tech stuff – Page 44 – Engineering Radio

Hot Elbow

Found this 3-inch rigid elbow to be a little warm when we were removing a dividing wall as a part of an AC upgrade:

As measured with my Fluke 62 mini IR thermometer, the temperature is 163°F (72.7°C) at the clamp and drops down in both directions.

This is at WEBE and this particular section of the transmission line is running 34 KW into the analog/digital combiner in the next room. The clamps are tight, but you can see a little scorch mark on the stainless steel clamp right over the slot in the field flange. That is where there is a gap between the outer conductors, which possibly means the inner conductor was cut slightly too long during installation. I suspect this and or a problem with the bullet is causing the heating issue. I was never (and still am not) a fan of those field flange-type elbows, I’d much prefer the flanged type with a field flange on the straight line section.

34 KW is getting into the semi-serious power level for FM broadcasting. At those levels, even small impedance mismatches can lead to big problems. We have a new elbow, field flanges, and bullets on order. Unfortunately, we will have to take the station off the air to replace this.

WEBE transmitter site with partition removed

This is all a part of an air conditioning project. There was a plywood partition wall between the front and the back of the transmitters which was impeding airflow. All of the HVAC contractors who bid on the AC job identified it as a problem that needed to be addressed before the big 5-ton wall-mount AC units were installed.

Update: Replaced elbow last night (8/4). Went off at 10 pm and back on at 10:25. Found the inner conductor had been pushed out of place and was off center on the outside (toward the wall side) of the elbow. This was an older elbow that did not have the nylon inner spacers on the center conductor. The inner conductor was dark purple. Before replacement, the elbow was 138°F (59°C) under full power (34 KW). After replacement, it was 97°F (36°C) as was the rest of the transmission line. At these power levels and frequencies, even small, minor imperfections cause impedance shifts and become issues.

I cleaned up and reused the bullets and the outer conductor with scotch brite. I also used more support wires because I believe the elbow was starting to pull apart, which can sort of be seen in the first picture.

The Onan RS-15000 Generator

It is a cute little thing. This one is being installed at a mountaintop transmitter site for a class A WKIP-FM in Ellenville, NY. It is way up in the air (at least by local standards) at 2,450 feet AMSL. As such, the TPO is only 300 watts into a one-bay antenna. Therefore, even this little generator will be loafing along. I added all the rack equipment up, both transmitters (main and backup), and the electric resistance heater and came up with a grand total of 6,300 watts. The working load today was 3,200 watts, which I would assume is about average.

Onan RS-15000 at transmitter site with ice shield

Denis, my sometimes helper, build an ice shield over the top of the unit with pressure-treated wood. This unit was placed about 40 feet away from the 140-foot tower, next to the concrete block building. Still, on a windy day, I could see some chunks of ice flying off the tower in this direction.

It has a Lister/Petter 1900 cc engine, 1800 RPM, 240-volt split phase generator. At 25% load, it burns 1.2 gallons of propane per hour.

This is annoying. The gas installer blocked access to one of the through holes in the bottom of the enclosure frame. Actually, more than annoying, downright annoying as it blocked the exact center of the hole. I had to move the regulator up about two inches so I could run the 1-inch flex under the gas line. This, in turn, led to some amount of swearing.

Gas supply to generator installed by selfish gas man — Gas supply to a generator installed by selfish gas man or woman

Another side of the engine:

Lister petter 4 cylinder 1900 cc engine — Lister Petter 4 cylinder 1900 cc engine

Pushrods going to rocker’s arms over the cylinders. Low-tech, under-head cam engine. That’s okay, so long as it works when it is supposed to.

Onan RS-15000 generator wired to transmitter building — Onan RS-15000 generator wired to the transmitter building

PVC conduit running into the transfer switch. The final connection is made with a liquid-tight flexible metal conduit (FMC). The control wiring is run in a separate 1/2-inch conduit, as required by NEC.

AM radio sucks! It’s horrible, sounds terrible and should be turned off!

This is a youtube video of a Police song from the 1980s received via skywave and recorded off-air on an AM radio.

