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VOA Site B, Greenville, NC

I took a brief vacation last week along the coast of North Carolina. It was relaxing and fun to be sure. I was also aware of and slightly curious about the Voice Of America shortwave site, a slight distance inland in Grimesland, NC.  Thus, I made arrangements visit the facility on my way home.  Chief Engineer, Macon Dail, was gracious enough to give us the guided tour.  The facility is an engineering marvel.  The scale and complexity is enormous.  The entire facility is scrupulously maintained.  Many of the transmitters and other equipment have been upgraded to make them more functional.   I tried to take meaningful pictures, but in many cases, they simply do not to justice.

Edward R Murrow Transmitting Facility, (VOA Greenville Site B) Grimesland, North Carolina

Officially known as the Edward R Murrow Transmitting Station of the International Broadcasting Bureau, VOA Site B was constructed in 1961.  Six of the eight shortwave transmitters are original to the construction of the building.  The other two (BBC SK55 and AEG S4005) were added in 1986.  All of the dipole curtain arrays, rhombics, transmission line and the antenna switching matrix are also original.  A few brief statistics about this site:

  • Land area is 2,715 acres (1099 hectare).
  • Over twenty six miles (forty two kilometers) of 300 ohm open transmission line rated at 500 KW.
  • Sixteen dipole curtain arrays, average antenna gain 17 dBi.
  • Twenty rhombic antennas, antenna gain 15 dBi.
  • Two of the dipole curtain arrays can slew azimuth and take off angle.
  • Three Continental Electronics 420A 500 KW Doherty modulated transmitters.
  • Three General Electric 4BT250A1 250 KW high level plate modulated transmitters.
  • One Brown Boveri Company (BBC) SK55C3 500 KW PSM transmitter.
  • One AEG Telefunken S4005 500 KW PDM transmitter.
  • Antenna switch matrix connects any of the eight transmitters to any of the thirty six antennas

While we were there, both of the newer transmitters were on the air, running at 250 KW.  The GE transmitters are used as needed and the Continentals are rarely used due to age, difficulty to tune, change frequencies and gross power inefficiency.

The station staff has, out of necessity, fabricated some very cool upgrades to the transmitters and facility.  The first of which is the alarm annunciator, which is based on a Star Trek (Original Series) sound scheme.  Once or twice I heard the bridge general alarm go off, followed by a female voice stating the problem: “GB8, OFF AIR.”

Chief Engineer’s office.  NCC-1701; no bloody A, no bloody B, no bloody C, and no bloody D

The GE 250 KW transmitters have been retrofitted with a computer controlled auto tune system for frequency changes.  The antenna switch matrix controller has been replaced by a PLC based system.  As the transmitters are so old, many of the transmitter specific parts need to be machined or fabricated locally.  The rest of the transmitter parts are stocked in a large parts storage room, all of which is meticulously labeled and tracked.  The floors are waxed and spotless, there is no dust on the horizontal surfaces, the work shop is clean, tools are put away, grass and weeds are cut, etc.  All of these little details did not go unnoticed and indicate great pride by the staff in the facility itself.

The heart of the facility is the control room which consists of four rows of equipment racks and a central operating position elevated above floor level.  Arranged around that are the eight shortwave transmitters in two long transmitter galleries.

VOA Site B control room

From this point, the operator can view all of the transmitters in the two transmitter galleries.

Operating position

Around the control operator are arranged a series of computer monitors showing various station function status.

Transmitter modulation and status indicators

Antenna Matrix status and control

VOA transmitter control and status (center)

Audio monitoring router

The equipment is installed into the equipment racks by type; one rack contains the frequency generators for each transmitter, the next contains first stage power amplifiers, the next contains audio processors and modulation monitors, etc.

Equipment racks and Shift Supervisor’s  office

Transmitter frequency generators

Audio processors, modulation monitors and patch panels

Backup audio feeds

The audio comes from the VOA studios in Washington DC via satellite. There are Comrex Access links as a backup and the Gentner EFT-1000s are used as a backup to the backup.  Prior to 1995, an eight hop microwave system covering the 300 mile (483 KM) distance was used.

GE 4BT250A transmitter with computer controlled tuning system installed

The station staff has created a computer controlled tuning system for the GE transmitters. Each transmitter can change frequency several times a day, during each frequency change, all of the transmitter stages need to be retuned. When done by hand, this can take several minutes to accomplish. The computer system uses follow pots and micro controllers to set the tuning elements to specific values. They can be touched up by hand if needed. A frequency change can usually be done in less than one minute.

GE 4BT250A transmitter

Your humble author and CE Macon Dail discussing the auto tune system

GE 4BT250A auto tune modification

GE 4BT250A IPA tube and input tuning.

