April 2019
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As requested: The old WSBS studio building

Alan asked that if I should ever find a picture of the old WSBS studio building to publish it.  Here it is:

WSBS old studio building

WSBS old studio building

I found this above the coffee machine in the lobby, nicely matted and framed.  I didn’t want to ruin the framing job, so I took a picture of the picture under glass and cropped it, thus the quality could be better.

I believe this is the original tower from 1959.  The current tower stands on a taller concrete pedestal and is further away from the road.  I think the roadway was widened and raised at some point, thus the new building sits higher in relationship to the tower base.  In any case, it little bit of radio history.

The Nautel XR6 AM transmitter

I’ve been away working in Burlington, VT (WVMT, 620 KHz, Burlington)  for the last coupla, installing this nifty Nautel transmitter:

Nautel XL6 transmitter, WVMT Burlington, VT

Nautel XR6 transmitter, WVMT Burlington, VT

I like the Nautel units, both AM and FM;  they are well designed, well built, rugged transmitters.  I have lost track of how many of these units we service in the field, partly because they are becoming pretty much standard equipment at all of our installations.

Continental 315R-1 AM transmitter, WVMT, Burlington, VT

Continental 315R-1 AM transmitter, WVMT, Burlington, VT

The transmitter it is replacing is a Continental 315R-1, which is based on the Collins Power Rock design.  It is a PWM transmitter with a 15,000 volt power supply.  In their day, these were not terrible transmitters, however, like their Harris MW-5/10/50 PDM brethren, frequent thorough cleaning is required to keep the dirt/dust from arcing over.  Unfortunately, it is becoming more and more difficult to obtain parts for these units. This transmitter was installed in October of 1983, thus, almost thirty years of service is quite enough.  This unit we did not cut up and scrap, rather, it is sitting by the back door, waiting for any takers.

Continental 315R1 modulator/RF sections

Continental 315R-1 modulator/RF sections

The interior of the Continental 315-R1 transmitter.  Modulator section is on the left, RF section is on the right.

The good news is, WVMT is another one of those “successful AM station” stories.  You know, the kind of station that has local programming, local sports, news, community presence and most importantly, makes money.  For all those diligently studying the “AM Problem” for the up and coming NAB conference this April, here is a clue: It’s the programming…

Nautel XR6 transmitter, wvmt Burlington, VT

Nautel XR6 transmitter, WVMT Burlington, VT

This is the Nautel XR-6 on the air.  Positive peaks, anyone?

AM modulation monitor

AM modulation monitor

We turned that down a little bit.  Also, the station does not run AM stereo, the AM stereo mod monitor is simply a usable relic of a bygone era.

WVMT is noted as the first radio station licensed to the state of Vermont, signing on on May 10, 1922.  It has a three tower directional array located down in the swamp.  For some idea of perspective, it is 1,150 feet (350 meters) from the transmitter building to the center tower, the towers are 411 feet (125 meters) tall spaced 405 feet (123 meters) apart.

WVMT three tower directional antenna array, Burlington, VT

WVMT three tower directional antenna array, Burlington, VT

WVMT antenna system from back of transmitter/studio building.  That is a long walk over rough terrain in the middle of the night or anytime really, but especially in the middle of the night.

Series surge suppressor

Radio facilities, particularly mountain top transmitter sites, are prone to power transients. The causes can be varied, but most often, lightning is the culprit.  Long power transmission lines to the site are vulnerable to direct strikes and EMF induced spikes from nearby strikes.  Other issues, such as switching transients, load fluctuations, and malfunctioning equipment can lead “clear weather” outages.  Of course, the best way to deal with such things is prevention.

