A nice pair

I am reminded of a Pink Floyd compilation album from the very early 70s. The music dates back to the late 60s and Syd Barrett. Poor Syd; shine on you crazy diamond!

I recently finished installing these rather nice GatesAir FLX-40 transmitters:

WXBK-FM New York, GatesAir FLX-40 x 2 installation

Audacy New York decided to move 94.7 from the East Orange, NJ location down to the WOR transmitter site in Rutherford, NJ. Acting as contractors for GatesAir, we installed these two transmitters. I can say, I like the liquid-cooled transmitters for several reasons. First, once installed, they seem to be very stable. I believe that the cooling scheme helps prolong the life of the RF devices by keeping the junctions at a constant temperature. Those semi-conductor junctions are tiny for the amount of current that they need to handle. Second, they cost less in the long run to operate. Anytime a refrigerant cycle can be skipped, that reduces or greatly reduces the electrical use. The Heat Exchangers in this system use VFD’s for fan motor control. That means more constant control over the HTF temperature and reduced electrical use on the fan motors themselves.

Heat Exchangers
Dual pump stations

The pump stations have backup pumps as well. In the newer transmitter firmware, the pump control needs to be set up to automatically failover to the standby unit. It is a couple of clicks in the GUI to do this.

BDI inline watt meter
ERI antenna

We didn’t have anything to do with the antenna installation, however, it is a good-looking antenna! ERI 4 bay 3 around mounted on one of the WOR towers.

Overall, this was a good project. Lots of moving parts during the installation, but we were flexible working with the client and other contractors and sub-contractors on site.

From the not too distant past…

And when such things were important:

Important Memo

While cleaning out a closet at home, I found a 3.5-inch disk with some interesting memos. When I left WGY in the spring of 1996, I made a backup copy of all the items in my documents folder. I figure it was an intelligent thing to do since I was still working for the same company in the role of Director of Engineering.

In those days, management wanted a precise accounting of all off-the-air incidents. The studio was staffed with a board operator who monitored the air signal at all times. Anytime the carrier dropped, there would be a note in the transmitter log. Those 5 second interruptions are likely due to thunderstorms. Lightning would strike somewhere nearby inducing an EMP on the tower. The venerable MW-50B would kill the PDM for a brief period as protection from VSWR. If I were at the transmitter site, the insulators in the guy wires would start crackling anytime a storm was within 10 miles of the site.

The helium balloon incident involved one of those metallic helium party balloons which escaped and ended up tangled in the 240-ohm open wire transmission line. This caused multiple VSWR trips for both the main and backup transmitters. I remember pulling up to the site and having a bit of a chuckle. By the time I got there, the balloon had mostly been burned into oblivion by the RF and the station was back on the air.

Another interesting item is our standard reception report form letter:

WGY reception report letter; name and address redacted because of the internet

These were printed out on WGY letterhead and mailed. I sent out several of them every week. I think the furthest away was Cape Town, South Africa.

Who has time to troubleshoot?

The model for Radio Engineering these days is such that one engineer is covering multiple stations in various locations. At the very least, this person has a full (if not overflowing) plate. Thus, when something breaks, the procedure very often is; to pull the suspected module or board, call the manufacturer and order a replacement. That works as long as the manufacturer supports the model in question or has parts. As we all have learned by now, replacement parts are subject to the global supply chain, which is tenuous.

Then there is the question of AM transmitters. Is it worth it to replace an AM transmitter these days? I suggest it would depend on the market and revenue. In some cases, yes. In other cases, keeping the older equipment running makes more sense.

Troubleshooting is becoming a bit of a lost art. In addition to the time it takes, we tend to be unfocused and obsessed with rapid gratification, ready for the next social media post. What is lacking is the ability to take apart the layers of a problem, accept our initial analysis may be flawed, move beyond those assumptions, and work until the issue is solved. Troubleshooting is often like a crime scene investigation. There are several logical steps;

  • Assess the current situation; take steps to ensure it is safe to proceed. Remove all power from the transmitter and don’t work on failed transmission equipment during thunderstorms
  • Gather evidence; look for fault indicators, alarms, automated log entries, burned components, abnormal meter readings, etc
  • Check external factors; power failures, lightning or storm damage, excessive heat, moisture, etc
  • Check internal factors; aged components, bad cables or connectors, improperly seated boards or components, and obvious signs of damage
  • Work from one side of the issue to the other
  • Check the maintenance logs (if there are any) to see if this problem has occurred before and what was the fix
  • Use available resources; troubleshooting guides provided in equipment manuals, factory support, and available test equipment
  • If a failed component is found, make sure that it is the problem and not a symptom of something else

Here is a good example of a recent troubleshooting evolution; I went to change over to transmitter #2 and these fault lights appeared:

DX-50 transmitter, faulted, no power output

The conversion error on the A/D converter indicates why the transmitter power output is zero.

The first step; secure the transmitter, remove all power, etc. Next, consult the book!

