A little transmitter "feature"

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BroadcastDoc
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A little transmitter "feature"

Post by BroadcastDoc » Wed Jan 08, 2014 10:00 am

This one is for Mr. Welton! ;-)

So, I get a call from a site night before last. The transmitter is running at about 30% power. So, I hop in the car and start to drive - it's 11:30pm and -22* outside. I flip on the radio, and can hear the station from about 40 miles out. Seeing as it's late and very cold, I make the executive decision that it's working well enough and head back home.

I go to the site last night to find out what happened. A little description for clarification: The transmitter is at a shared site, which is essentially a big, unheated pole barn. Inside are various rooms that are built with doors and insulated walls for the various tenants. My room, which is common in these parts, uses the transmitter exhaust as room heat. Because of the small room size and insulation, we've never had an issue with the room being too cold. In fact, even if the transmitter were off, it would generally be in the 40's - 50's in the winter.

OK - back to last night. The transmitter (a Nautel V5) has a "high reject load temp" alarm. I thought that was a bit odd, but I ack'd the alarm and reset the transmitter. Sure enough, the transmitter reset and came up to full power. So, I chalked it up to an anomaly. I figure since I'm there, I'll sweep out the room. So I prop the room door open into the "barn" area and start sweeping. All of a sudden the transmitter faults: "high reject load temp". I look at the front panel, and this is what I see for temps...note the bar graph:
IMG_20140107_211732.jpg
Hmmm. I scrounge up an electric heater, shut the door, and let the room warm up two degrees. All of a sudden I see this:
IMG_20140107_211933.jpg
And sure enough the fault clears!

The evil part of this? Once this fault triggers, the power on the transmitter drops, making it even colder in the room! Ahhhhh...the things you find during record cold weather! So new mental note: Don't let the room temp drop below 32*!
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Re: A little transmitter "feature"

Post by Deep Thought » Wed Jan 08, 2014 10:09 am

Somebody forgot to account for negative numbers on the alarm...if this was in degrees F it would never have happened. 8)
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Re: A little transmitter "feature"

Post by BroadcastDoc » Wed Jan 08, 2014 10:43 am

Fortunately it's a rare occurrence that the temp will get that cold.
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Re: A little transmitter "feature"

Post by RGORJANCE » Wed Jan 08, 2014 10:57 am

Many years ago when I was helping out at WISN in Milwaukee, we had a very severe winter storm. The chief was snowed in, but I could get out of my neighborhood. The Ampfet 50 Nautel shut down due to below freezing temps in the xmttr room. As I got to the site, I found the door to the building had a 12 ft. snow drift blocking it. The giant front end loader arrived about 5 minutes later, cleared the entrance and I got inside to find it was the same temp as the outside.

The cooling/heating system had gone nutso, and locked in on bringing in outside air. I was able to get the old tube 10kw RCA on to develop some heat, and the chief arrived shortly after that. We shut the air handling system down and unbolted the defective dampers to get the place warmed up. Took about two hours to get it warm enough to go back to the main xmttr. That was one nasty storm!

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Re: A little transmitter "feature"

Post by BroadcastDoc » Wed Jan 08, 2014 11:08 am

This room fortunately is always "warm enough" during normal winter temps - in fact it's usually comfortable with the TX running. This was just one of those oddball occurrences where the exhaust from the TX just couldn't keep up, especially when the TX power dropped!
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Re: A little transmitter "feature"

Post by kcbooboo » Wed Jan 08, 2014 1:14 pm

I know a lot of "new" broadcast equipment, especially pieces with a hard drive inside, have low operating temp ranges of around -40F (5C) because the lubrication in the disk bearings isn't happy when cold.

Does the xmtr really care if the temp gets down to 0F? Some do, some don't. I know of one site running a DAX-1 that puts out very little heat, so little the site needs a pair of 1500w heaters in the room just to keep it up to 40F. Seems a waste. The xmtr runs fine at 0F but none of the hard drives (in the other equipment) do. The backup MW-1A doesn't care either.

It sure looks like Nautel has a bug in their firmware as it is interpreting -1C as a negative (signed) value yet it's probably internally represented as 255 or 65535 which is a very large value, hence it trips the high temp alarm. Is there a way to display temps in Fahrenheit or even Kelvin? You'd have to adjust the limits accordingly but as was mentioned above, you'd be hard pressed to get the temp to -1F and it could never go below zero Kelvin.

