On 11/6/2013 3:34 PM, resluder@yahoo.com wrote:
What kind of bandwidth do you get with your inverted L, 50 kHz? Would I still
be able to use a tuner in the shack if I want to bend it for more coverage on
160?
Define bandwidth. Do you mean SWR bandwidth? Do you mean you can get
it to load?
If you can get the total wire length > 100 ft and connect it to a decent
radial system, a decent tuner should be able load it across all of 160M,
but you'll need to retune it as you QSY. The Ten Tec 229 and 238 series
tuners work very well on 160M with reasonably good antennas.
I have a Tee vertical for 160M that's 86 ft vertical with roughly 100 ft
on top. That makes it longer than a quarter wave, and I've adjusted the
length of the top section so that the feedpoint Z is 50 ohms resistive
plus some inductance (because it's electrically long). I then added
series C to tune out the L, giving me a nice match to 50 ohms. I can
work at least the bottom 75 kHz of 160M without much tuning.
A well known way of broadbanding almost any antenna is to make the
conductor fatter. An easy way to do that is to use two spaced
conductors, tied together at both ends, and that's what I did. The
vertical is two #10 THHN wires spaced about 6 inches. I did that, and
the SWR bandwidth improved by at least 50%.
As to loading a 45 ft wire on 160M, which Jim asked about. I'd guess
that the Ten tuners will LOAD it, but the radiation resistance of such a
short wire is pretty low, so it won't be very efficient without a great
radial system. Remember that a vertical is a simple series circuit --
radiation resistance (Rr), wire resistance (Rw), and ground resistance
(Rg). The radiation resistance is the "good" resistance -- it accounts
for radiated power, but the same current flows in all three resistors,
so the power divides between them. For the antenna to WORK, we want Rr
to be much larger than (Rw + Rg), but it takes a lot of wire to get Rg
below 10 ohms on 160M, and Rr of a 45 ft vertical won't be much more
than perhaps 6 ohms, yielding an efficiency of about 30%. That means
your 100W radio will put 70W into the ground and 30 watts into space. .
73, Jim K9YC
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