When WTTA-TV in Tampa, FL, installed an Ai two-tube ESCIOT depressed collector analog/digital transmitter last June, it saved $13,000 per month in operating costs.
Any long-time reader of this column will remember the author's continuous rants regarding maintenance. The argument has been made repeatedly that the least expensive action to increase both equipment life and performance is to perform regular and careful preventative maintenance. It doesn't take long, if done regularly, and the results are beyond argument.
The pity is that many of the large decisions at broadcast stations aren't being made by broadcasters anymore. Instead, some idiot with a fresh MBA looks at the books with the idea of improving the bottom line. Not understanding squat about the technical side of the business, the decision is made to get rid of those expensive technicians. The thinking is that modern equipment doesn't take all that work to keep it running — after all, his PDA doesn't require maintenance. That is the kind of thinking that leaves far too much work for the reduced technical workforce for them to be able to really care for their equipment.
The continued erosion of the technical workforce is also coupled with the really stupid idea of simply leaving everything alone until it breaks and then fixing it by doing the minimum necessary to get back on the air. That kind of thinking is similar to those who test for 240 v.a.c. by touching the wire.
Keep it clean
On the positive side, there is some merit to the argument that modern equipment is highly reliable — not necessarily a lot more than well-maintained older systems, but somewhat better. The biggest difference is in the exotic control systems now built into new transmitters. That refers to those systems that sample the output of the transmitter and use measurements to adjust the precorrection circuitry. That action corrects for a family of ills and can keep the on-air signal looking beautiful in the presence of otherwise severe problems. Still, there are some things that the station staff can do to help the situation and improve the useful life of the equipment.
First, and simplest, keep the equipment clean. That exotic solid-state transmitter is loaded with expensive devices that are not in love with heat. Allowing a heavy dust build-up reduces the ability of the cooling system to carry away the heat normally generated inside the equipment. Therefore, everything runs hotter than the design value, reducing the MTBF, increasing the down-time for the equipment, adversely affecting the overall performance and generally causing the management to get upset.
Check the voltages
It is a simple thing to periodically, at least once a month, shut the transmitter down for a couple of hours. Clean and/or replace the air filters, vacuum and/or wash the equipment (don't blow it out; that only moves the dirt around), and do a simple visual check for any problems.
Examine the precorrection circuitry
Next, go through all the power supplies and check that the voltages are correct. Most of these can be checked from front-panel metering, but there may be some low-voltage sources that require metering. Remember that the first criteria of system design is to determine the power supply voltages to be used. All the circuit design work follows from that point. If the power supply voltages vary significantly, the whole system performance will suffer.
Remember that all the precorrection circuitry is intended to predistort the signal to compensate for the errors inherent in a properly functioning system — that is, not a system that has major problems in its own right. As an example, an improperly tuned amplifier may stretch the ability of the correction circuits beyond their ability to adequately clean up the signal.
Remember the transmission line system
Turn off the corrections, and look at the system in its raw state. While the performance will certainly not be as sharp as would be desired, it should be reasonable. If not, look into where the big errors are being introduced. It may be possible to make some minor tuning adjustments to bring the system closer to proper performance. Doing so will allow the precorrection circuitry to perform as designed without having to cover up other improper operation.
Any discussion of maintenance at the transmitter would be incomplete without remembering the transmission line system. Two items should be checked. The first is the VSWR indication on the transmitter or transmission line monitor. In a correctly operating system, absent icing, the VSWR meter should be so stable that it looks like the needle is painted on. If it changes, a problem is either developing or has developed. There is only one way to respond to a VSWR change. That is to get someone in who can properly sweep the antenna system. If you're lucky, it will be possible to identify the cause of the problem and get it fixed before you end up sitting quietly looking at a cold transmitter and holding some burnt pieces that fell off the tower.
The other item worth checking is the pressure on the line, whether it is waveguide or coaxial cable. Yes, you must keep it pressurized; it does not matter how tight you think the line may be. Water will get into a transmission line unless there is a pressure difference between the inside and the atmosphere. If a dehumidifier is being used, check the desiccant, if used, to confirm that the air being placed into the line is actually dry. In the alternative, check that nitrogen still is available from the bottle in the system. Occasionally, actually check at the line to ensure that there is pressure in the transmission line as opposed to just in the little plastic tubes.
Now, for the cost part. A couple of years ago, EEV, now e2v, announced a new type of klystron. The company attached a water-cooled MSDC collector to its conventional plug-in klystron. The result was a device it called the ESCIOT, which demonstrated greatly improved efficiency.
The data shows that the efficiency for a 30kw device is improved from 40 percent for a conventional klystron to 59 percent for the five-stage ESCIOT. No significant change is anticipated in expected device life, and the cost is not a major factor. The ESCIOT is available in either a three-stage or five-stage version. The three-stage version, which doesn't have as big an efficiency improvement at the five-stage, can be retrofitted into many existing transmitters.
Then, along comes Nat Ostroff, who has already proved his outstanding ability to take a fringe company and develop it into a real competitor. He is now president and chairman of the board of Ai, previously Acrodyne. He led that company through the development of a transmitter to use the ESCIOT that has been both popular and successful.
Ai recently issued a pair of press releases showing the costs involved in operating an ESCIOT-equipped transmitter in analog or digital service. Once you strip away the advertising hype, the fact is clear that operating costs are greatly reduced over conventional klystrons. One system is at WTTA-TV in Tampa, FL. The old system used a three-tube pulsed klystron transmitter. The new ESCIOT system uses two tubes for the same power output. The difference in the power bill is $13,000 per month.
The second transmitter was at WNUV-TV in Baltimore. The ESCIOT system replaced a 240kw pulsed five-klystron transmitter. For a period of one year, the cost of operation was reduced by more than $28,000 per month. Now that isn't peanuts, nor does it necessarily tell the total story. For example, the question would obviously be how much the efficiency is improved over other MSDC klystron systems. For more information, visit www.e2vtechnologies.com.
Don Markley is president of D.L. Markley and Associates, Peoria, IL.
Send questions and comments to:email@example.com