All Pictures with borders can be clicked on for an enlarged version.
In the 60s, WMCA was the home of the top 40s WMCA "Good Guys." Some of those Good Guys, such as Harry Harrison and Joe O'Brien can now be heard on WCBS FM 101.1. See links at the bottom of this page for more.
I would like to thank Tony Dee (DeNicola) - WA2IHZ, and his son, Brian, for the tour of this site. Tony has been working at WMCA since 1992. Tony co-owns WODI AM 1230 with Dave Marthouse - N2AAM in Brookneal, VA, a small, beloved Mayberry-like town only about 120 miles from Mt. Airy, NC where Andy Griffith was born. Tony spent many hours with me at the WMCA site going over the equipment, telling me stories, looking through files for important historical information and most of all, really made me feel welcome. Tony and his son Brian are two great guys, whom I am glad to have met. Brian is looking forward to a career in radio and has, in fact, started that career. I wish you the best of success and fun, Brian! I would also like to thank Pete Tauriello, shadow traffic reporter for WINS, for his encouragement and connecting me to Tony for this tour, taken on 6/9/1998. Pete has also been a real boost for me.
WMCA Transmitter Building
This Building now houses both WMCA and WNYC AM transmitters. The outputs are diplexed at the antenna towers, allowing the two stations to share the same 3 towers. Part of the diplexing process is to add band stop filters to each transmitter output to prevent the RF signal from each transmitter from feeding back into the other transmitter.
WNYC transmitter and equipment
|Microwave feed dish pointed
toward the WMCA studios in
Rutherford, NJ. This dish is
also visible in the head picture on
|Input processors, compressors, and
|Main Nautel 10KW*
Model AMPFET ND-10 (running at 5KW) solid state transmitter with Pulse Width Modulation (PWM) on the collectors.
Chief Engineer, Tony Dee, and his son, Brian, at right.
|Continental 5KW Model 315R-1 standby
transmitter. It uses a "dc coupled series switching modulator."
|The Nautel is composed of four RF amplifier modules, each rated nominally for 1.4 KW. The modules each contain, PA/Modulator Assemblies and are all modulated equally. The outputs are combined to obtain the full 5+ KW. If a module should fail, it can be removed and replaced with another module while the transmitter is operating, causing only a brief power reduction during the change. Each module is broken down further into 3 boards.|
|Top of individual transmitter module board. There are three of these boards per module, designated as 'A', 'B'
and 'C'. Three
indicator lights on the parent module indicate if a board has failed.
|Flip side of transmitter module board. These boards "buzz" with
the sound of the audio modulation.
|View of rear of the four modules, each with its own cooling
fan. It used to be that a 5 KW transmitter required enormous,
noisy blowers making the transmitter room sound like a ship's engine room. This one is cooled with four muffin fans, not much
louder than a PC cooling fan. Even though there is actually more
power, modern transmitters do not give you the old time ambiance
of power, including the heat.
|This is the digital control board.|
Pulse modulation is called Class 'D' modulation. In a class D modulator, active elements (transistors) are never in a partially on or off state. They are either fully on or fully off. In these states, transistors dissipate a minimum amount of power. Either the current is near zero or the voltage is near zero so that the resulting power dissipation calculated as the voltage times the current (E * I) always results in a very low value. There are different types of class D modulation, but all are accomplished by using transistors as switches. In the case of Pulse Width Modulation, as the audio wave increases in value, the amount of time the transistors are switched "on" (duty cycle) is longer than the time they are switched "off." As the wave falls, the proportion of time "on" to time "off" is reduced and eventually reverses. Another characteristic of class 'D' modulation is a positive peak modulation which can go beyond 100%. How is this possible without clipping of the negative modulation peaks? Unlike the old high level plate modulation methods, with Class D modulation, the carrier can be controlled to "float" to a higher power when the modulation is pushed past 100%. I believe the FCC allows a maximum of 125%.
The Continental Electronic transmitter uses air cooled 3CX3000F7 tubes in the PA in the modulator. The 315R-1 is a PWM transmitter. According to David Herschberger of Continental Electronics, the 'R' in the transmitter model number referred to "Rockwell" from Collins/Rockwell which came out with what was called "The Power Rock" design. Otherwise most other tube designed Continental transmitters used Doherty linear modulation.
