I have looked, but cannot find, some kind of formula to indicate the
approximate diameter and number of turns needed to build an ugly balun
for some specific frequency.

Does anyone know where I might find that formula?

--
73 for now
Buck, N4PGW

www.lumpuckeroo.com

"Small - broadband - efficient: pick any two."

Buck wrote:

...
Does anyone know where I might find that formula?


Buck:

Some designs for the "ugly balun" appear to vary, sometimes widely.

I don't know how a fellow could go wrong if they take into the reactance
of the coil (to the freq/freqs in question) and make that at least 5X
the impedance of the coax in question. At the higher freqs, I prefer a
10X ratio, 160m makes the 10X ratio cumbersome.

Others may provide info to suggest other routes ... or more desirable
solutions ...

Regards,
JS

On Wed, 20 Jun 2007 06:40:34 -0700, John Smith I
wrote:

Buck wrote:

to indicate the approximate diameter and number of turns ...
Does anyone know where I might find that formula?


Buck:

Some designs for the "ugly balun" appear to vary, sometimes widely.

I don't know how a fellow could go wrong if they take into the reactance
of the coil (to the freq/freqs in question) and make that at least 5X
the impedance of the coax in question. At the higher freqs, I prefer a
10X ratio, 160m makes the 10X ratio cumbersome.

Others may provide info to suggest other routes ... or more desirable
solutions ...

Regards,
JS

Is this 5 times the diameter in turns?


--
73 for now
Buck, N4PGW

www.lumpuckeroo.com

"Small - broadband - efficient: pick any two."

On Wed, 20 Jun 2007 09:01:56 -0400, Buck
wrote:

I have looked, but cannot find, some kind of formula to indicate the
approximate diameter and number of turns needed to build an ugly balun
for some specific frequency.

Does anyone know where I might find that formula?

Hi Buck,

One does not normally build a frequency specific BalUn, unless it is
tuned transmission line based. As you are speaking in terms of
"turns," then that is obviously not the case.

73's
Richard Clark, KB7QHC

Buck wrote:

...
Is this 5 times the diameter in turns?

Buck:

No, I meant using a "single layer solenoid formula"/table/graph, pick an
inductive reactance which would offer an impedance (choking effect) of
10X the impedance of the coax in question--or in effect, 50 X 10 = 500
(depending on your physical limitations for the choke, this may not
achievable ... a lower value may have to be accepted.)

Also, you may wish to check the self-capacitance against the inductance
of the coil and note the resonate freq of the choke, making sure it is
working to your advantage rather than you disadvantage.

Regards,
JS

Buck wrote:

[stuff]

Or, you may just want to use an, apparently, tried and accepted design:

http://www.hamuniverse.com/balun.html

Regards,
JS

On Jun 20, 8:01 am, Buck wrote:
Does anyone know where I might find that formula?

How about a rule of thumb? Using a 2 liter pop bottle, make the number
of turns equal to the wavelength in meters. That will optimize for a
specific wavelength but will render it not very useful for any shorter
wavelengths, e.g. 20 turns is too many for 10m.
--
73, Cecil, w5dxp.com
..

Buck, N4PGW wrote:
"Does anyone know where I might find that formula?"

Look at the ARRL Antenna Book. The 19th edition (old) has a choke balun
for low-frequency antennas on page 6-9. The text says:
"In general, an isolation choke inductance of 50 to 100 microhenries
will be needed for 3.5 and 1.8 MHz, ground-plane antennas. One of the
easiest ways to make the required isolation choke is to wind a length of
coaxial cable into coil as shown in Hig 18. For 1.8 Mhz, 30 turns of
RG-213 wound on a 14-inch length of of 8-inch diameter PVC pipe, will
make a very good isolation choke that can handle full legal power
continuously."

On page 11 of Terman`s 1955 opus is found formula (2-2):
Inductance in microhenries = F n(sqared) d

F is a constant that depends on length/diameter. There`s a chart in the
book for F.
n is the number of turns.
d is the diameter of the coil measured between the centers of the wire
in the coil.

The purpose of the coil is to present a high impedance to currents on
the outsifde of the coax so quick and dirty is OK so long as there is
enough impedance. You may get away without a coil form at all. You might
lose some of the isolation that coil length provides so I don`t
recommend just coiling coax like garden hose.

Best regards, Richard Harrison, KB5WZI

On Wed, 20 Jun 2007 15:15:03 -0500, (Richard
Harrison) wrote:

Buck, N4PGW wrote:
"Does anyone know where I might find that formula?"

Look at the ARRL Antenna Book. The 19th edition (old) has a choke balun
for low-frequency antennas on page 6-9. The text says:
"In general, an isolation choke inductance of 50 to 100 microhenries
will be needed for 3.5 and 1.8 MHz, ground-plane antennas. One of the
easiest ways to make the required isolation choke is to wind a length of
coaxial cable into coil as shown in Hig 18. For 1.8 Mhz, 30 turns of
RG-213 wound on a 14-inch length of of 8-inch diameter PVC pipe, will
make a very good isolation choke that can handle full legal power
continuously."

Page 26-21 of the same 19th edition ARRL Antenna Book has a whole
table of choke baluns sized for each of the HF bands. I believe Mr.
Lewallen worked out the specs.

bob
k5qwg



On page 11 of Terman`s 1955 opus is found formula (2-2):
Inductance in microhenries = F n(sqared) d

F is a constant that depends on length/diameter. There`s a chart in the
book for F.
n is the number of turns.
d is the diameter of the coil measured between the centers of the wire
in the coil.

The purpose of the coil is to present a high impedance to currents on
the outsifde of the coax so quick and dirty is OK so long as there is
enough impedance. You may get away without a coil form at all. You might
lose some of the isolation that coil length provides so I don`t
recommend just coiling coax like garden hose.

Best regards, Richard Harrison, KB5WZI

Cecil Moore wrote:
On Jun 20, 8:01 am, Buck wrote:
Does anyone know where I might find that formula?

How about a rule of thumb? Using a 2 liter pop bottle, make the number
of turns equal to the wavelength in meters. That will optimize for a
specific wavelength but will render it not very useful for any shorter
wavelengths, e.g. 20 turns is too many for 10m.

So it is your "rule of thumb" that 160 turns would be used for 160m?
I don't think so, Cecil. Six or eight turns on such a form should work
fine for 20-10m.

Dave K8MN