[ARC5] Why an UNUN?

[mac]

OK, I remember hearing a figure in that range before. Now, the command  
xmtrs were designed to operate into antennas that presented highly  
reactive loads, a relatively low resistance and a large capacitive  
component and the function of the roller inductor was to cancel out  
the latter.  Reasonable to assume, then, (but not necessarily for  
certain) that the variable link alone would allow proper loading of  
the transmitter into a purely resistive 13 ohm load or something close  
to it and a 2:1 step-up (4:1 impedance ratio)  transformer (or UNUN if  
you prefer) would then provide a very good match to 50 and 75 ohm  
resistive loads with the inductor completely removed from the  
circuit.  Not clear from the many comments  whether or not anyone has  
actually verified this?  Also, seems to be some confusion as to   
whether or not a series capacitor would still be required which should  
NOT be the case.

I've never tried the UNUN approach, BTW,  series caps and the roller  
always worked FB here as I've mentioned before.

Dennis D.  W7QHO
Glendale, CA

****************
On Oct 24, 2012, at 3:16 PM, Mike Hanz wrote:

> The manual gives a range of values, John.  The upper limit is around  
> 13
> ohms resistive, but it also expects a capacitive component.  See para
> 1-28 in the ARC-5 manual, although the SCR-274-N and ATA manuals  
> contain
> the same data, IIRC.