Topband: T antenna or Cap hat?

[Eric Gustafson]

Hi Steve,

It sounds to me as though you should be looking for a bad
electrical connection.  This would have to be either between the
sections of the vertical conductor or between the vertical and
the top hat wires or between the feedpoint and the ground system.

Also, if there is any MW BC station anywhere near your location,
you might want to sweep the antenna with a TX and high power
directional wattmeter just to be sure that what you have is not
an instrumentation problem.  You may first want to find the
system resonance with a Grid Dip Oscillator and tune the top hat
wires to bring resonance into the band (after the bad connection
is fixed ;-).

It should not have been possible for the MFJ to indicate a
resistive component anywhere near as high as you state regardless
of how high the reactive component is due to resonance being out
of band.  It should be easy to get high SWR but it should not be
possible for that to be due to a resistive component larger than
50 ohms.  Radiation resistance should definitely be substantially
below 50 ohms.

See my other comments below.

73, Eric  N7CL

>My questions are:
>
>Is that a T antenna, or is it a short vertical with a capacity
>hat? (At the description of the T antenna one of the books says
>the horizontal wire should be about twice as long as the missing
>vertical part - that is, about 2x17 meters in my case, probably
>a little longer because of the slope of the wires)

These are really both the same thing so long as the top hat wires
are equal length (this is _really_ important) and symmetrically
disposed about the vertical radiator.

>Where is the problem? I thought the antenna should be about 25
>Ohms and resonate around 1830 kHz (based on calculations), and I
>even constructed a high-power 2:1 impedance transformer (S56A
>system) to match it to 50 Ohm coax.

You should be in the ball park once the system resonance is in
band.

>Sorry to ask these, but I am absolutely disappointed....

Don't worry.  Only unasked questions are not useful.  And you
will eventually track down the thing that is missing.





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