Frank,

The coil measures about 60 uH. The antenna is elevated about 3 feet on a short
tripod. The radials angle down the tripod legs and then out.

The coil is about 4 inchs in diameter, number 12, wound on a fiberglass form. It
is centerloaded. I am looking at it accross the yard, it is about 6 inches long.
It is would with about a point .5 pitch. Calculations for a 1:1 pitch predict a
Q of about 450.

Thanks,
Dan

Frank wrote:
I have been using an 80 meter loaded vertical for a couple of years with
moderate success. The ground system is a dozen 'untuned' radials 40 or so
feet laying on the ground. The feed line is about 100 feet of RG-8 coax.
The SWR in the shack is about 1.1 to 1.

I have done some research on the antenna and based on it parameters it
should have a radiation resistance of about 4 Ohms. This says that the
coil and ground are absorbing on the order of 45 Ohms. This is 10db
performance loss.

I have limited space and the most common solutions are not available to
me. From a practical perspective it would seem to me that building a 40
foot center feed loaded dipole and putting it in the attic or on the roof
would probably perform somewhat better.

Is this a reasonable assumption?

Would burying the radials and connecting them to several 4 square foot
buried screens substantially help the ground system?

Thanks,
Dan kb0qil


How high is the antenna, where is the loading coil placed, what is its
value, and Q?

Frank

Frank,

The coil measures about 60 uH. The antenna is elevated about 3 feet on a
short tripod. The radials angle down the tripod legs and then out.

The coil is about 4 inchs in diameter, number 12, wound on a fiberglass
form. It is centerloaded. I am looking at it accross the yard, it is about
6 inches long. It is would with about a point .5 pitch. Calculations for a
1:1 pitch predict a Q of about 450.

Thanks,
Dan

Thanks for the info Dan. From your comments the radials appear to be
parallel with the tripod legs to ground level, and then continue at ground
level for the rest of their length. What is the angle of the tripod legs?
I agree with comments about adding a horizontal wire to the top of the
vertical; it will probably be easier than a capacity hat. I am overloaded
with work at the moment, but would like to attempt a model in a week or so
when I have less work.

73,

Frank

Frank wrote:
. . .
I agree with comments about adding a horizontal wire to the top of the
vertical; it will probably be easier than a capacity hat. I am overloaded
with work at the moment, but would like to attempt a model in a week or so
when I have less work.

Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical. But
of course it might be more involved to construct.

Roy Lewallen, W7EL

Roy,

Thanks. This might be feasible. The site would support 50 foot wire from the
tip. At 500 watts what would the current in the horizontal leg be? In other
words what is the minimum effective gage?

What is the purpose of this leg? Is it capacitive or does it begin to look like
something else. What are it directional characteristics? Dipoles nodes are
perpendicular while long wire nodes are parallel.

Dan

Roy Lewallen wrote:
Frank wrote:

. . .
I agree with comments about adding a horizontal wire to the top of the
vertical; it will probably be easier than a capacity hat. I am
overloaded with work at the moment, but would like to attempt a model
in a week or so when I have less work.


Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical. But
of course it might be more involved to construct.

Roy Lewallen, W7EL

To determine the horizontal wire current, download the free EZNEC demo
from http://eznec.com. That's exactly the kind of thing it's good for.

If you put a single horizontal wire out to make an L shape, the wire
radiates a considerable amount. Being as low as it is, a lot of the
power will be dissipated in the ground, and only a small fraction will
be radiated at a low elevation angle. But if you connect to the center
of a horizontal wire to make a T shape, the fields from the two halves
of the horizontal wire will nearly cancel, so it'll radiate very little.
Its main effect, like a capacitive top hat, will be to even out the
current in your vertical wire, which will raise the radiation resistance
and therefore the efficiency.

EZNEC or a similar program will quickly show you the differences in
field strength in various directions for the antenna as it is, and with
either of the top loading configurations.

Roy Lewallen, W7EL

dansawyeror wrote:
Roy,

Thanks. This might be feasible. The site would support 50 foot wire from
the tip. At 500 watts what would the current in the horizontal leg be?
In other words what is the minimum effective gage?

What is the purpose of this leg? Is it capacitive or does it begin to
look like something else. What are it directional characteristics?
Dipoles nodes are perpendicular while long wire nodes are parallel.

Dan

Roy Lewallen wrote:

Frank wrote:

. . .
I agree with comments about adding a horizontal wire to the top of
the vertical; it will probably be easier than a capacity hat. I am
overloaded with work at the moment, but would like to attempt a model
in a week or so when I have less work.



Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical.
But of course it might be more involved to construct.

Roy Lewallen, W7EL

Now that is interesting, Roy. I was going to put up a 160 m inverted L this
summer. I am limited to only being able to go up about 45 feet, so I would
need about another 90 feet horizontal.

Are you suggesting that it might be a better arrangement to go up the 45'
and then put up the top "T"? If so, roughly how long should the top part of
the T be (each side of center) to get me to 160? I'm guessing it may not be
accomplished without some base loading...and that is what took me to the
Inverted L in the first place...direct coax feed, albeit not a particularly
good low angle radiator.

I am prepared to put down a radial field...but I want to stick with a simple
vertical wire, either extended horizontally as an Inverted L or as you
suggest, a T, if it can be done. I have about 100' either side of center
available to construct the top part of the T. In either case, the top
loading wires will need to be somewhat of the inverted v construction, as I
don't have 45' high supports for each end.

Thanks for any thoughts you might have. I need to get something done before
winter!

