Spiderbeam 160m Vertical Model 160-18-4WTH
27
160-18-4WTH Manual, Ver. 1.7 17-JULY-2021
4.1.1
It’s Time to Tune
With ground-mounted radials, the radials do not have much influence on the resonance
frequency. There is no need to adjust the length of radials. You will adjust for resonance by
adjusting the length of the vertical wi
re. If that doesn’t move resonance enough, the t
op-hat
wires will have to be adjusted.
Connect a
good quality
coax to the antenna.
Using an antenna analyzer or worst case a transceiver running very low power,
determine the frequency of minimum SWR of the antenna. Expect it to be outside of
the band. DO NOT TRANSMIT OUTSIDE OF THE BAND.
Write down your results. Record every step you take during the tuning process.
Note the frequency of minimum SWR & determine how many kHz it must be increased.
Calculate the amount of wire to be removed using 2cm per kHz as your initial formula
–
AND ONLY REMOVE ABOUT HALF THE LENGTH THAT YOU CALCULATED. BE SURE that
you remember how much wire you removed -
(write it down).
Measure the frequency of minimum SWR once again,
and write it down.
Determine how many kHz it has increased in
SWR
min
.
Now divide the number of cm cut off by the number of KHz of increase in
SWR
min
. The
result will tell you how many cm per KHz must be removed
at your specific QTH,
to
adjust
SWR
min
upwards.
Adjust the length again, but again cutting less than you calculated. It is better to achieve
SWR
min
in two more cutting steps, than to cut it too short.
Repeat this procedure until
SWR
min
is where you desire.
If you do cut it too short, simply solder some wire back onto it. Your kit contains 2m of
spare wire. Weather-proof the splice with liquid electrical tape or fingernail polish.
Problems may occur.
Perhaps you are unable to raise
SWR
min
far enough and now the vertical
wire is cut too short. No Problem. Just a little bit of work.
In that case, as stated above, simply solder enough wire back onto the vertical wire to
enable it to reach the connection box.
If you are only missing 10 to 30kHz, the easiest way to increase
SWR
min
(if you have no
more wire to shorten) is to move the 4 ground stakes for guying the top-hats closer to
the pole. Move them about 2 or 3m closer.
Check
SWR
min
again.
It should be possible obtain the desired
SWR
min
just by moving the top-hat ground
stakes, but if it looks like it is going to require a distance of less than 20m from the pole,
we recommend placing the stakes back out at 25m and shortening each top-hat wire by
50cm.
