On Sep 24, 12:07*pm, "Paul Remde" wrote:
Hi,

I'm hoping that someone on r.a.s. that is an expert in radio antennas and
SWR meters can help me out. *I just brought in a new line of 5/8 wave
antennas, but the manufacturer can't tell me what length to make them. *I
want to cut them for 123.4 MHz so they will work well at glider frequencies.
However, theoretically calculated antenna lengths don't usually agree with
ideal lengths because of things like "end effects" and coils.

I have an SWR meter, but I have not used it yet. The instructions are
non-intuitive.

My guess is that I will need to connect a radio - transmitting on 123.4 MHz
and measure and record the SWR value of the antenna. *Then I'll need to cut
a bit of the antenna off and see if the SWR value improves. *I am completely
ignorant so I don't know if low or high SWR value is better. *At some point
in the process the SWR value should level off. *I'd hate to continue on
until the SWR value goes the other way - because that would be a waste of a
perfectly good antenna.

Any suggestions? *Is there an easier way to do this?

I appreciate any help you can offer.

Soon I will offer some very nice antennas with precisely optimized lengths.

Thanks,

Paul Remde
Cumulus Soaring, Inc.http://www.cumulus-soaring.com

A 5/8 wave antenna has slight gain over a quarter wave for vertically-
polarized signals, which is their attraction. They are pretty close
to 5/8 of a wavelength (about 1.5 meters or 5 feet long for 123.4
MHz). In order to match the impedance of the antenna to a 50-ohm
feedline, a small inductor is needed, usually at the base of the
antenna. Like a 1/4 wave antenna, a 5/8 also needs either a ground
plane or several radials (1/4 wave are normally used).

Standing Wave Ratio indicates the impedance mismatch between the
antenna, feedline and transmitter. It's not critical, but most
transmitters are happiest if this is less than 2. An SWR of 1.5 or
less is generally considered very good.

The length of the antenna for best match depends on the loading
inductor and ground plane. If your antenna's close, but a bit long,
set the antenna up where it is going to be used, transmit on the
desired frequency and snip gently. I built a bunch of these in my
amateur radio days.

Mike