Back in the day, when tube transmitters ruled the broadcast world, the common practice was to have a big cooling fan moving outside air through the transmitter building connected to a thermostat. Temperature swings of 30 to 40 degrees were common, however, the tube rigs could handle almost any temperature that didn’t melt plastic or freeze water.
Today’s solid-state transmitters are not that rugged. They like to have their rooms around 70 degrees +/- 10 degrees or so. Not to mention the other computer-controlled equipment commonly found at a transmitter site. Things like air chain processors, STLs, remote controls, etc. So, lots of air conditioning is the norm, and with lots of air conditioning comes lots of maintenance.
Air handler air filters need to be checked and replaced often. Condenser coils seem to attract every type of flying debris on the planet and need to be cleaned once, possibly twice per year depending on tree and weed species near the site. Even with preventative maintenance, occasionally things like this happen:
AC condenser frozen dryer and piping
Of course, the entire cooling coil inside is frozen solid.
This condenser is low on refrigerant, causing icing problems. It has a slow leak somewhere and is about to be replaced. Other reasons for this happening are malfunctioning or non-existent low ambient kit on the condenser fan. Sometimes less than knowledgeable persons will install a 5-ton unit designed to run throughout the year but not take into account the effect of moving below-freezing air at high speed across the coils. Insufficient air moving across the cooling coil will also cause this. Insufficient airflow can be due to plugged air filters or clogged fan/blower blades.
This one is even better (same condenser unit):
AC condenser broken fan
The fan blade is sheared off and jammed into the condenser coil. This happened during power transfer from generator power to commercial power. Naturally, it was at 1 a.m. in the morning after a pole-mounted transformer had been replaced. When the building transferred back to commercial power, I went outside to use the “bathroom” before my two-hour drive back home. I thought I smelled something hot, you know that cooked paint/plastic smell, but couldn’t really track it down… the winds were kicking up and another thunderstorm was on the way.
The next afternoon, however, when the sun was up and the site was working on one air conditioner, the temperature alarm went off. Upon arrival, I found the condenser breaker tripped, resetting it caused the building lights to dim. The fan motor was shorted to the case. I would theorize the aluminum fan blade suffered from metal fatigue, likely because the blades were not balanced causing a vibration. When the power transfer occurred, there was just the right combination of torque and centripetal force to cause the blade to rip, and then lodge in the condenser coil.
The fan motor has been replaced, but I think it is time to replace the whole condenser unit, which will be expensive.
AC&R Gauge set
I found having a set of gauges to check the head pressure and suction is a good diagnostic tool to quickly pinpoint problems with HVAC units. This way, when the HVAC tech shows up, you can quickly point him in the right direction.
This is yet another addition of the “Burned up Sh*t” collection:
GE 30 Amp 3 pole breaker
It is a breaker from a 5-ton AC compressor. Back in the bad old days when I was the Director of Engineering for a 28-station group Headquartered in Harrisburg, PA, I received a phone call from one of the local engineers. He stated that the studio AC unit compressor had burned out again and the breaker kept tripping. What did I think, asked him. I thought perhaps he should dig a little deeper and determine why the breaker was tripping before throwing another AC compressor at it. When are you coming to town again, he cheerfully inquired.
Okay, I get it.
I started by calling the HVAC company to inquire what had gone wrong with the compressors. Winding shorted to the case for both units was the answer received. It being July and mighty hot out, the various worker bees in the studio were feeling inconvenienced by the sweat in their eyes and dripping on their work, etc. I called the local manager and asked for a hotel room, I’d be up tomorrow. Then I called the HVAC guy back and asked in to meet me at the studio tomorrow afternoon.
Upon arrival the next morning, I found the fifth-floor studios to be hot, as reported. I trip to the roof location proved to be hotter still. I tested the voltages at the compressor unit with a DVM and everything looked good. A trip down to the utility room found the electrical panel in reasonable shape. Then the local engineering guy chimed in, “Oh yeah, I forgot to tell you, the breaker hums and gets hot when the compressor is on.”
It’s always that little bit of missing information…
I took the breaker out and sure enough, the fingers were all arched and nasty-looking.
I replaced the breaker, the HVAC guy showed up, with a new compressor and the studios began to cool off around 3 p.m.
Since then, I have specified Square D QO bolt-on breakers for new installations, especially for heavy loads like AC units, transmitters, and so on. They are a little more expensive, but in light of two AC compressors, the unscheduled trip out of town, and the grumbling staff, it is better to pay upfront for better equipment than to put up with preventable outages.
Some days there are far too many obstacles to being an effective writer:
Cat likes using the computer
We were adopted by this stray cat last summer. He seems to be right at home napping on my computer keyboard. Actually, a little afternoon nap seems like a good idea…
At the place of my former employment, there is an issue with AM reception. The building is full of old, electrically noisy fluorescent light ballasts, computers, mercury vapor parking lot lights, and every other electrical noise generator under the sun. The second issue is that one of the EAS monitor assignments for two FM class B stations is WABC in NYC. Under normal conditions, WABC puts a fine signal into the area. Listening to it is not a problem at my house, in the car, and whatnot. However, at the studio, the station is audible but terribly noisy. Every time one of those FM stations ran a required monthly EAS test originating from WABC, it was full of static and just sounded bad on the air.
