This page is an E-Mail from Piero I5TDJ regarding
a procedure of making Solar noise measurements on the VHF bands. I found it so interesting
that I decided to publish it for general knowledge.
I have seen several messages asking for advice by newcomers to EME.
Lately, N7LQ said to have been using the signal from a nearby friend to check his EME system performance.
Mother Nature has provided us with a very useful mean to check our EME
system performance: solar radiation.
This is the message I sent some weeks ago to KU3T on the matter; I believe it could be of
some use to someone else:
"A very important thing you are not mentioning in your message, is how many dB of
solar noise do you measure. This way you are able to see if your system is working as it
should and if it still working as before. Moreover, using any of the available Sun
tracking programs, you can check if your antenna main lobe is aligned to the rotors az and
el indicators and if it is as it should. Very often I have heard of a split lobe: this
indicates some inversion on the cables feeding one of the array antenna.
The level of the solar noise is the best indication of the receiving capabilities of
your system.
To measure Sun noise, you dont need sophisticated equipment. Use your analogue (not
digital) multimeter in a low voltage AC position: most multimeters have a dB scale built
in. Connect it to your receiver audio output through a step up transformer; any 5V or 9V
to 115V or 220V does the job. The AC meter must be connected to the transformer high
voltage side. To have your receiver in a linear condition, turn the audio gain to its full
maximum and the RF-IF gain down to have a confortable loudspeaker level and the meter
needle around 1/3 of the scale. Aim the antenna to the Sun for the maximum meter
indication and then to a quiet sky point; record the dB difference between the 2
positions, or if your meter doesnt have the dB marks, make 20 times the decimal logaritm
of the two voltages you have read. Make the measure when the Sun is at least 20 degrees
above the horizon, to avoid errors due to Earth noise and reflections. Repeat often this
measure, keep a record of the levels you will find and check it against WWV solar flux
data, to see if your system performs, or continues to perform, as it should.
By the way, today (April 13, 1998) at 1030Z, I have measured 11 dB of Sun noise with my
system; WWV solar flux was 117 at that time. I have 4x19 elements, 4 meter boom Yagis and
a 0.4 dB NF preamplifier. If you have some doubt, please let me know. If your system
performance is as it should, we could make a QSO when conditions will let us have aligned
polarizations.
The best periods of the year to have good conditions are from October through February.
Ground reflection gain at Moon rise/set is not too helpful at 432 as it is at 144 MHz. The
Earth noise temperature is around 290 kelvin, or about the same
level of the sky noise at 144 MHz: the ground reflection gives some improvement. On 432
MHz, with sky noise temperatures around 50-70 kelvin and system noise temperatures around
100 kelvin, very often the "warm" Earth masks the ground gain."
73, Piero I5TDJ.
(Note: I'm not showing any E-Mail
address here in order to avoid them from being collected by SpamBots. You can
possibly find the E-Mail addresses of the above OM at QRZ.COM.)
This discussion is still not closed. If you have any opinions or additional
related information you would like to be published here, just send
me an E-Mail
Solar noise measurement
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