[NLRS] Looking for RF transformer

[Jason Godfrey]

Hello.

Thanks for all the responses.

Here is what I am trying to do. I'm helping out with the care and feeding of
a FM broadcast transmitter. The exciter is a 50 Ohm solid state device. The
transmitter is a tube device with a 4CX250B as the first stage. The transmitter
originally had an exciter built in that was 75 ohm.

A resistive pad has been used between the two as a match. We would like to try
a transformer instead to try to drive the first tube a bit better and get more
efficiency. 

We need about 150 Khz of bandwidth with 1 dB or less of dropoff to avoid AMing. 

- Jason

On Wed, Oct 27, 2004 at 11:57:33AM -0500, jcplatt1 at mmm.com wrote:
> 
> Hi Jason.   Not sure what your needs are, but have you considered a 1/4
> matching section ?    The coax matching section would be an electrical 1/4
> wavelength at the frequency of interest with an impendence of Sqrt (50 *
> 75), or 61 ohms (if I remember this right).    The problem will be to find
> a 61 ohm coax ..... not sure if there is one made or not.   I do know that
> there is 125 ohm coax and you can parallel two identical 1/4 sections to
> arrive at 62.5 ohms which is pretty darn close.  1/4 matching sections are
> fairly broad depending on what your definition is for good bandwidth.
> 
> On the other hand, a 50 to 75 ohm mismatch is only 1.5 to 1 SWR which is
> usually tolerable (depending on what your up to), especially if the
> transmitter loads into it.   The matching section could end up having more
> loss than the loss due to a 1.5 to 1 SWR mismatch.
> 
> Just some thoughts for ya.
> 
> 73, Jon
> W0ZQ