The author is senior broadcast engineer, Educational Media Foundation.
Have you ever dealt with one of those “nightmare” sites? You know the type … Constant problems due to poor environmental conditions, no heating or cooling, and questionable power.
These sorts of hostile environments are the worst possible place for modern broadcast equipment. Top it off with the fact that the site is inaccessible for nine months out of the year without a dedicated snow vehicle and you have a perfect recipe for extended downtime.
Move the heat
That was precisely the description of KLCX(FM) and KWRY(FM), two combined FM stations in Southern Colorado mountain country.
These sorts of conditions may have been perfectly acceptable for tube rigs to keep chugging away (for the most part) but modern air-cooled solid-state rigs are far more reliable with better controlled environmental conditions.
In some cases, however, it may not be possible to improve environmental conditions at the site. Furthermore, when you can’t access the site, it’s hard to keep up with air filter maintenance in such a dusty environment.
If you are not able to air condition the room, it makes a lot of sense to move heat outside in other ways and eliminate fans in the transmitter cabinet.
I had seen the Rohde & Schwarz liquid-cooled FM transmitters at a trade show but had never encountered one in the field. Their liquid-cooled television transmitters, however, seemed to be popping up everywhere during the television repack.
The TV engineers I talked to absolutely loved them. There was some hesitation over using liquid cooling due to lack of familiarity, but for a site like this it was worth trying something completely different. Clearly the status quo wasn’t working.
We undertook a massive project to replace both transmitters (30 kW for KLCX and 10 kW for KWRY) as well as the entire RF system all the way to the antenna. The price was competitive with air-cooled options.
Once the installation of the Rohde & Schwarz rigs started, I realized it really wasn’t all that much different than installing any other transmitter. Yes, installing the liquid-cooling loop and heat exchangers required learning a few “different” skills but it is not nearly as difficult as one would imagine.
Overcoming the dust
The transmitters are very well engineered (as one would expect). My only complaint was that the documentation, while complete, was very utilitarian. I found it a little difficult to navigate at times.
Another thing I encountered is that setting power on these rigs is slightly different than you might expect. It is set as a percentage of the full output capability.
The percentage is not calibrated against your TPO. Output power is displayed in kilowatts. An actual TPO percentage will need to be calibrated in your remote control. I made the mistake of activating the “Power Sensor Calibration” function without truly understanding how this worked. Thankfully, the touchscreen control panel made adjustments easy to access on site. The mobile-friendly HTML 5 GUI mirrored the front panel and was equally easy to use.
The transmitters have been in operation since about October of 2020 and have weathered the winter well, including multiple power bumps.
We have seen a couple of minor issues (one almost undetectable leak at the pump stand, and an erroneous power supply fault indication on one of the modules). Neither of these minor issues has kept the rigs from operating at full power. The factory will be addressing both issues under warranty once the snow clears.
Between getting the heat from the transmitters outside of the building and eliminating any fans in the transmitter cabinet itself (aside from a small fan in the controller) it has made for a much more reliable environment.
It never ceases to amaze me that even at a dusty site like this, the inside of the transmitter cabinet is still as clean as the day it was installed. The fact that redundant power supplies are integrated into the RF amplifier modules and liquid-cooled as well makes for a very robust system.
While I don’t plan to move away from air-cooled transmitters entirely anytime soon, there are certainly situations where liquid-cooling would be a good option. It’s nice to have yet another tool available to work around these sorts of challenging site issues.
Radio World User Reports are testimonial articles intended to help readers understand why a colleague chose a particular product to solve a technical situation.
For information contact Rohde & Schwarz USA in Maryland at 1-410-910-7800; for international requests contact Rohde & Schwarz in Germany at +49-89-4129-0 or visit www.rohde-schwarz.com.