Topband: Trap for 160m/80m inverted L

Jerry.Van jerry.van at
Fri Dec 9 10:17:33 EST 2005

After being licensed for almost 45 years now I'm thinking I'd like to
try my hand at 160m at my new QTH.  I'd like to start with an effective
and simple to install transmitting antenna and am thinking an inverted L
would fill the bill.  Since I also have some desires on 80m it would be
an advantage to build a wire trapped inverted L ala ON4UN's latest book,
Chapter 9 sections 6.4.1 and 6.6 (Battle Creek Special).  The
information discusses the impact of various L/C ratios to produce a
compromise bandwidth on both bands with a trap resonate frequency of
3.65 MHz.  A resonate reactance of around 200 ohms seems to produce a
reasonable compromise.

If possible I'd like to avoid building my own trap assembly and am
wondering if a commercially available trap, a Unadilla KW80C (80m CW),
would be an option that would have a ballpark reactance of 200 ohms.  In
an exchange of emails with Unadilla all they are willing to divulge is
the resonant frequency of 3.625 MHz which is fine.  But they seem
unwilling to tell me the reactance at this frequency nor are they
willing to divulge the inductance or capacitance values of the trap.

Is there anyone out there that has a KW80C not connected that could 1)
measure the resonant frequency with a grid dip meter and 2) measure the
length, diameter, and TPI of the coil?  With that I could calculate the
inductance and then the resonate impedance on my own.

If anyone has other ideas my ears are wide open.  Thanks in advance for
any assistance.

Jerry  N8BM

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