The GatesAir FLX-30

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 ways up.

GatesAir FLX-30, WVPS Burlington, VT

This transmitter replaced the previous backup transmitter, a Harris Z16 unit from the early 00’s. 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 others
Liquid cooled transmitter piping, WCAX’s left pair, WVPS right pair
Air 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 slops 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 though 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 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 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.

WEZF and WVPS four bay three around panel antenna

In this time of COVID-19

As most of you man know, I live in New York State (Hudson Valley region).  This is very close to the COVID-19 outbreak in Westchester County.  There has been one confirmed case in my town.  As such, we are experiencing the outbreak ahead of the curve from the rest of the country.  School has been cancelled for at least two weeks and perhaps indefinitely.   All public gathering places are closed; restaurants, bars, movie theaters, malls, churches, etc.  As a radio engineer, the COVID-19 virus has a several implications:

  • Things are still going to break and will need attention. The good news is that most transmitter sites are unmanned. The only social interaction my be during the travel phase (getting fuel, food, etc).
  • Many studios and offices are being abandoned as well. Over the last few days, we have set up DJ’s to operate from their houses.  Most sales and office staff have been told to work from home.
  • Broadcasters have been designated critical communications infrastructure, The Department of Homeland Security has issued letters that allow travel and procurement of fuel during the national emergency for critical personnel.
  • I managed, prior to the store shelves being emptied this weekend, procure some PPE.  I don’t know how effective it will be, but anything is better than nothing.
  • Since Hurricane Sandy, I have had in place many emergency supplies and equipment needed to restore service in the event of a long term interruption of basic services.

There are many long term economic implications. For commercial radio stations, the loss of income is going to be extreme.  As the virus has spread, businesses have cancelled pretty much all advertising.  During past disasters, radio was often the only means of getting information to the general population.  I am not sure if this is still the case.  How relevant is radio these days?

More AM work

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 60’s, 70’s and 80’s, 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 night time 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
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 night time array.  The night time towers are top loaded, adding about 30.7 degrees in electrical height.

The far tower
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, a set of before and after monitor points need to be taken.

WBNR tower, with translator antenna side mounted at 390 feet AGL
WBNR tower, with translator antenna side mounted at 381 feet (116 Meters) AGL

While I was measuring the base impedance, I decided measure all the towers instead of just the night time 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 paper work is missing.

WBNR tower #1 Antenna Tuning Unit
WBNR tower #1 Antenna Tuning Unit

The Phasor and ATU’s 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 night time towers.

The WBNR license application did contain an overall system diagram showing the Phasor and all the ATU’s.  It did not contain any component ID’s 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
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 a little more straight forward 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 night time towers.

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.

A few pictures

Some things I have been working on lately:

A nice row of transmitters
A nice row of transmitters

Finishing up a transmitter site rehab.  The BE FM20T is nearly 20 years old.  The BE FM2C transmitters are new.  There is also a rack of new fiber equipment and CODECs.  This site has good utilization; there are three stations on one tower with a shared STL antenna and generator.

Energy Onix ECO-6
Energy Onix ECO-6

Energy Onix ECO-6 tube type transmitter.  One of Bernie’s better designs, a grounded grid tube with solid state driver section.  This one needed some fans replaced and a new tube.

AM transmitter site.  Looks like these vines have not been cut in a couple of years.
AM transmitter site. Looks like these vines have not been cut in a couple of years.

I wonder how much the guy tensions have changed…

Noticed this after some particularly strong thunderstorms
Noticed this after some particularly strong thunderstorms

The reason why you do not use a POTS line phone during a thunderstorm.

USS Slater radio room
USS Slater radio room

I took a tour of the USS Slater, a museum ship in Albany, NY.  The museum has painstakingly restored the ship to its WWII configuration.  The main transmitter is the RCA TBL-8 seen in the left/center of this picture.  This unit put out 200 to 400 watts CW or 150 watts AM phone.  During the hostilities it was turned off as allied ships observed radio silence unless they were sinking (and sometimes even then).

A little ChiFi tube type RIAA phone preamp.
A little ChiFi tube type RIAA phone preamp.

I have been fooling around with this little 6AK5 preamp.  I find it works very well and sounds better than the built in phone preamp on my Kenwood VR-309.  The FU-29 tube amp did not come with a phone preamp.

This is a short video clip of an audio processor at one of our transmitter sites. The fancy lights around the control knob are designed for the program director. They are saying “Buy me… Buy me…”