On Sep 13, 5:19 pm, Owen Duffy wrote:
The NEC model I posted
shows that a 1k isolator (common mode choke) is not effective for that
purpose.

Here's a model of a Carolina Windom on 20m with a 2k choke (isolator)
20 feet down the coax from the antenna feedpoint at a height of 50
feet. The maximum current on the coax braid above the isolator is 0.72
amps. The maximum current on the coax braid below the isolator is 0.14
amps. The radiation pattern is close to the advertised one for 20m.

http://www.w5dxp.com/carwin20.JPG
--
73, Cecil, w5dxp.com

On 14 sep, 01:10, Cecil Moore wrote:
On Sep 13, 5:19 pm, Owen Duffy wrote:

The NEC model I posted
shows that a 1k isolator (common mode choke) is not effective for that
purpose.

Here's a model of a Carolina Windom on 20m with a 2k choke (isolator)
20 feet down the coax from the antenna feedpoint at a height of 50
feet. The maximum current on the coax braid above the isolator is 0.72
amps. The maximum current on the coax braid below the isolator is 0.14
amps. The radiation pattern is close to the advertised one for 20m.

http://www.w5dxp.com/carwin20.JPG
--
73, Cecil, w5dxp.com

Hello boys (greteengs Wimpi, how are you?

For monoband applications we can get more Z from a coaxial choke
making the winding for autorresonance. K1TTT have a good data table.

Time ago I want test differents antenna to lift with a kite and I
found =
http://www.io.com/~n5fc/rfd.htm, the idea seems to me interesting
enough to make some test that are descibed here =

http://www.solred.com.ar/lu6etj/tecn...evisada-en.htm

from here I think of another use of de "coaxial trap" to get more Z
from coaxial winding specially in monoband antennas, I named de
critter "The Trap balun" =

http://www.solred.com.ar/lu6etj/tecn...a_balun-en.htm

4NEC2 simulations and real field test show me both approachs works
fine :)

Miguel Ghezzi LU6ETJ

lu6etj wrote in
:

....
For monoband applications we can get more Z from a coaxial choke
making the winding for autorresonance. K1TTT have a good data table.

Time ago I want test differents antenna to lift with a kite and I
found =
http://www.io.com/~n5fc/rfd.htm, the idea seems to me interesting
enough to make some test that are descibed here =

http://www.solred.com.ar/lu6etj/tecn...ga_revisada-en
.htm

from here I think of another use of de "coaxial trap" to get more Z
from coaxial winding specially in monoband antennas, I named de
critter "The Trap balun" =

http://www.solred.com.ar/lu6etj/tecn...a_balun-en.htm

4NEC2 simulations and real field test show me both approachs works
fine :)

How did you arrive at the value of Q (=100) used in the modelling. Was it
measured, or guessed?

Based on some experimental work, I expect that the effective RF
resistance of a closed space solenoidal coil of braided coax is much
higher than the same straight length a copper cylinder.

BTW, if you want to make a more compact self resonant trap on the lower
HF bands, wind the coil in two layers. The article at
http://vk1od.net/antenna/7MDipole/7MDipole.htm shows a pic of a two layer
7MHz self resonant balun made with IIRC about 6 turns per layer of RG6.

Owen

On 14 sep, 17:34, Owen Duffy wrote:
lu6etj wrote :

...





For monoband applications we can get more Z from a coaxial choke
making the winding for autorresonance. K1TTT have a good data table.

Time ago I want test differents antenna to lift with a kite and I
found =
http://www.io.com/~n5fc/rfd.htm, the idea seems to me interesting
enough to make some test that are descibed here =

http://www.solred.com.ar/lu6etj/tecn...ga_revisada-en
.htm

from here I think of another use of de "coaxial trap" to get more Z
from coaxial winding specially in monoband antennas, I named de
critter "The Trap balun" *=

http://www.solred.com.ar/lu6etj/tecn...a_balun-en.htm

4NEC2 simulations and real field test show me both approachs works
fine :)

How did you arrive at the value of Q (=100) used in the modelling. Was it
measured, or guessed?

Based on some experimental work, I expect that the effective RF
resistance of a closed space solenoidal coil of braided coax is much
higher than the same straight length a copper cylinder.

BTW, if you want to make a more compact self resonant trap on the lower
HF bands, wind the coil in two layers. The article athttp://vk1od.net/antenna/7MDipole/7MDipole.htmshows a pic of a two layer
7MHz self resonant balun made with IIRC about 6 turns per layer of RG6.

Owen- Ocultar texto de la cita -

- Mostrar texto de la cita -

I do not remember Owen, I believe Q 100 was a number for the text
example, calculated Q on 7 MHz for ideal coil was about 400 and
measured real coaxial made coil with a GR-1606 A near 200. at that
time I did not think to use RG6, It is more light than RG58, isn't it?
Seven turns of RG 58 on 63 mm diameter with parallel condenser it was
very light, enough for the purpose, Rokkaku lifted 40 m "syringe"
antenna flied very well.

R, to two layers choke. Well... frankly to me common mode radiation it
is not something I lose sleep, I have not troubles in my shack and I
was not very lucky in all attempts to reduce nasty modern suburban
noise with baluns + chokes + grounded points, so many noisy companies
and neighbors cables around :( antenna height showed much better
results.

