"Owen Duffy" wrote in message
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"Ralph Mowery" wrote in
:


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

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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.