FM transmitters – Page 11 – Engineering Radio

Oh, damn: Una Parte

Guess what caught fire this time? It’s this thing, which has become the newest piece in my burned-up shit collection:

If you give up and are totally flummoxed, this is the IPA power supply regulator for a BE FM35A transmitter. Here it is in better days when it was actually working. The IPAs are in pull-out drawers on the right side of the transmitter cabinet, below the FX-30 exciter.

Said transmitter is aging not so gracefully, as it turns 26 this year. There does seem to be a finite life to transmitting equipment, something that should be kept in mind when planning out next year’s capital expense budgets. Regardless of all that, this event naturally occurred the day after Thanksgiving.

The good news, and there is always good news, we have many spare IPA regulators and PA modules in the shop ready to go. Upon investigation, there were numerous other problems with this transmitter, which have been or will be addressed.

Restarting a Harris HT35 FM transmitter

This transmitter was retuned from 107.9 to 92.9 and put back into service. Retuning an HT35 transmitter is no small matter, there are 32 pages of retune instructions. This unit is now in service as the main transmitter for WEZF, Burlington, VT.

The transmitter power output is 22,000 watts into a four bay, three around panel antenna, which gives it an ERP of 46,000 Watts at a height of 824 meters (2,703 feet) above average terrain. The tower is at the summit of Mt. Mansfield, which is 1,340 meters (4,395 feet) above sea level.

This is the Mt. Mansfield FM transmitter room. There are two TV stations in this building as well.

Final frames are of the WVPS Nautel NV-40 transmitter.

Australian Made Broadcast Equipment

Somebody working to preserve a record of past work:

Some of these have familiar looking cabinets and tube arrangements. They all look like classics to me and it is good that they are being saved. I noticed at the end of the video there is a Harris MW10A. As for the RCA Ampliphase transmitters; I maintained a BTA5J in Harrisburg PA on 580 KHz. It was reliable enough, but I could never keep it sounding good for more than a couple of days.

In any case, a worthwhile effort. More information at: AWA Transmitters.

Details

I found this small, yet very important detail on a DB-37 connector attached to the back of a Nautel V-1 transmitter:

DB-37 connector for Nautel V-1 transmitter

The black wire is the ground wire and the orange wire is the remote RF off command. A closer view:

DB 37 connector from Nautel V-1 transmitter

The transmitter had been shutting down unexpectedly since it was installed. When these shutdowns occurred, there was no overload, no fault, no power interruption or other indication of a problem. When the RF on command was issued, the transmitter would turn back on and run with normal readings until it shut down again. It was a bit of a mystery; the transmitter was removed from its mountain top home and hauled back to the shop to be repaired. It was connected to all sorts of test equipment and studied intently for many days. Still, the problem could not be replicated in the shop.

Then the transmitter was hauled back to its mountain top transmitter site and re-installed. It ran well for about a month and then started going off again. This time somebody looked at the event log and noticed that a “Remote RF off command” was being issued at the same time the transmitter would shut down. Ahhh, the missing bit of critical data. That prompted me to take apart the DB-37 connector used for the remote control interface. The problem was obvious as soon as I removed the hood.

Sometimes the most valuable piece of test gear is the venerable Mk I, Mod 0, EYEBALL.

I unsoldered the ground lead and put some heat shrink over the connection to the DB-37. Hopefully, that will take care of it.