Power line surge suppressors have been around for quite some time.  They usually take the form of a MOV (Metal Oxide Varistor) connected between the hot leg and neutral or ground.  There are a few differences in designs, however.  Typically, most facilities employ a parallel surge suppressor.  That normally take to form of an enclosure hung next to the main power panel with a group of MOV modules in it.  The MOVs are feed from a circuit breaker in the panel.  Like this:

LEA parallel surge suppressor

LEA parallel or shunt surge suppressor

This is an LEA three phase 208 volt shunt surge suppression unit, which has MOVs between all phases to ground and each other.  That is connected in parallel to the electrical service with the circuit breaker disconnect.  These function well enough, provided there is a good bit of series inductance before the unit and also, preferably after.  The series inductance can come from many sources, including long secondary leads from the utility company transformer or electrical conductors enclosed in metal conduit, particularly rigid (verses EMT, or FMC) metal conduit.  The inductance adds a bit of resistance to the transient voltages, which come in higher than 50 or 60 Hz AC waveform.

A better method of transient protection is the Series Surge Suppressor.  These units are installed in line with the incoming service and include an inductor to add the required series resistance coupled with MOVs and capacitors.  Most series surge suppressor also filter out harmonics and RF by design, something desirable particularly at a transmitter site.  Series surge suppressors look like this:

LEA DYNA systems series surge protector

LEA DYNA systems series surge protector

This is a LEA three phase 240 volt unit.  As in the other example, all phases have MOVs to neutral and each other.   There are MOVs and capacitors on the line and load side of this unit (line side is the bottom of the inductor).  A basic schematic looks like this:

Series surge suppressor basic schematic

Series surge suppressor basic schematic

A few things to note; MOVs have a short circuit failure mode and must be fused to protect the incoming line from shorts to ground.  MOVs also deteriorate with age, the more they fire, the lower the breakdown voltage becomes.  Eventually, the will begin to conduct current at all times and heat up, thus they should also be thermally fused.  MOVs that are not properly protected from over current or over temperature conditions have the alarming capacity to explode and/or catch on fire.  From experience, this is something to be avoided.  Matched MOVs can be paralleled to increase current handling capacity.

The inductor is in the 100 µH range, which adds almost no inductive reactance at 60 Hz.  However, it becomes more resistive as the frequency goes up.  Most transients, especially lightning, happen at many times the 60 Hz fundamental frequency used in power distribution (50 Hz elsewhere unless airborne, then it may be 400 Hz).

Capacitors are in the 1-10 mF range and rated for 1 KV or greater as a safety factor.  The net effect of adding capacitance is to create a low pass filter.  Hypothetically speaking, of course, playing around with the capacitance values may net a better lowpass filter.  For example, at 100 uH and 5 mF, the cutoff frequency is 225 Hz, or below the fourth harmonic.  Care must be taken not to affect or distort the 60 Hz wave form or all sorts of bad things will happen, especially to switching power supplies.

These units also need have a bypass method installed.  If one of the MOV modules needs to be replaced, power to the unit has to be secured.  This can be done by connecting it to the AC mains before any generator transfer switch.  That way, the main power can be secured and the site can run on generator power while the maintenance on the surge suppression unit is taking place.

Oh damn; La tercera parte

Now where did those vise (vice?) grips go?

Vice grip pliers used to clamp RF feed to tower

Vise grip pliers used to clamp RF feed to tower

Oh yeah, that’s right, they were used to attach the RF feed to an AM tower.  About ten years ago.

Vice grip tower clamp

Vise grip tower clamp

From this view, it looks like whatever tower crew installed this tower could not manage to solder or braze the copper RF connection to the steel tower.  The area was then painted, but it looks like there is some corrosion going on between metals.

Vice grips clamping RF feed to tower

Vise grips clamping RF feed to tower

Another view.

AM broadcast tower

AM broadcast tower

This is a relatively new tower.  Sadly, it is very likely that this station will be going off the air soon.  If the station is still on the air come springtime, I will drag the brazing outfit across the field/swamp and fix this.  If the station goes dark, then I won’t worry about it.

WKNR 1310; gone but not forgotten

Reflecting the state of the economy in Detroit, WDTW went silent on January 1st. Less than two weeks later, the towers come down:

Thanks, Chris R for the video link.

