We have this certain transmitter which has been on the same tube since June 6, 2001. Come to think of it, the transmitter itself has been on the air for the same amount of time without failure. A testament to its designer…
According to my calculations, that is 151,691 hours or 17 years 3 months and 22 days. The tube is the original EMIAC 4CX15000A that came with the transmitter.
I am a little nervous about turning it off to clean the cabinet.
We have a spare on the shelf for the eventual replacement of this tube, but I really want to see how long this thing will last. This is also one of the last tube transmitters we have in main service. There are several backup tube transmitters still around.
Installing transmitters requires a multitude of skills; understanding the electrical code, basic wiring, RF theory and even aesthetics play some part in a good installation. Working with rigid transmission line is a bit like working with plumbing (and is often called that). Rigid transmission line is often used within the transmitter plant to connect to a four port coax switch, test load, backup transmitter and so on. Sometimes it is used outside to go up the tower to the antenna, however, such use has been mostly supplanted by Heliax type flexible coax.
We completed a moderate upgrade to a station in Albany; installing a coax switch, test load and backup transmitter. I thought it would be interesting to document the rigid line work required to complete this installation. The TPO at this installation is about 5.5 KW including the HD carriers. The backup transmitter is a Nautel VS-1, analog only.
This site uses 1 5/8 inch transmission line. That line is good for most installation up to about 10-15 Kilowatts TPO. Beyond that, 3 inch line should be used for TPO’s up to about 30 Kilowatts or so. Even though the transmission lines themselves are rated to handle much more power, often times reflected power will create nodes along the line where the forward power and reflected power are in phase. This can create hot spots and if the reflected power gets high enough, flash overs.
Working with rigid line requires a little bit of patience, careful measurements and some special tools. Since the line itself is expensive and the transmission line lengthener has yet to be invented, I tend to use the “measure twice and cut once” methodology. For cutting, I have this nice portable band saw and table. This particular tool has saved me hours if not days of work at various sites. I have used it to cut not just coaxial line and cables, but unistrut, threaded rod, copper pipe, coolant line, conduit, wire trays, etc. If you are doing any type of metal work that involves cutting, this tool is highly recommended.
Next point is how long to cut the line pieces and still accommodate field flanges and inter-bay line anchors (AKA bullets)? The inner conductor is always going to be sorter than the outer conductor by some amount. Below is a chart with the dimensions of various types of rigid coaxial cables.
When working with 1 5/8 inch rigid coax, for example, the outer conductor is cut 0.187 inches (0.47 cm) shorter than measured distance to accommodate the field flange. The inner conductor is cut 0.438 inches (1.11 cm) shorter (dimension “D” in the above diagram) than the outer conductor to accommodate the inter bay anchors. These are per side, so the inner conductor will actually be 0.876 inches (2.22 cm) shorter than the outer conductor. Incidentally, I find it is easier to work in metric as it is much easier to measure out 2.22 CM than to try and convert 0.876 inches to some fraction commonly found on a tape measure. For this reason, I always have a metric ruler in my tool kit.
The next step is de-burring. This is really critical at high power levels. I use a copper de-burring tool commonly used by plumbers and electricians. One could also use a round or rat tail file to de-bur. The grace of clamp on field flanges is they have some small amount of play in how far onto the rigid line they are clamped. This can be used to offset any small measurement errors and make the installation look good.
After a bit of reflection and a few good conversations over the New Year’s Holiday, I decided that I should continue my work on this blog. I would like to thank all those that have stuck by and waited. I have received numerous emails and messages off line, all of which have been read and appreciated.
Since the abrupt stoppage last July, which was absolutely necessary for me, many things have happened within the business. Fortunately, during the hiatus, I was still taking pictures. After sorting through them, here are a few interesting things that happened:
This project required many steel mounting posts be driven into the ground around the AM towers. I don’t even know how many, but I would hazard a guess of over three hundred. Each one of those mounting posts was hand dug down a depth of 6-10 inches to look for ground wires. Where ever a ground wire was found, it was moved out of the way before the post was set.
Basically the solar array covers about 1/2 of the antenna array field. All of the steel mounting hardware is tied into the ground system, making, what I am sure is a pretty large above ground counterpoise.
View from the south looking north:
View from the north, outside of the transmitter building, looking south:
Power company interface and disconnect:
The utility company had to upgrade the transmission lines to the nearest substation to handle the additional power produced by the solar system. All in all, it was a fun project to watch happen.
At a certain studio building, which is over 150 years old, the roof needed to be replaced. This required that the 3.2 meter satellite dish and non-penetrating roof mount be moved out of the way while that section of the roof was worked on.
Dish ready to move, all of the concrete ballast removed and taken down from roof. The roofing contractors constructed a caddy and the entire dish and mount was slid forward onto the area in front of it. Since the front part of the roof was not reinforced to hold up the satellite dish, we did not reballast the mount and the XDS receivers ran off of the streaming audio for a couple of days until the dish was put back in its original position.
A couple of other studio projects have been underway in various places. Pictures to follow…
One of our clients sold their radio stations to another one of our clients.
There has also been a bankruptcy of a major radio company here in the good ol’ US of A. Something that was not unexpected, however, the ramifications of which are still being decided on in various board rooms. One of the issues as contractors is whether or not we will get paid for our work. All things considered, it could be much worse.
Learned a valuable lesson about mice chewed wires on generator battery chargers. I noticed that the battery charger seemed to be dead, therefore, I reached down to make sure the AC plug was in all the way. A loud pop and flash followed and this was the result:
My hand felt a bit warm for a while. The fourth digit suffered some minor burns. There is at least one guy I know that would be threatening a lawsuit right now. Me, not so much… All of the high voltage stuff we work on; power supplies that can go to 25 KV, and a simple 120 VAC plug is the thing that gets me.
The return of the rotary phase maker.
Mechanically derived 3rd phase used when the old tube type transmitter cannot be converted to single phase service.
Those are just a few of the things I have been working on. I will generate some posts on current projects underway. Those projects include a 2 KW FM transmitter installation, another studio project, repair work on a Harris Z16HD transmitter, etc