Description of the 315R modulation as explained by
David Herschberger, Principal Engineer at Continental Electronics
"High level amplitude modulation is normally achieved by varying the plate (and screen) voltages of
an RF amplifier tube. This varies the RF output of the tube, producing amplitude modulation. The voltage applied
to the tube consists of a DC voltage plus audio. There are many ways to produce this combination of DC+audio. Early
AM transmitters did it in a straightforward way: a high level audio amplifier produced the audio, which was then
added to DC with a coupling capacitor and a modulation choke.
A very simple, but inefficient way to produce AM is to place an RF amplifier tube and a class A audio amplifier (modulator) tube in series with the power supply. Without modulation, roughly half the power supply's voltage drop is across the class A audio amplifier tube, and the other half of the voltage appears across the RF amplifier. On positive modulation peaks, the voltage drop is low across the audio tube, which places a high voltage across the RF
amplifier, which raises the RF output. On negative modulation peaks, the class A audio amplifier is at or near cutoff, so that all of the power supply voltage appears across the audio tube and little or no voltage is applied to
the RF amplifier, which "pinches off" the RF output. This system will work, but the modulator tube will be inefficient because it is running single ended in class A. The RF amplifier, however, can operate efficiently in class C.
This simple system is the basis for a high efficiency transmitter using pulse width modulation. If the class A audio amplifier is replaced with a class D audio amplifier, then the transmitter becomes efficient. In class D, the modulator tube operates as a switch - it is either "on" or "off." When it is on, and current is flowing, the voltage across the tube is very low. So, dissipation (wasted heat) is very low. When it is off, there is a high voltage across the tube, but no current is flowing, so plate dissipation is zero.
A switch mode amplifier like this can be made to produce our DC+audio by producing pulses whose widths are proportional to the value of DC+audio that we want. The pulse rate is at a frequency above the audio range - typically 70 kHz. The output of this tube is then lowpass filtered, which removes the 70 kHz components and leaves just our audio+DC. In other words, the lowpass filter takes the "average" value of the pulses. When the pulses are narrow, the lowpass filter takes the average, which produces a low value for audio+DC, producing a low amplitude RF envelope from the RF amplifier. Similarly, when the pulses are wide, the lowpass filter produces a high average voltage at its output, which in turn results in a high RF envelope output.
So, we have a series combination of a power supply, a class D audio amplifier, and an RF power amplifier. The next issues are (1) where to put the ground, and (2) what to make the ordering of the blocks. In the Harris transmitters, the negative end of the power supply is grounded. The class D modulator connects between ground and the cathode of the RF amplifier. The positive end of the power supply connects to the plate of the RF amplifier. In the Collins/Continental transmitters, the positive end of the power supply is grounded, as is the plate of the RF amplifier (for DC). The class D modulator connects between the negative output of the power supply and the cathode of the RF amplifier."
David L. Herschberger
This design reminds me of the method used in DC switching regulators, for which I was on the development team at Singer General Precision back in 1967-1969. The input of the regulator was a full wave rectified power source. As the voltage varied, a switching or "pass" transistor would gate the current at a varied pulse width accordingly and the pulsed output would be passed to a filter network to smooth out the output. The output would be compared to a zener diode as a reference and the difference between the reference and the sampled output would determine whether the output would be switched on or off. The higher the sensed voltage, the narrower the pulses. The lower the voltage, the wider the pulses. The output was, of course a steady DC value, as long as the average input voltage source was higher than the output.
Now consider what would happen if the zener diode was replaced with an audio signal and compared to another reference, removing the comparison (feedback) to the output. The output of the power supply would become a power audio source, since the new reference voltage is no longer a DC voltage, but a voltage which varies with an audio signal. This is all accomplished by switching transistors completely on (very low power dissipation) and completely off (no power dissipation). The only devices which would be operating in an active Class 'A' manor would be the very low level voltage amplifiers for the input. This is a simplified, but this seems to be the principle involved in the modulation technique explained by David Herschberger. In the 315R, the single 3CX3000F7 modulator tube, takes the place of the pass transistor. It acts as the final high power switch before filtering.
