BUT, the requestor has a MOSLEY TA 33 Jr., not a Hy Gain.
The Mosley instruction sheets are pretty sparse and only thing you get is a
chart for sliding the tubing in and out to get either CW portion, or SSB
portion of the bands.
Without the chart for any beam, simply measure where the resonant frequency
is in each band with an Antenna Analyzer at the feedpoint or on short coax.
Point the beam straight up and have the reflector on wood sawhorse or stand.
You lengthen elements to lower frequency, shorten by swaging more into each
other to raise frequency. Thus a beam is longer if set to CW portion of
bands.
You see where it is set now. If only the highest band is not where you
want it, you adjust the tubing inside the trap to center section. If the
lowest band is affected, start with adjustment toward the outside of the
last trap. Mosley uses double traps in one enclosure, thus 10 and 15 are
the innermost tubing, and 20m is the outer tubing.
Each adjustment must be done equally on both sides of the antenna.
When you first measure the antenna, place that frequency down, and measure
the length of the affected section and record that as well.
Now set up a ratio calculation, The frequency of resonance as measured, is
to the desired center frequency as the length measured is to X, the final
length to which you adjust. In over words, Fr over Fd equals Lm over Ld
where m is measured, d is desired, r is resonance.
This same technique can be used with dipoles, and verticals. The only trick
with trapped antennas is to pay attention to the facts that shorter tubing
is for highest bands, and overall tubing length sets the lowest band.
Naturally, the adjustments may interact, and to preserve the lower bands
after adjusting the highest may require length adjustment outside the high
band trap, ie toward the free end of the beam elements.
Don't forget to make the same percentage change to each element, not the
same length change, since a reflector is overall longer than a driven and
that longer than a director element.
73,
Stuart K5KVH
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