FW: [FoxHunt] Turnstile antennas for 2M

[Kuon & Dale Hunt]

Of course, you should check your turnstyles to make sure the
pattern is really omnidirectional if that is important.  I've
built several that looked right, but didn't act as I expected.
The best way to test it is to hang it on a string and spin it
around while monitoring the signal strength.  Try this at
several different heights, as the element impedance and
therefore the current balance in the elements will change.
If your receiver has a VCO mode, just put that on a speaker
and listen as you spin the antenna.  A less optimum approach
is to hold the elements in the vertical plane with the
mounting hook aimed at a repeater or other source of vertically
polarized signal and spin the antenna about is axis.  This
isn't as good, though, since the effect of the ground will
be different than it will be in use.

You should be able to determine from the depth and location of
the pattern null whether you have an amplitude or phase imbalance
and which element to correct... but I never bothered.

I do like Jay's element mounting method using the threaded
standoffs.  I plan to convert mine, which have the elements
secured to a ring terminal held under a wing nut.  (Internal
construction basically the same.)  By loosening the wing
nut I can fold the elements parallel to the housing body
for transport, but the elements put torque on the bolts
and they don't always stay in the right direction.  (I've
had to splint the elements in the field with sticks and
first-aid tape to keep them horizontal.)

Not sure about the RF choke a quarter wave below the dipoles,
however.  Think it would be better right at the feedpoint.
Otherwise you could get a good standing wave (high current
at the feedpoint, minimum at the choke) providing vertically
polarized radiation.  Two sets of beads - at the feedpoint
and a quarter wave down the cable - probably gives the
best decoupling.

    - Dale WB6BYU


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