This is a replacement dish for the Comtech dish destroyed in a downburst event a few weeks ago. The first part of the job entailed placement of the new dish down on the ground. The town code enforcement officer was much happier with this idea than mounting it up above roof level along back the building as the old one was. Of course, this is possible due to the shift in satellites last year to AMC-18.
Finding a good spot on the radio station property was fairly easy. The studio is located in a business district, thus the side yard requirements where zero feet, which is great. The building inspector required that we dig a test hole to see what type of soil was there. It turned out to be fill. That required the footing design be changed somewhat and stamped by a licensed engineer. Not a major problem.
The footing is 36 inches wide by 7 feet deep.
The mounting pipe has flanges welded to the side of it to prevent it from spinning in the concrete.
After the pour, we let the concrete set up over the weekend.
The dish is assembled and waiting for lift. We used a back hoe to lift the dish onto the mounting pole, unfortunately, I was not able to take a picture as I was on a ladder attaching the dish to the pedestal with U-bolts.
Here it is installed and aimed at AMC-18. I used the Satellite Buddy, which makes the aiming job much easier. Once the signal is acquired, I like to peak the Eb/No on the West Wood One carrier, which seems to be the most sensitive to any type of change.
UPDATE:The registration deadline has been extended to October 17th, 2018. Switch back to procrastination mode…
Unless you have been sleeping under a rock, you should already be aware of the FCC request to register the C band Receive Only (RO) satellite dishes. This development comes from the never ending drive for more bandwidth from the mobile phone/data networks (remember the desire to use GPS frequencies for mobile data a few years ago). Normally, this type of registration would require a full frequency coordination study, however until July 18th, this requirement has been waived. The registration is completed online with the filing of FCC form 312 and a $435.00 filing fee. West Wood One has supplied and example form (.pdf) which shows the required information for each dish. Schedule B of FCC form 312 requires quite a bit of technical information required for each dish:
Site Coordinates (must be NAD27 according to the instructions on the form)
Site elevation AMSL in meters
Dish height to top of dish in meters
Dish make and model number
Dish mid band gain
Emission designator (WWO uses 36M0G7W other providers may be different)
Eastern and Western arc limits
Eastern and Western arc limit elevation angles
Eastern and Western arc limit azimuth angles
Most of this is intuitive. There are several steps to getting the information in the correct format. Google maps (or other mapping programs) will give coordinates in decimal format. To convert to Degrees Minutes Seconds in NAD27 use NADCON. Site elevation can be found using free map tools elevation finder. To determine the arc, a smart phone app such as Satellite Finder or Dish Pointer can be used. If not actually on site, then Dishpointer.com can be used to determine the arc.
My best suggestion is to include as much of the arc as possible for each location. The future cannot be predicted with any degree of accuracy and it is entirely possible that the current satellite position may not be used forever.
I have been working on another formerly direction class B AM station, this one is in Rutland, VT. WSYB has been on the air since 1931 with the same call letters serving the east central part of Vermont. In 1931, it was operating on 1500 kc with 100 watts of power. In March 1941 it moved to 1490 kc with 250 watts before settling, a few months later, on 1380 with 1,000 watts, directional night time protecting CKPC in Brantford, Ontario, Canada.
The transmitter site was first located at 80 West Street (now known as BUS US 4), in Rutland. It was moved to its current Dorr Drive (Formerly Creek Road) location in 1938, when the station was requesting a power upgrade to 250 watts. Whilst cleaning out the old transmitter building, a copy of an operating log, dated December 7, 1945 was discovered in the attic above the transmitter room:
Back from the time when readings were required every 30 minutes.
In 1956, WSYB was allowed 5,000 watts daytime non-directional with 1,000 watts night time directional.
At some point in the early 1990’s, the original towers were replaced with solid leg Pirod towers, each 195 feet tall.
After that, things went the way things do; AM steadily declined in favor of FM, local programming was mostly replaced by syndicated satellite stuff, there were several transfers of ownership, etc.
A translator on 100.1 MHz was added in 2016; the two bay Shively antenna was installed at the top of the South West tower. There is local programming on the station from 6am to noon on weekdays. There may also be some gardening shows and other such programming on weekends.
The current owner has decided, like they have done in other markets, that AM directional antenna systems are a maintenance nightmare, the risk of FCC sanctions are high for an out of tolerance antenna array, the ratings and income from the station do not justify the risk/cost. Thus, non-directional night time operation was applied for and granted. The station is now a Class D with 25 ass kickin’ night time watts.
WSYB had a two tower night time antenna system. The tower closest to the building (SW) was also the daytime, non-directional tower and it now holds the FM translator antenna and STL antenna. Thus, it was decided to ground that tower and keep those antennas in service. The far tower (NE), which was the second tower of the night time array would become the AM antenna. The night time ATU was built for less than 1,000 watts input power, so several components needed to be upgraded for 5,000 watt operation.
