Am transmitter site – Page 2 – Engineering Radio

The Temporary AM antenna

One of those things that I have written about before, but seems to be common these days as older AM towers need to be replaced. One of our clients had just such a tower. Erected in 1960, the hollow leg stainless tower was rusting from the inside out. When the tower crew came to put up the translator antenna, they discovered that there was a hole in one of the legs and climbed back down.

The tower condition was somewhat known about, there were braces installed several years ago at certain levels to keep the tower standing. The new owner had planned to replace the tower eventually, so those plans where moved ahead.

Temporary Wire antenna, WKNY, Kingston, NY

A temporary utility pole was installed near the transmitter building and a wire was strung to another customer owned pole about 170 feet away. At 1,490 KHz, that proved to be a pretty good length. The issue with these medium wave temporary antennas is always the height above ground. In order for the radiation resistance to be somewhat reasonable, the antenna needs to be at least 1/8 to 1/4 wave length above ground. That means a minimum of 78 to 157 feet at 1,490 KHz. The utility pole installed is 35 feet AGL.

Thus, the wire antenna has a fairly low resistance, with loads of inductive reactance. Something on the order of 20 ohms, +j480. Since this is temporary, we reused the existing ATU that was designed for the series excited tower. With a capacitor installed on the incoming wire to cancel out some of the inductive reactance, a simple T network was configured to match the 50 ohm transmitter output to the 20 ohm antenna.

In the end, we were able to run about 400 watts into the wire, which covered the city of license fairly well. While the new tower was being erected nearby, we had to reduce that to about 100 watts to protect the tower workers from the hazards of non-ionizing radiation.

The new replacement tower has been constructed. It is the exact same height as the old tower, but has a twenty foot pole on top instead of a normal tower section. The pole was installed to mount the translator antenna. In addition to that, there will be other wireless services installed on this tower.

WKNY will have a six wire skirt installed in the next few days. As this tower is close to 160 degrees at 1,490 KHz, the skirt can go anywhere from 60 to 120 degrees up the tower.

The Answer to Ailing Copper

I don’t know how things are in your neck of the woods, but here in the Northeastern US, our old copper TELCO networks are on their way out. This is a problem for broadcasters who still rely on POTS lines (Plain Old Telephone Service) for transmitter remote controls, studio hot lines, etc. The vast majority of my transmitter site access is through dial up remote controls. There are a few locations that have web based remote controls, but to be honest; the phone part of my smart phone still gets a lot of use. There are several locations where the old copper is just failing outright and not through a lack of effort by the repair techs. Generally, the copper pairs get wet and develop a loud hum, which makes the remote control unit either hang up or become unresponsive to touch tone commands.

The best course of action is to get some type of VOIP line installed. Here is the rub; many transmitter sites are nowhere near a cable system. Several times, I have contacted the cable company to see if they will provide a VOIP phone line at a certain site. The response is usually; sure, we can do that! However, it will cost you (insert some ridiculous amount of money) to extend the cable to your transmitter site.

LAN extensions to the transmitter site are a useful for a number of reasons. More and more transmitters are equipped with web interfaces as are processors, UPSs, transmitter remote controls, security cameras, etc. LAN extensions can also be used for backup audio in case of STL failure. Finally, an inexpensive ATA (Analog Telephone Adaptor) and DID line can replace a POTS line for a lot less money. One example; voip.ms has the following plans as of this writing:

Plan type	Per month per DID number (USD)	Incoming call rate (USD) per minute	Outgoing call rate (USD) per minute
Per minute	$0.85	$0.01 (USA)	$0.009
Unlimited	$4.25	$0.00	$0.009
Toll Free (800)	$0.99	$0.019	$0.009

Any of those plans surely beats the standard TELCO rate of $40-50 per month per line.

Design criteria for a wireless LAN system needs to take into account bandwidth, latency and reliability. Each VOIP phone call takes anywhere from 28-87 Kbps depending on the protocol being used. If the wireless LAN is being used for other things such as back up STL service, access to various GUI’s, etc then the total bandwidth of all those services need to be considered as well. Do not forget ethernet broadcast traffic such as DHCP requests, ARP, SMB, etc which can also take up a fair amount of bandwidth.

For LAN extensions, I have been using a variety of equipment. The older Moseley 900 MHz LAN links still work, but are slow in general. The Ubiquiti gear has proven to be both inexpensive yet reliable, a rarity to be sure. There are several links to various transmitter sites running on various types of Ubiquiti gear, usually without problem. One simply needs to remember to log into the web interface once in a while and make sure that both ends have all the firmware updates installed. They are cheap enough that a couple of spares can be kept on the shelf.

