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Broadbanding an AM antenna

Many articles have been written on the topic and it is still a black art to some.  Making a Medium Frequency (MF) antenna that has enough bandwidth to pass 10 KHz audio can be challenging, to say the least.  The VSWR out to +/- 15 KHz carrier needs to be kept at a minimum and the power needs to be evenly distributed between the two sidebands.  This can become problematic with complex Directional Arrays or towers that are tall or short for their operating frequency.

When we were working on the WFAS-AM tower in White Plains, NY, it became apparent to me that something was not right.  The tower is skirted and now holds the antenna for W232AL, a 250 watt translator broadcasting the WPLJ HD-2 channel.  After installing the FM antenna, some tuning of the AM antenna was required and this is the graph of the resistance and reactance curves:

WFAS 1230 KHZ, ATU output resistance and reactance

WFAS 1230 KHZ, ATU output resistance and reactance

This looked very similar to the resistance and reactance curves before the FM antenna work was done.  Red line is resistance, the blue line is reactance.  I think it had been like this for a long time.  While it is not terrible, it is not that good either.  As alluded to in a previous post, some re-working of the ATU was needed.  After some trial and error, this is the circuit that we ended up with:

WFAS 1230 KHZ White Plains, NY ATU schematic

WFAS 1230 KHZ White Plains, NY ATU schematic

Not quite what I expected, however, it was designed with the parts on hand, excepting the vacuum variable output capacitor, which was donated by me.  That part was key in making the proper adjustments.

After my redesign and tune up of the ATU, this the resistance and reactance curves at the input terminal of the ATU:

WFAS 1230 KHz resistance and reactance after ATU modification

WFAS 1230 KHz resistance and reactance after ATU modification

The graphs have a slightly different format, but you get the idea.  The red line is resistance, the blue line is reactance and the green line is overall impedance.  The resistance is symmetrical about the carrier as is the reactance.  Truth be told, I think there is a little more that can be had here, but for now, there is no reason to go any further.  I made the initial measurements at the input of the ATU and confirmed them again at the output terminals of the transmitter.  When we turned the transmitter back on, I noticed that the modulation index had dropped by about 15 percent.  I think the reflected power was getting back into the RF sample and fooling the mod monitor.  I also noticed that the high end in particular sounded much nicer.

WFAS 1230 KHz, White Plains, NY ATU

WFAS 1230 KHz, White Plains, NY ATU

The ATU building is a little cramped and it is hard to get a good picture.  The vacuum variable capacitors were salvaged from a scrapped AM transmitter years ago.  The tower is 202 degrees tall, which is also a factor.  It will be interesting to see what seasonal changes there are with snow cover, mud, etc.

Overall, this was a fun project.

Transmitter repair

Sometimes it is obvious and relatively easy, other times not so much.  This summer we have had wave after wave of afternoon thunderstorms.  It is almost like living in Florida; almost, but not quite.  Anyway, with the storms occasionally comes some lightning damage.  At most of the transmitter sites we service, every step has been taken to ensure good grounding and adequate surge suppression.  This is especially true of sites that have been under our care for a few years.  Even so, occasionally, something gets through.  After all, those five hundred foot steel towers do attract lightning.

Broadcast Electronics AM5E output tuning section

Broadcast Electronics AM5E output tuning section

This is the output section of the BE AM5E transmitter at WROW.  The transmitter got pretty trashed; a bad PA module and power supply and this capacitor in the output section.  This particular transmitter is 14 years old and this is the first major repair work we’ve had to do it.

Broadcast Electronics AM5E output tuning capacitor

Broadcast Electronics AM5E output tuning capacitor

The capacitor was fairly easy to change out.  As a general precaution, both capacitors were changed.  There was a spare PA module and power supply on the shelf, thus the transmitter was returned to full power relatively quickly.

Broadcast Electronics AM5E output forward and reflected power meters

Broadcast Electronics AM5E output forward and reflected power meters

The rest of the antenna system and phasor were inspected for damage, a set of common point impedance measurements taken, which showed that no other damage was sustained.

