"John Smith" wrote in message
...
Hi again!

Has anyone tried making the coiled coax balun work at UHF? Specifically,
on
the 70 cm band.

In "Antennas for All Applications", they say the coil should be resonant
at
the frequency of operation. The ARRL book(s) do not cover this band. Using
RG58 and a GDO, I've learned that one cannot leave long leads on one's
coax
coil as it will lower the resonant frequency drastically. Apparently, the
long leads in conjunction with the coil forms an
antenna/inductor/capacitor
combination.

It appears to be difficult to obtain the required resonance repeatably.
Or,
am I missing something (as usual)?

The diameter seems to be somewhat critical. Does the diameter need to be
much, much smaller than a quarter wave? What diamter would be a maximum?


By the time you get to UHF it is difficult to use coils. Baluns are usually
made of coax or some of the very small hard line like less than 1/4 inch in
diameter. The coax is just a fraction of a wavelength.

"Ralph Mowery" wrote in message
nk.net...

"John Smith" wrote in message
...

By the time you get to UHF it is difficult to use coils. Baluns are
usually
made of coax or some of the very small hard line like less than 1/4 inch
in
diameter. The coax is just a fraction of a wavelength.

Hi, Ralph -

Yes, I can see that now. A little over two turns of RG58, tightly wound, on
a .75 inch diameter is about right to be resonant around 440 MHz. However,
the resonant frequency moves with compression and expansion of the coil (not
unexpectedly) making it difficult to settle on the dimensions.

The problem here is that I must have no leads on the coil while
experimenting because the leads affect the frequency. Later, when I create
the coil at the base of the antenna, I will not be able to determine the
coil's exact resonant frequency and adjust it for my frequency of operation.

I think I'll give up on this idea.

Thanks for your comments.

John