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Converting electrical degrees to height in meters or feet

Here is one of those things that can often be a head scratcher for the uninitiated:

The FCC data base gives antenna height in electrical degrees when what you really want to know is how tall is that tower.  Never fear, to figure all this out, requires math.  Pretty simple math at that, too.  I prefer to do these calculations in metric, it is easier and the final product can be converted to feet, if that is desired.

First of all, radio waves travel at the speed of light, known as “c” in many scientific circles.  Therefore, a quick lookup shows the speed of light is 299,792,458 meters per second (m/s).  That is in a vacuum, in a steel tower, there is a velocity factor, most often calculated as 95%, so we have to reduce speed of light in a vacuum to the speed of RF in a steel tower.

299,792,458 m/s × .95 = 284,802,835 m/s (speed of a radio wave in a steel tower)

Frequencies for AM radio are often given in KHz, which is 1000 cycles per second.  For example, 1,370 KHz × 1000 = 1,370,000 Hz (or c/s)

Therefore:

284,802,835 m/s ÷ 1,370,000 c/s = 207 meters per cycle.  Therefore the wavelength is 207 meters.

There are 360 degrees per cycle, therefore:

207 meters ÷ 360° = 0.575 meters per degree

If the height of the tower is 90°, then 90° × 0.575 m/° = 51.57 meters.  Add to that the height of the base insulator (if there is one) and the concrete tower base and that is the total tower height.

To convert meters to feet, multiply by 3.2808399.

In the United States, that tower would be 169.78 feet tall.

If the CRTC has any sense….

They’ll run away screaming “NOOOOOOOO!” to this notion:

Canada’s plan “B” might include iBiquity.

(as reported by Inside Radio)

Let’s just hope that this is more of iBiquity’s wishful thinking, which is often presented as actual important news being based in fact.  By iBiquity.

Why does the CRTC need a plan B anyway?  Is in not enough that Eureka 147 failed mainly due to lack of public interest?  If it was something that was commercially viable, wouldn’t it have taken off on its own?  Now they are thinking of ruining the FM broadcast band, which, in my experience in Canada, is working perfectly fine.

Who says “digital” is better?  If anything, what has been discovered in this country is when it comes to HD radio, digital is worse.  Thus far, HD radio has the following going for it:

  • Proprietary system with expensive licensing fees
  • Complicated infrastructure
  • Insufficient building penetration
  • Poor performance in mobile reception evironments
  • Lack of original programming
  • Adjacent channel interference
  • Poor receiver sales
  • Lack of general interest and/or knowledge by public

All of these things have been well documented.  If you work for the Canadian Radio Television and Telecommunication Commission (CRTC) and are thinking about this, contact me.  I’ll even invite you down for a drive around and you can experience HD radio, in all its glory, first hand.

AM can’t wait (can it?)

Click on picture for original memo (.pdf)

I was digging through some old manuals at the shop today and I found this June 1987 memo from Orban to AM stations titled “AM radio CAN sound almost like FM.”

The main purpose of the memo was to get AM radio stations to implement the NRSC standard for pre-emphasis and high frequency roll off to improve the sound of AM broadcasts on ordinary radios.

I am not sure why the receiver manufactures never designed an IF filter that would be compatible with NRSC, it seems like a fairly simple design.  Instead, what we have is “digital” AM radio (IBOC) which does not work well, creates many more problems with interference that of pre NRSC broadcasting.

If one were to look at the entirety of AM broadcasting history, one would find some striking parallels with what is happening with IBOC today on both AM and FM.

To start, the NAB began petitioning the FCC to allow more AM broadcasting stations, even as it was known that these stations would create interference with existing stations, especially at night.  Still, the NAB persisted and the FCC relented and through the fifties, sixties, seventies, and eighties many more class II and III stations were established on what used to be clear channels (classes I and IA).

Once the AM band was chock full of stuff, they began going to work on the FM band with 80-90 drop ins.

You see, for the NAB, more radio stations means more dues money, greater lobbying power because of the larger size of the industry.   Then came deregulation of ownership limits.  By this time, Big Group Radio was calling the shots and they wanted more.  This led to the great consolidation rush of the late 1990’s from which the radio industry is still reeling.  The consolidation rush led to highly overpriced radio stations being leveraged to the absolute maximum, leading to the recent bankruptcies.