The license has been donated by Clear Channel to MMTC (Minority Media and Telecommunications Council), but not the land or towers. It remains to be seen whether the station will return to the air, however, given the costs involved and the economic conditions in Detroit, that is unlikely.

The station signed on in 1946, moving to 1310 KHz with full time operation in 1948.  Back in the day, it was a flame throwing top 40 station and is purported to be the source of the “Paul is dead” rumors that surrounded the Beatles in the late 60’s.  Much more history at Keener13.com.

Take pictures of your favorite AM stations now because tomorrow, they and all their history may be gone.

Nanobridge M5 wireless LAN link, Part II

After a bit of delay, we were able to return to the WICC transmitter site to install the Wireless LAN link.  The installation was pretty straight forward.  The studio unit was mounted on an existing STL tower on the top of the elevator room, the transmitter unit was mounted on an existing pipe on the roof of the transmitter building.

M5 Nanobridge mounted on transmitter building with radome

M5 Nanobridge mounted on transmitter building with RADOME

I included RADOMEs for a couple of reasons; first, there is a lot of critters around of the two legged and winged kind. The upright two legged critters may be attracted to the signal strength lights at night. This unwanted attention could invite the juvenile delinquents bored teenagers to throw various objects found laying around on the ground at the antenna, damaging it.  The winged type critter may be inclined to view the feed horn as a good nesting location. The other reason is this site gets a lot of rain, wind, ice and snow, therefore the RADOMEs afford some protection against the weather.

Aiming the antennas was pretty straight forward, but requires at least two people.  Using landmarks, we aligned the dishes in the general direction of each other.  Both ends of the system were turned on and we had a -89 dBm signal path, and somewhat surprisingly, the radios linked up and my laptop grabbed an IP address via DHCP.  Using the signal strength meter on the side of the antenna, each dish was peaked in turn:

M5 Nanobridge Antenna signal strength meter

M5 Nanobridge Antenna signal strength meter

Then, somebody on either end went below and looked at the signal strength screen on the web interface while the other end was peaked.  In the end, we had about -65 dBm signal strength, which is somewhat less than the -58 dBm predicted.  I think we can do better, so on the next clear day, I am going to peak the signal again.

The data rate initially reported was over 100 MBPS, however, once I started transferring files back and forth, that dropped to about 50 MBPS.  If it is raining, that rate drops to about 35 MBPS, which is still far above what we need this link to do.  As a test, I streamed a youtube video, downloaded a windows update, loaded several web pages and checked my email simultaneously.  There where no issues with the data rate while those tasks were being preformed.

It is quite amazing to me that these little inexpensive radios can work so well.  My boss thinks that they will be blown up by lightning during the first thunderstorm of the season.  I don’t know.  There are several of these units that have been installed at mountain top tower sites and have been working for several years without issue.

Next step, installing the IP cameras and warning signs on the fence, setting up the monitoring software, etc.

Transmitter site security cameras

Transmitter site security cameras

Cameras mounted on old chimney platform.  This is the first set of cameras covering the south, north and west approaches.  A fourth camera will be mounted on the back of the building covering the east approach.  Then, under the eves cameras will be mounted on all four corners of the building and the generator shed.  If anything moves, it will be recorded.

Oh, damn: la segunda parte

Emergency! The (AM) Transmitter keeps popping off the air and we can’t figure out why! YOU MUST HELP US!!1!!!


Some problems are easy to spot, difficult to fix

Some problems are easy to spot, difficult to fix

Well, with the ATU mounted about 1/4 inch away from the 90 degree, series excited tower, I wonder why.  It seemed to be especially problematic during rain, snow and ice storms.   When I asked how long this had been going on, I was told “About two years, ever since we put up the new tower!”

You don’t say.

We finally took care of this by moving the ATU back inside the shed after moving the transmitter to a different building.  The funny thing is, this was installed by a guy who had a BSEE.  I guess he must have been out sick the day they covered this in class.

