Scott wrote:
If the antennas are to be spaced more than a 1/2 wavelength (free
space), how can I use a 1/4 wavelength of 75 Ohm coax? I guess I would
have to splice in a 1/2 wavelength multiple of 50 Ohm coax between the
75 ohm coax and the T connection to make up the length.

Use any lengths of 50-ohm coax, and then connect them using the
"combiner" or "power divider" of your choice.

In practice the divider/combiner will be simply a quarter-wave impedance
transformer associated with a T-piece. The 75-ohm coax version will
transform each leg from 50 to 100 ohms (ideally you'd need 70.7-ohm coax
for that) and then the T-piece connects those in parallel to give 50
ohms. Alternatively, you can use the type of divider/combiner that
directly parallels the two 50-ohm lines, and then transforms the
resulting 25-ohm impedance back up to 50 ohms through a quarter-wave of
home made 35-ohm hardline.

There's not a lot of practical difference between the two methods,
except that the first one requires you to cut and terminate two sets of
equal lengths of coax. The second one is easier electrically, but
requires some basic metalworking skills.

I only need about 500Khz of bandwidth, so this might not be a concern.
But this was another question I was going to raise. Is there anyway to
calculate the bandwidth that I would see from a 1/4 wavelength
matching section? I guess that is a real easy one to test in real life
though.

If you need only 500kHz bandwidth at 144MHz, that will not be a concern.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek