"NM5K" wrote in message
...
On 7/31/2011 9:49 PM, Padraigh ProAmerica wrote:
Recently acquired a 50W 2 meter rig, and I'm wondering if using aJ-pole
made of 300-ohm twin lead as an emegency antenna would be feasable..or
would the rig be tuned for maximum smoke?


They say it can be done... Not my choice though. I prefer simple 1/4 wave
ground planes as simple emergency or temporary antennas.
IE: a 1/4 wave ground plane can be made with five pieces of wire
and an SO-239 connector. Or a telescoping whip that can extend that
far, and four pieces of stiff wire for radials, which would be bent
out at about 45 degrees.
I think the 1/4 wave ground plane will be a better decoupled antenna
vs the usual J-pole, assuming no other decoupling methods are applied.
Another advantage is no matching schemes are required.


You have a point Mark. I agree that a simple 1/4 wave groundplane is more
study and very easy to make using an so-239 and some piano wire. Steel wire
can be soldered right into the back, four bolts with nuts and four more
peaces of wire around 19" long with a bit of a downward bend and you have a
very good antenna.

Kevin, WB5RUE

On 8/1/2011 8:11 PM, Kevin wrote:


You have a point Mark. I agree that a simple 1/4 wave groundplane is more
study and very easy to make using an so-239 and some piano wire. Steel wire
can be soldered right into the back, four bolts with nuts and four more
peaces of wire around 19" long with a bit of a downward bend and you have a
very good antenna.

Kevin, WB5RUE


I'd use copper wire vs the steel or piano wire. They would work,
but I think the copper would be a better conductor. Steel in
particular is not too good. Also copper is a lot easier to solder to.
If you use solid wire of say 12 or 14 gauge, it's stiff enough to
stand up straight, but flexible enough to be bent and hold it's
shape.
If you are going to hang the antenna from something, you can use the
inner conductor of coax as the radiator, "shield stripped back 19
inches" and attach wire radials to the shield. All you have to do is
hang it up, and then bend out the radials at about 45 degrees, and you
are ready to become radioactive.

For a deluxe version, shave off the covering of the braid a 1/4 wave
below the radials at the feed point and add a second set of radials
to the braid.
That version would be well decoupled. Would blow most J poles out of
the water I suspect if you want to concentrate on the horizon, vs up
at some peculiar angle which is fairly useless for VHF/UHF.
Decoupling of the feed line is more important than radiator gain on
those bands. IE: a 1/4 GP can often outperform a 1/2 wave vertical if
the 1/2 wave has little or no decoupling. Which is the case for most
1/2 wave J poles.

You have a point Mark. I agree that a simple 1/4 wave groundplane is more
study and very easy to make using an so-239 and some piano wire. Steel wire
can be soldered right into the back, four bolts with nuts and four more
peaces of wire around 19" long with a bit of a downward bend and you have a
very good antenna.

It's worth noting that you don't actually need four radials. Two
radials (on opposite sides of the feedpoint, bent down at around 45
degrees) will produce a perfectly satisfactory ground-plane. The
patterns of 2- and 4-radial ground plane antennas are almost
indistinguishable. A 4-radial antenna may *look* as if it would
produce a much more circular pattern than a 2-radial antenna, but this
doesn't turn out to actually be the case.


--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On 8/2/2011 1:37 PM, Dave Platt wrote:
You have a point Mark. I agree that a simple 1/4 wave groundplane is more
study and very easy to make using an so-239 and some piano wire. Steel wire
can be soldered right into the back, four bolts with nuts and four more
peaces of wire around 19" long with a bit of a downward bend and you have a
very good antenna.

It's worth noting that you don't actually need four radials. Two
radials (on opposite sides of the feedpoint, bent down at around 45
degrees) will produce a perfectly satisfactory ground-plane. The
patterns of 2- and 4-radial ground plane antennas are almost
indistinguishable. A 4-radial antenna may *look* as if it would
produce a much more circular pattern than a 2-radial antenna, but this
doesn't turn out to actually be the case.


That's true as far as the pattern. But.. The more radials you
use, the better the decoupling from the feed line. Most of my
1/4 wave GP's actually use 6-8 radials. I've done tests, and
it does make a difference. But for casual use, what you say is
true. Only two radials are required to get a pretty good omni
pattern. Or one, if vertical.. But then you might as well call
it a 1/2 wave vertical instead of a ground plane.
And you will then require some kind of decoupling scheme below
the vertical for optimum results. I prefer radial sets, cones, etc
vs feed line chokes.