Hi all...
I am starting to work on something to use on 160 thru 20 meters.
I currently have an aluminum mast that is 32 ft long with a small cap hat on
top.
the antenna will sit in the center of an area approx 50 z 50' (backyard). I
plan to put down 40 plus radials, the majority which will be situated to
radiate out from the base of the vertical.
some will meander along the house foundation and property line..
I plan on also tying in the galvanized (not chain link) fence around the
back yard to the radial system, as well as the house plumbing.
40 meters should be direct feed.
I will homebrew a matching L network for use on 160 thru 60 meters.
I will also try a 20 meter tuning stubb.
Does anyone know what the size of the loading coil that MFJ uses in their 80
& 40 meter vertical?
I have read of just about everything I can find online of this sort of
project and have played with Eznec demo a bit and think this will be a
doable project.

Does anyone know what the size of the loading coil that MFJ uses in their 80
& 40 meter vertical?

Dentron, The size of the loading coil is not so important as the inductance
of the coil.
What I would advise is put the best ground radial system you can. Beg,
Borrow or Steal an antenna analyzer and determine the impedance of the vertical
at the frequencies you wish to work.
Then use the Smith Chart, to determine what L network configuration will
provide a match.







73 Gary N4AST

"denton" wrote in message
...
Hi all...
I am starting to work on something to use on 160 thru 20 meters.
I currently have an aluminum mast that is 32 ft long with a small cap hat
on
top.
the antenna will sit in the center of an area approx 50 z 50' (backyard).
I
plan to put down 40 plus radials, the majority which will be situated to
radiate out from the base of the vertical.
some will meander along the house foundation and property line..
I plan on also tying in the galvanized (not chain link) fence around the
back yard to the radial system, as well as the house plumbing.
40 meters should be direct feed.
I will homebrew a matching L network for use on 160 thru 60 meters.
I will also try a 20 meter tuning stubb.
Does anyone know what the size of the loading coil that MFJ uses in their
80
& 40 meter vertical?
I have read of just about everything I can find online of this sort of
project and have played with Eznec demo a bit and think this will be a
doable project.


Consider the input impedance on 160m. With 1.5 kW the voltage at the base
of the antenna is likely to be in the 20 to 30 kV range (about 5 - 7.5 kV
with 100 W) . Also for an "L" network, suggest you use a series "L", shunt
"L" configuration. Series "L" shunt "C" requires very large values for the
shunt capacitor.

73,

Frank (VE6CB)

"denton" wrote in message
...
Hi all...
I am starting to work on something to use on 160 thru 20 meters.
I currently have an aluminum mast that is 32 ft long with a small cap hat
on
top.
the antenna will sit in the center of an area approx 50 z 50' (backyard).
I
plan to put down 40 plus radials, the majority which will be situated to
radiate out from the base of the vertical.
some will meander along the house foundation and property line..
I plan on also tying in the galvanized (not chain link) fence around the
back yard to the radial system, as well as the house plumbing.
40 meters should be direct feed.
I will homebrew a matching L network for use on 160 thru 60 meters.
I will also try a 20 meter tuning stubb.
Does anyone know what the size of the loading coil that MFJ uses in their
80
& 40 meter vertical?
I have read of just about everything I can find online of this sort of
project and have played with Eznec demo a bit and think this will be a
doable project.

Also the series inductor should have a very high Q for 160 m. A Q of 1000
will loose about 30% of your power.

Frank

Frank wrote:

Also the series inductor should have a very high Q for 160 m. A Q of 1000
will loose about 30% of your power.

Can you tell us how you calculated this? How much ground loss did you
assume?

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
Frank wrote:

Also the series inductor should have a very high Q for 160 m. A Q of
1000
will loose about 30% of your power.

Can you tell us how you calculated this? How much ground loss did you
assume?

