ICOM AH-4 into Hy-Gain 64 foot Aluminum Mast
 

On Fri, 16 Apr 2010 10:19:40 -0700, Richard Clark
wrote:

Over the years, the topic of how many and how long of radials with a
horizontal has had so many variables that the discussion ran to
examining the trivial instead of being useful.

Somehow, that didn't come out right.

The number and length of radials is, of course, confined to the
discussion of a vertical antenna.

The number of variables in this relates to frequency, match,
efficiency, loss (which at first blush the last two "seem" to be about
the same thing), and (incorrectly) launch angle.

Another point that occurred to me: The notion of a tuned radial, and
it laying on the ground is an exercise in futility. The proximity of
ground is going to seriously detune the radial which will mock your
effort. Tuned radials are more a property of elevated verticals. Some
commercial verticals which come with tuned radials, or where you will
be expected to supply them, have a tacit expectation of your also
mounting the antenna some appreciable distance above ground.

73's
Richard Clark, KB7QHC

ICOM AH-4 into Hy-Gain 64 foot Aluminum Mast
 

Tom Horne wrote:

Jim
I had no intention of running a four square with four auto tuners.
Perhaps I should have put that inquiry into a separate posting for the
sake of clarity. We built a four square for field day two years ago.
Because the masts that we had then were only thirty feet high a kind
of capacitance hat was built into the guy lines. We had very good
performance from that four square until a severe thunderstorm
destroyed it. I was wondering if having sixty four foot masts would
allow us to adjust the height to resonance on forty meters so that the
four masts themselves could serve as the elements of the four square.
Since a half wave at 7150 kHz is nearly sixty seven feet I would have
to add three feet worth of additional tubing in order to get a
resonant half wave antenna. I had thought that half wave verticals
did not require a counterpoise was I misinformed? If a counterpoise
is needed it wouldn't be too hard to throw out four radials for each
mast. I was just looking for a quick way to put up a four square and
these aluminum masts seemed like they might fill the bill.
--
Tom Horne


If you put the feedpoint in the middle of the antenna and run the coax
up the middle of the bottom, and have a really good choke, it might
work. (basically, an elevated half wave dipole) There was such an
antenna scheme for a 4 square in one of the ARRL antenna compendiums (I
think they were doing it for 160m, and had a matching network (mostly
inductance) at the feedpoint to deal with the "electrically short" radiator.

Making it actually work is another story entirely. You've got to have a
pretty good choke, or the feedline starts to be a big part of the
system, and since it's laying on the ground, it's a pretty lossy part of
the system. The bottom half of the antenna is closer to the ground than
the top half, so there's those effects too.

SO, even if you sat at the bottom of the antenna with your antenna
tuning meter and carefully adjusted the matching network at the feed to
get 50 ohms, I don't know that when you set it all up, the phasing will
be right.

It might be close enough.. but the odds of not getting as good a F/B as
you want (e.g. null depth) are pretty good. The phasing isn't so
critical for forward gain (you can be tens of degrees off and not lose
much in forward gain, but that will completely kill your 10dB null)

But just feeding the end of a 1/2 wave wire sticking in the air is
asking for difficulties. Your coax is nominally 50 ohm sort of
impedance, and you'd be end feeding a dipole at a high Z point (a
thousand ohms, maybe).

ICOM AH-4 into Hy-Gain 64 foot Aluminum Mast
 

On Apr 16, 6:16*pm, Jim Lux wrote:


But just feeding the end of a 1/2 wave wire sticking in the air is
asking for difficulties. *Your coax is nominally 50 ohm sort of
impedance, and you'd be end feeding a dipole at a high Z point (a
thousand ohms, maybe).

Feeding it would be fairly easy.. But.. Just because it's a half
wave will not mean that there will be low ground losses if
ground mounted.
You would see less ground loss than a ground mount quarter
wave, but it could still be an issue. Note that most broadcasters
who run half waves, also use a set of half wave radials.
I'd probably rather use 32 ft masts supporting self supporting
32 ft radiators, and use a few sloping radials as radials, and
also to double as guy wires.
That will work fairly well with as few as three radials. More
to be optimum, but this is field day.. :/

ICOM AH-4 into Hy-Gain 64 foot Aluminum Mast
 

ICOM AH-4 into Hy-Gain 64 foot Aluminum Mast
 

On Apr 29, 1:03*pm, Jim Lux wrote:
wrote:
On Apr 16, 6:16 pm, Jim Lux wrote:

But just feeding the end of a 1/2 wave wire sticking in the air is
asking for difficulties. *Your coax is nominally 50 ohm sort of
impedance, and you'd be end feeding a dipole at a high Z point (a
thousand ohms, maybe).

Feeding it would be fairly easy.. But.. Just because it's a half
wave will not mean that there will be low ground losses if
ground mounted.
You would see less ground loss than a ground mount quarter
wave, but it could still be an issue. Note that most broadcasters
who run half waves, also use a set of half wave radials.
I'd probably rather use 32 ft masts supporting self supporting
32 ft radiators, and use a few sloping radials as radials, and
also to double as guy wires.
That will work fairly well with as few as three radials. More
to be optimum, but this is field day.. * :/

And would strongly resemble the radiators at WWV...

If you do this, you'd put the AH4 at the join point too. *For FD, you
might want to have the bottom 8-10 feet of the guy/radial be an
insulator, so that nobody touches the HV part of the antenna.

It would be above ground level with a 32 ft mast. So that would
be no problem. I've used that antenna here at the house, except
I had the 32 ft radiator on a 36 ft mast. I used four radials and
sloped them down and tied off to trees, fences, whatever..
I would not use the AH4 tuner. No need.. The antenna would
be resonant. It would work pretty well on longer paths at night.
The same antenna can also be used for 17m if you add a
matching coil to use it as a 5/8 wave. I had a 24 volt relay
rigged up at the feed point of mine, and could switch from the
shack.