Ubiquiti Nanobridge M5 IP radio

I am in the process of installing a pair of the Nanobridge M5 units as an IP network link between a transmitter site and the studio location. The path is relatively short, about 1.5 miles over mostly water.  The main reason for this is to replace the analog phone lines used for remote control data and backup programming delivery to the transmitter site.  One added benefit, we are also installing several  IP cameras to keep an eye on the place.  We purchased the Nanobridge system for $80.00 per side.  The price is pretty good, but the configuration and testing is a bit intensive.

Network diagram

Network Diagram

There are many versions of these spread spectrum radios, some are licensed, some are license free.  These are inexpensive, license free links that I would count on for short paths or use in non-congested areas.  In congested areas, licensed (Part 101) links should be used, especially for critical infrastructure like STLs.

Since I dreamed up this idea, I figured I should make sure it is going to work before recommending it to the powers that be.  I have learned the hard way, almost nothing is worse than a failed project with your name on it.  Better to over study something than to go off half cocked, spend a bunch of money, then realize the idea was flawed from the start.  See also: Success has a thousand mothers but failure is an orphan.

Nanobrige path study, 5.8 GHz

Nanobrige path study, 5.8 GHz, moderate noise floor, 1.5 miles

Looks pretty good.  300 MB/s bi-directional which is faster than the Ethernet port on the unit.  This will be set up in bridge mode with pretty robust encryption.  The transmitter site side is configured in the router mode, creating a second class A network at the remote site.

Nanobridge M5 22 dBi antenna

Nanobridge M5 22 dBi antenna

Next step, configuring the units.  The Nanobridge units were set up in a back to back configuration in the engineering room.  Each end comes with a default IP address of  The units were several steps behind the latest firmware version, therefore the firmware was upgraded first.  The default admin user, password, and IP addresses were changed.  There is no greater security risk than default user and password.  The wireless security feature is enabled using WPA2-AES PSK and a greater than 192 bit access code.  The unit allows for any access code length up to 256 bits.  With a key of between 192 and 256 bits, the number of possible solutions is between 6.2771 E 57 and 1.1579 E 77, which should be pretty hard to crack.  By way of reference, a 192 bit password has 24 ASCII characters and a 256 bit password has 32 ACSII characters.

Air OS main screen

Air OS main screen

The system requires an access point, which is configured for the studio side making the transmitter site stub network the station side.  The access point is configured not to advertize its SSID, thus it should be transparent to anyone sniffing around.  The WLAN is configured as a layer two bridge, which will cut down on the data overhead, as layer three framing will not need to be opened between the two units.  The transmitter site network is set up with SOHO router function built into the Nanobridge.  One static route is needed to get to the main network.  Once the security cameras are installed, PAT may need to be used to access individual camera units via the public network.

Ubiquity air os signal strength screen

Ubiquity air os signal strength screen

Next step, deploy the units and aligning antennas.  These are 22 dBi gain antennas, which have a pretty tight beam width.  Maximum transmit power is 23 dBm, or 200 mW.  The transceiver/antenna unit has a handy signal strength meter on the side of the unit, which is good for rough in.  The web interface has a more precise meter.  In addition to that, there is a java based spectrum analyzer, which is very handy for finding open channels in congested areas.  These units can also be used on UNii frequencies with special requirements.

According to the manufacture, UV resistant shielded Category 5e cable should be used for outdoor installations.  We have several spools of Belden 1300A, which fits the bill.  The shielded Cat 5 is necessary for lightning protection as the cable shield offers a ground path for the antenna unit.  The antenna mounting structure is also grounded.  I did not take the equipment apart to examine, but I believe the POE injector and antenna have 15KV TVSS diodes across all conductors.  It will be interesting to see how these units do at the transmitter site, where there are two 300 foot towers which likely get struck by lightning often.

More pictures of the installation when it is completed.

Next step, put the system into service and monitor the link.  At the transmitter site, a re-purposed 10/100 Ethernet switch will be installed for the cameras, computer, IP-RS232 converter and anything else that may need to be added in the future.  One thing we may try is an Audio of IP (AoIP) bridge like a Barix or Tieline for program audio and room audio.

