tech stuff – Page 51 – Engineering Radio

TIA/EIA 568

Radio stations more and more revolve around networked computers. Engineers need to understand computer networking, especially as it relates to audio distribution and playback. Eventually, I see broadcast engineers being more computer science types rather than electrical engineering majors.

What I have found out about computer networking is this: it is not rocket science. In fact, most of it is pretty easy. Physical networking and cabling are similar to audio and TELOC cabling. Automation computer servers themselves are not difficult to understand as most of them run on some type of Windows program. Other servers such as Apache for WWW and for FTP and streaming run on some type of LINUX OS. LINUX is also not difficult to understand so long as one knows the right command line prompts.

The first part of understanding computers is networking. Without a computer network, a computer is a glorified typewriter. Almost every automation system and or digital editor requires some type of network. Consoles and computers that use AOIP require well-constructed networks in order to operate properly. To that end; cabling choices, network interface devices such as switches and routers, patch panels, and so forth need to be specified and installed with care.

Most often, it is the simple things that will trip an installer up. The one area where I have found the most mistakes made is the pair’s connection to various termination points. There are two basic standards, TIA/EIA T568A and T568B. Neither is better than the other, both are often identified on terminating devices such as jacks and patch panels. The most important aspect of these standards for an installer is to pick one and stick with it.

When certifying networks, the most common problem I have encountered is crossed pairs. Almost invariably, one end will be punched down with the A standard and the other with the B standard. Jacks are particularly difficult, as the color-coding stickers show both. Many patch panels have a slide-out, reversible card with is an either/or situation. For some reason, I have stuck with the B standard, and on any project I am managing, I get rid of all the A color codes I can find and tell the installers that B is the only acceptable termination standard. That cuts down on a lot of errors and redos during certification. That is good, it saves time and I hate redos.

You can see that this color code marking can lead to confusion. I take a sharpie and cross out all the A markings to avoid installation mistakes.

Incidentally, on any new network installation, Category 6 cable should be used. As more and more data throughput is required for network applications, Category 6 Cabling has better performance specs and will likely have a longer service life than another cable. It may be a little bit more expensive than Cat 5, however, well worth the investment. It would be a great mistake and a waste of money to have to pull out the network and reinstall it in a few years because the cabling doesn’t have the required bandwidth.

Category 7 cabling is in the works.

It’s cold enough to…

Cause the STL receiver to unlock. A quick peak at the thermometer this morning showed -12° F outside. Meanwhile, out on the island, the WICC TFT STL receiver decided that it was just too cold to continue and gave up the ghost. Weak sister. This created quite a bit of hiss on the WICC signal until about 11 AM, when the program director finally called me to tell me of the situation.

Via remote control, we switched over to the backup analog ~~8 KHz~~ 15 KHz TELCO line, which sounds fine, given the talk radio program material.

Unfortunately, vehicle access to the transmitter site is now gone. I have the option of taking the Bridgeport harbor master boat over to the dock and walking .9 miles, or driving to the Long Beach parking lot and walking 1.3 miles in order to repair it. This will likely be tomorrow, as the weather is supposed to be better, 36°F and light snow. Well, it is what I get paid to do.

Regarding the analog 8 KHz TELCO line, that is an anomaly. These analog circuits where used to wire the country together, once delivering all of the network programming to affiliate stations before the widespread use of satellites. They require unloaded dry pairs and normally have an equalizer on the Z (far) end. Nowadays everything is digital, try and find a tech to repair one of these circuits when it goes down. Fortunately, this is a short distance circuit.

Center of Box, AMC-8

Satellite dishes have been a part of radio station technical equipment for years. I am surprised at the number of broadcast engineers that do not consider center of box when aiming dishes. As dishes get larger and focal points get smaller, center of box aiming is not a nice thing to do, it is a necessary thing to do. The latest generation of satellite receivers, (AKA XDS) have a somewhat less than lively RF front end, they require higher E/B than the previous generation Starguide receivers to stay locked.

For years, the majority of commercial radio networks were carried on AMC-8 or its predecessors living at 139° W. On the East Coast, particularly in the Northeast, that makes aiming points relatively low to the horizon, anywhere between 8-10° elevation.

3.2 meter comtech dish — 3.2 meter COMTECH satellite dish

This all means that precise aiming the satellite receive dish is critical for satisfactory performance. SES Americom owns AMC-8 and thus they have a web page about all of their satellites and important operating information. SES Center of box for AMC-8 is available in one-month blocks, which makes scheduling the aiming chore fairly easy.

I have always used a spectrum analyzer through a 3 dB splitter to look at the 950 MHz LNB output. This aiming setup allows the best combination of Azimuth/Elevation/polarization. Using the satellite receiver to confirm and maintain signal lock, peak the waveform that the receiver is locked to. It is pretty crowded up there, so there will be lots of signals on the spectrum analyzer trace.

It is a pain in the rear end to lug all that equipment out to the satellite dish, especially if it is on the roof. That is why it only need be done once; the right way the first time.

Any shortcuts will likely lead to those annoying chirps and dropouts or complete loss programming, particularly when the weather turns bad.

The mechanical tower light flasher

This is a Hughey Phillips mechanical tower light flasher that has been in service since 1960. Basically, it is a motor connected to a cam that rocks a mercury relay back and forth. These were standard technology for tower lights from the 1930s through about 1970 or a little later. They were very reliable, we still have some with a “pancake motor” in use on some of our towers. They were very robust and immune to lightning damage, RF interference, and other problems. The only maintenance that I can think of is lubricating the motor bearings. Eventually, however, they do wear out. Cold weather seems to take its toll, often causing the motor to stop.

Hughey and Phillips mechanical tower light flasher

This particular unit is mounted inside the tuning house for the far tower (north tower) at the WGHQ antenna array. It has finally reached the end of it’s existence; the motor bearings are shot and it has gotten stuck in both the on and off position this year causing the FAA to be notified of the malfunction.

Today, I am replacing it with a solid-state flasher (SSAC B-KON FS155-30RF). Solid-state flasher units have been known to malfunction in high RF fields, such as AM towers. To cure that, the manufacturer has built-in 0.01 uf bypass capacitors, hence the “RF” suffix. Older units did not have built-in bypass caps, so external 0.1 uf bypass capacitors were normally installed on units mounted to AM towers. While I was working on this, I turned the transmitter down to 500 watts, no need to get any RF burns.

Naturally, this has to happen after there is two feet of snow on the ground. Also, it should be noted that this is the furthest tower away from the transmitter building. Now where did I put those snow shoes? Never mind, it has been very cold and the ground is frozen solid, I’ll take the truck… This is good because I will have all the tools, drills, nuts, and bolts without having to walk back and forth several times in the snow.

Hughey Phillips mechanical beacon flasher

I removed the motor and mercury-filled relay. I’ll have to figure out how to dispose of the relay. I then drilled a mounting hole through the base of the old flasher housing and bolted the solid-state relay to it. This is required because the solid-state relay needs a pretty good heat sink.

Turn everything back on and: Ta-da! All works normally, the tower beacon is flashing away up there. Time to leave.

Pull forward about 2 feet to turn around and CRUNCH! The truck goes through the ice of a hidden stream. Any attempt to move only makes it worse:

Put in a phone call to the one guy I know that can get me out. About an hour later he shows up with chains, a shovel, and a come-a-long. We attach the come-a-long to the fence support post and pull the truck out backward 1/2 inch at a time. It took us about an hour and a half to get it all the way out so I could drive it back across the field. I’d have taken some pictures, but my guy; was a little grumpy.

I won’t do that again.

Still, I did the job I came to do, so it was a good day after all.