The state EAS folks were inflexible as to the monitoring assignment. “WABC is the PEP station for NY. You should have plenty of signal from WABC at your location,” said they.
At one time, the studio had an active loop antenna (LP-1A) from Belar, which worked but also seemed to amplify the noise. I decided that the best thing to do was go big and ditch the preamp. I made a diamond-shaped receiving loop on two pieces of two-by-four by eight-foot lumber. I wound four turns of #14 stranded wire around this frame and made a 4:1 balun to feed the unbalanced 75-ohm RG-6 coax.
That cured the noise problems and for eight years, WABC sounded pretty good on the EAS monitor.
Fast forward to about a week ago. The roof at the studio building was being redone and all the monitor antennas had to be removed from the roof. The homemade loop was not in good shape. The balun box was full of water, the lumber was cracking and falling apart, the insulation was degraded by UV exposure, etc. My boss asked, “How much to make a new one?” So I said something like forty dollars and a couple of hours. He then said, “Make it so we don’t have to ever make another one.”
Music to my ears. I started by checking my assumptions. I made a model and ran NEC to see what the electrical characteristics for that size loop were on 770 KHz. It came out better than I thought, with about 1-ohm resistance and 282 ohms inductive reactance. Fooling around a little more showed that roughly 1.3 uH inductance and 720 pF capacitance in an L network would bring this in line for a 50-ohm feed point. Since this is a receive-only antenna, that is not a prime consideration. I am more concerned with noise reduction and maintaining at least the bi-directional quality of a loop antenna.
NEC 2 model AM receive loop
Then, I decided to get fancy. What if the capacitance was put on the end of the loop to ground instead of the feed point? That, in effect, should make the loop directional off of the unterminated side. Driving the feed point with a 9:1 balun would also bring up the inductance on the feed point. Finally, grounding the whole thing with a separate ground lead might also get rid of some noise.
The final configuration looks something like this, which is essentially a top-loaded vertical:
Low noise AM loop antenna
Now to build it.
Once again, I felt that a non-conductive support was needed, so I used two by four by eight-foot lumber, but this time I painted them with oil-based paint. The side length worked out to be 5.7 feet per side, or 23 feet per turn for a total of 92 feet of wire.
I purchased 100 feet of PV (photovoltaic) wire (Alpha wire PV-1400), which is UV, heat, and moisture resistant and designed to last for 30 years in outdoor, exposed environments.
For the balun box, I used a metal outdoor electrical box with a metal cover. I put a ground wire jumper between the box cover and the ground common to maintain shielding. I used a water-tight bushing to feed the antenna wires and the ground wire into the box. I drilled a 3/8 hole for a type F chassis connector. Everything was given a little extra waterproofing with some silicone-based (RTV) sealant on all threaded junctions.
The spreaders for the wire windings are UV-resistant 1-inch PVC conduit. I drilled four holes, three inches apart in each spreader to run the loop wires through.
The balun is 7 trifiler turn of 24 AWG copper wire on an FT-43-102 toroid core. Trifiler means three wires twisted together before winding the toroid core.
I used all stainless steel screws and mounting hardware.
The loop is terminated with a 500 pF, 500-volt ceramic capacitor to ground. Once in place, I am going to experiment with this by jumping it out of the circuit to see what effect it has on noise and signal strength. I may also try replacing it with a 200-ohm resistor and or a 1000 pF capacitor.
The assembly was pretty easy, although time-consuming. My four-year-old son helped me paint the wood and string the wires through the spreaders.
I soldered all wire connections with 5% silver-bearing solder.
When the whole thing was assembled, I tested it out with my Drake R8 receiver. It performs much as expected, with low noise, directional away from the terminated wire loop. It does not appear to be too narrow-banded either, as the stations on the high end of the dial were also received with good signal strength.
Next was loading it on the pickup truck, driving it in, and mounting it on the studio building. I got some funny looks from my fellow travelers, then again, I usually do.
For the ground, I purchased an eight-foot copper-clad grounding rod and pounded it into the ground at the corner of the building. This area is always wet as it is the lowest area around the building and all the gutters drain there. This is not best RF ground, but for the purposes of this antenna, it should work fine. I used about 28 feet of leftover #12 stranded wire from the ground rod up to the balun box and connected it to the common ground point inside the box.
The frame itself is mounted on a standard wall-mount antenna pole. Stainless steel clamps hold the wood frame to the pole.
Once it was installed, I used my Kenwood R-2000 receiver to find the best mounting azimuth and locked everything down. I also put a toroid on the RG-6 coax coming up from the rack room to keep any shield noise from getting into the antenna.
AM receive loop PVC wire spacers
AM receive loop wood frame
AM receive loop balun transformer
The tuning capacitor is in there too, behind one of the loop wires.
AM loop antenna installed on roof
Antenna installed. I did try substituting the 500 pF capacitor with a 220 resistor. The signal strength came up somewhat, but the noise increased more, therefore the capacitor is a good termination for this antenna.
With this antenna, the signal from WABC is nice and clean and sounds good on the FM station when a monthly EAS test is retransmitted.