Next, the 30 year old Harris SX2.5 A transmitter at WSBS.  This failure was slightly more exotic; the transmitter started randomly turning itself off.  The culprit in that case was this:

Harris SX2.5 remote control interface bypass capacitor

Harris SX2.5 remote control interface bypass capacitor

Literally, a two cent part.  The transmitter remote control uses opto-isolators.  The inputs to these opto-isolators are RF bypassed to ground on the back of the “customer interface board.”  After determining that the remote control was not malfunctioning, it was down to either a bad opto-isolator or something really silly like a bypass capacitor.  This capacitor was on the ground side of the remote off terminal.  It shows short on the capacitance meter and 4.1 K on the ohm meter, just enough to randomly turn the opto-isolator on and shut down the transmitter.  Being a Harris transmitter, removing and replacing the “customer interface board” was no easy matter.  Overall, it took about three hours to find and repair this problem.

Troubleshooting an AM array

Today, there will be a quiz.

Recently, we had an AM antenna array go out of tolerance by a good margin.  This has been repaired, however, I though I’d post this information and see if anybody could identify the problem and the solution. Unfortunately, I don’t have a prizes to give away, however, you can show off your AM engineering prowess.

All of the information is pertinent:

  1. The station has two directional arrays (DA-2) using the same towers; the night time array is out of tolerance, the daytime array is not effected and is performing normally.
  2. There were no weather events connected with this event; no electrical storms, no major temperature changes, no rain events, no freezing or thawing, etc.
  3. The problem happened all at once, one day the array was performing normally, the next day it was not.
  4. Station management reports that some listeners were complaining that they could no longer hear the station.
  5. The ATU’s and phasor were inspected; all RF contactors were in the proper position, no damaged or burned finger stock, no evidence of damaged components (inductors or capacitors) was observed.  Several mouse nests were cleaned out of the ATU’s, however, this did not change the out of tolerance antenna readings.
  6. The towers are 1/4 wave (90 electrical degrees) tall.

Readings:

Tower Phase angle as licensed Current ratio as licensed Phase angle as read Current ratio as read
1 147.2 0.583 149.5 0.396
2 (reference) 0 1.00 0 1.00
3 -137 0.493 -125.8 0.798
4 107.5 0.481 92.7 0.355
5 -38.1 0.737 -60.2 0.623
6 -178.7 0.382 142.8 0.305

Licensed values for common point current is 13 amps, impedance is 50 ohms j0 and there is normally no reflected power on the transmitter.  On this day, the common point current readings were 8.9 amps, impedance 38.5 ohms +j5 the transmitter had 340 watts of reflected power.

This is the overall schematic of the phasor and ATU:

WDGJ overall RF schematic diagram

WGDJ overall RF schematic diagram, click for higher resolution

Aerial view of transmitter site, oriented north:

WGDJ aerial view showing towers as identified in schematic diagram

WGDJ aerial view showing towers as identified in schematic diagram

So, where would you begin?  Ask questions in the comments section.

The AM Receiver problem

The technical problems with AM broadcasting can be broken down into three broad categories:

  • Interference from other AM stations
  • Interference from unintentional radiators (AKA electrical noise)
  • Poor receivers

Much of the poor fidelity issues with AM broadcast audio comes from the narrow IF bandwidth of the typical AM receiver.  Older AM receivers had much wider IF bandwidths, sometimes as much as 15 KHz +/- carrier.  As the AM band was over filled with stations starting in the late 1940’s, this became a big problem.  The tube type front ends with great sensitivity but not very much selectivity were unable to cope with adjacent channel interference, leading to what was known as “monkey chatter.” This type of interference can be technically described as the higher audio frequency peaks from an adjacent channel stations being demodulated.  Those hearing this type of interference found it very annoying and rightly so.  Thus, receiver manufacturers were deluged with complaints about the poor quality of their units.  The solution was simple; narrow the bandwidth until the “monkey chatter” disappeared.  This new de facto standard IF bandwidth turned out to be +/- 3 KHz carrier.