The Harris DX-50 manual gives good troubleshooting guidance. This transmitter was manufactured on March 22, 1990. It has been a reliable unit, to date. Section K.4 Analog to Digital Converter (A34) of the manual suggests loss of audio clock frequency sample due to the following;

  • Loose connection with the carrier frequency sample cable coming from the RF drive splitter (A15)
  • Bad or missing jumper connections on P-10, frequency divider section
  • Bad U-29 (74HC161, 4 bit binary counter, only in use if the carrier frequency is above 820 KHz, Not Applicable)
  • Bad U-12 (74HC14, Schmitt trigger)
  • Bad CR13 or 14 (1N914)

Fortunately, there was a working DX-50 about 15 feet away, so I was able to make some measurements at various places on the A/D converter board.

On the working transmitter (DX-50-1), at the RF sample input (input of R83) on the A/D converter board, I see a nice strong sine wave, on frequency:

WABC carrier from RF drive splitter to A/D converter board
WABC carrier frequency

Second, I measured the logic pulses on TP-6, as described in the manual. Those look good.

On the non-working transmitter, I made the same measurements and found a fuzzy sine wave way off frequency on the input of R83. The logic pulses on TP-6 were normal.

Definitely lost the RF sample. Since the transmitter is 32 years old, I suspected the cable (#92, RG-188 coax) between the RF drive splitter and the A/D converter had gone bad. Perhaps rubbed though on a rough metal edge or something like that. Several checks with a Fluke DVM showed that there were no shorts to ground or internal conductor shorts. End-to-end check on both the shield and inner conductor proved good. So, not the cable…

I then went on a bit of a wild goose chase suspecting the output from the oscillator to be low or the drive regulator power supply was defective. The drive level going into the PA was close to normal but slightly lower than the previous maintenance log entry. Also, drivers 8A and 8B were both on, which is not normal and made me suspect the drive regulator.

I made a call to GatesAir and spoke with a factory rep, who had me swap out the A/D converter, oscillator, driver power supply regulator board, and the buffer amp/pre-driver module between the working and non-working transmitter (while the low power aux was on the air). With the working transmitter close by, I was able to confirm that these boards or modules were not the cause.

Finally, I went back to the RF drive splitter and use my camera to take a picture:

DX-50 RF drive splitter (A15) J-17, board side

There is a 6-pin connector on the underside of the board (J-17). Pin 2 (from the right) is the center conductor and pin 1 is the shield of the cable going to the A/D converter board. Upon closer examination, the solder joint on pin 2 is suspect. I re-heated this connection with a soldering iron and viola, the transmitter started working again.

WABC DX-50-2, returned to service

The extenuating circumstances; the air conditioning at this site was slowly failing and that part of the transmitter was subjected to heat cycling several times. More recently the HVAC system was in the process of being replaced, of course, on one of the hottest days of the year. This pulled a lot of warm, humid air into the room. Also, as this is transmitter #2, it was not in regular use until recently (we began a procedure for operating on alternating transmitters for two-week periods).

All of this work took place over the course of two and a half days or so. That would be a lot of time for the module swap guys who tend to move on to the next outage quickly. On the other hand, buying a new 50 KW AM transmitter is an expensive proposition these days and there are very long lead times on some of these units. Being persistent and focused paid off in the end.

Filters for Over The Air Television

Many people are surprised that OTA TV (Over The Air Television) is still a thing. I am here to say that there are lots of TV stations still broadcasting. OTA is alive and well, especially around big cities. To wit; I noticed this older TV antenna on the roof of a transmitter building in Lodi, NJ. Being curious, I connected an ATSC 1.0 TV to the antenna lead in the kitchen. One scan captured 62 TV channels and sub-channels OTA in the NYC market.

Somewhat aged TV/FM antenna pointed at Manhattan

That site is 10 miles northwest of the Empire State Building.

I also noted that the satellite dishes on site have had Terrestrial Interference (TI) filters on the LNB’s for many years. Recently, 5G filters were installed as well. Thus, I added a 5G/LTE filter made by Channel Master (part number CM-3201) to the TV antenna splitter. A rescan captured 79 channels. Interesting.

I began ordering TV receiver filters and testing them with my network analyzer. There are many different units made by different manufacturers. The smaller, cheaper units do not have as good performance as the larger, more expensive ones. Go figure.

Here are a few sweeps of various filters:

Channel Master CM-3201 5G/LTE filter. Cut off 608 MHz
Silicon Dust USA LTE LPF-608M. Cut off 608 MHz
Phillips LTE-5G. Cut off 616 MHz

There is also an FM band-stop (Channel Master CM-3202), which is effective for blocking out 87 to 113 MHz.

Channel Master CM-3202 FM band-stop

Sometimes I get questions from non-technical readers, thus for the uninitiated; these sweeps are return loss. The higher the line on the right-hand graph, the less signal will get through the filter. A flat line at 0dB means that little or no signal is getting through on those frequencies.

These filters are helpful, especially with inexpensive consumer-grade TV receivers. If you live near an FM transmitter site, then an FM band-stop filter may help, especially with the low and high-band VHF stations. If you live anywhere near a cell site (and most of us do) then a 5G/LTE filter will likely help.

Happy cord cutting!