Hi Bob,

Thanks for the quick reply. That Cebik site is a great resource, I'm
still going through the antenna basics article, but "wi're we using
wire" has already shed some light on things.

Here's a bit more detail on my project: I want to set up an antenna in
such a way that most of my signal will be natural (ie not man made
radio). Then, over a year, make a map of the sky as seen from my back
yard. Basically my plan is antenna into amplifier into A/D converter into
the serial port of a PC in my basement. The PC will poll the antenna
every couple of minutes, and use the signal strength to make a
stripchart, and an overall skymap where each pixel represents the signal
strength at a given day and time.

I think I might start with one antenna, to keep things simple starting
out, and then add on more antennas if it seems practical.

Thanks again,

R.

Bob wrote in
:

Hi Rapheal

If you are specifically aiming at radio astronomy be aware that the
"pattern" of the antenna (in your case the "best strength" direction)
will be affected by height above ground. The ground acts as a
reflector of sorts. Have a wander through http://www.cebik.com and
you'll see what radiation/response patterns look like. To give you an
idea I once had a crossed dipole 3/8 of a wavelength above a metal
sheet that radiated/responded mostly to signals about 20 degrees above
the horizon and gradually less and less till directly above. This was
of course for satellite use. You probably want a fairly vertical
pattern to reduce local/man made noise so the spacing will be less.

In using an array of dipoles what kind of directional response are you
after? This will govern their spacing, height above ground and so on.
If you are feeding the dipoles to get a directional pattern, cable
length does become something to consider but for a single dipole isnt
very important.

What is your exact intended use, direction of operation and frequency.
I'll try and be more specific...

Cheers Bob VK2YQA