AM Radio Improvement Plan

There has been lots of hand wringing and ink spilled regarding the sorry state of affairs in the senior service. AM is plagued with problems; interference, poor bandwidth, etc. To that end, the NAB has launched studies and initiatives and hired all sorts of pricey consultants to consult with. Here is my own AM improvement plan and it is rather simple:

  1. Clean up the transmitter site.
  2. Get rid of AM HD radio.
  3. Variable IF bandwidth receivers.
  4. Improve Programming.

How many of us have seen AM transmitter site dumps? Deferred maintenance, malfunctioning directional arrays, trees growing up on the ground system, flooded buildings and ATU’s,  rusty towers, transmitters not a full power, ground system deteriorated or missing all together, just to list a few problems.  Many AM transmitter sites are technical disasters.  Think that these things have no bearing on the AM station’s signal?  Think again.

differed maintenance, AM transmitter site

Differed maintenance, AM transmitter site (there is a tower in there somewhere)

Trees growing around the tower base can attenuate the signal by 30%.  A comment from a well known engineering firm:

…Recently XXX field engineers had occasion to measure an AM station at XXXX kHz before and after removing vegetation in the vicinity. The station had a quarter-wave tower. The base area had grown up in brush and hardwood trees to a height of perhaps 30 feet (9m) and this extended from near the base across the entire ground system. After clearing (cutting, no ground system disturbance), the signal measured at some 16 locations on four radials went up a uniform amount of about 15% or 1.2 DB. That’s about a 30% increase in radiated power…

That is an inexpensive power boost and they didn’t even have to file with the FCC! A 1 – 2 dB power gain is pretty nice and can mean the difference between a listenable signal and static.  How many times have I heard the lament that AM band is full of noise and not listenable.  Certainly, there are major challenges in the urban listening environment.  Putting forth a better signal will overcome some of this electrical noise.

There is a reason why engineering standards were developed for the physical plant; they work.

There is no cure for the noise that AM HD Radio puts out into the adjacent channels.  This self interference benefits none, not even the station transmitting AM HD Radio.  This dubious technology has proved itself a non-starter and should be discontinued.  For smaller station owners, the cost of implementing AM HD Radio is prohibitive.  Licensing of a proprietary modulation scheme, new transmitting equipment, specialized exciters plus any needed bandwidth improvements to AM antenna arrays can easily exceed $100,000.00.  Unfortunately, it is often the small AM radio operators that are making a good showing, and serving their community of license and making money.  These are the very stations that are hurt the most by adjacent channel AM HD Radio interference.

Receiver design over the last twenty to thirty years has been the greater issue with perceived low AM broadcast quality.  AM receivers have an average bandwidth of just 3-4 KHz, which is slightly better than telephone quality.  AM broadcasting has gotten a bad wrap because of this and there are many comments about how AM is “inferior quality” to FM.  With a quality older receiver, AM can sound very good.  Of course, the receiver manufactures all point adjacent channel interference as their rational for reducing IF bandwidth.  Why not leave it in the hands of the user? The GE Superradio had this feature with a “wide” and “narrow” setting for AM reception.  They worked remarkably well.   A receiver could also be designed to automatically increase IF bandwidth at higher received signal strengths.

Finally, as the saying goes; Garbage in, Garbage out (GIGO).  This holds true for many things including radio programming.  Expecting that mediocre satellite syndicated news talk will garner great ratings and huge revenues is silly.  For years and years, station owners have put minimal effort into AM radio and expected big returns.  It is not working.  AM stations that go against that trend; those with unique formats (Gasp! Music, on AM?), local content, and community oriented programming can and do succeed.  They are fighting an up hill battle in both directions.  With all of the business pressures from larger broadcast groups, interference issues and negative viewpoint on the viability of the AM band, one wonders how long they can last.

