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The Gates Air FAX-10

This is the first one of these transmitters that I have installed. This particular unit is analog only, but there is lots of room left over for an HD exciter, if need be.

GatesAir Flexiva FAX-10, 10.000 watt FM transmitter

GatesAir Flexiva FAX-10, 10.000 watt FM transmitter

The size of a 10 KW FM transmitter these days is pretty small, basically taking up the equivalent of one rack. This is a relatively small transmitter room, the old tube transmitter basically took up the entire room. With this unit, there is room to install a full power spare, if that was desired.

GatesAir Flexiva series RF modules.

GatesAir Flexiva series RF modules.

RF modules use LDMOSFET devices, each module has a power output of approximately 1,600 watts.

GatesAir Flexiva FAX10 power amp section

GatesAir Flexiva FAX10 power amp section

There are eight power amp modules and seven switching power supplies.

GatesAir FAX10 transmitter on the air

GatesAir FAX10 transmitter on the air

GatesAir FAX10 power output

GatesAir FAX10, licensed transmitter power output

One issue at this site, there is no reliable three phase power available.  There was a three phase open delta, but man, that thing scares me a little bit.  Since this is a single phase setup, I was curious to know what the current draw on each leg was at full power. I measured with my clamp on ammeter; 54.3 Amps at 120 volts, or 6516 watts per leg. Overall power draw 13,032 making the AC to RF efficiency 65.2%. VSWR calculates out to 1.21, which is not great.  I think the antenna could use a little bit of tuning love.

Upgrading the firmware

The original V series Nautel transmitters have required a couple of firmware upgrades in some cases.

Upgrading the power module firmware, WDVT, Rutland, VT

Upgrading the PA module firmware on Nautel V-5D transmitter, WDVT, Rutland, VT

The first was for the controller to add a little bit of bias to the PAs during analog operation.  The second one I have had to do is to the PA modules themselves which was to keep the power supplies from shutting off during re-transfer from Generator power to commercial power.

I have done several of these and once you get the hang of it, it only takes a few minutes to complete.  Still, I remember when transmitters didn’t have firmware.  The low voltage control circuits were either 120 or 240 VAC with big relays and contactors that loudly confirmed their closure before any meters began to move.

Regarding Nautel transmitters in general; the newer models are not same rugged, reliable designs that were common in the past.  We have AM ND series transmitters that have been on the air for 20 years without a single failure.  The models rolling out of the factory these days often have switching power supplies fail without reason or warning and RF pallets that are fragile things.  Ah well, I suppose all things are cyclical.

Nautel V-10 repair

Not exactly sure how it happened, but one of our Nautel transmitters malfunctioned!  It is a pretty rare event, so I thought the exclamation point was needed.  One of the PA pallets went bad and the transmitter lost 1/2 a PA module.  Since the TPO for this particular station is 7 KW, they remained on the air at full power.  In the interest of staying on top of things, we fixed it anyway.

Diagnostics were simple:

  • Fault lights on front of transmitter observed
  • Press status button to find out faults, which were Module D failed
  • To to module sub-menu, find Module D and discover Q1 disabled, Q3 shutdown.
  • Problem is with Q3, order new pallet from manufacture

Upon removing module, I did not see the damage at first:

Nautel V series FM transmitter PA module

Nautel V series FM transmitter PA module

It is board A3, which for this particular flavor transmitter is a Nautel Part number NAPA16-B. Once I replaced the defective module with a new one, I discovered what looks like a symptom of the greater problem:

Nautel NAPA16-B defective board

Nautel NAPA16-B defective board

Over to the in the left-middle-lower section of the board, R10 and R8 are burned open. These are surface mount 2 watt, 20 ohm resistors.  A glance at the schematic shows that these are part of the bias supply.  A quick set of measurements with a DVM shows that Q1 seems to be intact and not shorted.  Interesting…

The question is: Is it worth trying to fix this board or should I just trash it an buy a new spare?

Update: Schematic diagram as requested:

Nautel NAPA16-A schematic

Nautel NAPA16-A schematic

Modifying the old Broadcast Electronics Transmitter

In the previous post, the issue with the WVOS-FM transmitter was detailed: The PA feed through/bypass capacitor had arced to the PA cavity causing lots of unwanted off air time. When I went to order the replacement parts, of course, they were not available. It seems that Broadcast Electronics changed the design of their transmitters in the late 1980’s to use a different feed through arrangement.

They were nice enough to send us a nifty retrofit kit; BE part number 959-0272 which replaces BE part number 959-0115.  If interested, the six pages of installation instructions are available here, for your reading pleasure.

