[Elecraft] Balun at input or output of tuner

[Ignacy]

Dean,
Nice analysis.

One can take it a step further. Assume your 3 foot RG-213 balun that
dissipates about 8% of power or about 40W for 500W input. It would contain
some 36 beads and would weight perhaps 2 pounds.

An input balun with identical choke impedance would be a single bead with 6
turns of RG-174. One foot of RG-174 has 1% loss at 30 MHz and 0.25% at 2
Mhz. Also RG-174 is rated 200W average at 30 Mhz and 750W at 2 MHz. Most
likely it would carry 500W intermittent on 10m when matched. 

In this case, an output balun would weigh 36 times more, be 36 times more
expensive, and have 8 times higher losses. Mind this is for extreme 3000 Ohm
load. 

I would not use an input balun for large stationary setup because stray
capacitances and switching would make it less efficient and cumbersome. I
would use an output balun in portable situations because it is so much
lighter, has so low losses, and one can have very large common impedance by
adding extra turns. 

Ignacy, VK2/NO9E


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