RadioBanter - View Single Post - A short 160M antenna

[email protected] · November 8th 14, 06:03 PM posted to rec.radio.amateur.antenna

John S wrote:
On 11/8/2014 10:45 AM, wrote:
John S wrote:
On 11/7/2014 12:58 PM, wrote:
wrote:

snip

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

snip

I realized I should expand on that.

With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz.

By staggering the values of the inductors in the four legs the bandwidth
can be improved by a little bit.

The best I could accomplish was about 1 Khz by making the leg values
.96, .98, 1.02, and 1.04 times the central leg value.

Going beyond a step factor of .02 made little difference in the bandwidth
and the resonant frequency SWR started to increase.

Okay, but the starting target was to be able to feed a short antenna
with good efficiency and I think you hit that target. I know you want to
keep it as practical as possible, but I am impressed with your results.

Thanks.

The whole point of the exercise was to show there are way to overcome
the generally low impedance of short antennas.

Exactly! It was a challenge which has been shown to be surmountable by
design. Feed losses become less of a burden this way.

Do you think your results could be practical? Could ground resistance be
used to widen the BW? I know, there are losses. But, maybe worth it?

What do you think?

I think if the goal is a practical antenna, the starting point should be
how high can you practically go keeping in mind that a 1/4 wave 160M is
on the order of 130 feet and in general the higher the greater the
bandwidth and the less you have to be concerned with minimizing losses.

In my urban lot, anything over about 30 feet becomes a problem.

I do have a 33 foot tall vertical in the back yard with an autotuner
at the base. It started out as just a 40M vertical.

With the addition of the autotuner, it will tune and load 160 through
6 M. The performance on 6M is horrible as it is a cloud warmer at
that frequency, but most of the other bands are OK or better.

The 160 and 80 performance was poor, which I attibuted to losses in
the tuner, so I put in a relay controlled high Q tapped coil to take
some of the burden off of the autotuner on those bands. That helped
quite a bit.

I have been thinking about using the folded monopole technique to
further improve things.

That would require some more relays to switch the folded parts into
the main radiator, essentially making it a fat radiator on other bands.

The biggest issue is mechanical so until I figure out that part, I
have left that project on the back burner for now.

--
Jim Pennino