"spamhog" wrote in message
...
K1TTT
just wind a coil choke

Richard
What do you REALLY want?

There is a difference between a 12:1 and a 3:1 mismatch, especially in
a long coax run. What I want is a rough mid-of-the-range estimate of
where impedance in a 50'+50' squat inverted-V dipole across say
3-20MHz.

There is a gazillion description of such antennas fed via 450 ohm
ladder lines, and a few with 600 ohm lines:
- ready made 450 ohm plastic clad line is commercially available
- 600 ohm line can be made with commercially available spacers for
standard wire gauges.

Neither suggests that the corresponding impedance is a good midpoint.
The advantage of ladder lines is extremely low loss, allowing for
massive mismatches without much loss due to the exponentially-
decreasing but still substantial backwave.

Being forced to use a coax, I am looking for a ballpark match not
inspired by the current commercial availability of things I am not
going to include in the design.

The random dipole and the T2FD and related antennas ( like the
ubiquitous 3-wire damped dipole sold by many companies for
professional use) are operationally somewhat similar. All are
compromise antennas usable in a large spectrum, all are rather funny
in terms of losses, radiation efficiency, and radiation pattern.

The damping resistor is there exclusively to smooth the response over
the spectrum, at a cost. One could even argue that a balun+coax fed
tuned random dipole and an untuned T2FD of roughly similar size
exhibit similar losses, ^cept one heats the coax more (once the ATU is
peaked), and the other heats the resistor more, which should be handy
in determining deicing strategies. ;-)

There is plenty of literature, including some baseline simulations,
for the T2FD etc.. I haven't found the same for inverted-V random
dipoles. Any pointers? Have I been googling for the wrong things?




If you are going to feed the dipole with coax, there is no balun ratio that
would work over the whole range. I would say the best you can do is make it
into the G5RV type antenna if 100 feet is about all you have to work with.
I do not like the G5RV antennas, but for those that must make a big
compromise system, it is one way to go.
If you must use coax, you may also want to look at getting some of the
highest impedance coax you can find. Around 100 ohms if you can find any.
Then feed the antenna with two runs of it. I am thinking that you just use
the center conductors hooked to the dipole ends. Then treat it like open
wire and feed it with a tuner.