Finally, the NAB’s great push toward adopting IBOC digital radio in the early years of the 00’s.  IBOC was supposed to save the day, greatly improving quality of both AM and FM and bring radio into the 21st century.  Except that the promised technical advances never materialized.  IBOC remains a great expensive boondoggle and I am beginning to think that perhaps we should stop listening to the NAB.

The memo itself is a fascinating thing, which were one could substitute AM with RADIO and come to some of the very same conclusions today regarding analog and IBOC digital radio.  For example, this paragraph on AM stereo:

AM stereo was thought to be an answer (to improve AM), but AM stereo was embraced with the false assumption that having ‘stereo’ automatically meant having ‘high fidelity’.  While AM stereo did provide somewhat better fidelity, it was not comprehensively engineered to get the best fidelity from AM.  It was hoped that the gimmick of having two channels would be enough to save AM.

AM stereo could have been an improvement, had it been properly implemented.  Unfortunately, the underlying problem of bad sounding receivers was never addressed.  About which, the same memo notes:

Receiver manufactures did what they could to reduce listener complaints – – they narrowed the bandwidth (thereby reducing audio fidelity) until the complaints about interference stopped.  Listeners clearly indicated, through their buying habits, a clear preference for lower fidelity over continuous irritating static, buzzes, whistles, and “monkey chatter’ from adjacent stations.  People accepted this situation for a long time – – until the simultaneous advent of improved receiver technology and the FCC’s anti-simulcasting rules created the FM boom of the late 1970’s. (ed note: I remember listening to FM because there were fewer commercials, not better sounding audio)

Then the memo goes on to stress the importance of implementing NRSC standard for AM broadcasting that included the sharp frequency roll off at 10 kHz, noting that receiver manufactures would design “fine new receivers” that would take full advantage of the new standard, but only if broadcasters first showed good faith by widely and promptly implementing it.

As I recall, NRSC-1 was adopted as rule of law by the FCC in 1989, about two years after this memo was written.  One could reasonably expect that receiver manufactures then started producing radios that took advantage of the NRSC pre-emphasis curve with IF filters that did not cut off audio frequencies above 3.5 kHz, but rather rolled them off in a gentle slope until about 7 kHz, more aggressively after that until 10 kHz, where they cut off.

Except they didn’t.

Instead, twenty years later, AM radios universally sound bad, with audio bandwidth of about 3 kHz or so.

I believe that AM receivers could be made with three IF bandwidths, automatically selected based on signal strength.  Within the 5 mv contour, full (10 kHz) audio can be reproduced using a high frequency roll off described above.  In the 1 – 5 mv contour, a 6 kHz bandwidth and less than 1 mv a 3 kHz bandwidth.  The automatic selection could be defeated with a “wide/narrow” IF bandwidth selection switch like the GE superradios have.  Of course, if one where listening to stations transmitting AM IBOC, the “narrow” setting would be the best.

Half of me thinks that the ship has already sailed on AM broadcasting.  The stations on the air will continue to decline until they are no longer able to broadcast due to expensive repairs or replacement, at which time they will be turned off.  The other half thinks that AM radio, as evidenced by the huge public response to WEOK and WALL broadcasting the true oldies channel, can be revived.  With the impending inevitable FM IBOC power increases, translator shoe ins, LPFM, etc; the FM band may become worse than the AM band.  At which point the public will have to decide whether free radio is important to them, or 3G/4G services will become the new method of broadcasting.

NAB Engineering Handbook

I just found my old copy of the NAB Engineering Handbook, sixth edition. I have enjoyed throughly looking at the AM antenna sections. It reminds me, that while we tend to think we have come up with new answers to old problems, really most of this was figured out a long time ago, this particular edition was copyrighted in 1975.

It is a thick book and covers AM, FM and TV broadcasting technology as it was understood in 1975.  There are several chapters about “current” things that no longer apply, there are also many very useful items, such as studio construction, AM and FM broadcast antennas, tower maintenance and so on.

