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
It is on the air as the main transmitter for WINE-AM in Brookfield, CT. These are not necessarily bad transmitters, although they do seem to require regular infusions of MOSFETS to stay at full power. 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 MOSFETS and audio transistors. The output of all twelve modules are combined for a carrier output of 1,ooo watts with +125% modulation. Thus, I would call it low level AM 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 MOSFETS 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 MOSFETS 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.
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 MOSFETS etc. Will it last another thirty years? Depends on if the RF and audio devices remain in production.
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®.
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
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.
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
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.
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
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 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
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.
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
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
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
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
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.
And:
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.
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.
This time of year is when we all sit back and asess things that we did in the past 365 or so days. It is called reflection, which is just a civilian term for SWR (Standing Wave Ratio).
Thus, I though I would take a little time and make a few observations about the business, my part in it, and this blog.
1. The business of Radio:
Let us be honest, Radio is not what is used to be. Many times, what it used to be was somewhat of a free for all, wheeler dealer radio station owners cutting corners and making do with less than optimum equipment and staff. And trade, lots and lots of trade. Only in large metropolitan areas did radio stations make enough money to throw it around, but sometimes not even then. Radio was by no means a huge money making operation and therefore, those that worked in mostly it did it as a labor of love. That may or may not have come across on the air. By far, the funnest station I ever listened to was run from a closet, with a sound reinforcement board and the program directors CD collection. What made it so much fun was they had nothing to loose, there were no restraints placed on the staff. Once that on air enthusiasm translated to ratings, then to revenue, the magic was gone and they were just another radio station filling a spot on the dial.
The radio business has fully transitioned from a fun, seat of the pants entertainment operation to a mega money making corporate mentality under the control of mostly non-entertainment types. Even those stations owned by smaller group owners are forced to rely on the tactics developed by the big two in order to stay in business.
Group owners will continue to extract money in whatever way they can until the money train runs off the rails. Then, radio will be replaced by something less.
2. Radio Engineering:
Engineering will continue to grow smaller, with more emphasis on computers, networking, and IT infrastructure. The future distribution of music and program material will take the form of streaming (live events), pod casts (specialty shows) and subscription services. Over the air free radio will become less and less relevant as younger “listeners” trend toward new media. The idea of listeners may be archaic in lieu of “subscribers” or “users.” Thus, in order to remain relevant, broadcast engineers are going to have to keep their skill sets current. I would recommend to anyone getting into the business to get current with routers, routing tables, Cisco equipment and whatnot. The cloud is coming and will rain on all those not adjusted to the new “broadcasting” reality.
3. My part in the business:
A somewhat superannuated broadcast engineer who’s skill set lies mostly within the RF and heavy duty electrical areas, I am going back to college in January. Cicso Network Administrator is the degree I am shooting for, for that is where the local jobs, both in and out of broadcasting will be. Network Administrators are going to be the backbone of cloud computing, those that can configure routing tables will be desired.
That being said, I continue to be involved with larger RF projects and transmitter work. It is fun for me, most of the time. Having to drive two hours,one way on Christmas Eve to fix a backup transmitter, not so much, but those situations tend to be the exception, rather than the rule.
All in all, it is great fun to press the high voltage on button, not knowing if the transmitter will cycle on normally, or put on some type of display.
4. The blog:
This little thing we have here has been fun. I get good response to most articles. I welcome all the comments and the off line e-mails that come my way. My original intent, which is to provoke thought and dialog, remains unchanged. This year, I have delved into areas not covered by the trade magazines, but do have at least some bearing on radio or radio related arts. To that end, there have been several negative responses, which is fine. I don’t pretend to know everything, if you know more, then by all means, speak up. By and large, however, the majority of responses continue to be positive.
I continue to grow the overseas audience, with roughly 36% of the page views coming from non US IP addresses. Persons from The UK, followed by Canada, Netherlands, Australia and Germany are the top five non-US readers of this blog.
So, I will continue to post about things in the coming year. If any of you have any suggestions or requests, shoot me an email of leave a comment.