It does not take a rocket scientist to see that 3 KHz audio is only very slightly better than telephone quality.  This was the beginning of the perceived AM low fidelity problem.  In the mean time, FM broadcasting, after years of lagging behind in spite of it’s superior audio, made great strides into mainstream acceptance.

NRSC-1 was supposed to reduce this type of interference by limiting AM broadcasting stations audio bandwidth to 10 KHz.  The idea was to attempt to keep the modulation index somewhat within the allotted channel.  This standard was mandated by the FCC in 1989, after which receiver manufacturers were to change their design to allow for wider IF bandwidths, thus improving AM fidelity.  There was even an AMAX standard adopted by some receiver manufacturers.  Unfortunately, by this time, the majority of AM stations were transitioning from music to talk radio.  The new standards were too little much too late.

A quick scan with a quality AM receiver shows that many stations are transmitting high quality audio, which, with a properly adjusted IF bandwidth can sound remarkably good:

Screen shot - WEOK true oldies channel

Screen shot – WEOK True Oldies Channel

This is a screen shot from a SDR (Software Defined Radio) showing WEOK, Poughkeepsie, NY broadcasting the True Oldies Channel.  The signal strength is slightly low, but this is a rural area and the noise floor is also low.  I limited the bandwidth to +/- 7.5 KHz carrier because of the pre-emphasis used on most AM stations makes the high end sound strident.  Looking at the spectral display, there is more audio available beyond what I am listening to.  Which brings me to this; AM fidelity is not inherently inferior, it can sound quite good.  There is no reason why AM receiver manufacturers cannot improve their product to include some advanced features;

  • Variable IF bandwidth based on signal strength
  • Variable user selected IF bandwidth
  • Sharp selectivity – adjacent channel rejection
  • Selectable side band demodulation (carrier plus upper or carrier plus lower sideband)

While this will never sound as good as FM stereo, it still can sound pretty good, especially with older music recorded before say 1975 or so.

Manufacturers would have to have some impetus to include these features in their chipsets, such as multiple requests by listeners who are looking for better AM quality, which leads us back to programming…

The other issues with AM electrical noise reception and interference from other radio stations are surmountable, so long as there is a reason to.  Which, leads us back to… programming.

AM revitalization comments

I have been reading the comments regarding the FCC’s NPRM (13-249).  Clearly, many people are interested in keeping the AM broadcasting band both active and relevant.  Some of these suggestions have merit, but are unlikely to be adopted by the FCC.  Others are viable and could alleviate at least a few of the technical shortcomings of the AM band.  The rest fall along expected positions.  Here is a brief rundown:

