January 2012
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How much is prevention worth?

I sometimes get the distinct impression that the corner office doesn’t understand what it takes to keep a radio station on the air and in good repair.  It is most often the problems or “issues” that tend to get the most attention.  The things that are working well tend to get ignored. After all, how often do you hear a news report about the airliner that landed safely.

Lightning strike TV tower

Lightning strike, TV tower

When lightning strikes the tower and knocks the transmitter off the air causing major damage and expensive repairs, that is a problem.  When lightning strikes the tower and nothing happens, no problem.  What is the difference between those two situations?

Grounding strap, FM transmitter site

Grounding strap, FM transmitter site

If the generator starts and runs during every power outage and has done so for the last five years straight, it is obviously a reliable unit, does it need all that maintenance?

Caterpillar 75 KW diesel GENSET

Caterpillar 75 KW diesel GENSET

Money spent on preventing undesirable outcomes can be difficult to quantify as disasters and events that do not happen are ill defined.   It is difficult to quantify the “amount saved” on something that didn’t or won’t occur.  Using past situations is good start, but that only covers a fraction of possible outcomes.  In order to invest money wisely, one has to look at the probabilities.  If there is an unlimited budget, then the probability exercise should be minimal, however, there is very seldom an unlimited budget.

For example, how much does a back up STL system cost vs the risk of being off the air while the main STL system is being repaired?  How often do failures occur, when are they likely to occur and for how long are all good questions.  Is there an alternative to a full back up like an IP CODEC?  Such a solution would cover all aspects of the STL system including antennas, transmission line, transmitters and receivers.

There are certain FM stations north of here that have neither RADOMES or antenna heaters.  Once every two years or so, the antenna ices up and the transmitter folds back due to VSWR.  How much of an impact to listeners notice when this happens?  If it happened more often, say two to three times a year, would it be wise to invest in some type of deicing equipment?

What is the ownership and management opinion on off air conditions?  I have often heard tell “Oh, its only the AM, we don’t mind if it goes off the air.”  That is, until it actually goes off the air, then it is a big problem.

Based on my and others experiences, these are the things that will happen at an average transmitter site:

  • The electric will go off at least once per year for several hours.
  • The main transmitter will fail at least once every two years.
  • Lightning will strike the tower at least once per year.
  • The STL system will fail, at unknown intervals.

At studio sites, these things will occur:

  • The file server will crash depending on the operating system
  • The telephone lines and or T-1 service, internet service, ISDN etc will go out
  • The electric power will go out for several hours
  • The satellite dish will fail once every two to three years
  • If there is a tower, it will get struck by lightning

Other site specific things can occur like floods, blizzards, earthquakes, fire, etc.

Money spent on backup systems for those items is good insurance.  Not only will the station stay on the air, the on call engineer’s phone will ring less often, which, if you are the on call engineer, should make you happy.

If a full backup is not available, a second transmitter for example, having a good stock of spare parts on hand can mean the difference between an early evening and an all nighter.   Keeping good maintenance logs and well documented repair records can point out trends and give a good basis for ordering spare parts.

Repair trends are important.  If the same part seems to be going bad over and over, it is time to dig deeper and find the cause of failure.

The old adage “An once of prevention is worth a pound of cure,” still holds true.

Work ethic

We have this guy that works for us who is atypical. We call him Pete because that is his name.  The other day, he was slacking off on the job again, this time figuring out how to take a nap in a transmitter:

Pete working on a Harris FM25K

Pete working on a Harris FM25K

What are we going to do with him?

Actually, he is rebuilding the grid tuning section (AKA input tuning section), which is no small matter.  Soon, we will have this 26 year old transmitter running good as new, or better than new.  It already sounds much better on the air than it did before, the input tuning is broader and there is much less AM noise.

Currently, it is running about 70% power while we wait for a replacement amplifier from Silicon Valley Power Amps.

The Harris MW1A

They say the first thirty years are the hardest, perhaps it is true. This Harris MW1A transmitter turns 31 this year:

Harris MW1A AM transmitter, WINE, Brookfield, CT

Harris MW1A AM transmitter, WINE, Brookfield, CT

Truth be told, these are not bad units.  They have some quirks, however, the overall circuitry is simple, the design is simple enough and parts for repair are readily available.  They require regular infusions of RF transistors, but those are easy to change and are inexpensive to buy off the shelf from places like Mouser or Allied.

It is on the air as the main transmitter for WINE-AM in Brookfield, CT.   This is Harris’s first solid state AM transmitter design, based on the work of Himmler Swanson.  This is not a PDM transmitter, rather, each module has RF transistors and audio transistors.  The output of all twelve modules are combined for a carrier output of 1,000 watts with +125% modulation.   Harris calls this PSM (Progressive Series Modulation), which is sort of high level modulation.

