Yagi Troubleshooting Guide
37
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Two or More Elements are Swapped:
This is easy to do if you don’t mark the 4 conductor cables before you tape them along the
boom. The SWR will usually be high on every band. Often by changing the controller
frequency, while keeping the transmit frequency fixed, the SWR may go quite low at a
higher or lower controller frequency. In any case of SWR problems don’t be surprised if the
SWR is okay when you switch to the 180 degree mode. If it isn’t good in the forward mode
you have a problem.
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If you Suspect Elements are Swapped:
First try to identify which one is the driven element. You can identify the driven element
easily because it has a much greater effect on SWR than the passives do. The driven element
is also very easy to identify by retracting all of the elements and then use “Create, Modify”
to extend each element individually until signals are heard in the receiver. Obviously you
will only hear signals when the driven element is extended. The best way to determine if the
passives are switched is to point the antenna in the normal mode at a station you know the
location of and then switch the antenna to 180-degree mode, if he gets stronger you probably
have switched the passives. If it seems like they are switched you can use “Create, Modify”
mode to “swap” the elements back by first recording what the controller says each one
should be and then go put the reflector length into the director and vice-versa for the director.
If the antenna now works normally you have swapped the cables of the two passives and will
need to correct the wiring.
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One or More Elements are not Moving:
If the driven is not moving you will have very high SWR at all frequencies. However, it may
have stopped at some length and you might have good SWR only at one particular
frequency. Set the controller to 14.200 Mhz and monitor the SWR at that frequency. Next
go into the “Create, Modify ” mode and vary each element length and monitor the SWR
while you do it (100 watts or less is okay) and watch for dramatic changes (.5 SWR change,
minimum). When you adjust the driven element driven you should be able to get an SWR of
5:1 or greater. Always return the element you have just tested to its original length before
testing the next one. The passive elements can only cause an SWR of 3.5:1 maximum no
matter what length you make them. Adjust the passive elements from minimum length to
maximum length and you should see at least a .5 change at some point. When the passive
element is near the length of the driven element interaction is the greatest and you should see
very noticeable change in SWR. You will find that Director 2 (on 4 element models) has
much less of an affect on the SWR because it is so far away from the driven element, but you
should still see at least a .4 change in the SWR reading. A classic symptom of one passive
element not moving is a high SWR in the normal direction and a markedly better SWR in the
180 direction.
If any element does not affect the SWR the cause is one of the following:
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Bad or intermittent cable, check it again.
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Damaged driver board in the controller
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Mechanical problem with the element
Be aware that lightning or shorting the cable can partially disable a driver chip and it will
still limp along moving the tape but you will see inconsistent SWR when changing from
band to band.
