Liquid cooling for transmitters seems a bit exotic to many radio engineers, but truthfully, it’s anything but. I was speaking with Don Backus of Rohde & Schwarz recently; he reminded me that liquid cooling has been used for years with the large AM “flamethrowers” of the ’50s and ’60s, as it was the only efficient way to push the heat out of the high-power AM tube transmitters.
Engineers who have exposure to TV transmitters will know that liquid cooling is prevalent there, both with solid-state and IOT-based transmitters. Liquid cooling is becoming more prevalent in FM transmitters lately. Don said that today’s liquid-cooled transmitters are actually safer, simpler and easier to maintain than air-cooled models — and far more efficient overall.
Most engineers have heard the “horror stories” of liquid-cooled transmitters springing a leak and spraying water all over the transmitter, causing major problems. Rohde & Schwarz has taken a number of steps to prevent this kind of problem, starting with the design of the amplifier and power supply modules. A channel is cut into the actual heatsink, through which the coolant flows. The modules use a quick-disconnect to the liquid cooling system, so that even if you forget to turn off the valve to the module before removing it, there is no fluid leakage.
To further simplify operation, liquid coolant is delivered to the modules and combiner from a single intake port inside the transmitter and then, after circulating, exits from a single outtake port seen in Fig. 1. There are no multiple hoses. Both ports are connected to the pump stand (Fig. 2), and the heat exchanger (Fig. 3), using industrial-rated hoses. A cross section of one of the hoses is shown in Fig. 4.
Another misconception is that liquid cooling requires more maintenance. So what are the regular maintenance tasks regarding the liquid cooling inside the transmitter? Don says there are none — plain and simple. Since a liquid-cooled transmitter has no fans for amplifiers, no fans for power supplies and no general cabinet exhaust fan or blower, there are no fans to check, bearings to replace or filters to clean or change. This also results in a much cleaner environment.
Besides the reinforced hoses, the system includes two additional components, the pump stand and the heat exchanger. The pump stand typically will have two fully redundant pumps per cabinet, and a cabinet can run up to 40 kW of FM power. Should one pump fail, the other can pick up the entire load and you remain on the air at full power. Typical maintenance on the pump stand is to change or clean the liquid filter once per lifetime, at about the one year mark of operation. Since it’s a closed system, you’re not likely to have any contamination of the fluid after any possible flakes or grit left over from manufacturing are removed with that first filter cleaning, so one filter change will typically suffice.
In addition to keeping the transmitter cleaner, Don pointed out, you don’t need to run your HVAC system for a liquid-cooled transmitter. Users will find their HVAC load will be greatly reduced, and power savings can be considerable, typically in excess of 13 percent.
The SNMP/GUI interface of your liquid-cooled transmitter will alert you to issues that may come up with the integral cooling system so you’ll know about any performance issues.
Get more information from Don Backus by emailing firstname.lastname@example.org. Tell him you saw the Workbench article.
Five years ago, Workbench outlined a project that Rhode Island Public Radio IT and Engineering Director Aaron Read completed to heat the satellite dish used to receive some of RIPR’s satellite-delivered programming. Ice is common in this part of New England, and the heated dish saved Aaron from clearing the dish after each storm.
Aaron has added an update to this project, using SNMP.
I had to laugh when reading Aaron’s piece. SNMP stands for “Simple Network Monitoring Protocol” but, Aaron writes, “There’s nothing simple about it!” Having worked with the protocol myself, I have to agree, but Aaron also points out that it is quite powerful, especially when linked up with the Burk Arc Plus Touch with SNMP Plus.
Aaron includes a useful tutorial in setting up SNMP monitoring, and you can find it online: http://ripr.org/post/theec-snmp-sfx4104-denkovi-wonkish and http://ripr.org/post/theec-satdish-heater-2-son-dish-heater.
Special projects engineer Dan Slentz writes about the new mics that are using 3 to 5V “Plug-in Power.” Headphone and microphone manufacturer Rode is making an adaptor that takes 12 to 48V phantom power, and converts it down to the 3 to 5V needed by these new mics, seen in Fig. 5. A neat feature that I noticed were the threads on the TRS connection (see Fig. 6). The TRS plug can be screwed down so it won’t come unplugged — a novel idea.
The 3.5 mm female TRS socket adapts to a male XLR, permitting the newer mics to be used with professional broadcast XLR connections. The adaptor is the Rode model VXLR+ and can be purchased from www.sweetwater.com for under $30. Search for Rode VXLR+.
Thanks to Sweetwater for providing the photos.
Contribute to Workbench. You’ll help fellow engineers and qualify for SBE recertification credit. Send Workbench tips and high-resolution photos to email@example.com. Fax to (603) 472-4944.
Author John Bisset has spent 48 years in the broadcasting industry and is still learning. He handles Western U.S. radio sales for the Telos Alliance. He is SBE certified and is a past recipient of the SBE’s Educator of the Year Award.