Hi,

ALl I have available in my areas is RG 6 or RG58. I know 58 is 50 ohm
and 6 is 75. SOmeone said using 75 ohm would cause my swr meter not to
read right. I only need about 10 feet of cable to "test" some antennas
I am going to build this weekend. It is for 2 meters and 440.
Should I just use rg 58?

You are between a rock and a 'hard place' as both RG-6 and RG-58 will
cause incorrect readings on your SWR meter. The first, simply because it
will introduce a mismatch and the second because higher cable losses
will make the SWR appear to be lower than it actually is. However, if
you are just interested in seeing how well you can communicate, use the
lower loss RG-6 and work out what the meter readings mean later. Of
course, any matching adjustments at the antenna end will have to be
remade when you get some low-loss 50-ohm cable. If you were to make the
75-ohm feeder an odd number of half wavelengths down to the bridge
though, the antenna's impedance would be roughly duplicated there.

You can calculate the effect that feeder losses have on SWR from the
equations in the ARRL Handbook. If you are just going for a minimum then
these won't matter as long as you take the final figures with a pinch of
salt. Remember that cable losses act twice as far as SWR is concerned
and that mismatch loss is higher than straight cable loss.


Cheers - Joe, G3LLV