This is also the only transmitter that I know of where blown fuses can cause damage to the RF devices.

The RF output transistors and audio transistors are still available from Harris.  Non-OEM parts for this include the 2N5038 for the RF transistors and the MJ15011 for the audio transistor.  Inside the front of the transmitter is a row if incandescent light bulbs that glow increasingly as the various transistors go bad.  At 1,000 watts carrier power, the ratio of PA volts to PA amps is 52.5/22.5 respectively.  If that ratio is off by any measure, there is a problem.

Original sales brochure for the MW1 (no A):

Harris MW1 sale brochure

Harris MW1 sale brochure

Entire brochure available here.

Harris MW1 interior view

Harris MW1 interior view

The other thing with this transmitter is it is very sensitive to any kind of VSWR.  Any change in the output impedance will quickly make itself apparent.  My Harrisburg MW1A had two ATU settings, one for winter and one for summer.  It was a slightly tall tower on 1230 KHz, thus any change in the ground system (e.g. snow cover) would upset the tower base impedance.

The other thing that goes bad is the large Rotron fan in the bottom of the cabinet.  They go bad about every 10-15 years or so.

The owner has spent some money on this particular unit, rebuilding and replacing several modules with new transistors etc.  Will it last another thirty years?  Depends on if the RF and audio devices remain in production.

The never ending HD radio debacle continues to not end

Especially on the AM band.

Radio World, bless them, has yet another article about the public’s lack of awareness regarding HD Radio®.  Calling it “lack of awareness,” is overly kind and I think they are missing the point.  It would be better phrased “apathy” or “indifference.”

There is a general misconception in the world that one either loves or hates something.  That is not true, the opposite of love is indifference, not hate.  The public has voted, with their wallets, for things like 3 and 4G wireless devices, satellite radio, iPods and other entertainment venues.  Why?  Because HD Radio® is not an advance, it is a repackaging of old ideas with slick marketing.  The general public has viewed the great digital radio conversion with a jaundiced eye, opting to sit on the fence and wait for something better.  What has iBiquity given them?

The technology itself is a step backwards with many band aids needed to affect the same coverage area as analog FM.  A technology that has poorer building penetration, less coverage area , mobile reception issues with no appreciable difference in sound quality or program material offerings.  A power increase from 1% to 10% analog carrier power (20dBc to -10dBc) hasn’t really made a difference.  Now, studies are underway looking at asymmetrical sidebands and same frequency repeater networks for FM IBOC.  All of these things, not to improve radio reception, but rather to achieve the same coverage as analog FM.

The AM HD Radio® has even greater issues.

There is nothing at all surprising about the public indifference toward HD Radio®.

SOPA/PIPA protest

Yesterday, January 18, 2012, I blacked out engineeringradio.us for the day in protest of the internet censorship bill working its way through congress colloquially known as SOPA or PIPA.  There were some 17,000 or more others that did the same.

SOPA PIPA protest screen shot

SOPA PIPA protest screen shot

If the internet is indeed the new media, destined to replace the old media, then having in place draconian restrictions that allow the government to block websites and content with no due process for the website owner is censorship, plain and simple.  Imagine a country where the government can come in and shut down any newspaper, TV station or Radio station, give no reason other than some weak statement about copy write laws.  See also: China, North Korea, Cuba, Soviet Russia, etc.

It is important to check the corporate power in this country.  It is widely reported that Congress has a 9% approval rating.  It is also hard to imagine their approval rating is actually that high.  While signing petitions and writing senators and congressman may provide some relief, the shortest path to ending this is to boycott the corporate sponsors of the legislation.  Hitting companies bottom line will speak louder than any internet protest, petition, letter writing campaign, etc.  Thus, if so inclined, here is a list of producer companies that like the idea of internet censorship.

WRKI WINE transmitter move, update 2

Man, this is taking longer than I though it would. We moved the Harris FM25K last week, all went well. The only hangup, as you can see, is the harmonic filter and the height of the racks next to the transmitter. The transmitter had to go on a 4×4 to get the filter up over the racks. The output from the transmitter to the harmonic filter cannot be changed in any way, shape or form (e.g. adding a little bit of line section to the top of the transmitter), else the transmitter will not run. So, up on 4×4’s it is.

WRKI WINE transmitter room

WRKI WINE transmitter room

There we were, all ready to turn the transmitter on.  Press the high voltage on button, lots of volts but no current and no power output.  Seems something is wrong with the outboard IPA driver (over in the bottom of the rack, that thing pulled out with the manual on it).

