Re: KAT500 update

Posted by Ignacy on Dec 08, 2011; 11:17pm
URL: http://elecraft.85.s1.nabble.com/KAT500-update-tp7072932p7076303.html

It seems to me that the story is more complex than it sounds.

The input balun always works at low SWR and at 50 Ohm. It is very easy to have such  balun. A small balun would easily handle a KW without heating.

The output balun can work at high complex impedances. Ferrite baluns are known to absorb nearly all the power at high impedances (including BL200) and be very hot even at low power. Iron baluns work well with true balanced antenna but do not provide enough choking with less balanced antennas.

Even if there is balun on input, there are stray capacitances that can disturb the balance. Probably bigger for a bigger tuner and also bigger if a tuner is close to metal boxes.

Those who travel and use portable antennas such as random length wires, they find ferrite baluns on output nearly always hot on some bands. Now, I use Z11Pro where both antenna connectors and the control cable are looped through a toroid many times; antenna wires to the tuner are connected directly. No heating whatsoever. No hot touch to the radio. But the tuner is usually on wood 2 ft from the radio.

What can be done with portable tuner with single output cannot be done with 500W tuner in a shack with multiple outputs. So Elecraft's decision to not use the input balun is a good one. Balun on input would not be very effective but would increase costs. If an output balun heats up too much or doe not provide enough choking, change the antenna or the balun. Rules of QRO are different than rules of QRP or even 100W.

Ignacy, currently VK2/NO9E