On the other hand, Doherty Modulation is a modified linear amplifier, low level modulated at the driver stages. What distinguishes it from others is that it uses two RF output tubes, one which handles the carrier and the negative modulation swings (the "Carrier tube") and the other tube (the "Peak Tube"), which normally is cut off, but goes into action during the positive peaks of modulation. The 315R shown here, however, was an exception.
|This picture shows Brian holding
one of the 3CX3000F7 tubes.
OK, I'll be honest, this is a pose, but Tony
|Antenna phasing unit allows each tower to be fed at a different phase, relative to other towers.
This phase relation, causes
different degrees of radiation cancellation to create a desired
pattern of directional coverage.
Stations with one tower, are
|Three-tower array phased to cover mostly New York
City. Antennas were built by Truscan Steel Products.
The Empire State Building can be seen in the distance at the right of the farthest tower. WNYC has a slightly different directional pattern.
Part of tower blueprint shows dates of 12/8/1937
If you're standing on the WMCA tower catwalk
you will hear THIS! or, maybe THIS!
The sound is far more impressive when you're there. It is intended to
discourage birds away from the towers. It triggers periodically with
a few different sounds and adds to the somewhat mystical feeling this place.
|From afar, these towers look fairly ordinary,
but up close, the structure is exceptionally
beautiful with great detail. (Click on photo)
|View of tower foot showing porcelain insulator,
Austin Isolation transformer for tower lights,
tuning house to left and NJ Turnpike in the
distance. The dark mass on the tuning house
is a mass of flying insects called midgies. There
are swarms of these insects in the meadows.
Fortunately they don't bite. I had to spit one out
of my mouth. I wasn't sure of its nutritional value.
|Looking straight up into the tower. Notice the RF feed
directly to to a center, hexagonal plate. This distributes
the current equally to the three sides.
|View down catwalk to first tower with NJ Turnpike and
Laurel Hill (nicknamed "Snake Hill" mountain) at the
right. If you commute from Newark, NJ to Penn Station,
NYC on a train, you pass the foot of this mountain.
Brian is showing the size of this
Spare studio which can
Emergency Diesel Powered
One of the spare parts
Broadcast continuous loop
I used to think tower lights were just
This is the type of light bulb that is used
Looking back at the transmitter
Prior to the Nautel was the RCA
Open PA cabinet of the BTA-5U1
Master Control Room in New York City
(From WMCA Brochure supplied by Tony Dee)
This 5KW RCA transmitter installation was completed in 1940.
Recollections of Pete Tauriello of WINS News
On January 21, 1999 at about 01:20AM Tony Dee had to shut down the WMCA transmitter for maintenance. Here are the sounds heard on 570 KHZ just before and about 1.5 minutes after WMCA dropped out.
|Click this button.|
First the shutdown announcement, then the carrier drops out revealing a Spanish speaking station and a ticking noise every second and a beep every minute on the minute followed by two morse code Rs. I posed a question as to what I was hearing on New York Radio Message Board and was told the following:
"Radio Reloj" is Spanish for "clock radio." At the top of each minute this network broadcasts code IDs ... dit-dah-dit, dit-dah-dit ... "RR" in Morse code. The audio might be bad, but it's one of the easier Latin-American stations to find and identify. The clock ticking and code IDs can be copied when voice and music can't.
- Tom Sanders
The Spanish-language station with the time pips and Morse "RR" identifier on 570 is CMHI, Radio Reloj, in Santa Clara, Cuba. Radio Reloj is Cuba's national time-standard station and is based in Havana. It has transmitters all over the island...its Havana outlet is on 760 (CMCD). The format of Radio Reloj consists of two announcers taking turns reading news with time pips superimposed. Time checks are given on the minute, followed by a brief time tone and the "RR" sounder. There are no commercials.
- Phil Galasso
Cuba is about 1500 miles away and from here and groundwaves from Cuba are almost completely over ocean salt water, unobstructed by any land.
All images are Copyrighted and are provided for your personal enjoyment. Use of these images for commercial purposes including their distribution on CD-ROM or any other media without my permission is prohibited. Contact: Jim Hawkins