Hi all...
I've got one of these "squid pole" telescopic fibreglass fishing poles
that I presently use for supporting a vertical 20m dipole. Being the
highest point on the property, I thought if I could build a nice
lightweight antenna to go high up the top of it, it'd work well as a
mast for a 2m antenna.
I'm looking for a lightweight antenna, and feedline, suitable for this
purpose. I wish to operate around 144.300MHz USB... so horizontal
radiation pattern would be better. I get heard perfectly well on a
quarter-wave vertical at present, so I think the gain of a loop will
be sufficient... but a bit extra height would help a great deal.
The full-wave loop looks almost ideal... nice and simple, apparently
good gain over a dipole for an omnidirectional antenna. I have some
300ohm ribbon I can feed it with (RG58 makes the pole bend over... and
of course anything low-loss will be unworkable).
The catch is, I'm not sure how to go about impedance matching, with
the loop having a theoretical impedance (so I hear) of 100ohms, the
ribbon being 300ohms, and a radio that expects 50ohms. I'm not sure
how the feedline characteristic impedance will impact on things, being
300ohm... there's no such thing as 50ohm ribbon in the shops
AFAIK.
I'm not sure this has to match though. The antenna itself though,
does need some sort of transformation back to 50ohms.
Giving it some thought... another way to achieve this would be to use
two loops in-phase. 100 ohms in parallel with 100 ohms gives 50
ohms. I'm just not certain of the spacing, and how close they'd need
to be. I've got the wire cut to make two loops (no idea what gauge...
approx 1.5mm diameter solid copper) to a length of 2.08m.
I'd like to know if anyone has an idea how far apart these need to be
(vertically) on the pole so that they work together in-phase (or
alternatively, 180° out-of-phase... I just swap the connections on one
loop... I suspect this will halve the required distance). I could
just experiment, but if someone's been there done that, then I'd
appreciate their insight.
Regards,
Stuart Longland VK4MSL