[TenTec] high swr for short time - can it do damage?

[Ken Brown]

the swr went to about 5 or 6:1 for a click of a mic second or two - this is the second time i did this (stupidity) - wondering if this can do damage? 

It depends.
> . the radio seems to be fine and didn't seem to have any problems with this short burst - but just wondering if this short duration high swr could do damage? by the way how high an swr is acceptable - just wondering? 
It depends.

A 5:1 SWR could be either a high impedance load or a low impedance load. 
With a 50 ohm source, your transmitter, 5:1 SWR could be a 250 ohm load. 
In that case the current supplied by the PA transistors, and the current 
drawn by them from the DC power supply, would be 1/5th of normal. This 
would most likely not damage anything.

On the other hand a 5:1 SWR could be a 10 ohm load. I which case your PA 
transistors would be trying to deliver 5X the normal current, and trying 
to draw 5X the normal DC current from the power supply. Even if you do 
not have a supply with current limiting at the correct level for this 
radio, your power supply will most likely not be able to deliver a full 
five times the nominal supply current for proper operation of the rig. 
Even if the power supply could do it, the resistance in the power cables 
and connector contacts would probably limit the current to some value 
less than 5X the nominal current.

The above is of course an oversimplification, since a high SWR is likely 
a partly resistive and partly reactive load. The simplification does 
serve to illustrate that "it depends".

Also since you say it was just a click of the mic, I am guessing the rig 
was in SSB mode, there may have been very little audio input to the mic 
input for that short period, and therefore very much less energy (power 
integrated over time) than if your mistake had occurred in CW or FM 
mode. Beware however that when in CW mode, the mic PTT button does work 
as a CW key, and you could be transmitting full power at 100% duty cycle 
when you press that button.

As others have recommended, it would be best to get the appropriate 
Ten-Tec power supply or other means of limiting the DC supply current in 
order to protect your PA transistors from mistakes like this. Also it is 
good to get into the habit of turning down your MIC and RF power knobs 
to their minimum settings while you are not actually ready to transmit.

DE N6KB