Video Description:

The classic 1983 #1 smash hit, as received in analog C-Quam AM Stereo… in Japan… via nighttime skywave in the Tokyo area, roughly 500 miles away from Sapporo (ed: where the station is located). The audio quality is among the best I’ve ever heard from analog AM radio, thanks in large part to an excellent wideband receiver, very quiet band conditions, and the Orban Optimod-AM 9100 audio processor being used by HBC Radio to its maximum extent: 12.5 kHz audio bandwidth with stereo enhancement added (above and beyond the amount naturally provided by the matrix processing used by AM Stereo).

Absolute trash, I tell you. Just awful.

Of course, I know several FM stations around here that wished they sounded as good. Naturally, Japan, they have sought to minimize night-time interference problems by limiting the number of stations on the air and enforcing the rules and regulations in place to protect those stations on the air. They also seem to allow greater bandwidth, out to 12.5 KHz in spite of the narrower channel allocations (9 KHz in ITU regions I and III, vs 10 KHz here in the US, ITU region II). One other thing to note, there is no digital buzz saw occupying several channels of the broadcast spectrum. Keep in mind, this was received in Tokyo, likely a very high noise environment.

I was trying to find out the power level of the transmitter, the call sign is JOHR in Sapporo Japan, frequency is 1287 KHz. HBC is the Hokkaido Broadcasting Company, a privately held company. The state-run radio outlets in Japan are NHK, which has several radio and TV stations throughout the islands.

Anyway, AM is dead. Killed by the very owners of the broadcasting companies themselves with help from the NAB. They are the ones that petitioned the FCC to loosen up the allocations and allow more and more stations to be crammed into the band. That is old news. The new news is same forces that killed AM radio are diligently working their magic on the FM band as well. More stations, translators, digital IBOC nonsense that doesn’t work, more of everything. After all, more is better. Until it is not. Then it’s too late.

Secretly, I like it when things break, sort of

Not that I am a glutton for punishment or anything, but I enjoy troubleshooting. There is a certain satisfaction in the analytical aspect of tracking down a problem and fixing it, hopefully in a permanent fashion. Figuring out where a problem is requires a good bit of detective work;

Examining the clues; what happened before the failure, what are the fault indications, are there any external factors
Round up the usual suspects; a good maintenance log is helpful here to track re-occurring failures. If the failure cannot be attributed to an external source (such as a power surge or lightning storm), what was the last thing that was changed or worked on?
Following the trail back to the origin; Often the first failed part found is a symptom, not the actual problem. It takes some skill in reading schematics and making sense of a failure to trace it back to the real problem.

It can sometimes be exciting, like turning on the 25 KV high voltage supply and having big blue flashes issue forth from the top of the transmitter. Sometimes it can be quite frustrating, like when the station owners refuse to spend money to fix a problem. Sometimes it can be dull, like fixing the same problem over and over again because of the previously stated money problem. It’s also disheartening when the problem was caused by the stupid DJ spilling soda in the console. Not that all DJs are stupid, just the ones that spill things into consoles.

The challenge of finding the root cause can often be enlightening. I have often discovered unrelated problems waiting in the wings while investigating the why of an outage. It is great to fix those things before they burn the house down, but this approach often goes unnoticed by the ownership or management. Lately, for some reason, an ounce of prevention goes unnoticed or unappreciated.

There is quite a bit of science to troubleshooting, but there is some combination of personal traits that make a good troubleshooter. These are:

Inquiring or curious disposition. It is fairly easy to get to the first failed module or part. Discovering the reasons behind the failure and or getting down to the component level takes a good deal more effort.
Patience. This goes with the second part above, it takes some stick-to-it-tive-ness to trace out the not readily apparent problem.
Good analytical skills. Often failures generate a cause-and-effect scenario. The effects can be startlingly distractive and mask the causes and the underlying problem.
Ability to view the large picture. This is critical to discover outside influences and other issues that are indirectly connected to the system or issue at hand.
Ability to analyze the system design. This requires background training and experience to look at a circuit diagram and discover non-error-tolerant systems. Sometimes these systems can be modified for better fault tolerance.

Poorly designed equipment is the bane of the broadcast engineer. Equipment manufacturers can sometimes fail to follow two key principles: KISS and maintainability. KISS stands for Keep It Simple, Stupid. There is no better design criteria than the KISS principle. Adding layers of complexity increases the failure expectations. Maintenance can be something as simple as cleaning or changing air filters. Making maintenance tasks difficult almost ensures that they will not be done.

Eventually, all things wear out. It also takes some large-picture skills to know when it is time to replace equipment and that can vary greatly from situation to situation.