Thanks, Mike! That's good and useful information!! I agree that 450 ohms of reactance is large enough to be "negligibly large" relative to 50 ohms. So Jim might, indeed, be OK with a 2-turn primary. Of course, he's basically just constructing a "balun" for his twisted pair to coax transition. So, he could probably just wind a twisted pair on a core, for a 1:1 current-mode balun, and ignore the small mismatch loss.
73, Charlie, K4OTV -----Original Message----- From: kd9sv [mailto:[email protected]] Sent: Thursday, August 22, 2013 12:10 PM To: 'Charlie Cunningham' Subject: RE: Topband: Two 2:1 transformers to choose from!! Charlie, on a typical 73-202 binocular core I measure about 450 ohms of open circuit reactance for two turns so if you make a 9:1 transformer using two turns pri and 6 turns sec for 50:450 or 75:600 ohms you would have way more than the recommended 5 times of reactance needed for a good transformer. (450 ohms inductive reactance is about 40uHy at 1.85mhz) 73, de gary, kd9sv -----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Charlie Cunningham Sent: Thursday, August 22, 2013 11:34 AM To: 'Mike Waters'; 'James Rodenkirch'; 'topband' Subject: Re: Topband: Two 2:1 transformers to choose from!! As I recall, Jim is using 73 mat'l cores. I'd be interested to see what sort of magnetizing inductance he would have looking into the 2-turn primary and what its reactance is at 1.8 MHz. Charlie, K4OTV -----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Mike Waters Sent: Thursday, August 22, 2013 11:21 AM To: James Rodenkirch; topband Subject: Re: Topband: Two 2:1 transformers to choose from!! P. 7-69 of Low Band Dxing (5th ed.) by ON4UN says a maximum of 4 turns on the low-Z primary for binocular cores. It might work, but there are other turns ratios you might try. Here is a list of turns ratios for those cores I made: http://www.w0btu.com/Binocular_core_turns_ratios.pdf If you get a 500 Server Error message, contact me directly and I'll e-mail it to you. 73, Mike www.w0btu.com On Wed, Aug 21, 2013 at 3:49 PM, James Rodenkirch <[email protected]>wrote: > I received enuff "info" and thoughts to know I'll utilize the 5:7 winding > version. > _________________ Topband Reflector _________________ Topband Reflector _________________ Topband Reflector