73

Miguel LU6ETJ

On Sep 14, 3:02*pm, lu6etj wrote:
For monoband applications we can get more Z from a coaxial choke
making the winding for autorresonance. K1TTT have a good data table.

Good idea. Choose your favorite band for your Carolina Windom and wind
an "ugly balun" choke just below the isolator. An "ugly balun" choke
is capable of forcing a common-mode standing-wave current node
(minimum) on the outside of a coax braid just like a trap is capable
of such on a trapped dipole.
--
73, Cecil, w5dxp.com

On 9/14/2010 3:37 PM, Cecil Moore wrote:
On Sep 14, 3:02 pm, wrote:
For monoband applications we can get more Z from a coaxial choke
making the winding for autorresonance. K1TTT have a good data table.

Good idea. Choose your favorite band for your Carolina Windom and wind
an "ugly balun" choke just below the isolator. An "ugly balun" choke
is capable of forcing a common-mode standing-wave current node
(minimum) on the outside of a coax braid just like a trap is capable
of such on a trapped dipole.
--
73, Cecil, w5dxp.com

OK, I'll ask, "I am correct in thinking that most are using a 'voltage
balun' (ruthroff 1:4) as the 'Low Loss Matching Transformer' and a
'current balun' (guanella 1:1) as the 'Special-High Isolation Line
Isolator?'"

I mean, logic dictates this to be the best combination ... however, one
is best to ask ...

Regards,
JS

"John Smith" wrote in message
...
OK, I'll ask, "I am correct in thinking that most are using a 'voltage
balun' (ruthroff 1:4) as the 'Low Loss Matching Transformer' and a
'current balun' (guanella 1:1) as the 'Special-High Isolation Line
Isolator?'"

I mean, logic dictates this to be the best combination ... however, one is
best to ask ...

Regards,
JS


That is what I am using on a home built version. Using a 4:1 voltage balun
at the feedpoint and the ferrite bead type about 20 feet down from the
feedpoint.

The ferrite choke is doing something as it gets warm while running around
about 1 KW to the antenna. Doesn't heat up when going into a dummy load.

My 'Windom' usually works beter than an 80 meter dipole on 80 meters plus
gives me the option to operate several other bands.

On 9/14/2010 4:11 PM, Ralph Mowery wrote:

...
That is what I am using on a home built version. Using a 4:1 voltage balun
at the feedpoint and the ferrite bead type about 20 feet down from the
feedpoint.

The ferrite choke is doing something as it gets warm while running around
about 1 KW to the antenna. Doesn't heat up when going into a dummy load.

My 'Windom' usually works beter than an 80 meter dipole on 80 meters plus
gives me the option to operate several other bands.



Sounds like you must be using A LOT of beads for 80m. Why not a couple
#43 toroids, stacked? Or, a t300-X or t400-X?

Regards,
JS

On Tue, 14 Sep 2010 19:11:43 -0400, "Ralph Mowery"
wrote:

That is what I am using on a home built version. Using a 4:1 voltage balun
at the feedpoint

This is like using a lighter to find a gas leak in the basement.

and the ferrite bead type about 20 feet down from the
feedpoint.

The ferrite choke is doing something as it gets warm while running around
about 1 KW to the antenna. Doesn't heat up when going into a dummy load.

Hi Ralph,

Through the 4:1? Probably not, or you would have said so (and
unlikely you have gone to the trouble to build a 4:1 dummy load).

As the dummy load is most likely enclosed and shielded, then that
suppresses common mode currents due to your test transmission.

And, yes, when your ferrite choke (AKA 1:1 BalUn) heats up that is due
to common mode currents that were not snubbed by the voltage balun (by
design - so why choose it?).

Add a second ferrite choke (AKA 1:1 BalUn) at the feedpoint -before
feeding the voltage balun.

My 'Windom' usually works beter than an 80 meter dipole on 80 meters plus
gives me the option to operate several other bands.

Better in what sense?

73's
Richard Clark, KB7QHC

"Ralph Mowery" wrote in
m:

....
That is what I am using on a home built version. Using a 4:1 voltage
balun at the feedpoint and the ferrite bead type about 20 feet down
from the feedpoint.

The ferrite choke is doing something as it gets warm while running
around about 1 KW to the antenna. Doesn't heat up when going into a
dummy load.

I am not surprised at your results with a dummy load. If it is a well
screened unbalanced dummy load, you should expect zero dissipation in the
balun cores.

The fact the balun cores are heating in the antenna scenario indicates
there is some common mode current. You probably have no idea of the
current.

Something to keep in mind is that the average power of uncomressed voice
SSB is about 3% of PEP, so if your 1kW was uncompressed voice SSB, the
average transmitter power might be more like 30W, or half that in a 50:50
over scenario over the long term.

Another thing is the ferrite toroids heat and cool very slowly, so the
operating temperature might still be rising half an hour after the
transmitter is applied (so long as you haven't exceeded their Curie
temperature).

It would not surprise me if the common mode choke consumes a significant
portion of transmitter power on some bands, the portion will depend a lot
on your own scenario.

Owen