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Most engineers have had to open the back of the phasor and connect an OIB to a jack in an individual tower cable. This generally requires opening a phasor door or even occasionally removing a piece of the cabinet. It is not uncommon to find a slight change in the measured circuit values when the cabinet door is closed or the piece of cabinet replaced. I have also noticed this occurs occasionally when opening or closing ATU cabinets in the field. In view of the reliance placed on circuit values and measurements in the new computerized directional antenna proof of performance this may be a point worth considering by equipment manufacturers.
One of the bete noires of many station engineers (myself included) is the tapped inductor. This is a useful device, but in my opinion, in many cases its time has passed. For one thing, positive identification of critical tap positions is comparatively difficult to determine. Nail polish is still good, provided it doesn't unwittingly interfere with clip connection. But every time it is changed the flexible lead can also move and change reactance values. The actual tap changing also requires transmitter shutdown and reentry into the phasor or ATU. After this has occurred several times while trying to find the correct tap position, a good-enough position may be accepted through laziness or sheer fatigue.
The use of continuously adjustable inductances is preferred. Not only is correct tuning usually achieved more quickly, but precision adjustments can be made very easily via smooth turning panel mounted control knobs. There is no need to open cabinet doors or remove cabinet panels. Excessive transmitter ons and offs are avoided leading to longer component life and generally improved operational economy. Although continuously variable inductors are more expensive than tapped coils, the additional cost is worth it overall.
Even the lonely ATU inductor in a doghouse or all-weather field mounting would benefit from a change to a continuously variable coil. The time may be ripe now for phasor and ATU designers and manufacturers to look at operational flexibility in the design of such equipment. Maybe the upcoming generation of radio engineers will encounter a new ease of measurement as a facet of the Commission's new directional antenna proof rules.
E-mail Battison at firstname.lastname@example.org.
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