I will keep this on my shelf because it is an interesting primer on AM broadcast antennas with all attendant formulas and charts.  It is quite interesting and fun if one is looking for the theoretical efficiency of a 185 degree radiator at 1 mile.  I remember WPTR (now WDCD) in Albany had a three tower with 206 degree radiators, 50 KW carrier power on 1540 KHz.  It seemed to be quite effective, when I was chief engineer there, we used to get reception reports from South Africa.

Perhaps one day, I’ll put some of that information to good use with an AM station of my own.

Breakaway Broadcast

I am a strong proponent of non-computer based air chain processors.  Something about listening to dead air while the computer reboots is annoying and every computer needs to be rebooted every now and again.

All of that being said, I recently had a chance to play around with Breakaway Broadcast audio processing software.  I have to say, as a low cost, very versatile platform, it can not be beat.  I would put it up against any of the high end FM audio processing, provided one uses a high quality sound card with an adequate sample rate.

Claesson Edwards Audio has developed several software based audio processors for a variety of end uses.   They make several recommendations for hardware and operating systems, Pentium 4 3.2 GHz or better, dual core preferred.  If one is interested in used the sound card to generate composite audio, then any sound card capable of true 192 KHz sample rate will work.  They list several that have been successfully tested on their web site.

For approximately $1,200 dollars or so, one could buy a decent computer, the Breakaway Broadcast software and the Airomate RDS generator software.  For a Mom and Pop, LP or community radio station that is looking to do some high end audio processing and or RDS, that is a good deal.  I would add a UPS to the computer and keep back up copies of the software installed on an emergency computer just in case.  One can never be too safe when it comes to computers, viruses, hackers and other malicious persons.

Things that I like

  1. Inexpensive, the fully licensed version is $200.00.  The demo version is free but there is a 30 second promo every thirty minutes.
  2. There are several factory presets, but everything is fully configurable, changes can be named and saved allowing some experimentation.
  3. Audio cards with 192 KHz sample rate or greater can be used to generate composite audio, eliminating the need for a separate stereo generator
  4. RDS capable with additional software (Airomate2, approximate cost $35.00)
  5. The same processing computer can be used for streaming audio and or AM audio processing simultaneously.
  6. Full set of audio calibration tools for AM and FM transmitters, allows correction for tilt, overshoot and linerity.  Can add pre-emphasis at any user selectable rate.
  7. Fully adjustable phase rotators.

Things that I don’t generally like:

  1. Computer based system using Windoze operating system

WXPK in White Plains, NY has been using this software to process their streaming audio for about 2 years now.  The software itself is extremely stable running on a stand alone Windows box with XP service pack 2.

Yeah, there is an app for that

In the never ending evolution of remote broadcasting equipment, Comrex has yet another way to connect to the studio with broadcast quality audio.  For use with their Comrex Bric-link or ACCESS equipment, they have authorized an iPhone app called Media5.   It requires a SIP account and costs $4.99 to download, which last time I checked, was pretty reasonable.  I am not surprised that remote equipment manufactures have tapped into the 3G/4G wireless networks that span most of the country.

Time was when a remote required ordering an equalized phone line from Ma Bell.  This usually required 2-4 weeks, depending on the local branch.  Spontaneous remotes were but a pipe dream.  Then came Marti with inexpensive RPU transmitters and receivers, this greatly reduced the lead time required for establishing remote broadcasts.  The downside to Marti equipment is it takes at least some technical know how to set up because of all the antennas and coax and such.

Comrex came on the market with Telephone Line frequency extenders then with 3 line comrex units (3XP/3XR).  A three line unit split the incoming audio into three different sections, reducing each to 300 to 3,400 Hz telco line base band.  At the other end, the answering unit changed the sections back to their original frequency range, then recombined them into pretty good sounding audio from 50 to 10,000 Hz or so.  I have used these units on several occasions.  I believe that one of the stations I work for still has one of these in their storage unit, along with several EFTs.

