PROBLEMS
If you find antenna monitor phase and ratio readings are off more than a few degrees or a tower radio is off more than 5%, then do not start adjusting the phasor to compensate. Keep your cool. Write down all the phasor dial readings for future reference. Do a complete physical inspection, including eyeballing the inside of the phasor cabinet and antenna coupling networks. Look for broken connections everywhere and on lines running to the towers. Go out and measure the monitor points. You may find they are in spec and that your real problem is in the antenna monitor or other part of the sample system. Jumping to the wrong conclusion could result in chasing your tail to fix an antenna problem that you don't have. 

TOO MANY KNOBS
An engineer maintaining a two-tower AM directional antenna station called me for advice recently. He is one of the engineers I am mentoring. A station's commonpoint impedance (RF input to the phasor) was difficult to adjust because the variable commonpoint resistance coil was at one end of its travel. All had been well a few months before. Today, solid-state transmitters want to see exactly 50 ohms with near zero reactance, as you know, so setting the commonpoint impedance correctly is very important. 

As it turns out, the phasor has phase and ratio controls for both towers. In this case, it was too many knobs.   The ratio controls could be tweaked on either tower to keep the station in specs. This led to the commonpoint problem when he used both to get the correct antenna monitor phase and ratio numbers. The phasor input matching network was looking at a phasor buss impedance that was not according to the original plan. 

PHASOR DESIGNS
It's important to understand how phasing systems are designed and built. A transmitter feeds RF power into a phasor cabinet, where there is a  three-coil impedance matching network. It feeds RF energy to a point called the buss. This is where power is rationed out to phase and ratio controls for each tower. The buss is rarely 50 ohms, and it is normal to have the impedance change a bit as an engineer tweaks phase and ratio controls to maintain FCC licensed specifications. The input matching network normally has enough operating range to compensate for these adjustments.    

Not all phasors have a front panel adjusted ratio control for the reference tower. That is for good reason. The reference tower normally gets more power than the other tower or towers. There is normally no need to adjust power to the reference tower after the station is initially tuned and licensed. It is the standard/reference that the other towers or towers are compared/referenced to. 

I told the engineer to carefully adjust the reference tower ratio control to full, or close to full on, while keeping the other tower ratio and phase correct. Then, don't touch the reference tower radio control again. Mark it as don't adjust.  That solved his commonpoint problem. He then had good resistance and reactance control because the buss impedance was as expected in the design. Also, running both ratio controls down to their lower ends could cause some phasor components to run hot. 

Phasor systems did not typically have front-panel adjustable input matching networks years ago when tube transmitters were the norm. That changed when solid-state transmitters came along. Now input resistance and reactance controls are required to keep reflected power low and transmitters happy. 

Fig. 1 shows a 1967 vintage Gates three-tower phasor. It did not originally have an input matching network that is adjustable from the front panel. I added those knobs to help control the input impedance and transmitter power when switching from 5 kW non-directional day to 5.4 kW directional night. One control is for resistance, which is tweaked to keep the input at the licensed 50 ohms. The other is commonpoint reactance. Fig. 2 is the dial I normally adjusted to get the transmitter to make just the right amount of power at night. 

In this case, the day non-directional antenna coupling unit has clips on fixed coils for adjustments. Once set, it was good to go. The maintenance procedure is to get the transmitter running at the correct power level in the day mode, then switch to night and adjust the night commonpoint reactance control to get the correct directional antenna power. It is that simple.

You'll also note there are FCC-required operating parameters listed on the front of the phasor and transmitter. They are right where needed most.     

Yes, that is a Gates BC-5H Transmitter next to the phasor. It has been in full service, running 5,000 watts day and 5,400 watts night since 1973. That's 46 years! This transmitter is on its third high-voltage transformer, third set of AC contactors, fifth set of high-voltage rectifiers and the solid-state audio driver section has been rebuilt four times on site without sending it to a factory for repair. The transmitter lives on, but will likely be replaced by my engineering successor when the next serious failure occurs. Fortunately there is a Collins 5 kW AM to back it up. Both are excellent tube designs. 

ANTENNA EFFICIENCY
Can you assume that all is well when the monitor points are below FCC limits? Not necessarily. You might have serious impedance mismatches and power divider mismatches, as described above. RF power could be turning to heat. 

You can get a readout on antenna efficiency by going to the original proof of performance documentation and making six or more measurements in the major lobe or lobes. The readings should agree, although there are seasonal variations. RF travels better over frozen ground so winter signals are inherently a bit higher. It is not a big deal in the first couple miles from the transmitter. Ground loss changes become more apparent the further out you go, especially at  20 miles and beyond.

OOS, OOM
Just because the phasor doesn't have active components, that doesn"t mean it should be ignored. Rodents get in sometimes and need to be dealt with. Loose hardware is common on RF contactors because they are usually operated twice a day with plenty of vibration in the process. RF contacts wear and should be replaced before they fail completely. 

HEAT
Get one of those infrared temperature meters and go through the phasor, then antenna coupling networks looking for hot spots. Use it around electrical load centers too. You might be amazed to find hot electrical contracts and wires that are about to fail. Best to take care of the problem before it causes an off-air emergency at a bad time.