TopBand: Three eighths wave inv-L

[Steve Ireland]

G'day from WA!

I have recently put up a three eighths wave inverted-L antenna for 160,
which I also hope to use on 80m as a three quarter wave antenna, and would
be very interested to hear from those out there with similar antennas as to
what kind of matching/matching network they use.

The antenna is sited remotely from the house, in order to cut down
electrical pickup from domestic appliances, so the simpler the network is to
tune/configure the better.  It is fed against an elevated G6XN-type
counterpoise.

At present the antenna has a 140' horizontal top, with a 60' vertical
section, and is fed with 50 ohm coaxial via a series capacitor of  around
350pf. Although I can tune out the inductive reactance with the series C,
the antenna is showing an SWR of around 5:1 at the antenna (3:1 in the shack).

I can bring down the feed impedance towards 50 ohms by shortening the
antenna by 30' or so, but would like to keep the dimensions roughly as they
are, in order to keep the present current distribution/radiation pattern.
The obvious way to match the antenna seems to me to use an L-network, which
is switched by relays for 80/160m and uses a servo-tuned capacitor, but
perhaps there is a simpler solution?

If anyone who uses/has used this kind of antenna can provide me with a few
component details of their matching network (L-network, or whatever) it
would be much appreciated.  Any other comments on this type of antenna would
be of great interest!

By the way, the antenna is much quieter than the previous dipole antenna,
which was fed with open wire from the shack via a voltage balun and a
T-match.  If anyone is having problems with lots of electrical noise and can
feed their antenna remotely from the house, it is certainly worth a try!  

I would be especially interested to hear from anyone who has changed to this
kind of antenna from a dipole.

Many thanks! 73,

Steve Ireland, VK6VZ 


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