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Re: A little transmitter "feature"

Post by BroadcastDoc » Wed Jan 08, 2014 1:52 pm

To be fair, Nautel rates their transmitters for 0c to 50c so -2c is below spec. I imagine that the transistors and other heat-generating components don't appreciate 30f air being blown across them!
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Re: A little transmitter "feature"

Post by techboywi » Wed Jan 08, 2014 2:03 pm

I was thinking of posting something asking if the extreme cold most of us are seeing has any impact on broadcast equipment. Are the solid state or tube transmitters more prone to problems in the cold?
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Re: solid state or tube transmitters more prone to problems

Post by RGORJANCE » Wed Jan 08, 2014 2:24 pm

Well, back in the dark ages, some tube transmitters used mercury vapor tube rectifiers which really didn't care for super cold temps if you were in a hurry to turn the rig on for sign-on. Like if you came in one minute before sign-on and needed to get on the air in a hurry. They need to be cooked for a bit on the cold days before applying plate voltage. They do tend to arc and spark when cold, kinda like me. It can be pretty impressive.

On the other hand, some transistorized rigs don't care much for the cold, reference my post on the AMPFET 50. That is the only situation I can remember encountering. And the temp that day was either zero, or a bit lower with a very, very strong wind causing what they call "drifting and blowing" around here.

Wisconsin only has two seasons----winter and tourism.

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Re: A little transmitter "feature"

Post by NECRAT » Wed Jan 08, 2014 4:18 pm

The HT-10 with the DigitCD exciter for WAQY in Springfield had similar issues. The room they were (are) in, is a poorly conditioned "add on" room to a 1953 building, with a supplemental heating/cooling system that until it was replaced, had been touchy at best. The room one night dropped to around 35° with all the gear running and it caused the exciter to drift off frequency, far enough to dump the rig. (At the time the exciter wasn't mounted in the rig, but rather in a nearby rack). We got the 11:30pm call (we owned the building and maintained that heating system), and ended up rigging up a space heater to get the rack heated, and a more permanent heater was installed near that equipment to keep it going. (The station has an offsite backup transmitter at the studio that was put into use until the main could be heated up back onto frequency)

Since then, the transmitter has been relegated to backup duty to a Nautel NV20.
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Re: A little transmitter "feature"

Post by TPT » Wed Jan 08, 2014 5:41 pm

Hop over to the FM thread where I report on an Energy-Onix exciter that wouldn't work when it got cold.

BTW: Was 51 here in southern Ohio on Monday. Unfortunately, that was the inside temperature in my living room. 1900's vintage big old house not built for -6 weather.

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Re: solid state or tube transmitters more prone to problems

Post by ChuckG » Thu Jan 09, 2014 12:03 am

RGORJANCE wrote:Well, back in the dark ages, some tube transmitters used mercury vapor tube rectifiers which really didn't care for super cold temps if you were in a hurry to turn the rig on for sign-on.
They didn't much care for being set on their side either, lol. You'd have to bake them all over again. Some of us built baking jigs out of old filament transformers and kept a spare set in the rack ready to go to avoid the 'cr-ACK' followed by lights out.

Our Gates 5 had issues with cold temps a few years ago, I had a PA board torid crack one morning at power change when the building heater failed. Got down to zero or so in there overnight.
Occasional problems years ago when stations used to sign off at midnight, the filaments alone weren't enough heat if it got really cold. The blower bearings in the old Gates AM transmitters would scream until they warmed up. They came up and ran though.
I think in general the older transmitters will have fewer problems in the cold, provided the crystal stays on frequency and the blowers turn at proper speed. The resistors and caps might change value a bit, but tube or simple transistor circuits won't care.

Newer electronics seems to be rated for a minimum temp of 32F, I'm curious why? Other than hard drives, what might have issues in the cold? Semiconductors shouldn't fail until -40C or so, no? Maybe I answered my own question with the Gates torid. :lol:
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Re: A little transmitter "feature"

Post by Deep Thought » Thu Jan 09, 2014 12:53 am

I know of a couple instances where mechanical grid and PA tuning/loading linkages snapped when the sleeve bearings froze up in old transmitters, but other than occasionally having to chase down an errant exciter it was mostly a temporary situation.

What gets me about Chris' scenario is that the computerized monitoring took the transmitter down, not an actual fault. Didn't we learn anything with the SX series AM transmitters? This sort of thing should not be happening and Nautel needs to fix it pronto.
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Re: A little transmitter "feature"

Post by ChuckG » Thu Jan 09, 2014 1:38 am

Deep Thought wrote: What gets me about Chris' scenario is that the computerized monitoring took the transmitter down, not an actual fault. Didn't we learn anything with the SX series AM transmitters? This sort of thing should not be happening and Nautel needs to fix it pronto.
In Nautels' defense, it probably doesn't get this cold in Canda! :mrgreen:
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Re: A little transmitter "feature"

Post by awsherrill » Thu Jan 09, 2014 9:22 am

I would guess a clip-on work light stuck in the bottom of a rack (with an incandescent light bulb, of course) would provide enough heat to keep critical stuff working. If there's room inside the Nautel cabinet, maybe stick one in there also.

I recall doing this at sites where we had all solid-state rigs, when I worked in the Midwest years ago.

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