July 2011
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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:

MYAT 3 inch elbow

MYAT 3 inch elbow

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 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, bullets on order.  Unfortunately, we will have to take the station off the air to replace this.

WEBE transmitter site with partition removed

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 air flow.  All of the HVAC contractors who bid on the AC job identified it as an problem which 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 10pm 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.

Myat 3 1/8 inch elbow

Myat 3 1/8 inch elbow

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.

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4 comments to Hot Elbow

  • Ed B

    Paul are there any plans to put the digital back on the air?
    I see at the top hour ID they no longer ID the digital.
    Glad to see Cumulus is investing in a real AC system for that building. It has been on the burner for many years.

  • Paul Thurst

    Ed, at some point when the ac problems are taken care of, I think they want to turn it back on, but there doesn’t seem to be any urgency.

  • I guess the 3 or 4 people with HD radios haven’t noticed or complained, yet? 😉 Or are all of them station employees, so they already knew? 😉

  • Paul Thurst

    They may have received one phone call since it was switched off. I’d say that there are not too many people listening to HD Radio on WEBE. They probably have saved over $10,000 in electrical costs, in the mean time.

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