Fastest and Slowest Pattern Changes

[RadioFan2J3]

Two engineers were required for the transmitter switching, which was done every two hours to rotate between the three "main" transmitters to give each equal airtime.

I can understand the concept of rotating transmitters for equal air time, but changing transmitters every two hours seems to be excessive and opens up the possibility of problems 12 times a day.

One might think that if there really was a need to rotate transmitters, once every 24 hours would be sufficient. At the end of three days, the number of plate hours is still the same.

 

[1L6E6VHF]

Sorry for the delay in this, I had three failed attempts to capture the unique WNZK 690-to-680 frequency and pattern change (first because camera was in wrong mode, second because the change happened 20 seconds early, and third, when the change was 20 more seconds even earlier).

So, here is a link to the WNZK frequency and power change:

http://www.youtube.com/watch?v=hVX6XOu1agM

 

[davideduardo]

I can understand the concept of rotating transmitters for equal air time, but changing transmitters every two hours seems to be excessive and opens up the possibility of problems 12 times a day.

One might think that if there really was a need to rotate transmitters, once every 24 hours would be sufficient. At the end of three days, the number of plate hours is still the same.

I think, in part, it had to do with replenishing the water in the cooling system. And the other part was to let the whole unit cool off. Mexico City is at 7500 ft AMSL, so components get hotter than rated values. In fact, the transmitters were built on the floor, inside cages, instead of in cabinets so that cooling would be better.

 

[RadioFan2J3]

I can understand the concept of rotating transmitters for equal air time, but changing transmitters every two hours seems to be excessive and opens up the possibility of problems 12 times a day.

One might think that if there really was a need to rotate transmitters, once every 24 hours would be sufficient. At the end of three days, the number of plate hours is still the same.

I think, in part, it had to do with replenishing the water in the cooling system. And the other part was to let the whole unit cool off. Mexico City is at 7500 ft AMSL, so components get hotter than rated values. In fact, the transmitters were built on the floor, inside cages, instead of in cabinets so that cooling would be better.

Interesting. I had thought it might have it might have been related to cooling, and I guess it took about two hours of operation for the heat to build up, as you point out.

All of the water cooling and vapor phase cooling systems I've worked with could all be filled, well, more correctly, topped off, without taking the transmitter off the air. If the water levels were too low, we always got a cooling fault, or supposed to get one.

 

[kenglish]

This reminded me of the old KSL-AM transmitter, which had it's very own water "still" (distillery), complete with a license.
Funny! The Mormons haven't made booze since Brigham Young's days.

 

[FreddyE1977]

I can understand the concept of rotating transmitters for equal air time, but changing transmitters every two hours seems to be excessive and opens up the possibility of problems 12 times a day.

That almost sounds more like union contract boilerplate than any sort of technical requirement.

 

[davideduardo]

I can understand the concept of rotating transmitters for equal air time, but changing transmitters every two hours seems to be excessive and opens up the possibility of problems 12 times a day.

That almost sounds more like union contract boilerplate than any sort of technical requirement.

No, it mostly had to do with the fact that the transmitter used an open-air chilling pond for the water that was recycled through the high power tubes. Due to the peculiarities of altitude, and the dry dusty air in the area of the transmitter site, they wanted to allow the particulates in the water to settle to the bottom of the pond every few hours.

The station also had its own water distillation plant on site, and they periodically cleaned the ponds and put new distilled water in the system.

I do have the feeling that some of the procedure was overkill by a station that, in the 30's through the 50's often had 25% or more of the radio listening in Central Mexico, and was a true herd of cash cows.

The transmitters were home-made, with 3 x 250 kw MW transmitters on 900 kHz and two short wave transmitters as well. All were housed in a roughly 600 sq meter building and kept meticulously clean. There were always at least two engineers on duty, as well as a staff to maintain the grounds and the building.

I don't think the engineers and groundskeepers were unionized; the announce staff definitely was (Sindicato Único de Trabajadores de la Radio, Televisión y Ramas Anexas).

 

[davideduardo]

All of the water cooling and vapor phase...

Vapor phase and Ampliphase. Two of the more notorious "Engineers' Full Employment Act" devices.

The Vapor Phase apparently keep the local fire department in business in a couple of places, too.

 

[RadioFan2J3]

[Vapor phase and Ampliphase. Two of the more notorious "Engineers' Full Employment Act" devices.

The Vapor Phase apparently keep the local fire department in business in a couple of places, too.

I guess I am missing the connection between vapor phase cooling sytems and fire department activity.

Gates/Harris, Continental, Hughes, and GE seemed to do pretty well with vapor phase cooling systems. The Hughes transmitters had their own problems, but transmitter cooling wasn't generally a problem.

Steam leaks were sometimes an issue, but probably not as much of a concern as a water leak. One major concern with a vapor phase cooling system is that it was difficult to do major troubleshooting right after operation, as the tube and boilers were, well, hot, and it would take some time for the hot side to cool down enough to handle the tubes and the steam lines. Made for much smaller water flow requirements.

You will have to clue me in on the relationship between vapor phase cooling and fire departments.

 

[davideduardo]

You will have to clue me in on the relationship between vapor phase cooling and fire departments.

The Gates / Harris VP rigs had several incidents of leaks > shorts > fires.

 

[RadioFan2J3]

You will have to clue me in on the relationship between vapor phase cooling and fire departments.

The Gates / Harris VP rigs had several incidents of leaks > shorts > fires.

Fires due to water and steam leaks?

Interesting. Are these incidents due to vapor phase cooling system design flaws or the result of poor maintenance? I suppose in the grand scheme of things, it might not make much difference, but one is more easily controlled.

I am not aware of fire issues with any of the vapor phase cooling systems I’ve worked with. I just talked with someone operating a VP-100B Gates/Harris vapor phased cooled system - fire was never a concern. Arcing on some coils, but that wasn’t cooling system related.

The biggest concern with the vapor phase cooling systems is the control circuitry, specifically, the water level controls to maintain the minimum and maximum water levels in the tube boilers. Maximum levels might not be much of a problem, as a simple overflow line would simply divert the excess water to a drain. Below minimum water levels could have major issues, as the tube would overheat and fail, but as soon as the tube elements distorted, current overloads should drop the transmitter high voltage.

I am not saying there have never been issues with vapor phase cooling systems, but if leaks in a vapor phase cooling system have resulted in fires, one might think there would be an equal issue with water leaks in water cooling systems. Water is water.

Air cooling is fine, up to a certain point, but there limits to effective air cooling in transmitters.