How effective are they at filling in or expanding coverage for FM stations? The answer is, it depends. Most have heard of the quadcast around New York City on 107.1 MHz formed in 1996-98. It was well documented in Radio World and several other publications as a cleaver way to overcome the suburban rim shot problem. Four signals on 107.1 were synchronized using GPS timing data, then fed the same program material. They were WYNY, Braircliff Manor, NY; WWXY, Hampton Bays (Long Island), NY; WWYZ, Long Branch, NJ; and WWYY Belvidere, NJ. These being four separate Class A FM stations, the 60 dBu contours did not overlap. There was some mutual interference in some areas, but there were few if any reception negative zones where the signal strength is equal between stations.
In early 2003, I was a part of the disassembly of the quadcast. In the end, it is difficult to point to any one thing that lead to the breakup. The station’s owners, Big City Radio, had filed for bankruptcy. I am not sure if the company ever had the correct formula for marketing and sales, given the strong suburban, but weak and lacking building penetration in Manhattan signal. The station initially had a country format, something that arm chair quarterbacks said would not work in New York City. After a few years, Big City had changed the format to Rumba, a Spanish/Caribbean music format, which did worse than Country. The fact is, that it never lived up to expectations and the station were worth more separately than together. Given the right circumstances, it could have worked.
The other synchronized FM broadcasts are those where boosters are employed. These are a good deal more difficult to configure because the booster signal is within the main stations 60 dBu contour. Often cases, where there is severe terrain shadowing or other limitations, a well positioned booster that is in a population center can greatly improve the signal in those areas. This was formerly the duty of an FM translator, however, those stations seem to be taking on a life of their own, without regard for the intent of the current FCC rules. Boosters can also be called a single frequency repeater or single frequency network (SFN).
The disadvantages of a SFN are the aforementioned negative reception areas. To the receiver, this will create a multipath or picket fencing situation, which is objectionable to most listeners. The advantages are, of course, better coverage in key areas, spectrum efficiency, and the ability to create a network of common frequency systems. Think of how easy it would be if all NPR stations were all on the same frequency, for example.
The key to making a booster work is to synchronize several aspects of the RF and Audio signals:
RF carrier frequency
Stereo pilot frequency and phase
Audio amplitude and phase
This is best done using GPS receivers to synchronize the exciters and an AES/EBU audio path from the studio to both transmitters fed by one processor. Once this is accomplished, a certain amount of delay can be added to the audio content on either the main or booster transmitter to move the interference zones away from heavily populated or trafficked areas.
WDBY, Patterson, NY 60 dBu contour
This is the situation with WDBY in Patterson, NY. The main transmitter site is located on a hill in Patterson and has a power level of 900 Watts at 610 feet (186 meters) HAAT. The main population area is Danbury, CT, to the south east, about 12 miles away. Between the two, there are several imposing hills, which create reception issues in Danbury. Therefore, WDBY FM1 was placed in service on the Danbury Medical Center. The booster has a power output of 1,200 Watts, at 0 feet (0 meters) HAAT (49 meters AGL).
WDBY FM-1 signal, Danbury, CT 60 dBu contour
Therefore, the southern area of the 60 dBu contour is filled in by the booster. The interference zone between the two transmitters is determined by the amount of delay in the audio between the two units. If both are time the same, the interference will occur at precisely 1/2 the distance between the transmitter sites, which in this case is 10.18 KM from booster. Looking at the population maps, it might be better to move that more toward the north, away from Danbury.
The formula for computing audio delay time is:
A-B=C where A is the distance between the transmitters and B is the distance to the interference zone from any given transmitter. The product of that is multiplied by a constant of 3.34 to obtain the time delay in micro seconds. Therefore, if the interference zone is desired to be further outside of Danbury, say 15 KM away, then the equation looks like this:
20.358 kM -15.0 kM = 5.358 KM
5.358 KM x 3.34 = 17.89 μS delay from the main transmitter site will put the interference zone out in the middle of nowhere, away from Danbury. This is total delay between the two stations, therefore any difference in STL paths needs to be included in this figure.
Nautel equipment has most of these features built into it, therefore, the implementation of a SFN using Nautel exciters and transmitters should be relatively straight forward.
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
Those who would give up essential liberty to purchase a little temporary safety, deserve neither Liberty nor Safety.
~Benjamin Franklin
...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
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
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