The 2nd IPA and PA input tuning work the same way. The copper sleeve slides up and down over the coil to change resonant frequency. The vapor cooled tube sits inside the tub at the top, anode facing down. These tuning sections are a mechanical nightmare according to Macon. One of the reasons why VOA site A was closed down was due to the frequent frequency changes at that site causing excessive wear and tear on the old GE transmitters. This particular transmitter was being repaired; the staff was rebuilding a tuning network bypass capacitor assembly

GE 4BT250A transformer vault

The GE transmitter transformers still contain PCB’s. The plate transformers are in the back, basically pole transformers, one for each phase. Primary voltages is 4,180 volts, secondary rectified voltages are 12 KVDC (PA plate supply)  and 15 KVDC (modulator plate supply).

Hallway and maintenance access to back of GE transmitters

AEG Telefunken S4005 500 KW transmitter on the air

While we were there, the newer transmitters were in operation transmitting Spanish language programming to the Cuba on 13,605 KHz and 11,930 KHz.  Currently, the Greenville site is broadcasting mostly Spanish language programming with some English, French and Bambara language programming for Africa.

A fact that does not escape the notice of the staff.

VOA transmitter gallery, showing transmitters GB8 through GB4

Continental Electronics 420A 500 KW Shortwave transmitter control and metering panel

The three Continental 420A transmitters (GB-1, GB-2 and GB-3) are essentially a pair of 250 KW amplifiers combined. As these are Doherty power amplifiers, frequency changes are very difficult to effect. These transmitters spend most of their time in backup service.

Electrical distribution panel

The antenna matrix building is very impressive. Routing eight 250 or 500 KW transmitters to 36 different antennas takes a bit of doing. Mechanizing that set up is no mean feat. The pictures I took of the antenna matrix building do not show the size and complexity of the system.

Transmission line between transmitter building and antenna matrix building

For that, we need a satellite photo:

VOA Site B antenna matrix building

Basically, the transmitter building is in the lower left hand side of the picture. The transmission line go over to the antenna matrix building (looks like rectangular duct work), then run all the way to the back of the building. Each antenna transmission line come into the building and runs to the other side. Pneumatic arms then couple the transmitter line to the antenna line. This is all controlled by a custom made PLC and controlled by the operator from the main operating desk.

Custom made antenna matrix control system

300 ohm open transmission lines

300 ohm open transmission lines

Some of these lines are very long but have low loss due to the air dielectric. The most used antennas are the dipole curtain arrays.

Dipole curtain arrays

These consist of a series of broadband dipole antennas arranged side by side and stacked three or four high. behind those antennas is a reflector screen. There are two curtain arrays that are slewable. The dipole antennas phase relationship to each other can be changed to adjust the take off angle and azimuth, thus giving optimum coverage to the targeted area.

Close up curtain array

In this picture, the dipole antennas are to the right. Behind them is the reflector screen, behind that is the antenna feed system. Each antenna feed goes through the reflector screen to the center of the dipole antenna.

Each array requires four towers to support it.

Curtain dipole array supporting towers

Curtain dipole array supporting towers

Remote Antenna Switch.  Allows two antennas to use one transmission line.

The entire antenna field is viewable from an observation platform on the main building

Observation room

Entrance gate and slewable curtains in background

Curtain arrays

The entire facility is very impressive. The truth is, I could have spent several more hours there, but I know that people have jobs to do and I felt that I had taken up enough time. We often forget in this country that not everyone in the world has access to the internet. Shortwave broadcasting has a long reach and is not subject to government controlled firewalls or other forms of electronic censorship. Currently, the Greenville site is broadcasting mostly Spanish language programming with some English language programming for Africa. There are many areas in the world that are in political tension right now, some startlingly close to home. Places like Brazil, Argentina and Venezuela have been in the news lately. I do not see a time when these long reach broadcasting services will not be needed. Becoming a welcome source of good information for those affected people is good for brand USA. It would be money well spent to invest in a couple of new Continental 419H (still made in the USA) DRM capable transmitters for this facility. While the old GE and Continental units are great, the time may come when they are really needed but unavailable due to being down for repair.

Special thanks to Macon Dail for his time, knowledge and patience.

Middle Aged Iron: Cetec/Bauer 701B transmitter

In service as a backup unit at WALL 1340 KHz in Middletown, NY:

WALL 1340 KHz, Middletown NY AM1A on air, 701B into test load

WALL 1340 KHz, Middletown NY AM1A on air, 701B into test load

I believe the Cetec transmitter is from the early 70s. I wouldn’t really call it old, we have much older units in the field that are still in backup service.  WALL itself has been on the air since 1942 from this site. The tower out back was replaced in the mid 90’s and is 147 degrees tall. It broadcasts the “True Oldies Channel” and is currently owned by Cumulus, soon to be Townsquare.