The following diagram shows how I replaced all of the copper pots lines at various transmitter sites with VOIP:

Diagram of LAN extensions to various transmitter sites

List of equipment:

Nomenclature	Amount	Use	New or used
Ubiquiti Rocket M5	3	AP and station units	New
Ubiquiti AirMax 5G-2090 90 degree sector antenna	1	AP point to multi-point antenna	New
Ubiquiti Rocket Dish 5G-30	2	Station antennas	New
Ubiquiti ETH-SP-G2	3	Lightning protection	New
Trastector ALPU PTP INJ	6	Lightning protection out door units	New
Cambium PTP-250	2	Point to Point link	Existing/Used
Motorola Canopy 900DA PCDD	1	AP point to multi point	Existing/Used
Motorola Canopy 900DA PCDD	2	Station	Existing/Used
Microwave Filter #18486 diplexer	3	Diplexer 900 MHz ISM band and 944-952 STL band	Existing/Used
Cisco SPA122 ATA	9	Dial tone for remote controls	New

The main studio location has the gateway to the outside world. This system is on a separate subnet from the automation and office networks. From that location a point-to-multipoint system connects to the three closest transmitter sites. This setup uses the Ubiquiti Rocket M5’s with various antenna configurations. Then, from one FM transmitter site, there is an existing 5.8 GHz path to another set of transmitter sites. This uses Cambium PTP-250s.

The next hop rides on the STL system, using Motorola Canopy 900 MHz radios and Microwave Filter Company #18486 dilpexers. These are long paths and the 900 MHz systems work well enough for this purpose. The main cost savings comes from reusing the existing STL system antennas which negates the cost of tower crews to put up new antennas and or rent on the tower for another antenna.

There is a smaller sub system many miles away that is connected to the outside world through the cable company at the AM transmitter site. Unfortunately, due to the distances between the main studio and those three stations, there was no line of site shots to these sites available on any frequency.

When installing the 5.8 GHz systems, I made sure to use the UV rated, shielded cable, shielded RJ-45 connectors and Lightning Protection Units (LPUs). Short cuts taken when installing this equipment eventually come back in the form of downed links and radio heads destroyed by lightning.

Regardless, I was able to eliminate seven POTS phone lines plus extended dial tone service to two sites that previously did not have it before. In addition to that, all of the transmitter sites now have Internet access, which can be useful for other reasons. All in all, the cost savings is about $310.00 per month or $3,720.00 per year.

WKIP

This was the radio station that I listened to (or rather, my parents listened to) when I was a very young kid. From this source, things like school closings, weather, lunar landings, news, sports and traffic could be heard. At one point, there was a guy called the “Traffic Hawk,” (real name Don Foster) who flew in a Cessna 172 east and west over main street in Poughkeepsie advising drivers of any slow downs in the area. That’s right, Poughkeepsie, New York, population 30,000, had it’s own eye in the sky, broadcasting live from the aircraft overhead. Actually, I think he also flew up and down South Road (US Route 9) in the vicinity of the IBM plant, which employed quite a few people in those days.

There was also a guy who tried to break the Guinness Book of World Records by staying awake the longest, this happened several times.

For me, it was the school closings. I hated school with an absolute passion. Everyday, I would ride the school bus and say a little prayer; “…please God, make it today. Make the boiler stop working, or the electricity to go out. Make the kitchen catch on fire or the roof to cave in. You are a great and mighty God and I don’t ask for much. Please destroy my school today.” Alas, God did not seem interested in this.

Anyway, back to the topic at hand.

WKIP first signed on in 1940 with the studios and transmitter located at The Nelson House, 42 Market Street, Poughkeepsie. That building is long gone and the location appears to be the parking lot for the Dutchess County Office building. Being neighbors with some influential guy from Hyde Park made for a nice dedication speech:

It signed on with a power of 250 watts on 1,420 KC on June 6th, 1940. Soon thereafter, it changed frequency to 1,450 KC as a part of the AM band shift brought about by NARBA.

Over the years, the station went through several ownership changes. The first major technical change came in 1961, when the station transmitter site moved to it’s current location, then called Van Wagoner Road, now Tucker Drive. The station increased power to 1,000 Watts and installed a direction antenna for daytime use. It is one of those rare night time non-directional, day time directional stations.

The directional antenna consists of two towers; tower one is 180 degrees tall (103.4 Meters or 340 feet) with 35 degrees of top loading. That is used for both the day and night time array. Tower two is 85 degrees tall (48.8 Meters or 160 feet) and is used only for the daytime array. This pushes the major lobe of radiation towards the north. I don’t know the reasoning behind that, but somebody spend a good amount of money to make it so.

Here is a air check from the early 1980’s. Weather on that day was “Sunny, cloudy, whatever… take your pick.”

Good old Steve Diner.

Today, the station looks like this:

The 1961 WKIP transmitter building with tower

When I was growing up, my cousins lived within walking distance of this. We used to come over than throw rocks at the tower when the station was unmanned on Saturdays and Sundays. At least, I think it was unmanned because no one ever came out and yelled at us.

WKIP backup transmitter, phasor and main transmitter

Mid 1980’s MW-1A still runs. The BE AM1A is the main transmitter. The phasor is the Original 1960’s Gates Phasor.

This video shows how the studios used to look, before they were rebuilt by Clear Channel Circa 2002 or so. At about the 2:02 mark, you will see the room pictured above as it looked in 1990.

The space between the video above and the picture below looked bad with nothing in it. It looks better now.

That clock is a collectors items and belongs in a museum.

AM station downgrade

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.