The retrofitting itself was quite the job; drilling six mounting holes and one one inch feed through hole in the PA cavity, mounting the new feed through housing, rewiring the high voltage connection to the tube and back to the HV bleeder assembly, ect.  What with all of the drilling, sawing, filing, deburring and whatnot, I began to wonder if the transmitter would ever run again.  This is the transmitter before the modification:

Broadcast Electronics FM3.5A PA cavity

Broadcast Electronics FM3.5A PA cavity

This is the old high voltage feed through hole, arc mark clearly evident.

Broadcast Electronics FM3.5A old high voltage feed though

Broadcast Electronics FM3.5A old high voltage feed though

This is the modified feed through/bypass configuration.

Broadcast Electronics FM3.5A new PA feed through capacitor

Broadcast Electronics FM3.5A new PA feed through/bypass capacitor

While doing this work, I removed the tube and put a plastic sheet in the bottom of the PA cavity and around the HV parts in the bottom of the transmitter.  Somehow, getting aluminum filings in the tube socket seemed like a bad idea.  I also thoroughly vacuumed out the entire transmitter once all of the metal work was done.

I removed the Kapton capacitor plates from the old feed through arrangement and reinstalled the Teflon insulating plates to keep the air flow out of the tube cavity going in the correct direction.  The new capacitor looks very beefy, perhaps it will never fail again.

Once the installation work was done, I brought up the transmitter first with no screen and no connection to the tube anode.  Then with the tube connected, and finally with the screen supply turned on.  The tuning needed a brief touch up but all in all, the transmitter came up and ran well with the new feed through arrangement.

The old Broadcast Electronics Transmitter

Alternate title: More blown up stuff

This Broadcast Electronics Fm 3.5A will be thirty years old in April. We should have a party!

Broadcast Electronics FM 3.5A, WVOS-FM, LIberty NY

Broadcast Electronics FM 3.5A, WVOS-FM, LIberty NY

Unfortunately, this transmitter is not doing too well these days. The PA high voltage feed through capacitor has arced over to the PA cavity, causing the station to be off the air.

BE FM3.5A HV feedthru capacitor

BE FM3.5A HV feed thru capacitor

Naturally, this happened over the weekend, parts will not arrive until Tuesday at the earliest, and the station is without a backup transmitter.

Obviously, trouble shooting this was a two person job.  Never work alone on HV equipment.  The symptom was the main circuit breaker was tripping after the HV on command.  Starting from the transformer end of the HV power supply circuit and working toward the anode of the PA tube, all of the components were tested by isolating each component then turning the HV on.   Special care was taken to discharge all components after each test.  The capacitors and bleeder resistors were reconnected at the same time.  There is too much risk involved with charged 8 KV capacitors and no way to bleed that charge to ground.  Everything worked up until the PA cavity was reconnected (without the tube), then the breaker tripped again.  Thus, the above feed through capacitor was removed and disassembled, revealing the damage.

The question is, how long should transmitting equipment last? After all, if one were running a freight delivery company, you would not be driving around in thirty year old trucks, would you? No, not if you wanted to stay in business. Like all electro-mechanical equipment; transmitters, consoles, STLs, antennas, computers, etc wear out.  A smart plan would be to have a replacement schedule and be putting money into a capital equipment replacement fund.   Equipment life varies with the type.  Getting twenty years out of a main transmitter is pretty good service life, going beyond that is pressing one’s luck.  Ten years on any one computer is a very long time.  Then there are certain transmitter manufactures that drop support on older units, which makes it difficult to keep them operating.  Owners and managers need to be cognizant of the age and condition of critical infrastructure.  As field engineers, how much time do we devote to keeping antiquated equipment running or should we even be servicing it at all?  As independent contractors, we incur a liability whenever we touch something.  Where does the ownership’s responsibility lay in providing safe, functional equipment for their stations?  All interesting questions.

WDST, Woodstock, New York

WDST is a well known radio station in Woodstock, NY. Formatically, I would call it Adult Album Alternative (AAA) and it is one of my favorite stations to listen to. We also do the engineering work for this station.  While I was there last week, I snapped a few pictures of the studios:

WDST air studio, Woodstock, NY

WDST air studio, Woodstock, NY

All of the studio use Audioarts R-60 consoles, which are in good condition considering their age.  Lots of guest microphones and the windows look out into a performance venue.

WDST music library, located in hallway outside of studio

WDST music library, located in hallway outside of studio

The music library is extensive.

WDST main production room

WDST main production room

The production room, another R-60 console. I don’t know where the microphone disappeared to, perhaps it was borrowed by the morning show.

