold tests using ice and boiling water, I didn't
think it was practical.

You finally measured a receiver noise temperature of 50K with hot and
cold loads of 270 and 370.

That means a Y factor of 1.059dB.

If Y were just 0.1dB greater, NF would be 0.78dB, 0.1dB lower and, NF
would be 1.66dB.

With this configuration the sensitivity of NF to changes in Y are
extreme, 0.4dB change in NF per 0.1dB change in Y around that point.

If you made the Y measurements using the audio output of a narrow band
receiver, it is very hard to make high resolution measurements (eg to
0.01dB resolution) with say, a multimeter.

I have done these tests with a liquid nitrogen cooled load and room
temperature load, and that gives more practical Y ratios, 3.7dB for a
1.2dBNF, and the sensitivity in NF is 0.08dB per 0.1dB change in Y. This
still demands high resolution measurement of noise power.

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

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

Jeff wrote:

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.

I'd agree with 5-6dB as much more typical, but more like 2-2.5dB when
the muTek board is simply plugged in. Another 0.5dB can be gained by
avoiding the card edge connector, and installing a direct coax link from
the antenna relay onto the board.

As the person who designed the original FT221 board (which Chris Bartram
at muTek re-engineered for production) I wore out two dial drives
chasing 2m DX with that rig! But in all that time, I never saw S9 sun
noise. The only time I've seen anything approaching that level, it has
been from a major solar flare.


--

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek

Owen Duffy wrote:
Dave Oldridge wrote in
9:


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.


I haven't tried hot/cold tests using ice and boiling water, I didn't
think it was practical.

You finally measured a receiver noise temperature of 50K with hot and
cold loads of 270 and 370.

That means a Y factor of 1.059dB.

If Y were just 0.1dB greater, NF would be 0.78dB, 0.1dB lower and, NF
would be 1.66dB.

With this configuration the sensitivity of NF to changes in Y are
extreme, 0.4dB change in NF per 0.1dB change in Y around that point.

If you made the Y measurements using the audio output of a narrow band
receiver, it is very hard to make high resolution measurements (eg to
0.01dB resolution) with say, a multimeter.

I have done these tests with a liquid nitrogen cooled load and room
temperature load, and that gives more practical Y ratios, 3.7dB for a
1.2dBNF, and the sensitivity in NF is 0.08dB per 0.1dB change in Y. This
still demands high resolution measurement of noise power.

Owen

Indeed, this would be a very challenging measurement, because you also
have to take into account the match of that load, and if it's just a
resistor that you're plunging into hot and cold, its resistance will
almost certainly change. At microwave frequencies, a more common
technique for radiometers is to use a flat plate absorber that has been
characterized for changes in absorption over temperature.

One might want to take a look at how NIST does this kind of thing.
Here's the slides from a talk by Jim Randa
http://www.boulder.nist.gov/div818/8...t%20Crs_06.pdf

he's a noise measurement guru at NIST.. check out the website:

http://www.boulder.nist.gov/div818/81801/Noise/



I've had a precision noise source (used to do Y factor measurements on a
precision 13.402 GHz receiver) measured in their lab over a week. The
measurement uncertainty (for a system with waveguide connections) was in
the few Kelvins range (out of a noise power of 7000K or so), and the
connect/reconnect uncertainty dominates. I doubt one could get this kind
of performance with a coaxial connector (the uncertainty in the mismatch).


By the way, a good noise diode source is probably a better standard for
the hot side than heating a resistor. They're very, very stable over
time, once calibrated, and if properly designed, have a very stable
match as the noise is turned on and off. (that's what we were using in
the above system, a temperature controlled Noise/Com style source).

http://www.boulder.nist.gov/div818/8...ability_IM.pdf
http://www.boulder.nist.gov/div818/8...ility_CPEM.pdf

describes the performance


Another useful link might be:
http://www.boulder.nist.gov/div818/8...97_Amps_IM.pdf
D.F. Wait, J. Randa, "Amplifier Noise Measurements at NIST", IEEE Trans
on Inst. and Meas., v.46, n.2, Apr 1997

They give measurement uncertainties of 0.04dB on a 0.5 dB NF for 2-4 GHz..