The IPA is a Silicon Valley Power Amplifier 500 watt unit, which replaced the internal IPA driver about ten years ago.  The tube in the Harris FM25K needs at least 390 watts to drive the transmitter to full power.  Unfortunately, this particular amplifier was not in the best environments prior to the recent move.  It was sitting in an unconditioned building on top of the backup transmitter in high heat and humidity.  According to the manufacture, such abuse is bound to take it’s toll sooner or later. The later being, of course, the night we want to turn the thing back on and go home.

Time to drop back and punt.  I found an old RVR 250 watt amp at a sister station nearby, which was also in pretty bad shape but repairable.  That unit was pressed into service temporarily and with 200 watts drive, the old 25K put out about 11 KW.  We need to affect permanent repairs to the RVR power amp before we place into temporary service.  I don’t want any 2 am phone calls.  The Silicon Valley Power Amp needs to have the amplifier module sent back to the manufacturer and rebuilt.  They will refurbish the entire thing for something like $900.00 plus shipping.  Considering what it does, that is worth it.

This is a little short cellphone video of the turn on at half power.  This is a very loud transmitter, as such, I think the audio is a little distorted.

When this beast gets up to full power, I will update this, again.

Low Pass Filter design

Every good transmitter, tube transmitters in particular, require harmonic filtering.  The last thing any good engineer or broadcaster wants is to cause interference, especially out of band interference to public safety or aviation frequencies.  All modern transmitters are required to have spurious emissions attenuated by 80 dB or greater >75 Khz from carrier frequency.  In reality, 80 dB is still quite high these days, especially in the VHF/UHF band, where receivers are much more sensitive than they used to be.  A good receiver noise floor can be -110 dB depending on local conditions.

The principle behind a low pass filter is pretty easy to understand.  The desired frequency is passed to the antenna, while anything above the cut off frequency is restricted and shunted to ground via a capacitor.

Low pass RC filter

Low pass RC filter

In this case, the resistor is actually an inductor with high reactance above the cut off frequency.  Often, these filters are lumped together to give better performance.  This is a picture of an RVR three stage low pass filter:

RVR three stage low pass filter

RVR three stage low pass filter

RVR is an Italian transmitter maker that sells many transmitters and exciters in this country under names like Bext, Armstrong, etc.  The inductors are obvious, the capacitors consist of a copper strip sandwiched between teflon insulators held down by the dividers in between the inductors.

Schematically, it looks like this:

Low pass filter schematic diagram

Low pass filter schematic diagram

For the FM broadcast band, a good design cutoff frequency would be about 160 MHz. This will give the filter a steep skirt at the first possible harmonic frequency of 176 MHz (88.1 x 2 = 176.2).

Values for components:

Capacitors Value Inductors Value
C1 20 pf L1 74.7 nf
C2 54 pf L2 75.1 nf
C3 54 pf L3 73.9 nf
C4 20 pf

The inductors are wire, or in this case copper strap, with an air core.  It is important to keep the transmitter power output in mind when designing and building these things.  Higher carrier powers require greater spacing between coil windings and larger coil diameters.  This particular filter is rated for 1 KW at 100 MHz.

Update: WINE WRKI transmitter site move

I have been spending my days in Brookfield, Connecticut, dragging transmitters around and reconnecting them in various ways.  The WRKI-FM WINE-AM transmitter site is finally moving into the “new” transmitter building at the base of the tower.  Today, we moved WINE.

WINE was first signed on in 1963 on 940 KHz from a 170 degree non-directional tower on top of a pretty high hill.  That same tower serves as the antenna support for WRKI, which signed on in 1957.  The station runs 680 watts daytime, however since it is non-directional, it has some pretty serious power reductions at night.  The post sun set power drops in two steps, 450 watts for the first hour, then 189 watts for the second hour, followed by 4 watts night time.

The 4 watt night time signal goes about 2-4 miles before it becomes unlistenable.  The Post Sun Set Authority (PSSA) allows the station to stay on the air with at least some coverage up to about 6:46 pm in the winter time and 10 pm in the summer, which is better than nothing.

The problem is, the Harris MW-1A transmitter goes down to 250 watts and no lower.  In order to make the night time power, the station switches to a dissipation network to burn off 246 watts of RF, at 50% percent AC-RF efficiency, which just ends up being a waste of power.  Further, the station engineers have been ignoring the PSSA because there are too many steps and it was easier to just switch to night power at sunset.

What we decided to do instead, was install a small low power night time transmitter, a Radio Systems TR-6000.  The MW1A can then be set to use the low power level for the first step of the PSSA, then switch the dissipation network in for the second step of the PSSA, finally switching in the night transmitter at the proper time.

Harris MW1A AM transmitter, WINE 940 KHz, Brookfield, Ct

Harris MW1A AM transmitter, WINE 940 KHz, Brookfield, Ct

This is the Harris transmitter, new Circa 1981, was cleaned up and moved into the new transmitter building.