WDST technical operation center

WDST technical operation center

Technical Operation Center (TOC). WDST uses NextGen from RCS for music storage, playback and automation.  Other equipment includes ISDN, POTS phone, Distribution Amps, Limiters, streaming computer, STL, etc.

WDST transmitter, Broadcast Electronics FM5C

WDST transmitter, Broadcast Electronics FM5C

The transmitter site is on Hallihan hill, across the street from the old ATT long lines site. The station uses a Broadcast Electronics FM5C transmitter.

WDST forward power meter

WDST forward power meter

Forward power, almost five whole kilowatts of flame throwing power.

WDST antenna, Hallihan Hill, Kingston, NY

WDST antenna, Hallihan Hill, Kingston, NY

The antenna is a Shively 6810 2 bay half wave spaced.

The curious case of the WKZE Notice Of Violation

On June 19th, WKZE received a notice of violation from the FCC’s New York Field office.  The crux of the issue seems to be interference being generated on 784.8 MHz (WKZE 8th harmonic) to a new Verizon Wireless installation located nearby:

47 C.F.R. §73.317(a): “FM broadcast stations employing transmitters authorized after January 1, 1960, must maintain the bandwidth occupied by their emissions in accordance with the specification detailed below. FM broadcast stations employing transmitters installed or type accepted before January 1, 1960, must achieve the highest degree of compliance with these specifications practicable with their existing equipment. In either case, should harmful interference to other authorized stations occur, the licensee shall correct the problem promptly or cease operation.” The eighth harmonic of Station WKZE-FM (784.8 MHz) was causing interference to the Verizon Wireless transmitter located approximately 500 feet away.

First off, we note that the WKZE transmitter is not allegedly causing interference to a Verizon Wireless transmitter, but rather to a Verizon Wireless receiver.  That may be splitting hairs, however, since the FCC is quoting a technical rules violation, they can at least get the technical language right.

A brief examination of rest of FCC part 73.317 is in order to find the specification cited in section (a).  Section (d) states:

 (d) Any emission appearing on a frequency removed from the carrier by more than 600 kHz must be attenuated at least 43 + 10 Log10 (Power, in watts) dB below the level of the unmodulated carrier, or 80 dB, whichever is the lesser attenuation.

Since 784.8 MHz – 98.1 MHz is greater than 600 KHz, this is the section that applies to the WKZE situation.  Thus, the interfering signal must be greater than -80 dBc to trigger the Notice Of Violation (NOV) from the FCC.  The station ERP is 1,800 watts or +62 dBm.  Measurements were made with a an Agilent N992A spectrum analyzer using an LPA-1000 log periodic antenna.  At a 12 foot distance away from the WKZE transmitter cabinet, the signal on 784.8 MHz was found to be -94 dBc or 0.000063 watt.  At the base of the Verizon Wireless tower, the measurement was -124 dBc, or 0.000000025 watt, which is barely perceptible above the -130 dBm noise floor.  There does not appear to be any violation of 47 CFR 73.317.  Rather, the issue seems to be Verizon Wireless’s deployment of 700 MHz LTE band and the use of high gain antennas coupled with high gain preamplifiers on frequencies that are harmonically related to broadcast stations nearby.  In this particular installation, the antenna has 16 dB of gain, minus a 4.5 dB of transmission line loss into a 21 dB preamplifier before the receiver.  At the output of the Verizon preamplifier, the signal on 784.8 MHz was measured at -89 dBc, which is still in compliance.

By these measurements, clearly WKZE is not in violation of any FCC regulation.  It makes one wonder, does the FCC understand it’s own rules?  Or, is this a matter of favoritism towards a huge corporation over a small independent radio broadcaster.  Is it a matter of “broadband at the expense of all others?”  There are several of these broadcast to 700 MHZ LTE interference cases pending throughout the country.  This could set a dangerous precedent for broadcasters and other RF spectrum users as wireless giants like Verizon throw their weight around and eye even more spectrum to press into broadband service.

Commlaw blog has a good post this subject: Harmonic Convergence?

Update: Response from WKZE attorney can be found here, includes the above mentioned actual measurements.

The Shively Branched combiner

Did some work a while ago at a transmitter site that had three transmitter combined into one antenna.  The site uses a Shively branched combiner:

Shively Branched combiner

Shively Branched combiner

Each transmitter can be tested into a separate 20 KW dummy load:

Three inch coax switches

Three inch coax switches

Transmitter themselves are Nautel NV15s:

Nautel NV20 transmiters

Nautel NV15 transmiters

Except the one on the end, which is an older BE FM20A.

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…

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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