I made a test of ordinary TV twinlead years ago. I had a 200 watt PA and
my only exciter was for 80 meters. I hooked a foot or two of twinlead
with the end away from the tuner shorted to my link coupled tuner set
for series tuning. I was able to get a match. The tuner coil is 1/4"
wide edge wound copper strap. The capacitors are air variables with
probably 1/16" air gap. Key down for a while nothing, including the feed
line under test warmed up seriously. Then I cut the short off and
reconnected the tuner for parallel tuning to get the maximum voltage.
With the tuner resonated I got lots of corona off the cut ends but no
arcing. So I opened up the end insulation and added blobs of solder to
the sharp ends of the cut wires to hide the sharp edges that were
inducing the corona. Still no arcs at all the voltage I could muster.
Those are as extreme conditions as possible and at 200 watts the line
stood up just fine.
73, Jerry, k0CQ
On 1/9/2011 12:00 PM, Steve Hunt wrote:
Power handling really isn't an issue in this application. Connected to a
multiband doublet, the SWR wont get much higher than 10:1 on 300 Ohm or
400 Ohm cable. That would put the maximum localised current at just 1.8A
rms when carrying 100W.
Steve G3TXQ
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