All,

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

Put a capacity hat on the top of the antenna. This will give you the most
performance increase with the least effort.


"dansawyeror" wrote in message
...
All,

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

Burying the radials will make zero difference in performance.

"dansawyeror" wrote in message
...
All,

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.
[stuff]

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

Thanks,
Dan kb0qil

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

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

"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

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

Dan, I have just run a NEC 2 model of your antenna. I have used the
Sommerfeld/Norton ground, with average parameters of: Er = 13, and Sigma =
5 S/m. The top of the antenna is at 18 ft, and the base at 3 ft. I have
twelve 40 ft radials, spaced at 30 deg, and within the limitations of NEC 2,
placed them at 3" above ground. The first 5 ft of the radials drops from 3
ft to 3" at an angle of 45 deg. The monopole is center loaded with an
inductor of Q = 450. The model has 640 (6") segments and takes 3 minutes to
run (3.5 - 4.0 MHz in 50 kHz increments). What I notice is that I need 92
uH to resonate at 3.9 MHz. The input impedance is 12 ohms. I used a lumped
element model for the inductor. I may try a physical helix later. These
data do not seem to agree with your measured results. NEC 2, with the
Sommerfeld/Norton ground solution, is supposed to give a reasonable result
with wires at 10^(-3) wavelengths above ground (Basic Antenna Modeling,
Cebik p. 15-16 Nittany Scientific).

Gain and take-off angle are excellent, with max gain of -3 dBi at 28 deg.
elevation. The lower 3 dB point (8 deg elevation) gain is -6.6 dBi. The
NEC output file indicates an antenna efficiency of 54%. A free space model
shows an input impedance of 8 ohms, so your ground losses are not
significant (At least with my model).

Apart from adding horizontal wires, in "T" or inverted "L" fashion, I doubt
any antenna you could put up would match its performance at distances over
500 miles.

With 100 ft of LMR 400 the additional loss is about 0.45 dB. I would be very
interested to know if anybody has any ideas why my calculations appear to be
different from the measurements.

Regards,

Frank