Cetec 701B tube deck.  4-500As.

Cetec 701B tube deck. 4-500As.

The site is also home to sister station WRRV (92.7 MHz) which has a side mounted antenna near the top of the WALL tower. We are currently reconnecting the CCA transmitter as the backup for WRRV. That unit is also from the early 1970’s.

WRRV WALL transmitter site, Middletown, NY

WRRV WALL transmitter site, Middletown, NY

WRRV WALL transmitting tower, Middletown, NY

WRRV WALL transmitting tower, Middletown, NY

Nautel NV/NX firmware release

This is a Youtube video of the Nautel webinar regarding the NV and NX 4.0 firmware release.  I missed the original, live version due to other commitments.  For your viewing pleasure (55 minutes):

The upgrade seems a bit lengthy, but well worth it. Do not be scared away by Linux, which is a wonderful operating system. Once one understands some basic Linux commands, the operating system itself is very intuitive. I’d recommend anyone with interest in IT and networking to have a basic grasp of Linux and other open source software.

Well designed circuit boards

Sometimes it is the little things that catch the eye.  When I was installing a Nautel transmitter recently, I was admiring the circuit boards used for the transmitter controller.  I have seen a few circuit boards that are functional, but leave a little to be desired in the form department.  Does it really matter?  Perhaps not, but often times those tiny, almost insignificant details come back to bite you.  Little things like having the voltage regulator pins correctly placed or putting a toggle switch on the correct side of the board.  I have seen both mistakes from another, well known transmitter manufacturer.

Nautel NV controller board

Nautel NV controller board

Anyway, these are a few photographs of some well designed, well laid out circuit boards.

Controller board, NV transmitter

Controller board, NV transmitter

This is the main controller board.

NV controller board surface mount components

NV controller board surface mount components

Surface mount components.

NV controller board

NV controller board

Logic chips.

Nautel XR harmonic filter, part back part is the circuit board

Nautel XR harmonic filter, part back part is the circuit board

Part of the harmonic trap for the XR series transmitters.

It really is the little things that make big differences.  A circuit board under a cover that few people will ever see may seem like a very small and insignificant detail, but I notice and admire these things…

Proper drive levels for a Harris SX serries transmitters

I was working on a Harris SX5 the other day and snapped a picture of the scope while measure RF drive levels.  There are still quite a few of these units out the in the field, judging from my search engine results.  I thought it would be helpful to post something about it.  The RF power amp boards for the Harris Gates solid state AM series transmitters are the same design, I believe.

In order to fully drive the RF MOSFETs in this particular series transmitters (Harris SX1, 2.5 and 5 including A models) at least 26.5 volts peak to peak is required.  Less than that and the device will turn full on and internally short.  To measure RF drive, the transmitter must be in local with control voltage on, with the rear door interlock defeated (this can be safely done if the transmitter is wired with separate AC feeds for control and RF power supply). Make sure the RF power supply is defeated and will not turn on.  Measure across the input of the each of the toriods that feed the gates of the RF devices.

Harris SX series transmitter drive level test

Harris SX series transmitter drive level test, 27.45 volts, 1,110,000 Hz

It should measure between 26.5 and 29.5 volts. This one measures 27.45 volts peak to peak. Each input toroid on every PA board should be measured as the toroids themselves have strange failure modes and may pass resistance and continuity tests, yet still not provide proper drive voltage to the attached devices. This has to do with core permeability.  Each toroid feeds two RF MOSFETs, replace part is IRF-350.

As always when dealing with a SX transmitter, good luck.

Oh damn, La cuarta parte

Today there will be a quiz.  Ready?  Look at this picture and see if you can spot the problem:

Problem with Harris SX2.5A transmitter

Problem with Harris SX2.5A transmitter

If you said “Hey, that green wire seems a little odd; it disappears behind the heat sink next to that screw then reappears again at the top,” you are correct.  What really sucks is the green wire is the transmitter off connection to the remote control.  So, when the PA board was secured to the heat sink, the wire was trapped between the board and the heat sink.  Since the components were cold, it did not pinch through the insulation right away, no.  Rather, after the transmitter ran for several hours at full power, it got hot enough to displace the wire insulation and cause a short.  Doh!  The transmitter is off and it won’t come back on!

This is a picture of the wire after it was removed:

Pinched wire

Pinched wire

Haste makes waste.  Unfortunately, it someone else’s haste that ruined my Saturday afternoon when I was supposed to be taking my son to little league practice.  I am sure that some not so kind words will be exchanged very soon.

Always double check your work.

