Errr, impedance of the winding should be "inductive reactance"--excuse me,
these "unreal" things are confusing to me... grin

here is an piece I got somewhere I have been using with tollerable
results...
CALCULATING THE TURNS COUNT



Lets calculate the turns count for impedance matching a beverage antenna
with an impedance of 450 ohms to 50 ohm coax. Because this is a step-down
transformer, the primary (attached to the antenna) will be the larger
winding and we'll deal with that first.



The first formula to use will give us the desired inductance of the primary
winding:



desired L of winding = XL/2p¦



where L= Inductance in millihenries XL=Reactance in ohms ¦=Lowest
frequency of operation in kHz



XL may be found by multiplying the impedance of the antenna to be matched by
a factor of 4. This XL would be

4 x 450 ohms or 1800 ohms. To make things easy, lets use 500 kHz. as our
lowest frequency of operation.



So, L of the primary winding = 1800/2 x3.1416 x 500 or .573 mH

Now that we know the inductance (L) needed for the primary winding, we can
apply the following formula to determine the number of turns needed for the
primary winding.




N = 1000 ÖL/AL



In narrative, this formula should be read: Number of turns required (N) is
equal to 1000 times the

square root (Ö) of the Inductance (L) divided by the constant AL.



The constant AL is determined from the Amidon technical literature and takes
into account the RF qualities and the size of a Type 43 toroid that is 1.14
inches in diameter. The AL for the FT-114-43 is 603.



So, working the formula above, N = 1000 Ö.573/603 = 1000 x .030825 = 30.8
turns, use 31


DISCLAIMER:
If your radio blows up from the use of my advice I can ONLY be held to feel
sorry...

Warmest regards,
John
"John Smith" wrote in message
...
|I think, others will correct me if I am wrong--the "optimal" number of
turns
| would would present an impedance of 4x (four times) the impedence
| (resistance) of the load/feed, at the lowest freq of operation...
sometimes
| this cannot be met, and other values must be used... you should be able to
| compute this with the "Al" value of the toroid--with data from the
| manufacturer...
| Remember, I am a "newbie", greater authorites will provide finer
details...
|
| Warmest regards,
| John
|
| "Fred W4JLE" wrote in message
| ...
||
|| Using a T200A-2 for a 1:1 balun, what is the optimum number of turns and
|| best wire size? 200 watts max power.
||
||
||
||
||
||
|
|