[Elecraft] QRO in a QRP Society

[Fred Jensen]

A good point was raised in the KPA800/KPA1500 threads -- those in this 
community (probably many) who are accustomed to QRP power levels and 
have never messed around with QRO need to beware.  We sure don't want 
any of our ham brothers/sisters hurt, and trust me, it does hurt (As a 
kid, I wasn't the fastest learner, but I did learn).  I think the RF 
actually cooks your tissues and the effects take months to heal.  And, 
it's always on your fingers ... those things you use the most.

I would not consider an inside antenna with QRO power levels, and even 
at 100W, the voltages can be truly astounding.  I once strung some bell 
wire around the living room of an apartment near the ceiling in a 
U-shape on push pins, and fed it with my S-line and a tuner.  The end of 
the wire was at the top of the wood moulding around the sliding door 
that opened onto the "patio."

At first tune-up, a 2" RF arc jumped from the end of the wire to a 
drywall screw covered by paint screwed into the metal stud, and started 
the corner of the wood moulding on fire.  Andrea and I were newly 
married.  Everything you can possibly imagine about her reaction to this 
example of physics is both true, and also quite insufficient to describe 
the ensuing "discussion" about my radio habit, the safety of living with 
me, and how the kids we had yet to make might survive to adulthood with 
me in the house.

Theoretically, the voltage at the un-fed end of an antenna is infinite, 
and Ohms law tells us the impedance is infinite too.  Infinities don't 
really happen in our everyday world, but an impedance of perhaps 5,000 
ohms on a lossy inside antenna is quite reasonable.  800 watts in 5K 
ohms yields 2KV at the end of the antenna.  Beware!

73,