[Elecraft] Balun at input or output of tuner

[Jim Brown]

On 12/13/2011 11:48 AM, Alan Bloom wrote:
> Is that a valid assumption?  I thought that much of the loss in coax is
> due to the dielectric loss of the insulation.  That implies that the
> bifilar winding should have less loss than coax.

This is a very common misconception, and it is VERY wrong below UHF for 
nearly all practical transmission lines that aren't defective (for 
example, a wet dielectric). If you do the math, you see that below UHF, 
the loss is virtually ALL due to copper (taking skin effect into account 
for both conductors).  There's an excellent paper by Frank Witt in one 
of the ARRL Antenna Compendiums (which Dean also edited) showing that 
window line exhibits significant dielectric loss at HF when it gets wet.

You can see the equation for coax on datasheets for Times LMR coax types 
on their website, with the equation for each cable type reflecting the 
physical constants for that particular cable. There are two terms, one 
for copper loss, the other for dielectric loss. Measured data for a few 
cables that I've measured track those computed curves, and if you put 
them into a spreadsheet and plot the two terms vs frequency, you can 
clearly see which terms are contributing.  I suspect that they are also 
used in Dean's TLW program. Right, Dean?

73, Jim K9YC