Roy Lewallen, W7EL

I have run a number of NEC models (NEC-Win Pro), for ground mounted
verticals with a radial system, using the Sommerfeld/Norton ground models
(usually in the range of: Sigma = 0.02 S/m Er = 17) -- although not for the
specific dimensions indicated. My models would be approximately 0.001
wavelengths above ground (as per Cebik: Basic Antenna Modeling). The input
impedance calculated is of the order of 1.5 - j1500. From these data it is
relatively trivial to estimate the required Q of a series inductor.

I have been very interested in such antennas, but have never actually gotten
around to building -- just modeling! If the original poster is interested,
I would be very happy to model the specific dimensions.

Frank Meredith (VE6CB)

I doubt that the coil will have a Q of more than 300 if that !
Art





"Frank" wrote in message news:JCe1d.97059$jZ5.12695@clgrps13...
"denton" wrote in message
...
Hi all...
I am starting to work on something to use on 160 thru 20 meters.
I currently have an aluminum mast that is 32 ft long with a small cap hat
on
top.
the antenna will sit in the center of an area approx 50 z 50' (backyard).
I
plan to put down 40 plus radials, the majority which will be situated to
radiate out from the base of the vertical.
some will meander along the house foundation and property line..
I plan on also tying in the galvanized (not chain link) fence around the
back yard to the radial system, as well as the house plumbing.
40 meters should be direct feed.
I will homebrew a matching L network for use on 160 thru 60 meters.
I will also try a 20 meter tuning stubb.
Does anyone know what the size of the loading coil that MFJ uses in their
80
& 40 meter vertical?
I have read of just about everything I can find online of this sort of
project and have played with Eznec demo a bit and think this will be a
doable project.

Also the series inductor should have a very high Q for 160 m. A Q of 1000
will loose about 30% of your power.

Frank

"Art Unwin KB9MZ" wrote in message
m...
I doubt that the coil will have a Q of more than 300 if that !
Art





"Frank" wrote in message
news:JCe1d.97059$jZ5.12695@clgrps13...
"denton" wrote in message
...
Hi all...
I am starting to work on something to use on 160 thru 20 meters.
I currently have an aluminum mast that is 32 ft long with a small cap
hat
on
top.
the antenna will sit in the center of an area approx 50 z 50'
(backyard).
I
plan to put down 40 plus radials, the majority which will be situated
to
radiate out from the base of the vertical.
some will meander along the house foundation and property line..
I plan on also tying in the galvanized (not chain link) fence around
the
back yard to the radial system, as well as the house plumbing.
40 meters should be direct feed.
I will homebrew a matching L network for use on 160 thru 60 meters.
I will also try a 20 meter tuning stubb.
Does anyone know what the size of the loading coil that MFJ uses in
their
80
& 40 meter vertical?
I have read of just about everything I can find online of this sort of
project and have played with Eznec demo a bit and think this will be a
doable project.

Also the series inductor should have a very high Q for 160 m. A Q of
1000
will loose about 30% of your power.

Frank

Based on Terman's "Radio Engineers Handbook" dated 1943, pp 31 - 53. I have
written a program In MathCAD Pro, which indicates a coil made from 1/4"
copper pipe, 12" long, and 3 inches diameter has an inductance of 39 uH and
a Q of 1132 at 1.8 MHz. (6" in diameter and 24" long shows a nominal Q of
1600). To be honest I have never built such a coil, and it would probably
be very difficult to measure. I agree that typical "Airdux" coils have a Q
in the range of 300 or so.(Silver plating, or gold, would also be desirable
to prevent lossy copper oxide build up). Anyway if you are interested I
can send you the MathCAD file. I would be very happy if somebody could check
my math. It think the point I was trying to make it that electrically short
antennas have such a low real input impedance that building an efficient
matching network is challenging to say the least. Even if such networks are
feasible the huge voltages developed at the base could prove to be a
problem.

73,

Frank

The input resistance of 1.5 ohms you quote implies an extremely good
ground system. I suspect that very few people, particularly ones putting
up such a short vertical for 160, have the room for that elaborate a
system. As ground loss increases, the fractional loss caused by the
inductor decreases. So I don't agree with your blanket statement that an
inductor with a Q of 1000 will lose that fraction of the power. It
might, if a person had an extremely elaborate ground system, but not
otherwise.

