We just finished installing one of these units on Mount Beacon for WSPK. Mount Beacon is around 1,500 feet high and is accessed by a road that is a little bit rough. After the snow flies, the only way to get there is a snow machine or perhaps a helicopter. Thus, whatever is installed there needs to be reliable.
BE STX 10 mounted in Middle Atlantic Rack, WSPK, Mount Beacon, NY
My first comment, I recall 10 KW FM transmitters being much larger. This unit is pretty compact and we probably could have fit two of them in this Mid-Atlantic rack had we wanted to.
BE STX 10 FM transmitter
The transmitter itself is pretty simple, four RF modules powered by seven OEM switching power supplies with two fan power supplies, one for each fan unit. This is driven and controlled by an STXe 500-watt exciter.
The back has a 1 5/8 inch EIA flange output, some power connections, remote control interface, etc. Pretty simple overall.
I can also say, there was a noticeable improvement in the audio quality when this was placed in service.
This is the second time I have installed one of these liquid-cooled transmitters. This time, it is for WVPS in Burlington, VT. WVPS is the flagship station for Vermont Public Radio. The station is a full class C, a rarity in the North East. The transmitter is located on Mount Mansfield giving it a HAAT of 2,717 feet (828 Meters), which is a good way up.
GatesAir FLX-30, WVPS Burlington, VT
This transmitter replaced the previous backup transmitter, a Harris Z16 unit from the early ’00s. There was nothing really wrong with this unit, it just was not a full power backup.
Harris Z16 transmitter
The new transmitter came in two pieces, which is typical for the 30 and 40 KW GatesAir liquid and air-cooled transmitters.
New Transmitter, being placed in Radio Transmitter room
For the cooling part of this installation, 1 1/2 inch type M copper pipe was used. This matches most of the other TV transmitters down the hall. In the same building are the transmitters for WCAX-TV, WPTZ-TV, WFFF-TV, and WVNY-TV.
FLX-30 Heat Exchanger, outside with all the othersLiquid-cooled transmitter piping, WCAX’s left pair, WVPS right pairAir purge valve, sight glass, cross-connect and distribution manifold, above the transmitter
The highest point in the liquid-cooled system is the air purge valve and distribution manifold just above the transmitter. From here, everything slopes down to a few low points; the heat exchanger outside, the pump station, and the power blocks. This is to make it easier to drain if that ever needs to happen. There is also an air inlet valve to aid in draining.
GatesAir pump station
All of the cooling work is controlled by the pump station. The fans are connected to VFD modules, which control the flow of air through the Heat Exchanger.
Milwaukee Press Tool
All of this plumbing work was greatly sped along with the use of this Pro Press pipe press tool. This thing is great! No more sweating connections. Dry fit a section to make sure that it is all cut correctly, then go to work with this and it is done in a matter of seconds. Of course, there are no re-dos, so the dry fit procedure is a little more important.
System flush and pressure test
Prior to filling with Heat Transfer Fluid (50/50 water/antifreeze mix), the system was first pressure tested with air, then filled with clean water for a 12-hour flush. The water was drained out and the filter screen was cleaned, then it was filled with the appropriate Heat Transfer Fluid.
Testing into dummy load, TPO is 25,995 watts with -14 dBc HD Radio
Final system checks, remote control test, and HTF top off and the transmitter is ready to go pending the HD Radio installation.
I am talking about the type of TV you need an antenna for. I have been installing a few of these low-power digital TV transmitters at various places and it is good work.
Anywave MPTV 2.2 KW digital TV transmitter, WCRN BostonLPTV antenna side mounted on tower in Quincy, MA ERP is 15 KW.
Anywave MPTV unpacking, rolling into the building, Ellenville, NY
This transmitter’s dry weight is about 500 pounds, which was a little bit too much for our appliance hand truck, so we built a ramp. They have a nice set of wheels on the bottom, so they roll into place.
Carrier power after pre-correction files updated
There are a few differences in the way things are done. First of all, there is a different set of acronyms:
ASI- Asynchronous Serial Interface, format for MPEG transport stream, max speed 270 Mbps.
SDI – Serial Digital Interface – Similar to ASI but can run much faster, up to 12 Gbps.
TS – Transport Stream, Encoded video and audio streams into the exciter. Same idea as composite audio input on an FM exciter.
TSID – Transport Stream ID, a unique number assigned to each DTV station and encoded with the transport stream.
PSIP – Program System Information Protocol, carries program and system data about the transport stream.
ATSC 3.0 – recently updated ATSC standard that allows TV stations to do more with their transport streams than before. Will also change the modulation from 8VSB to COFDM.
Then, some things that look familiar are called by different names, BNC cable vs ASI cable… I am a neophyte in the TV world, so there are still many things to learn.
EAS is still EAS, but now there is a locally generated video to go along with the audio.
A while back, some fool wrote their congressman because THE COMMERCIALS ON THE TEE-VEE WERE TOO LOUD, so there is something called CALM Act compliance.
However, at the output connector on the exciter, through the amplifier, filters, directional coupler, etc; it is RF and behaves like RF. Even more interesting; Mr. Doherty’s name is used to describe the RF amp. Doherty amplifier or Doherty modulation was designed by William Doherty for Western Electric in 1936. It was not until Continental Electronics began using it in their AM (317B) and Shortwave (420A) transmitters that it became known broadly. Old things are new again:
Continental Electronics 420A 500 KW Shortwave transmitter, Greenville site B
That picture is from my visit to Greenville, NC in 2017. This is the control console, the transmitter is behind the glass and takes up half the building. It was installed when the site was built in the early 1960s. The new Doherty UHF amplifiers use LDMOS devices, notably the BLF888E in the Anywave units.
