KC3VO modified his Tarheel antenna to handle a KW, as he demo-ed at a recent
club meeting and at Dayton. He told us what changes inside he had made but
I can't remember what he
said. 73 - Rich, KE3Q
----- Original Message -----
From: "Tom Rauch" <email@example.com>
To: "Jim Lux" <firstname.lastname@example.org>; "Towertalk" <email@example.com>
Sent: Wednesday, June 02, 2004 10:36 AM
Subject: Re: [TowerTalk] power handling limits of screwdriver antennas
> > What's the limiting mechanism and/or failure mode from
> running too much
> > power on a screwdriver antenna?
> I tested several antennas to destruction. The weakest
> frequency is in upper HF near 15-6 meters (depends on
> manufacturer and style) where the coils in some antennas
> have series-resonance. At those frequencies the coil is
> fairly easy to overheat in a short time with only a hundred
> watts or so. You can find the self-resonant point by
> sweeping the unit with the coil almost totally collapsed and
> looking for a base impedance that is abnormally high.
> At other frequencies, even a few hundred kilohertz off
> series resonance, the standard sized Tarheel and High Serria
> antennas took 400 watts or so for long periods of carrier.
> An MFJ cheapened antenna took less time to fail.
> I wouldn't be afraid to run a kilowatt PEP SSB or more,
> watching the SWR on a peak reading meter for a sudden spike
> as a warning something was arcing. For CW, 500 watts would
> probably be OK.
> > The 4:1 transformer or matching network at the base?
> I never use a 4:1, I always use a shunt coil. I never tested
> matching systems, except to say the tiny enameled wire used
> to match handles a kilowatt OK.
> I expect most antennas would fail by arcing limits for low
> duty cycle modes and by heating on high-duty modes like CW.
> The failure points I've found were always heat related in
> the coil. Away from coil self-resonance near the finger
> stock, otherwise in the area of maximum voltage where the
> coil is self-resonant.
> 73 Tom
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
> any questions and ask for Sherman, W2FLA.
> TowerTalk mailing list
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list