Re: [HCDX]: Build a balun

["Thorburn, Gary" <gthorburn@xxxxxxxxxx>]

 >In fact, it's not easy to derive the impedance of a random length
inverted-L
 >antenna, but a good guess at the tropical and mediumwave frequencies would
 >be in the 1000 ohm range, so the impedance ratio of the transformer could
be
 >1:20 .

Yes, this is hard to predict.  The 1:20 ratio may be a "correct
match", but a lower ratio will make the antenna more broadbanded.
I'd suggest trying something with an impedence ratio of
between 1:4 and 1:10.  If you are end-feeding a longwire or
inverted L, you need the antenna connected to one leg of the
higher imp winding, and a ground rod or radial counterpoise to
the other side.  The low-imp side feeds the center and shield
of the 50-ohm coax to your radio.  This is an arrangement that
works well, but its not really a "balun", but just a transformer. 

Unless you plan to transmit thru this, look into the DIP-package
broadband transformers from "Mini-Circuits", in Brooklyn NY. 
You can buy a handful and experiment to find the ratio that
works best. 

Anyone wanting more info, email me off-line.

-- Gary

/****
*  Gary W. Thorburn  KD1TE
*  email address:  gthorburn@xxxxxxxxxx
****/

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