 

Radio Caroline, 49 years after

Radio Caroline went on the air forty nine years ago this weekend, broadcasting from the MV Caroline off the coast of England.  Why is this important?  Before off shore broadcasting was attempted, in Europe the only radio stations (and TV) were government owned.  As such, they had a monopoly over the air waves and were very restrictive on which groups or types of music they allowed to be broadcast.  Many of the so called “British Invasion” groups like The Beatles, Rolling Stones, The Who, The Kinks, etc got their first airplay on offshore radio stations like Radio Caroline or Radio London.

This video “Radio Caroline – A day in the life,” shows what it was like to be an offshore broadcaster:

By the haircuts and music, that appears to be sometime in the eighties.

Check out the Radio Caroline website for more information.  From 1983 onward, Radio Caroline was broadcast from the MV Ross Revenge. This is an overview of the Ross Revenge transmitter hold.  The movie “Pirate Radio” is loosely (very loosely, by most accounts) based on Radio Caroline/Radio London composite.

Radio London was the one of the other well known offshore radio ships.

I am sure that there are other tribute sites with lots of technical information on how they broadcast. Much of offshore radio was outlawed in the late 1960’s by several European countries. Radio London signed off August 14, 1967. Radio Caroline continued on in various iterations until about 1991 or so.

WBCQ is airing a radio ships special on Sunday March 31, 2013, 5,110 KHz starting at 6 pm eastern daylight time (2200 UTC).

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.

The Continental D323C medium wave transmitter

I found a 1981 Continental Electronics equipment catalog at an old transmitter site. These finds are great if one is interested in history and looking at the way things used to be done.  This particular transmitter is a 2,000 KW (2,000,000 watt) medium wave unit:

Continental Electronics D323C, Circa 1981

Continental Electronics D323C, Circa 1981

I believe most units like this were destined for use by government broadcasters either the middle east or western Europe.  I know there were several 1,000 KW medium wave stations in West Germany at one time.   The Continental transmitter is basically two 1,000 KW units (323C) combined.  They used a modified version of Doherty modulation, that is called “Screen and Impedance,” which accurately describes how it works.  More information from the Continental Catalog can be found here: Continental D323C.  The tubes (or valves depending where you are located) used in the D323C were 4CW25000A tetrodes as modulators and IPA the final was a pair of X2159, which is an impressive tube.

EIMAC X-2159 water cooled power tetrode

EIMAC X-2159 water cooled power tetrode

The tube sat anode up.  The filament, grid and screen connections are underneath.  Cooling water was pumped through the two connections on the top at about 130 gallons per minute depending on the plate dissipation.  With a 30° C rise, that equals about 96,000 BTU per minute.  The D323C had a dissipation of 400,000 watts for the carrier tube and 240,000 watts for the peak tube (640 KW total) under 100% modulation.  That equals about 2 million BTU per hour.  Notice the lifting hook, this tube weight in at 175 pounds.  Tube date sheet here.

Continental no longer makes medium wave transmitters, their closest high powered broadcast product now is the 418/419 and 420 HF (shortwave) transmitters.  The 420D does a wimpy 500 KW using a solid state modulator section.

I remember in the early 1990’s when I was at the Harris plant in Quincy, they were working on a 1,000 KW solid state DX series AM transmitter for Saudi Arabia.  It had to be liquid cooled, which added another layer of complexity to an already complex system.

I don’t know if there is much call for 2 MW medium wave transmitters anymore as there are more efficient ways to reach remote populations and I can’t even imagine what the electric bill would be like.

The Gates BC1H

In my never ending fascination with broadcast transmitters, I bring you the Harris/Gates BC1H. This is an updated model of the BC1G, the main difference being the solid state audio and oscillator sections in the later H model. This design uses the simple 833 parallel final and 833 push pull modulator

Sales brochure, click to down load the four page .pdf

Harris/Gates BC1H AM transmitter

Harris/Gates BC1H AM transmitter

Schematic:

Gates/Harris BC1H overall schematic diagram

Gates/Harris BC1H overall schematic diagram

Harris/Gates BC1H

Harris/Gates BC1H

Harris/Gates BC1H Transmitter running at 1,000 watts into the antenna.  Like many old tube transmitters, this sounds great on the air.  The transmitter was made in 1975 and is in backup service.  For a 37 year old transmitter, it runs like a champ and comes on consistently.  Like the preceding Gates BC-1 models, this transmitter is rugged and reliable.   My only comment is the transistors in the solid state driver section are no longer available.  If that were to become an issue, one can always look up the tube audio driver from previous versions (T and H models).  It would be a shame to throw away a good transmitter for lack of a couple of transistors, but I know some who have done just that.

Axiom


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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