  • Clear Channel, iBiquity: Allow stations to transmit in all digital mode.  Likelihood: Possible.  The hybrid version of AM HD Radio has been a failure on several fronts; added interference to adjacent channels, self interference, poor adoption, wonky CODECs, etc.  However, letting stations choose to broadcast in all digital AM HD Radio may decide the issue once and for all.  As long as the all digital carriers fall within the current analog channels, this would be fine.  Actually, I would add that station transmitting in all digital be allowed to choose DRM as well as HD Radio
  • REC Networks, MMTC: Move AM stations to former TV channels 5 and 6.  Likelihood: Unlikely.  It would be a neat solution, however, there are currently many full and low power TV stations still using those frequencies.
  • Clear Channel, SBE, MMTC, Crawford, et al: Allow AM stations a special translator filing window.  Likelihood: Almost assured.  This has been broached by the FCC itself.  I would add that Class D and Class C stations be given priority.
  • SBE, du trial, Lundin and Rackely, MMTC et. al: Remove the “ratchet rule,” reduce antenna efficiency requirements and city of license contour requirements.  Likelihood: probable.  Over the years, the FCC’s rules and regulations designed to help AM broadcasting’s technical product have done the opposite in many cases.  This is especially true of the “ratchet rule.”
  • SBE, du Trial, Lundin and Rackely, MMTC: MDCL (Modulation Depended Carrier Level) Likelihood: Possible.  MDCL does not do much to improve AM signal quality, but it can save the station owner some money on the electricity bill.
  • Alabama Broadcaster’s Association, et al: Better FCC enforcement.  Likelihood: Not very.  This is another area were interference and AM noise problems can be fixed.  Given Ajit Pai’s desire for “non-regulatory” relief, stepped up enforcement seems to be a non-starter.
  • Hatfield and Dawson: Eliminate substandard AM stations.  Likelihood: Not very.  Getting rid of substandard stations and let the remaining AM stations enjoy a little breathing room is actually a big step in the right direction.  H&D notes that the FCC should petition congress for tax relief for those stations that choose to surrender their licenses.  Unfortunately, it does not appear likely that the FCC, congress and the current station owners would go for it.
  • du Treil, Lundin and Rackely: Do away with skywave protection for class A stations  Likelihood: Possible.  The argument goes; skywave listening represents a very small number of mostly hobbyists (AM DXers) as other, better methods for program distribution exist for serious listeners.  Sad but true.
  • du Treil, Lundin and Rackely: No more new AM stations.  Likelihood: Possible.  There is a cogent argument to be made regarding the overcrowding of the AM band.  Stopping any further crowding is a good idea.
  • SBE, Cohen, Dippell and Everist, et al: Tighten regulations on electrical noise emitters.  Likelihood: Unlikely.  The FCC does not have the mettle to tighten regulations against powerful manufacturing and technology lobbies.
  • iBiquity: Do not let anything get in the way of the HD Radio rollout.  Likelihood: Is it possible to get in the way of something that is standing still?

Talking amongst engineers and AM broadcasters, many of these ideas have merit.  The real question is, will any of this bring more listeners?

The Kintronic Isocoupler

Had a problem with this Kintronic FMC-0.1 isocoupler the other morning.

Kintronic FMC-1.0 STL ioscoupler

Kintronic FMC-1.0 STL isocoupler

After an overnight drenching heavy rain and very high wind, the STL transmitter associated with this unit was having high VSWR faults.  This isocoupler crosses a base insulator of an AM 50 KW directional antenna.  This particular tower has negative impedance, which is to say, it sucks power out of the pattern and feeds it back to the phasor. An interesting discussion for another time, perhaps.

Using a dummy load, we isolated the problem to the isocoupler by first connecting the load to the output on top of the unit (problem still exists) then to the transmission line prior the unit (problem went away).  Of course, the AM station had to be taken off the air to do this work.

Once the issue was confirmed as the isocoupler, I opened the unit up and found that water had entered and pooled in the top of the bottom half of the isolation transformer.

Kintronic isocoupler transformer

Kintronic isocoupler transformer

The isolation transformer consists of two loops to ground capacitively coupled through air dielectric. The issue is with the opening around the top of the unit, under the lip of metal lid. Apparently, this allowed water in.

Kintronic isocoupler isolation transformer

Kintronic isocoupler isolation transformer

It is difficult to tell with the lighting in this photograph, however, the bottom part of this isolation transformer has water pooled around the center insulator.  Using a rag, I cleaned out the water and dirt from the center insulator.  After reconnecting the antenna and transmitter transmission line, a quick check revealed the problem was much better, but still not completely gone.  I suspect water seeped further down into the bottom half of this unit.  The repair work was good enough, however, to return both stations to the air.

Glad to get that bit of work done while it was still relatively warm out.

AM stations being donated

WGHQ was donated by Pamal Broadcasting to Tri-State media over the New Years Holiday.  Originally signed on in 1955 as WSKN in Saugerties, NY, WGHQ had been struggling to hang on over the last few years.  The station had been on a syndicated satallator automation format with the only local show being Kingston Community Radio, airing weekday mornings from 6-9 am.  In the end, it was either go dark or donate the station.

Tri-State Media is the owner/operator of WHDD AM/FM and WLHV, which are NPR affiliates.  They also simulcast on WBSL-FM, owned by Berkshire High School, when the students and faculty are not on the air.  A look at the program schedule shows a variety of music, local and national news and talk.

