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When Old and New Don’t Mix
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!
A Little Harris (GatesAir) HTHD+ Repair
Not to focus on anything like this, but, damn, I have not posted in a while. Let’s start flooding you with some real boring stuff! A few weeks back I had the un-welcomed 12:30am phone call from the remote control. How we love those calls. The basics were there: No forward power, off air alarm, etc. I do the normal, let’s try and turn it back on. Nothing. I tried to switch to the Auxiliary transmitter, but that did not happen. My first thought was “great there goes a UPS” which would explain lack of control, but my remote control was working. Up on the Aux site I went. Mind you all this took place quick enough the person in building was never aware of the condition.
Off to the site I go ready to find some melted metal. First lesson of the evening: Make sure all connections are tight and good even on the remote control! A wire backed out of the Phoenix connector on my command for the coax switch. Doh, no wonder it didn’t switch. Fixed that and put the Aux transmitter on the air and turned off the Aux site. (Nice to have an actual auxiliary site.) Crazy how that switch ALWAYS remotely switched until this night. Now on to the main transmitter.
The HTHD+, as all HT series transmitters, has the mimic panel. I see red LEDs for the Plate and a Fault indicators. Well, isn’t that nice. I did just replace the tube a month prior. Let’s see what happens if I shut everything down and start it up again. This usually clears a strange fault or situation especially with a power fluctuation. Wham and Bam. Nope. Immediate slam, in your face, time to troubleshoot sound. I checked the obvious PA cavity and tube. Always check that plate blocker. No obvious signs and no arcing. Jeez, it was clean. Give the tube a shake. Not rattle. Good. Let’s give it another chance, so I turn on the filament, then plate. Same result. Nothing. At this time I take a step back and glance at the big picture. Plate and Fault indicators on the mimic panel. I glance at the High Voltage Power Supply (HVPS) cabinet and there I see it, a MAG OVLD indicator.
How I didn’t notice it when I first walked in I cannot say. Tired or just fixated on the mimic panel. Time to focus on the HVPS. First step is I verified the fault through the multimeter overload faults. Code 21. A cross check corresponded with the MAG OVLD which indicates either relays being open or control voltage was not there. I did all the basic checks: Input line volage, cabinet connections, and interlocks. All good. So, I either had a bad relay or, worst case, a shorted transformer, though I did not smell any magic smoke. I messaged GatesAir via the customer portal, and then studied the schematic. As all line voltages were good I was beginning to suspect a set of relays, and after a nice chat with GatesAir, we determined to focus on magnetic relays 3K1 & 3K2. I set out to do just that. There happens to be contacts on those relays that are exposed. I gave them a little burnshing. I did a quick test into the load. Everything came up flawless. As I had the aux transmitter on the air, I decided to proceed with a cleaning of the HVPS cabinet.
After cleaning up I placed the HTHD+ back on the air. I still find it odd that this failure occurred in the middle of the night. I also find it all that something got in between the contacts on either or both relay contacts while they are normally closed. I did go through a cleaning while I did the tube replacement earlier, but it never occurred to me to burnish these contacts. In addition all was running fine up to that point. As power at the site can be somewhat inconsistent, I wonder if a phase dropped briefly and upon an automatic restart an arc or some dust affected the relay contacts. I have an HT-25, I’ve installed and maintained an HT-30 in the past. I have never had this situation, and they were in environments worse that this.
I love this job as there is always something to learn even if it is a minor, and somewhat obvious item. We do not “know it all” and I love to learn. Pack it in your data bank of a brain so next time the repair is a no-brainer.
Cheers!
Harris Fix?
Apparently we me be on the road to the answer of why our HTHD+ transmitter randomly drops off air. If you have followed my posts these random events are annoying to say the least. Recently we discovered the transmitter recovers on its own within 2 minutes, a long time in radio land. What is this potential solution?
Set the Exgine Buffer such that the Buf Used and Buf Max is in the 20-30% range. We moved ours from Default to 0.836 and the system seemed to stabilize. We still experience Exporter Sync Unlocks, but are not as often. Also when using thos setting the Lock Indicator does not swing as much. This will count down to zero, go negative, reverse, and “swing” between random limits. Apparently if the swing is within some tolerance the sync indicates a lock and the buffer is running optimal.
If the buffer is over utilized there seems to be a DSP barf which mutes the exciter. Seems odd that this could happen, but since changing our settings we surpassed our 2 week wall and shut offs. After checking this morning the sync was unlocked and we noticed our T-1 circuit took a hit. Makes sense that some corrupt packets came in and caused loss of sync. We await a re-sync. Too bad there is no good way to remotely monitor this.
I will keep on top of this, so look for tweets and future blog updates.
Harris HTHD+: More?
Yesterday we had our HTHD+ drop off the air again. When I arrived at the site the mimic panel showed an Exciter Fault!
1. Was it the Flexstar at fault?
Right now we are assuming, between us and tech support, that the PA module in the Flexstar is not happy with something. This is based on a fluctuating forward power of a few tens of a watt while the APC voltage remains constant. To troubleshoot this we await a new PA module for the exciter.
2. Did something else cause the exciter to fault?
What if the IPA is asking too much from the exciter? Seems to be stable and the fluctuations on its forward power follow that of the exciter, so it appears to be working fine.
3. What was the fault?
There is no indication nor have I found log files that would suggest what actually occurred. I need to research to see if the Flexstar keeps any log files. As it is an early “software controlled device” I suspect not or it is well hidden. A call may be in order.
On that note, when I powered up after tests it has remained on the air since. I will deal with the power fluctuations as long as I can maintain legality and on-air. We are a BTC/Navteq station. Believe it or not it is important for us to run HD. We will see if a new PA module actually works. If not, I will suggest a swap of the IPA.
New Tube for the HTHD+
In the last couple of weeks I had an interesting series of events with the Harris HTHD+ transmitter. I was out there with my assistant a couple of weeks prior to these events and I made a comment that we should consider replacing the tube some time this year. Of course I was thinking conventional wisdom when it comes to tubes and I figured a couple of months before the actual replacement.
Well, the bottom line I was wrong. Here is the events that occurred. If you saw my tweet on Memorial Day, I experienced an IPA overload on the rig. I visited the site and checked everything. All looked good, even the readings. I had the transmitter back on in about an hour. I visited the site the following day to verify all readings and make sure I did not miss anything. All good again. I decided to purchase the tube and have it on site ready to go for a routine replacement.
Friday morning, 2:30am, I get the remote control call. The rig is off again. Off to the site and sure enough the IPA was indicating overload again. Well, I suspected that this soft tube may be the issue. As protocol, I called Harris tech support and discussed the situation. I had cleaned and checked all the internals for obvious issues. We both agreed that the tube could be the cause. Plus, for the HD rig we were pushing 2 1/2 years on the tube!
With luck, I tracked down our UPS delivery dude as he was making a delivery across the way. The tube was on board, so I signed for it and off to the site. Talk about timing. I performed the installation and tweaked the transmitter up. We were back in business. The end of last week I began my filament management and backed off a bit. All is still looking good.
We are coming up on two weeks after the first occurrence. After the tube replacement we have not experienced the IPA overload. In our case apparently a soft tube caused IPA overloads to occur. The story has been relayed to another in Harris. Interest has been piqued. I must note this is an early HDHT+ transmitter, so we may see some oddities. I intend to talk with Harris and compare notes.
Once again, do not rule out anything when tackling a problem. Eliminate the items not causing the issues and narrow it down to the specific item. In this case, the tube. Another learning experience completed.
Tech Notes from the Field 