Antenna sweep, channel 30 UHF slot antenna, WCRN BostonAntenna with channel band pass filter, Channel 30 WCRN Boston
The Channel Band Pass Filter is required by the FCC, basically, it ensures that the TV transmitter is staying in its allotted 6 MHz channel. They add phase rotation, as noted above. This is why pre-correction is needed to keep the ATSC signal linear across the entire 6 MHz bandwidth. RF is RF and we like RF.
I have been working on an AM station lately. WBNR signed on in 1959 and follows the now familiar AM trajectory; after making bank in the ’60s, ’70s, and ’80s, revenue declined, maintenance deferred, yada, yada, yada…
After a stint with a news-talk format, the station changed to “Real Country,” a few years ago. WAT! Music on the AM? Actually, it is doing quite well. The perception is that AM sounds terrible and nobody listens to it. The stock AM radio in my Subaru (made by Pioneer) sounds pretty good on AM. I have noticed that when I first tune a station in, it sounds narrow-banded, slightly better than a telephone. However, after a second or two, the bandwidth opens up and it can sound quite good. I have also heard this station playing at several local businesses. When we turn it off to do maintenance, the phone starts ringing. Clearly, somebody is listening…
This station is part of a three-station simulcast. The AM station to the north got rid of its directional antenna and added an FM translator a few years ago. That has made a big difference. Thus a translator was acquired for this station as well.
The translator was held up by an informal objection filed by Prometheus, Et. Al. as part of a blanket filing against all new translator licenses by the LPFM advocate. In any case, the Construction Permit has been on hand for a while, so the owner felt it was time to move forward with building out the new FM signal.
Hoisting the Shively 6812 antenna
Installing the single-bay Shively 6812 antenna on the side of one of the nighttime towers triggered some other things. A bit of the deferred maintenance was addressed; new stockade fences around all the towers replaced the original fences put up in 1988. Those original fences were falling down.
4 Tower antenna system, WBNR, Beacon, NY
The antenna system for WBNR is actually quite elegant, perhaps even beautiful. A simple two-tower system for the daytime array and a separate two-tower system for the nighttime array. The nighttime towers are top-loaded, adding about 30.7 degrees in electrical height.
The far tower
The CP for the translator required some extra steps because of the mounting on the night tower of the AM array. Before and after impedance measurements need to be taken on the tower in question. Another requirement of the CP, is a set of before and after monitor points need to be taken.
WBNR tower, with translator antenna side mounted at 381 feet (116 Meters) AGL
While I was measuring the base impedance, I decided to measure all the towers instead of just the nighttime tower that has the translator antenna mounted on it. This is a good point of reference if any problems arise in the future. Often, this information can be found in the technical paperwork from the original license application. Those files can be a treasure trove of information. Unfortunately, it appears that a good portion of the original paperwork is missing.
WBNR tower #1 Antenna Tuning Unit
The Phasor and ATUs are a late 80’s Harris product. They are actually in remarkable shape, all things considered. All of the RF contactors are Harris HS-4P motor-driven units. They are rated at 30 Amps, RF-RMS. I don’t think that they are supported by GatesAir. I have a small stock of spare finger stock and contact bars. I suppose, if I had to, I could make or adapt parts to repair.
Looking at the base currents and the base current ratios for both the day and night patterns (base current ratios are on the station license), the tower impedance has changed very little over thirty years. That is good news, especially with those 215-degree-tall nighttime towers.
The WBNR license application did contain an overall system diagram showing the Phasor and all the ATUs. It did not contain any component ids or other information. I scanned that in, created a vector graphics file, and expanded it to a 24 x 36 inch size. I was able to fit all the component values and other information on the diagram.
Schematic diagram WBNR day/night antenna systems
The other issue is the monitor point descriptions. They include statements such as “Point is marked with yellow and white paint on a tree,” or “In the northeast corner of the Texaco research facility parking lot.” Those references are long gone and I would prefer to use a set of GPS coordinates. Using the topographical maps from the proofs, I found each monitor point and then recorded a set of GPS coordinates for each. In the future, they will be much easier to find. If anyone is still doing monitor points, I would recommend this method.
Yet another problem; the phasor control system was damaged by lightning. The overly complicated Harris Phasor control card was replaced with something more straightforward and reliable. I designed a simple set of relays, one for daytime and one for nighttime, to change the antenna system over. The transmitter interlock goes through the relay contacts, so the transmitter PDM is killed while the power changes. Tally back from each of the towers is handled by a set of relays for each pattern, which is also interlocked with the transmitter. All of this prevents the RF contactors from switching hot, something that has caused some damage in the past.
W243EM is 100 ERP watts, non-directional with a 1 bay Shively 6812-1R antenna installed at 381 feet (116 Meters) AGL on one of the nighttime towers.
The transmitter is a BW Broadcast TXT-600. The power calculation is as follows:
ERP 100 Watts = 50 dBm
System gains and losses:
Transmission Line loss, 500 feet (152.4 Meters), RFS LCF78-50JA = -1.75 dB
Isocoupler loss, Kintronic ISO-170-FM = -0.8 dB
Antenna gain, Shively 6812-1R = -3.39dB
Total system losses and gains: -5.94 dB
TPO: 55.94 dB or 393 Watts
With all that work completed, the license application was filed to cover the construction permit. Once that was accepted by the FCC, program test authority was granted and the transmitter was turned on. Hopefully, with the translator on the air, the perceptions regarding listeners will change and the station can bill more.
I really enjoy working on Medium Frequency antenna systems. I don’t know why, but antenna systems in general are always fascinating to me.
