FM broadcasting transmitters
Did some work a while ago at a transmitter site that had three transmitters combined into one antenna. The site uses a Shively branched combiner:
Each transmitter can be tested into a separate 20 KW dummy load:
Transmitter themselves are Nautel NV15s:
Except for the one on end, which is an older BE FM20A.
Sometimes it is the little things that catch the eye. When I was installing a Nautel transmitter recently, I was admiring the circuit boards used for the transmitter controller. I have seen a few circuit boards that are functional, but leave a little to be desired in the form department. Does it really matter? Perhaps not, but often times those tiny, almost insignificant details come back to bite you. Little things like having the voltage regulator pins correctly placed or putting a toggle switch on the correct side of the board. I have seen both mistakes from another, well known transmitter manufacturer.
Anyway, these are a few photographs of some well designed, well laid out circuit boards.
This is the main controller board.
Surface mount components.
Logic chips.
Part of the harmonic trap for the XR series transmitters.
It really is the little things that make big differences. A circuit board under a cover that few people will ever see may seem like a very small and insignificant detail, but I notice and admire these things…
Something that I eluded to in a previous post, we finalized the move of the WSBS translator, W231AK, from the Fairview Hospital in Great Barrington to the side of the AM tower.
The move was started by hanging a new Shively 6812B antenna from the side of the AM tower, located off of US 7, north of Great Barrington. This is a half-wave-spaced circularly polarized antenna.
While this work was going on, some guy from OSHA showed up and started taking pictures without asking permission or telling anyone who he was. We informed him that he was on private property and asked him his reasons for being there. He got in his car and left, no doubt to a parking lot down the road so he could keep the tower climbers safe… mostly from themselves… by levying huge fines for free climbing… Wasn’t there something in the news about the government running out of money? Anyway…
WSBS had been using this translator for a few years. The advantages for the station from the translator move are greater power output (from 35 watts to 250 watts ERP) and less operating expenses in the form of TELCO line charges and roof top rental at the Hospital.
In addition to that, the reliability of the translator should increase, as there have been several instances in the past when TELCO line problems have taken the translator off the air for days at a time.
The transmitter for W231AK was changed from a Crown 35 watt unit to a BW Broadcast T600. These units are made in the UK and it is an all-in-one processor/exciter/transmitter. We took the cover off to make a few configuration changes and the entire unit is very well made.
One of the nice features of this particular transmitter is the screw-down clamping method of connecting the RF devices. Lets face it, unsoldering MOSFETS is a PITA. This screw down clamp eliminates all that.
The audio input and processing board is pretty neat too.
There are several different processing settings which we played around with. All in all, it seems like a pretty solid unit and I would recommend it to anyone looking for a low to moderate power transmitter.
We are scrapping several old transmitters these last few weeks as part of a site upgrade A couple of Harris FM20 and 10H transmitters are out the door.
Some people like these transmitters. I am not one of those. I found that they were of dubious reliability, tended to drift out of tune and have AM noise problems, and had multiple catastrophic failure modes. If it was not tuned just right, it also had a tendency to have HF oscillations and internal arcing in the PA cabinet.
This transmitter had a non-factory authorized modification installed as a tuning aid. Tune for best efficiency, and minimum AM noise then check and see if it is arcing. It is also advisable to wear hearing protection during the tuning process.
This particular transmitter was my nemesis for a couple of years. It is actually possible to hate an inanimate object, I can tell you. Goodbye, you piece of shit.
We tend to scrap these instead of dumpster them. It saves the client a little bit of money on dumpster charges. If all the metal is sorted out by category, e.g. all the copper windings are cut from the HV transformer and PS filter inductors, and all the brass, aluminum, and wiring harness are separated, then it is almost worth the time and effort. Personally, I’d rather see all that material reused than landfilled.