73,

....hasan, N0AN

"Roy Lewallen" wrote in message
...
To determine the horizontal wire current, download the free EZNEC demo
from http://eznec.com. That's exactly the kind of thing it's good for.

If you put a single horizontal wire out to make an L shape, the wire
radiates a considerable amount. Being as low as it is, a lot of the power
will be dissipated in the ground, and only a small fraction will be
radiated at a low elevation angle. But if you connect to the center of a
horizontal wire to make a T shape, the fields from the two halves of the
horizontal wire will nearly cancel, so it'll radiate very little. Its main
effect, like a capacitive top hat, will be to even out the current in your
vertical wire, which will raise the radiation resistance and therefore the
efficiency.

EZNEC or a similar program will quickly show you the differences in field
strength in various directions for the antenna as it is, and with either
of the top loading configurations.

Roy Lewallen, W7EL

dansawyeror wrote:
Roy,

Thanks. This might be feasible. The site would support 50 foot wire from
the tip. At 500 watts what would the current in the horizontal leg be? In
other words what is the minimum effective gage?

What is the purpose of this leg? Is it capacitive or does it begin to
look like something else. What are it directional characteristics?
Dipoles nodes are perpendicular while long wire nodes are parallel.

Dan

Roy Lewallen wrote:

Frank wrote:

. . .
I agree with comments about adding a horizontal wire to the top of the
vertical; it will probably be easier than a capacity hat. I am
overloaded with work at the moment, but would like to attempt a model
in a week or so when I have less work.



Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical. But
of course it might be more involved to construct.

Roy Lewallen, W7EL

hasan schiers wrote:
Now that is interesting, Roy. I was going to put up a 160 m inverted L this
summer. I am limited to only being able to go up about 45 feet, so I would
need about another 90 feet horizontal.

Are you suggesting that it might be a better arrangement to go up the 45'
and then put up the top "T"?

It might be. You might benefit from the radiation from the horizontal
portion of an L, and you might not. But if it's quite low, the radiation
will be mostly straight up, and a fair amount will be expended warming
up the ground. Neither will occur with a T.

If so, roughly how long should the top part of
the T be (each side of center) to get me to 160?

That's just what antenna modeling programs are for! Dust off your EZNEC
and you'll have the answer in minutes.

. . .

Roy Lewallen, W7EL

I think Roy is referring to a T configuration rather than an upside-down L.
The currents will balance in the T so wire size is limited by physical
considerations rather than electrical. This is just another form of a
capacity hat. The net result is to raise the radiation resistance.

"dansawyeror" wrote in message
...
Roy,

Thanks. This might be feasible. The site would support 50 foot wire from
the
tip. At 500 watts what would the current in the horizontal leg be? In
other
words what is the minimum effective gage?

What is the purpose of this leg? Is it capacitive or does it begin to look
like
something else. What are it directional characteristics? Dipoles nodes are
perpendicular while long wire nodes are parallel.

Dan

Roy Lewallen wrote:
Frank wrote:

. . .
I agree with comments about adding a horizontal wire to the top of the
vertical; it will probably be easier than a capacity hat. I am
overloaded with work at the moment, but would like to attempt a model
in a week or so when I have less work.


Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical. But
of course it might be more involved to construct.

Roy Lewallen, W7EL

Fred W4JLE wrote:
I think Roy is referring to a T configuration rather than an upside-down L.
The currents will balance in the T so wire size is limited by physical
considerations rather than electrical. This is just another form of a
capacity hat. The net result is to raise the radiation resistance.

In a tee type antenna, there will be considerable current at the
junction of the horizontal and vertical wires. While it's unlikely that
any wire strong enough to be used won't be able to handle the current
from a heating standpoint, it is possible that using a wire on the small
end of the range might result in noticeable loss. A quick run with a
modeling program would show whether or not that might happen with a
given set of dimensions.

One thing I should mention. If the horizontal portion is higher than
about 0.2 wavelength, MININEC-type ground can be used for modeling
either a T or L. The vertical wire is connected directly to ground, and
ground loss can be inserted at the base as a resistive load. If the
horizontal wire is much less than 0.2 wavelength high, the MININEC-type
ground can still be used with reasonable accuracy only for the T type
antenna. For an L type antenna where the horizontal wire is less than
0.2 wavelength high, a model has to use the High Accuracy ground model,
with the ground system modeled as radial wires just above the ground.

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
Frank wrote:
. . .
I agree with comments about adding a horizontal wire to the top of the
vertical; it will probably be easier than a capacity hat. I am
overloaded with work at the moment, but would like to attempt a model in
a week or so when I have less work.

Take a look also at a tee type arrangement. That is, a horizontal wire
with the tip of the vertical connected at or near its center. It might
have some advantages over connecting the wire's end to the vertical. But
of course it might be more involved to construct.

Roy Lewallen, W7EL

Roy,
I built basically a loaded mobile antenna that went onto an airport
building in Raleigh, NC (about 60 feet) I was reluctant to build it because
I was afraid the people that I made it for (CAP) might not know how to do
the elevated radials. I was afraid they might come back on me. I reckon I am
one of those "trial and error" hams that has tried about everything in the
last 40 years and I am still learning. Anyhoo, BOY was I WRONG! They put
the thing on the air and it really puts out a good signal! None of us have
done any measurements or NEC modeling, etc. Frankly, I was surprised as I
had done very few vertical installations (well, I've got an AV8 vertical
all-bander). All I know is, at the 60-70 foot level with tuned radials, it
really sings!

73

Jerry
K4KWH