Over the last five years or so, several AM stations have been donated to community oriented groups and organizations, most notably the MMTC.  Often, these stations are in rough to very rough technical condition and many are silent.  It is noted that WDTW no longer has a transmitter site and KWHN was suffered severe damage due to flooding.  Those stations donated to the MMTC often find themselves LMA’d to a local group to run for a while before ownership is transferred.

Call Letters City of License From To Frequency Power D/N
KWOD Salem, OR Entercom MMTC 1390 5,000/690
WGHQ Kingston, NY Pamal Tri-State 920 5,000/78
WSHU Westport, CT Graham Sacred Heart 1260 1,000/9
WKRT Cortland, NY Saga Bible Broadcasting 920 1,000/500
WDTW Dearborn, MI Clear Channel MMTC 1310 5,000/5,000
KFXN Minneapois, MN Clear Channel MMTC 690 500/4
WMNY McKeesport, PA Renda Pentecostal Temple dev 1360 5,000/1000
WGBN New Kensington, PA Salem Pentecostal Temple dev 1150 1,000/70
WNRR North Augustsa, GA Clear Channel MMTC 1380 4,000/70
WHJA Laural, MS Clear Channel MMTC 890 10,000/-
KWHN Ft. Smith, AR Clear Channel MMTC 1650 10,000/1,000
WTOC Newton, NJ Clear Channel MMTC 1360 2,000/320
WBHA Wabash, MN Clear Channel MMTC 1190 1,000/-

There may be other stations that were donated to various other groups, but this is all I could find using Google.  I notice several of them are on the current list of silent stations.  I wonder how many are currently on the air and successful.  Are they being locally programmed?  If so, how has the reception been in there respective communities?  What remediation was required for the technical facilities and how much did it cost?

Happy New Year

I wish everyone a Happy New Year and hopefully, a prosperous 2014.

Another year has gone by, and there were few things remarkable about it. Among those are:

From the digital radio front; HD Radio continues to be a non-factor in the bigger broadcasting picture.  FM HD Radio continues to make very small inroads, especially with public radio groups who’s HD Radio expenditures are mostly tax payer subsidized.  AM HD Radio continues to backslide slowly from it’s high water mark of 310 stations in 2007.  It is difficult to nail down the exact numbers of AM HD Radio broadcasters, however, Barry McLarnon notes that 177 stations are currently transmitting AM HD Radio.  No official numbers are available from either the FCC or iBiquity itself.

The great 2003 translator log jam (Auction 83) was finally fixed so that the FCC could move ahead with the LPFM application window in October.  In the end, some 1,240 translators were granted, with more conflicting applications still in the works.

The LPFM filing window opened in October amid the government shutdown.  Many groups were predicting 10,000 new applications for 100 watt LPFM licenses.  The actual number is closer to 2,800.  The final number of Construction Permits issued with likely be somewhat lower as defective and competing applications are dismissed.  This number seems low to some LPFM proponents.  When I approached a local interest group about launching a low power radio station, I was basically met with indifference.  With a very complex set of application guidelines and operating rules, plus very low power levels, it is not surprising at all.

The NAB and the FCC have been working diligently on revitalizing the AM broadcasting band.  Results of these efforts are yet undetermined as the proposal works it’s way through the regulatory process.  The so called “analog sunset” still lurks in the background somewhere, waiting to be trotted out at the most opportune moment.  I remain skeptical of the current proposal.

Cumulus Broadcasting purchases Dial Global and renames it West Wood One.  Some people lose their jobs.

Nielson buys Arbitron rating service and renames it Nielson Audio.  Some people lose their jobs.

Clear Channel tries to fly under the radar with “staff reductions.”  Some people lose their jobs.

Long time online radio forum “Radiodiscussions.com” ceased existence.  Starting out as Radio-info.com in the mid 1990’s, radio discussions was largest, longest running radio forum in the country.  It held tens of thousands of posts on almost every radio topic under the sun.  Unfortunately, it was bought and sold a few times over the last few years and the new owners could not figure out how to monetize it.  The end.

