[Boatanchors] output xfmr measurement

[Al Klase]

Dick and Ian,

I think you'll find that both of your explanations are a bit garbled.

Comparing the voltage on the windings will give you the turns ratio.

I apply 1 volt to the primary and read 2 volts on the secondary.  
Therefore the turns ratio is 2.

The impedance ratio is N^2 (N squared).  Assuming no losses, the power 
on both sides of the transformer is E^2/Z.

For instance, a 75 to 300 ohm (1:4) balun has a turns ratio of 2.

With apologies for lack of mathematical rigor,
Al



On 2/16/2010 6:51 PM, Ian Wilson wrote:
> The principle is that if the turns ratio of the transformer (pri:sec) is
> 1:N, then
>    - the voltage across the secondary is N times the voltage across the
> primary
>    - the current through the secondary is 1/N times the current through the
> primary
>
> If you see an impedance Za looking into the primary, the secondary is
> connected
> to an impedance of Za^2. Alternatively, if you see an impedance of Zb
> looking into
> the secondary, the primary must be connected to an impedance of sqrt(Zb).
>
> Note that this tells you nothing about the impedance of the transformer
> windings
> themselves. The assumption is that the reactance of the transformer winding
> at the
> frequency of operation is much higher than any source or load connected to
> the
> transformer.
>
> Hope this helps.
>
> 73, ian K3IMW
>
>
> On Tue, Feb 16, 2010 at 3:27 PM, Dick KF4NS<kf4nsradio at verizon.net>  wrote:
>
>    
>> Some time ago a friend (now SK) sent to me a brief test method for 'Z'
>> of output xmfrs.
>>
>> It is a bit vague but maybe someone can decipher it. He said:
>>
>> "Apply 60hz at 1 volt on the secondary and measuring the primary will
>> give you the turns ratio. The 'Z' ratio would be the square root of
>> the turns ratio".
>>
>> Can someone give me a mathamatical example of his test? Measuring what
>> in the primary and how do you compute the square root of a ratio?
>> Guess my math knowledge is a bit hazy.
>>
>> thanks and 73, Dick KF4NS
>> St Petersburg, FL 33714 USA
>> Keep The Glow!
>>
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/