"erniegalts" wrote in message
...
The 2 metre band extends from 144 to 148 MHz. So if were cutting an
antenna for center of this band at 146 MHz would be 75 / 146 =
0.513698630137. So a quarter-wave vertical would be roughly .513
metres long, or 513 mm. (millimeters) or 20.2244 inches.

This is good math, but usually for a 1/4 wave radiator, 5% is subtracted for
velocity factor, leaving the basic 1/4 wave radiator for 2m at approximately
19".

On Tue, 19 Aug 2003 06:34:35 +0900, "Brenda Ann"
wrote:


"erniegalts" wrote in message
.. .
The 2 metre band extends from 144 to 148 MHz. So if were cutting an
antenna for center of this band at 146 MHz would be 75 / 146 =
0.513698630137. So a quarter-wave vertical would be roughly .513
metres long, or 513 mm. (millimeters) or 20.2244 inches.

This is good math, but usually for a 1/4 wave radiator, 5% is subtracted for
velocity factor, leaving the basic 1/4 wave radiator for 2m at approximately
19".


True, but the formula is only a rough guide anyway. Even at much
lower frequencies there are a few variables, and at VHF and UHF
wavelengths antenna length can be very critical.

On Australian UHF CB band can make a nice little handheld 3 element
Yagi out of a UHF socket and an old coathanger which will give around
3 or 4 dB gain. [Perfectionists would probably use aluminum, copper,
or even silver wire, though. ]

Passing thought: Will Brock rush into print claiming that copper is a
better conductor than silver? :-)

Corner reflectors or arrays usually a better choice for more gain,
although even high gain rhrombics with theoretical 25 dB gain are a
manageable size at UHF if looking for really reliable point to point
communication.

Can make up 9 DB collinear omnidirectional verticals for UHF from RG-8
coax and plastic electrical conduit, although fiberglass is better.
Not much margin for error at these frequencies, though.

Can make a pretty decent UHF TV antenna using an phased array made up
of a chicken wire reflector and beer or soft drink cans as elements.
Not as good as an 18 element Yagi, but cheap and easy alternative.

Antennas can be great fun to play with. Was raised in a rural area,
and when TV first became available some local farmers were spending a
lot of money for tall masts and high gain Yagis to pull in a good VHF
signal.

However, I was highly amused when one old farmer who knew no antenna
or propagation theory whatsoever pulled in nearly as good as signal by
using a junked bedspring from a double bed, which he mounted on an old
apple crate and leaned against a tree, using rubber from old inner
tubes as insulation. He was just using flat 300 ohm lead in, split
the antenna end and fitted with alligator clips, and played around
with trial and error until found the proper feedpoint. He had no
terrain advantage over the others and doubt if an expensive Yagi at a
similar level would have worked much better.

His neighbors who had spent a lot more on their antennas weren't quite
as amused, though. :-)

When I was a kid, a lot of amateurs used "home brew" equipment, but
most amateurs these days seem to take their transceiver back to the
dealer for anything more complicated than replacing an incandescent
bulb or an LED indicator. :-)

The radio scanner enthusiast might consider building a large discone
antenna if has the space. No gain, but good SWR over many decades of
frequency range. Simple to build, size of disk and skirt not
especially critical as long as large enough to cover lowest frequency
of interest. Most libraries should have a reasonably current ARRL
Antenna handbook.

erniegalts