Incidentally, although 30% power loss sounds impressive, it'll reduce
the signal less than 1.6 dB.

So it won't be worthwhile for most people to make heroic efforts to
produce extremely high Q loading inductors. (And, even if they can make
one with a Q of 1000, it would have to somehow be suspended well above
the ground and away from other conductive objects in order to retain
that sort of Q.)

Roy Lewallen, W7EL

Frank wrote:

"Roy Lewallen" wrote in message
...

Frank wrote:

Also the series inductor should have a very high Q for 160 m. A Q of

1000

will loose about 30% of your power.

Can you tell us how you calculated this? How much ground loss did you
assume?

Roy Lewallen, W7EL


I have run a number of NEC models (NEC-Win Pro), for ground mounted
verticals with a radial system, using the Sommerfeld/Norton ground models
(usually in the range of: Sigma = 0.02 S/m Er = 17) -- although not for the
specific dimensions indicated. My models would be approximately 0.001
wavelengths above ground (as per Cebik: Basic Antenna Modeling). The input
impedance calculated is of the order of 1.5 - j1500. From these data it is
relatively trivial to estimate the required Q of a series inductor.

I have been very interested in such antennas, but have never actually gotten
around to building -- just modeling! If the original poster is interested,
I would be very happy to model the specific dimensions.

Frank Meredith (VE6CB)

Yes, agree with everything you say. I have measured my ground conductivity
as 50 mS/m, so it is possible I used that figure to arrive at the results.
Much of Alberta and Montana have very high ground conductivity in the order
of 15 - 40 mS/m (Reference Data for Radio Engineers, 6th ed, pp 30-7, 30-8).
I must admit to being fixated on super high Q inductors to minimize matching
network losses. Your figure of 1.6 dB loss with a Q of 1000 -- based on a
1.5 Ohm resistance is of course correct. Just the same I plan to model the
vertical, as described in the original post, and see what I get for various
soil conditions, and the loss effects of some typical Qs. I know it has all
been done before, but enjoy doing it just for fun.

Frank Meredith (VE6CB)


"Roy Lewallen" wrote in message
...
The input resistance of 1.5 ohms you quote implies an extremely good
ground system. I suspect that very few people, particularly ones putting
up such a short vertical for 160, have the room for that elaborate a
system. As ground loss increases, the fractional loss caused by the
inductor decreases. So I don't agree with your blanket statement that an
inductor with a Q of 1000 will lose that fraction of the power. It
might, if a person had an extremely elaborate ground system, but not
otherwise.

Incidentally, although 30% power loss sounds impressive, it'll reduce
the signal less than 1.6 dB.

So it won't be worthwhile for most people to make heroic efforts to
produce extremely high Q loading inductors. (And, even if they can make
one with a Q of 1000, it would have to somehow be suspended well above
the ground and away from other conductive objects in order to retain
that sort of Q.)

Roy Lewallen, W7EL

Frank wrote:

"Roy Lewallen" wrote in message
...

Frank wrote:

Also the series inductor should have a very high Q for 160 m. A Q of

1000

will loose about 30% of your power.

Can you tell us how you calculated this? How much ground loss did you
assume?

Roy Lewallen, W7EL


I have run a number of NEC models (NEC-Win Pro), for ground mounted
verticals with a radial system, using the Sommerfeld/Norton ground
models
(usually in the range of: Sigma = 0.02 S/m Er = 17) -- although not for
the
specific dimensions indicated. My models would be approximately 0.001
wavelengths above ground (as per Cebik: Basic Antenna Modeling). The
input
impedance calculated is of the order of 1.5 - j1500. From these data it
is
relatively trivial to estimate the required Q of a series inductor.

I have been very interested in such antennas, but have never actually
gotten
around to building -- just modeling! If the original poster is
interested,
I would be very happy to model the specific dimensions.

Frank Meredith (VE6CB)