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."

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 Wed, 20 Jun 2007 11:31:19 -0700, John Smith I
wrote:

Buck wrote:

[stuff]

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

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

Regards,
JS

That's close. they say it is good for 160-10 meters, but what if I
only want one for 10 meters or just 2 meters? Is there a rule of
thumb to build x turns at x diameter.

--
73 for now
Buck, N4PGW

www.lumpuckeroo.com

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

Buck wrote:

...
That's close. they say it is good for 160-10 meters, but what if I
only want one for 10 meters or just 2 meters? Is there a rule of
thumb to build x turns at x diameter.


Buck:

Personally, I just use a big toroid with sufficient turns of coax looped
through it (if using large diameter coax, I stack two or more toroids.)
Ferrite beads are another path one can utilize ...

I consider a +jX of 10X the coax impedance at the freq(s) in question
sufficient (and yes, I know some get by with 5X, and 5X is much more
"handleable" at 160m)--it is just a glorified choke; examine all the
formulas, equations, tables and charts you wish, and complete your
experiments--you will only reach this same conclusion. Since you are
only choking the currents on the outside of the braid, too much +jX is
not a real critical consideration--having enough is ...

Unfortunately, no black magic is used in its construction, but still,
and even at my age, I am fond of fairy-tales :-(

Others who have actually used the air core chokes of coax would be,
better, able to provide you with real world data, no doubt.

With the junk drawer of toroids I purchased decades ago--I have a
lifetime supply. (Indeed, I may need another lifetime to make full use
of 'em!)

Regards,
JS