I had available these nice vacuum capacitors that came out of another decommissioned antenna system. The vacuum capacitors are great because the voltage/current ratings are much higher than the mica capacitors that were in the circuit before. You can see black goop where one of the Sangamo mica capacitors on the input leg failed several years ago. These vacuum capacitors are rated at 15 KV and the current rating at 1.38 MHz is probably in the 70-80 amp range. I had to move the base current meter from the former daytime (SW) tower out to the NE tower. The day night switch was taken out of the circuit. The transmission line to the far tower was replace with 7/8 inch foam dielectric cable. A slight touch up of the coil on the input leg of the T network was all that was required to bring it into tune.
The electric lines to the tower have been temporarily disconnected. As soon as they are reconnected, I will vacuum out all the mouse crap and other debris. The ATU building also needs some work sealing in up against the elements.
The tower base impedance is 75 ohms, +j95 making the base current 8.6 amps daytime and 0.58 amps night time.
For me, the magic of radio exists at that boundary between the real objects (towers and antennas) and the ether. The transference of electrical voltages and currents into the magnetosphere is something that still fascinates me to this day. Coupling a 5,000 watt medium wave transmitter to a tower and watching it work is something that I will never grow tired of.
I have done several of these posts in the past, but it always seems to be of some interest, so it bears repeating. AM antenna systems are not black magic. They are actually pretty easy to understand if the fundamental knowledge is in place. Medium Wave frequency wavelengths are fairly large compared to other broadcast frequencies. Thus, the components are larger.
The three basic components of an AM antenna system are the tower, the ATU (antenna tuning unit) and the transmission line (AKA Coax). The tower is the radiating element and they come in a variety of flavors; uniform cross section guyed, self supporting, series excited, shunt excited, etc. A series excited tower has a base insulator and is fed directly from the ATU. A shunt excited tower has a grounded base and uses a skirt or folded monopole design to transfer the RF to the main radiating element. This design has an advantage as the tower can be used for other wireless and broadcast services.
The antenna work in question for this project is WINE, 940 KHz, Brookfield, CT. The skirted tower is used for WRKI. It also has two way and cellular clients. The issue is instability of the WINE antenna system, which is likely due to improperly attached shorting wires between the skirt at the tower. Over the years, the impedance of the skirt has gone way up. The tower itself is 152.1 meters (499 feet) tall, or 170.3 electrical degrees. The skirt length is about 82 electrical degrees and it is shorted at about 72 degrees. There have been several papers written about folded monopoles for Medium Frequency (AKA AM or Standard) broadcast service. The recommendations state that for best performance, the short to the tower should be between 62 and 90 electrical degrees. Since the existing system falls in that range, there must be other problems with the antenna skirt and or shorting wire to the tower.
If one looks at this diagram, that configuration should look something like a gamma match, often used on dipole and yagi type antennas. A gamma match can be thought of as a stub of transmission line which is bonded to the radiating element at some favorable wave length corresponding to the desired radiation resistance. This is one of several configurations for folded monopole antennas and this type is most often seen on towers that support other wireless service antennas such as cellular and two way systems which are installed above the skirt.
There are a few interesting data points when looking at these type of antennas. First is the ratio of the diameter of the skirt over the height of the tower, or D/H. The larger this ratio is, the better the bandwidth characteristics of the antenna system are. This makes sense, when you think about it. In this instance, the tower is 151 meters (495.4 feet) tall and the skirt is 3.3 meters (10.83 feet) wide, thus the ratio is 0.0218.
The licensed base impedance if 234 ohms with a good amount of inductive reactance. When Sprint and T-mobile changed their configuration on the tower, that impedance shifted dramatically. The existing skirt is in fairly rough condition. The bottom ring that connects to the ATU is made out of copper tubing. It is attached to the skirt wires with steel saddle clamps, all are rusted and all of which are lose and can slide around. At some point, the tubing filled up with water, then froze causing the tubing to split open. At the top of the skirt, the jumper wire looks suspicious and the top ring does not go all the way around. The shorting stub to the tower looks like it is made out of battery jumper cable. I purchased new cross wire clamps and found some spare copper weld skirt wire at another site. Both the bottom ring and top ring were replaced as well as the shorting stub to the tower.
After the repair work was done, I had the tower crew reattach the short slightly below the last skirt to tower bonding point. In that position, I found the impedance went way up. Thus, going lower was going towards a resonance point. I had them move the short up to the former shorting point and remeasured and found the impedance was 235 ohms, only 1 ohm off from the previously licensed values.
Initially, I thought it would be nice to find a better position for the shorting stub and get a lower base impedance. This would make the whole antenna system work better (improve bandwidth, stability, etc). However, there was a set of guy wires above the bonding point. The tower crew would have had to disassemble the top ring to move above the guy wires. We were running out of daylight and weather so I had them lock everything down where it was. On a station running an all sports format that has no listeners and does not make any money, it does not make a lot of sense to spend gobs of money and time to rebuild the ATU for a new base impedance. When I got the impedance back to within 0.11% of the licensed values, it was time to declare victory and go home.