Dave Schwarberg Transmitter Engineer WCPO-TV /
06.19.2013 01:41 PM
e2v Is a Transmitter Engineer’s Friend Indeed
e2v’s IOTs are really a dream to tune and operate
Dave Schwarberg

 

CINCINATTI —WCPO-TV, the ABC affiliate here, uses a 54.4 kW TPO Axcera Visionary UHF two-cabinet transmitter that first went into service in 2003 on Channel 55. It was converted to Channel 22 in 2010 and upgraded from IOTD2100 tubes (23 kW) to the higher power IOTD2130 (30 kW). An interesting problem occurred in April when we had a primary fuse blow in the circuit feeding the transmitter, shutting off gun and cavity air blowers. After restoring power, we found that we couldn’t bring the transmitter back up due to constant crowbarring.

COULDN’T HAPPEN AT A WORSE TIME
Unfortunately, this outage occurred shortly before ratings sweeps. While we were able to stay on the air at half power with the other amplifier, we really needed get back to 100 percent operation as soon as possible.

After several attempts to solve the problem ourselves, we called the good folks at e2v. (And this is where that company shines the most, as when you give them a call there’s always a live person on the other end. ) In no time we were connected with a couple of superior troubleshooters in e2v’s New York office, Dominic Piarulli and Mark Strohecker, who offered their services.

They suggested that we roll out the heavyduty test equipment, including a Hipotronics high voltage tester, to try and rule out failure of several transmitter components that could be causing the crowbarring. However, after completing these tests nothing unusual was found, pointing us back to the IOT with a suggestion that a thorough grid outgassing might be in order.

Dominic and Mark had theorized that the tube’s grid had overheated due to loss of the blower and that the high temperature liberated some entrapped gas.

(For those not familiar with grid outgassing, it involves connecting an external DC power supply to send current in the reverse direction through the grid element in a slow and controlled manner so as not to cause it to overheat or overload the ion pump associated with the tube.)

CURE FOR A BIG GAS PAIN
After our instruments showed that the outgassing process was successfully completed we were able to get the tube to take high voltage, and after a little retuning we were making power and back in business.

The wonderful phone support from Mark and Dominic couldn’t have been more helpful at a critical time. In addition to offering troubleshooting tips, they even sent us a loaner IOT to help us locate the problem.

In my experience, I’ve found that in happier (normal) times, e2v’s IOTs are really a dream to tune and operate. They feature a typical gain of some 22 dB, a very low noise floor and a beautifully linear sweep throughout the entire channel bandpass. This sort of performance, along with the level of customer support and service supplied by e2v, will certainly be factors to consider when it finally comes time to retube the transmitter (and based on our experience, this will probably be quite a ways into the future).

David Schwarberg is a transmitter engineer at WCPO-TV and has 46 years of RF experience. He may be contacted at dschwarberg@wcpo.com.

For additional information, contact e2v at 800-342-5338 or visit www.e2v.com.



Comments
Post New Comment
If you are already a member, or would like to receive email alerts as new comments are
made, please login or register.

Enter the code shown above:

(Note: If you cannot read the numbers in the above
image, reload the page to generate a new one.)

No Comments Found




Thursday 10:05 AM
NAB Requests Expedited Review of Spectrum Auction Lawsuit
“Broadcasters assigned to new channels following the auction could be forced to accept reductions in their coverage area and population served, with no practical remedy.” ~NAB


 
Featured Articles
News Technology
News Technology
Discover TV Technology