Tech Notes from the Field

A few months back the decision was made to “rush” a MaxxCasting system. The company teamed up with GEO Broadcasting and GatesAir to have this system installed. Currently in analog mode it works fairly well. When the baseball season finally ends, we become the test for doing HD as well. Check it out, it is interesting. The part I have issues is making the old, a 2006 Harris (GatesAir) HTHD+, and the new, a Flexiva FAX50 exciter, play nice.

I knew I would have issues from day one with this installation. Having no involvement other than being told what needs to be done, providing input was limited. At the onset I informed everyone on this project by interjecting a simple question: Will there be any issues utilizing our old HTHD+ transmitter for this? An early 2006 edition of the HTHD+ transmitter as we were “forced” into the early adoption of HD radio, this transmitter installation was a rush job from the get go. As an amplifier I have never had any issues with the transmitter, but I have had issues with exciters. We had 3 different Flexstar exciters in this thing, yet I have only replaced the tube 4 times. Anyways, the answer to the question was basically, yes, don’t worry about it.

Without being involved other than do as you are told routine, the day came to install the FAX50 as an exciter. Without a full rundown of the Geo-synchronization of the whole system, let it be known the Flexstar was not capable, thus the swap. I has the exciter out. I had the filler plate. I had cable adapter kit. Whoa, hold on. The kit labeled for a Z series transmitter? I told everyone this was an HTHD+. Hmmmm? Let’s proceed with getting the new exciter installed in the transmitter. After the first indicator of an issue (the cable), the second indicator of more fun to come was the fact that the exciter did NOT go into the transmitter! I was told otherwise, and I was provided with no instructions. Phone call time. Sure enough, the interface kit was wrong, and no, the FAX does not fit inside the transmitter, but must be externally mounted. New interface cable kit and instructions were on their way.

The new cable kit arrived with the new instructions. Now things began to make sense. I cleared out rack space and place the exciter in a location that was just accessible to comfortably been seen, i.e. not at the top of the rack, but at least a quarter way down. That was the maximum length of the new cables. Installation complete. Testing into the station load I got to learn how to setup the exciter as it did not come setup for our station. It was setup on the wrong frequency and as a transmitter, full 50 watts, not as an exciter of which we run about 4 watts. Details of this for another time. Rest assured it was not too bad and I had the transmitter back on the air soon enough.

Mixing the old and new. As we all know, the HD E2X, or Exporter to Exgine, stream will have packet drops on occasion or some other ISP induced oddity. In the case of anything somewhat prolonged or unusual, the exciters are designed to shut the HD off, suppress the carriers, and the station goes analog only for that brief time. When the E2X stream returns, the exciter detects it and HD carriers return. All good. Well, the FAX series exciters are some fancy boxes and are designed as stand alone transmitter. These range in power from the 50 watts to high power. As such when the E2X is gone, FAX is designed to drop power level and normalize to analog operation. When the E2X stream returns, the FAX adjusts, the power level changes to accommodate the HD carriers. All good when in an all inclusive box, when driving an external transmitter it causes some serous output power swings, and at times even a brief no power out. Our transmitter is licensed for 18kW TPO. I have witnessed this drop to zero and shoot to about 20kW all within a few seconds. I had four occurrences just this morning of lower power alarms followed by high power alarms. The APC and drive level required drops suddenly during this incidences that the transmitter PA cannot handle it. I wonder what stress this will place on my recently replaced tube?

GatesAir is aware of this and is considering options. I have suggested to the company they may wish to just upgrade the transmitter. We will see. I think the lesson that reinforces my philosophy is not to attempt a new project which mixes technology without considering all the pieces, and be prepared to invest in replacing the old even if it is going to cost you. Consistency is key to a smoothly running plant.

Cheers!