Hi Raphael

I doubt you'll see much on a multimeter by itself. Most measuring devices
like that would have a hard time measuring AC past 20kHZ!

I think it was the Parkes radio telescope site (you know the movie "The
Dish") that has a list of freqs used for radio astronomy. Be a handy place
to start as you'd be able to avoid "human" band users. Sorry dont know the
URL. It has "csiro" in it somewhere. I'm going to be driving past Parkes in
a month or so. Might go have another look...

One of the nice things about magloops is their very narrow bandwidth. You
may even be able to get away with a simple diode and capacitor detector.
Kind of like an AM receiver (aka crystal set) but with a longer time
constant so the DC voltage can be measured. You'll need an amplifier
somewhere. I saw a magloop article with a built in preamp, cant remember
where. If you are using a soundcard note that it will be AC coupled. ie
wont be able to measure slow moving DC voltages. Back to an A-D converter
or make up a voltage controlled oscillator feeding from the detector!
(Noted the comment in the your other post. The sound card sampling rate
isnt going to be so good for direct data capture. Hence my suggestion of
the VCO)

Remember that a magloop bandwidth will be a percentage thing so if you go to
high in frequency it may become too broad. Maybe the thing to do might be
to build one on the Jove freq (abt 21.5MHz). Also protect the magloop
tuning from the weather. Rain/changes in humidy will affect it and your
measurements will change.

You might find it cheaper to build an A/D plugged into the parallel port.
You could even write a 4 line DOS debug/bat script to read the port and
dump the value to a file. Simple.. Only issue would be only 8 bits. From
memory the port has 3-4 more control lines that could also be used for
more. (Or get another printer interface card) I use to use a parallel port
to drive a stepper motor and ez-al antenna for satellite tracking using the
debug script method. Remember that the data acquisition speed deosnt need
to be fast. (ie more $$$)

Okay good luck!

Cheers Bob



Hi Bob,

my plan was to go with the fixed antenna, and let the motion of the
earth sweep out a path in the sky.

I'm still trying to figure out the frequency, and from that the size. I
was looking at RadioJove (http://radiojove.gsfc.nasa.gov/) and they use
a 7.09m simple dipole antenna to listen to radio storms from Jupiter. I
think, at least for my first experiments, I might try something in this
range. Eventually it would be nice to listen at 1420mhz, but from what
I've read simple dipoles aren't too good for high frequency signals. I
also checked out Mag-loop antennas, and they look pretty interesting. I
wish I could be more specific about my antenna plans, but my radio
experience wouldn't fill a 3x5 card. I think I'll start with a small
simple dipole, and just hook that up to my multi-meter to see what comes
over the line. but after that I think I might try a mag-loop, this place
(http://www.iri.tudelft.nl/~geurink/magnloop.htm) has a pretty good
howto. But, I need to do a bit of spectrum research, and see where I'm
most likely to find "natural" signals.

I'm planning on direct sampling. Since this project is all happening
under my wife's watchful eye, my funds are limited. If I can get my
hands on a cheap, low noise RF amplifier I'll go that way, otherwise, I
have a cookbook with some schematics I can copy. As far as the A/D
converter I was going to build something along these lines:
http://dbserv.maxim-ic.com/appnotes....ote_number=151

thanks for all the info!