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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.

Australian Made Broadcast Equipment

Somebody working to preserve a record of past work:

Some of these have familiar looking cabinets and tube arrangements. They all look like classics to me and it is good that they are being saved. I noticed at the end of the video there is a Harris MW10A. As for the RCA Ampliphase transmitters; I maintained a BTA5J in Harrisburg PA on 580 KHz. It was reliable enough, but I could never keep it sounding good for more than a couple of days.

In any case, a worthwhile effort.  More information at: AWA Transmitters.

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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