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

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

Just for the sake of posting something that Jim Weir can say is
wrongedy wrong because he's a EE and I'm not:

If you're talking about relatively simple whip antennas of relatively
small wire size, you can probably do fine using the theoretical value,
but breaking out the SWR is a good plan.

One thing you can do is SWR tune the antenna by trimming it to a
longer wavelength frequency, and use that to figure out a correction
factor that you can apply to the theoretical length for 123.4 MHz.
That way you can achieve a pretty high degree of confidence in your
tuning without ending up with a shorty. The easiest thing to do would
be to use the numerically lowest frequency your radio transmits on.

Getting back to fundamentals, for the theoretical wavelength, it's
sometimes reassuring to go back to first principles:

wavelength=speed of light/frequency

in our case, it's:

w=186000 miles per second / 123,400,000 cycles per second
= 0.0015072933549432739059967585089141 miles

Ok, so not many people have measuring tapes marked out in miles.
Multiply by 5280 for feet:

= 7.9585089141004862236628849270665

And then multiply by 12 for inches:

= 95.502106969205834683954619124797

That agrees pretty well with the 11800/f value that Weir suggests in
RST-802. Jim's number results in a slightly longer antenna, so it's
probably a better place to start since as you observe it's easier to
shorten than lengthen.

11800/123.4=95.62

Multiply that by the 5/8 wave of your whip:

95.62 * 5/8 = 59.76"

So consider maybe tuning for 118.0 Mhz:

11800/118 * 5/8 = 62.5"

And once you get the ideal length for 118 MHz apply that correction
factor to find the corresponding ideal length for 123.4 MHz.

Over to you, Jim!

Thanks, Bob K.