[hfsig] Sidebands on Raspberry Pi WSPR carrier - how to build an ground isolation balun

Ron Ott ronott at sbcglobal.net
Mon Sep 5 14:17:31 CDT 2016


Hi Tom -- I agree that 30 turns is probably too much inductance at 14MHz.  When you say bifilar, do you mean simply interleave the two windings round the toroid? Looking at baluns made by Balun Designs, I see only a handful of turns at HF - of course this depends on the ferrite too. So, how about:
* 5 turns each of 20 or 22 ga enamelled wire for the primary and secondary windings* Interleave the primary and seconday windings* Amidon FT 37-75 core
Ron/W6XY

      From: Tom McDermott <tom.n5eg at gmail.com>
 To: TAPR HF Modes SIG Mailing List <hfsig at tapr.org> 
 Sent: Monday, September 5, 2016 11:55 AM
 Subject: Re: [hfsig] Sidebands on Raspberry Pi WSPR carrier - how to build an ground isolation balun
   
Hi Ron, thanks for the pointer.

For use at 14 MHz, winding the two transformer windings on opposite sides of the ferrite core
could be an issue. That causes a lot of leakage inductance, and at 14 Mhz, depending on load
Z may attenuate the desired signal. 30 turns might be a bit much at 20 meters

Forming a bifilar twisted pair of the two windings reduces the leakage inductance a lot.

Minimizing the interwinding capacitance would not seem to be much of a consideration
at 60 or 120 Hertz.

-- Tom, N5EG




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