Bernie Wise passed away on December 13th.  This is truly unfortunate as Bernie was a character perfectly suited to the radio business.  He started working for RCA and is responsible for UHF television broadcasting in the US.

On the blog front, we continue to grow in page views and readers.  As of this date, Engineering Radio gets approximately 540 page views per day and has 227 RSS subscribers.  The split is 60/40 percent domestic/international readers.  The top five international traffic sources are; Canada, UK, India, Germany and Brazil.

2013 stat counter image

2013 stat counter image

There are some 634 articles with 2,640 legitimate comments and 429,600 spam comments.

Regarding site outages, there were 343 minutes of server down time.  Two DDOS attacks lasting six and three hours respectively and one incident of a corrupted .htaccess file rendered and error 500 message for six hours.  Total down time 1,243 minutes or 20:43 hours which gives a 99.87% availability for the website.  Not bad, but we can do better as the uptime goal is 99.99%.

On a personal note, my college studies are progressing well.  I have three more classes or 10 credit hours left until I am done.  My GPA is 3.90 which is not terrible considering I am working full time and going to school almost full time.  Truth be told, I cannot wait until it is finished.

The last AM station

AM; it has a future or not?  I cannot make up my mind sometimes.  As some AM stations can and do make a profit, many others do not.  Truth be told, the engineering effort that goes into an AM directional antenna is becoming a black science.  And some people may say, “oh, but that gives you job security,” but that is not usually how it works.  Instead of paying somebody more money (or any money) to maintain something, the business philosophy these days seems to be to chuck the baby out with the bath water.  Because after all, if not AM then FM right?  Yes, of course!  Except, the very thing that happened to AM is happening to FM too.  Increasing noise floors, jamming signals into every possible nook of the frequency spectrum, no thought toward technical facilities and infrastructure, and horrible, horrible programming will result has resulted in the decline of listening for FM too.  Mark my words and the date; FM broadcasting will suffer the same fate as AM if current trends continue.

Guy wires in trees

Guy wires in trees

How will it end?  I would hazard with more of a whimper than a bang.  I imagine something like this:

One day, in the not very distant future, at an AM station somewhere, the transmitter faults and goes off the air. Chip, the computer guy, goes in the back room, moves a bunch of cleaning supplies, cases toilet paper, a garbage can and the remote gear out of the way so he can reach the ON button on that box the old guy told him about. The big box makes some clunking noises and comes on for a second, but then the fault light called “VSWR” or something comes on and the transmitter shut off again.

Chip, the computer guy, remembering what the old guy said about that big tall thing behind the building, pushes the back door open.  What used to be a field is now completely overgrown with weeds, brush, and trees. He follows the pipe from the back of the building, through the prickers until he comes to an old fence, which is falling down. He pushes on the locked gate and it falls off the hinges. Inside the fence, there is a rusty tower and a white box. Finding the box unlocked, he opens it and sees a baffling array of metal coils, copper tubes, and black round things. He sees that one of the black round things is cracked in half and black goop is coming out of it. The computer guy takes a picture with his cellphone and emails it to the market manager/vice president of sales.

A few minutes later, the the market manager calls back and Chip tries to explain what is going on, stating the the transmitter went off and the black thing in the box by the tower looks broken.  The market manager/vice president of sales asks “Has anyone called and complained?”  Chip says no, not that he is aware of.  The market manager says, “Eh, fuck it leave it off.”

The end.

Horby and Solvesborgs transmitter site

This is a video of Radio Sweden’s shortwave and medium wave transmitter sites:

Håkan Widenstedt at Hörby and Sölvesborgs Transmitter sites from HamSphere on Vimeo.

This was filmed in 2006. In 2010, Radio Sweden ceased broadcasting on medium and shortwave, thus I believe these sites have Horby (HF) has been dismantled.  Medium wave installation Solvesborg is visible starting at 15:30. Two tower directional array 180 degree towers with 600 KW carrier power. Quite impressive.

There is an effort to at save the Solvesborg site, perhaps as a museum.

Transmitters were in Skane, Sweden:


View Larger Map

h/t Shortwave Central

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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