Hums no more

My first job as Chief Engineer was at WPTR and WFLY in 1991. I was young and it was a learning experience. The WPTR transmitter was a Harris MW50A, which reliably went off the air every six months. The transmission lines going out to the towers had fallen off of their wooden support posts, trees were growing up in the antenna field, sample lines were going bad. In short, it was a mess.  Even so, the station was well known and well liked in the community. One could still see echos of greatness that once was.

When Crawford Broadcasting purchased the station in 1996, they put much money and effort into renovating the facility.  Replacing the Harris transmitter with a solid state Nautel, replacing the phasor and transmission lines, cutting the trees from the field, painting the towers, renovating the old transmitter building into a new studio facility and finally removing the old Butler building that formerly housed the “Gold Studios.”

Then the depression of 2008-20?? hit.  Once again, the place has fallen on hard times.  WDCD-AM has been silent since last April.  The cost of running the 50 KW AM transmitter being too much to bear in the current economy.  Formatically, the station drifted around for several years.  According to the the STA to go silent:


They may need to do something slightly non-religious to survive.

While we were waiting for the utility company to turn the electric back on after yesterday’s fire, I took a short walk around the WDCD-AM site and took some pictures.  Transmitter disconnect thrown,  fuses are pulled,  it is kind of sad to see the Nautel XL-60 dark:

Nautel XL-60 AM transmitter.  WDCD Albany, NY

Nautel XL-60 AM transmitter. WDCD Albany, NY

I apologize greatly for the blurry picture, it was taken with my cellphone camera, my good camera being back at home on my desk.  Radio stations, when they are on the air, seem like they are alive.  Machinery hums, fans move air, meters move, and there is a sense of purpose.  Silent radio stations give me a sense of foreboding, like something is terribly wrong.

WDCD three tower array, Albany, NY

WDCD three tower array, Albany, NY

View of the towers without Butler Building.  The towers are 340 feet tall, which is 206 electrical degrees on 1540 KHz.  The site was constructed like this to suppress skywave signals toward ZNS, Nassau, Bahamas.  ZNS is the only clear channel station allotted to the Bahamas by NARBA.  The other station WDCD is protecting is KXEL, Waterloo, IA.  During the 90’s, I received many QSL requests from Norway/Finland and even a few from South Africa.  I know that the station had a large following in most of New England.

WDCD tower base, tower three

WDCD tower base, tower one (furthest from building)

Tower one tower base.  This IDECO tower had to have the top 60 feet replaced after it was hit by an airplane in 1953.  The tower base also had to be replaced in the late 1980’s as it was crumbling and falling apart.  To do this, Northeast Towers used railroad jacks and jacked the entire tower up off of the base insulator.  They re-formed and poured a new base, carefully letting the tower back down on a new base insulator about a week later.

WDCD towers looking back toward the transmitter building

WDCD towers looking back toward the transmitter building

Antenna field looking back at the transmitter building.  If you work at radio transmitter sites, I encourage you to take pictures of all these things, as someday, they will all be gone.

WDCD bomb shelter

WDCD bomb shelter

The “bomb shelter” and 220 KW backup generator,  constructed by FEMA in 1968 as part of the BSEPP.  This used to have an emergency studio and enough diesel fuel for fourteen days operation.  Now, the bomb shelter has a kitchen and bathrooms.  The underground storage tank no longer meets EPA standards and has been pumped out.

WDCD Onan generator

WDCD Onan generator

The Onan generator is conservatively rated at 220 KW, surge rating 275 KW.  These things were way over constructed, so it is likely it would easily run 225 KW all day.  It has an in line six cylinder engine with a massive fly wheel.  When the engine is stopped, it takes about twenty seconds for the generator to stop turning.

Three phase service

Three phase service

National Grid, 3 pot, 480 volt, 3 phase service, original to the 1947 building.

I wonder if it will return.


A pessimist sees the glass as half empty. An optimist sees the glass as half full. The engineer sees the glass as twice the size it needs to be.

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin

The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is hard business. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.
~Rudyard Kipling

Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19

...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner

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