Measurements for a CDMA450 coaxial dipole
 

I would like to experiment with a few different antennas to be used
with a CDMA450 usb modem for portable use. The design frequency would
be 455 MHz (second TX carrier of Scandinavian NMT-CDMA450). Boomer
cells are now being introduced allowing for ranges beyond 62 km (up to
120).

The first design would be a coaxial dipole, i.e. with a tubular sleve
covering the cable below the quarter wave tip. The design could be for
RG58 with 0.66 velocity factor. From various sites I've seen a
velocity factor estimate of 0.95 for the sleeve but no discussion on
the diamter vs width of the sleeve. Also, I'm not sure that the sleeve
should be an exact quarter wavelength. Reading the Franklin antenna
Patent introduces a whole bunch of variables but for UHF use, the
design should be well known.

I'd like to connect to the antenna with a TMC or SMA connector.

The tip would be a bare wire protected by a ball pen housing or the
like.

Would using a ferrite ring on the cable below the sleeve help any?

I could compare this antenna to some commercial end fed half wavelegth
antennas that I already have. I found a coaxial dipole to be a very
good antenna on top of a 4 meter fishing rod 20 years ago when NMT 900
was started up and base stations few.

Regards

Jonas

SM0WJY

PS I'll post questions regarding a multielement coaxial antenna in a
separate thread