WINE Parallel dissipation network and dummy load

WINE Parallel dissipation network and dummy load

The dissipation network.  This will have to be reconfigured for the proper power levels, once the night transmitter is installed.  The dissipation network is on the right, a dummy load is on the left.  The two large RF contactors switch the dissipation network in and out, or select which transmitter is feeding the antenna/dummy load.  This is the really, really old school way of doing it.  Most transmitters manufactured after 1990 or so can run at any power level, making a dissipation network unnecessary.

Before re-installing the dissipation network/dummy load, we lined the enclosure with copper mesh.  I don’t want that thing interfering with any of the other equipment nearby, which would be the STL receivers, satellite receivers or Town of Brookfield police dispatch radios.

Schematically, it looks like this:

WINE 940 KHz Brookfield, CT night time dissipation network

WINE 940 KHz Brookfield, CT night time dissipation network

This is the picture behind the transmitters, shows the coaxial cable feed through ports and the dissipation network on the wall.

WINE WRKI transmitter room, behind the transmitters

WINE WRKI transmitter room, behind the transmitters

It is a work in progress, so forgive the mess.

Shocker: LPFMs have little or no impact on commercial FMs

The long awaited report, required by the NAB as a part of the Local Community Radio Act has concluded that LPFMs have little or no impact on commercial FM stations. No kidding?

The executive summary states that:

LPFM stations serve primarily small and rural markets and have geographic and population reaches that are many magnitudes smaller than those of full-service commercial FM stations. In addition, LPFM stations generally have not been in operation as long as full-service commercial FM stations, have less of an Internet presence, and offer different programming formats. We also found that the average LPFM station located in an Arbitron Radio Metro Market (“Arbitron Metro”) has negligible ratings by all available measures and has an audience size that lags far behind those of most full-service stations in the same market.

Followed by:

Although each of the stations differs considerably in its individual characteristics, the results of the case studies show that the selected LPFM stations generally broadcast a variety of programming continuously throughout the day, operate with very small budgets, rely on mostly part-time and volunteer staff, do not have measurable ratings, have limited population reach, and do not generate significant underwriting earnings. All but one of the station managers that we interviewed stated that the LPFM station is not competing directly for listeners with any specific full-service stations.


We conclude that, given their regulatory and operational constraints, LPFM stations are unlikely to have more than a negligible economic impact on full-service commercial FM stations.

Forgive my excessive block quoting of the FCC report titled: Economic Impact of Low-Power FM Stations on Commercial FM Radio, I found those portions of text far better than anything that I could write on the subject.

The NAB is reportedly “reviewing” the results, which the cynical me thinks is just another way of stalling a potential LPFM window later this year.

I don’t know what it is that I like about you but I like it a lot

Alternate title: How Important is College Radio?

If Radio as an entertainment medium is to survive; vital. College Radio is the alternative to corporatist radio and is fertile ground for new artists and music.   The big three radio groups control (Clear Channel, Cumulus, CBS) something like 75% of the radio revenue while owning 13% of the commercial radio stations.  Against that wall, the remaining radio groups and independent operators hurl themselves to make a living.  While there are few (precious few) commercial independent operators who do break new music, perform community service and provide a valuable asset to their city of license, the majority of the remaining 87% of radio stations run some sort of repeater/automated format.

In this risk adverse society, which large radio group willing  take even small calculated risks?

Who is going to replace Dick Clark and where will that person come from?  By the way, God bless Dick Clark but, man, enough already.

Where will the newest crop if disk jockeys come from?

If one wants to hear something new, or at least different, there is no better place to listen than a student run college radio station.

It was in this setting that several college boards had a Eureka! moment when they discovered that those FM licenses were actually worth money.  Money! and in not so small amounts in several cases.  The collective wisdom being that kids these days don’t listen to radio, nobody will miss those programs anyway.  Even so, when Rice University sought to transfer KTRU there was a large backlash from Alumni and the student body.  When the University of San Francisco sold KUSF to Entercom, they did so over Christmas break.  At Vanderbilt University, the WRVU staff was locked out of the studio.  The whole sordid tale can be found in 2011: The Year that College Radio Fought Back and College Radio’s fight for FM.

There are other stations who’s fate is less well known, no doubt.

It is disappointing to see the various college boards deciding that broadcast radio is no longer a desired and to see the campus radio station regarded as an extra curricular activity or so much excess real estate.

There are still many college radio stations in this area that are worth while to listen to, just to hear something other than blended crap, super specialized satellite radio channels, or some personality-less internet stream with computer picked songs.

So kudos to WRPI (Rensselaer Polytechnic Institute), WVKR (Vassar College), and others like them for having student run radio stations and not selling out or morphing into the borg like collective that is NPR.


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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