Calculating linear load lengths
 

Does anyone have a good source for calculating the length of linear loads
for a shortened 40 meter Vertical? I'm experimenting with a 20' vertical
and a pair of 10' parallel lines moved the resonant point near the 7 Mhz
band. Any suggestions?

Does anyone have a good source for calculating the length of linear loads
for a shortened 40 meter Vertical? I'm experimenting with a 20' vertical
and a pair of 10' parallel lines moved the resonant point near the 7 Mhz
band. Any suggestions?



More elegant and efficient solution is to use loading coil placed abour 2/3 up
the radiator. Best is to use top loading with hat or wire.

Yuri, K3BU

Thanks - I guess I should have added some background

I've tried top loading and it works but is unwieldy. I'm working on an
variant of the St Louis vertical which does use a loading coil (at the
bottom) Since this antenna starts with the assumption that a light weight
portable mast will be used, a top load solution puts too much stress on the
weak top whip of the pole. For example, the calculation of a top load
cylinder is about 13" long by13" wide. I built on out of light weight
aluminum window screen and it worked but dragged the top down.

By contrast, using a length of 450 ohm ladder line, I hoped to build an
easily transportable antenna with a better SWR range than the SLV. I'm
iterating on the solution but still looking for some analytic approach.

Tom
W2TER

Back to my
"Yuri Blanarovich" wrote in message
...

Does anyone have a good source for calculating the length of linear loads
for a shortened 40 meter Vertical? I'm experimenting with a 20' vertical
and a pair of 10' parallel lines moved the resonant point near the 7 Mhz
band. Any suggestions?



More elegant and efficient solution is to use loading coil placed abour
2/3 up
the radiator. Best is to use top loading with hat or wire.

Yuri, K3BU

Here are a couple of articles I found.

http://www.qsl.net/pa3hbb/arframe.htm
http://www.arrl.org/tis/info/pdf/0207040.pdf

The last link is for a 40 meter linear loaded dipole, but I think the
formulas should work.
GL es 73,
Terry, WK0F



"news" wrote in message .com...
Does anyone have a good source for calculating the length of linear loads
for a shortened 40 meter Vertical? I'm experimenting with a 20' vertical
and a pair of 10' parallel lines moved the resonant point near the 7 Mhz
band. Any suggestions?

I saw both these articles but they are still both fairly weak on theory.

K4VX's article was what inspired me to try using a ladder line. He
apparently tried several lengths in NEC and then built an antenna from that
result. I've done that as well and it gives you a good start but doesn't
expose the theory of calculating the loads.

Reid's article starts with a very simple model. He makes the load length
equal to the "missing" length of the radiator! Then he complicates the
analysis with a top hat which he uses to create an "adjustment". That
apparently got close and then he pruned till he got resonance in the range
he wanted. It wasn't clear how the size of the top hat relates to the
length of the load.

The ARRL Antenna book has great analysis of the calculation for top hats but
no similar analysis for linear loads - at least I didn't find any.

Any help appreciated



"Terry Ashland" wrote in message
om...
Here are a couple of articles I found.

http://www.qsl.net/pa3hbb/arframe.htm
http://www.arrl.org/tis/info/pdf/0207040.pdf

The last link is for a 40 meter linear loaded dipole, but I think the
formulas should work.
GL es 73,
Terry, WK0F



"news" wrote in message
.com...
Does anyone have a good source for calculating the length of linear
loads
for a shortened 40 meter Vertical? I'm experimenting with a 20'
vertical
and a pair of 10' parallel lines moved the resonant point near the 7 Mhz
band. Any suggestions?

According to ON4UN - linear loading can be made virtually loss free (pg
9-39). Can't do that with coils.

He suggests making the linear load stub 30% longer than the missing portion
of 1/2 wavelength. (page 8-13) Then trim and try.
--
Radio K4ia
Craig "Buck"
Fredericksburg, VA USA
FISTS 6702 cc 788 Diamond 64


"news" wrote in message
. com...

Does anyone have a good source for calculating the length of linear loads
for a shortened 40 meter Vertical? I'm experimenting with a 20' vertical
and a pair of 10' parallel lines moved the resonant point near the 7 Mhz
band. Any suggestions?

According to ON4UN - linear loading can be made virtually loss free (pg
9-39). Can't do that with coils.

Why not? You can get less ohmic losses from less wire (tubing) in the coil than
from the stub. We just went through long argument about current in the loading
coils. People that replaced loading stubs with loading coils in say KLM 3 el.
80m antennas, found better efficiency and improvement on the pattern. Reality,
not a "calculated truth" :-)

Radio K4ia

Yuri, K3BU

It was a great news to hear that my "noSaddam" addition to my aol address
became reality. If this helped in any way, then I am changing it to
"noBinLaden" and we will see how long will that take to materialize.

So my future post will have that change in my no spam measure.

73 Yuri, K3BU@AOLnoBinLaden

73 Yuri, K3BU@AOLnoBinLaden


oops, AOL will allow only 10 more letters, so it is noBLaden

BUmmer

Yuri Blanarovich wrote:
According to ON4UN - linear loading can be made virtually loss free (pg
9-39). Can't do that with coils.

Why not? You can get less ohmic losses from less wire (tubing) in the coil than
from the stub. We just went through long argument about current in the loading
coils. People that replaced loading stubs with loading coils in say KLM 3 el.
80m antennas, found better efficiency and improvement on the pattern. Reality,
not a "calculated truth" :-)

Yep, completely understandable since the resistance of a coil goes up
proportional to the number of turns and the inductance of a coil goes
up (nearly) proportional to the square of the number of turns.
--
73, Cecil http://www.qsl.net/w5dxp



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