Latter, Comrex came out with POTS line codecs like the Hotline, Matrix and Blue box.  Now only one phone line was needed to do a remote. This greatly simplified remote availability and set up.  The downside to these is it had to be straight dial tone, no PBX’s or any thing like that.  A noisy line can create problems with audio quality and dropouts.

The Matrix can be used with ISDN and they used to have a GSM module to use with certain cellular networks.

The latest Comrex products include IP and VOIP capabilities.  These systems are great when a broadband WIFI networks is available to be used.  Unfortunately, an open WIFI with good signal strength is not always at hand.  So the 3G/4G option is a natural.

Lightning Damage

It is that time of the year again, at least in the northern hemisphere, for thunderstorms.  I am a big proponent of grounding everything, there is simply no such thing as too much grounding.  I took a course when I was in the military given by Polyphaser in which grounding for lightning protection and EMP was emphasized.  It was very interesting in several respects.

One commonly held belief is that when lightning strikes an object, the ground immediately absorbs all of the charge.  That is not true in most cases due to ground resistances.  Eventually, the ground will absorb the charge but it can take several seconds to do this, especially with a big strike.  Equipment is damaged by current flow, therefore, every effort must be made to keep all of the equipment at the same potential, even if that potential is 10KV.  That is where a single point ground buss comes in.  Bonding every piece of equipment to a common ground buss ensures that no one device is at a lower potential while the charge dissipation is occurring.

The second misunderstanding about lightning is that it is DC voltage.  That is true, however, a lightning strike has an extremely fast rise time, on the order of 30 microseconds.  That makes it behave more like AC voltage around 10 KHz.  Therefore, ground buss wires need to have a minimum inductance.  Solid #2 wire is best, keeping it as straight as possible and using long sweeping turns where needed.  All bonds should be exothermically welded (CAD weld).

Ground system installed at WKZY, WHHZ and WDVH, Trenton Florida

Ground system installed at WKZY, WHHZ and WDVH-FM transmitter site in Trenton, Florida.  Central Florida is the lightning capital of the US.  Prior to doing this work, the Harris FM25K transmitter was knocked off the air at least once a month.  Since this was installed in 2005, they have had zero lightning related damage.  The ground rods are 20 feet long, driven down into the water table, spaced 20-30 feet apart.

All coax shields and metal conduits that come into the building should be bonded to the ground system where they leave the tower and where they enter the building.  At most tower sites, I install a ground ring around the outside of the building with rods every 20 feet or so.  From that ring, 5 to 6 radials outward 40 feet with ground rods every twenty feet works well.  I also install 5 to 6 radial out from the tower base with the same configuration.  The tower and building grounds are bonded together.  This is important because when the tower gets hit, the ground will quickly become electrically saturated.  If the building and the equipment is inside is at a different potential, current will begin to flow toward the lower potential, thus damaging gear.

All Coax, control and AC cables in and out of sensitive equipment should have ferrite toriods on them.  Transmitter manufactures normally supply these with new solid state transmitters, as MOSFETS are particularly sensitive to lightning damage.

Lightning damage to rack mounted equipment

This is a Potomac Instruments AM-19 directional antenna monitor.  It was damaged by a lightning strike two weeks ago on the WBNR tower in Beacon, NY.  The case arced to the rack it was mounted in.  This was a large strike, as several components in the phasor control circuit were also damaged.  The fact that this arced means that somehow the sample lines are not attached to the single point ground for this site, which needs to be corrected.

Insulated AM towers present special design problems when it comes to lightning protection.  Generally speaking, tower arc gaps should be set so there are side by side and there is no arcing on positive modulation peaks.  Depending on power levels, this can be anywhere from 1/2 inch to 2 inches.  Tower impedance also plays a roll in setting arc gaps.  The final link between the ATU and tower should have several turns in it.  The idea is to make that path a higher impedance path for the lightning, causing it to dissipate through the arc gaps.  Incoming transmission lines from the towers should be bonded to a copper buss bar at the entrance to the building.  All of this grounding needs to be tied to the RF ground at the base of the tower.

Arial phone cables can act like large lightning antennas for strokes several miles away.  It is very important that the cable shield and the cable termination device is bonded to the building ground buss.  I have seen installations where the TELCO tech pounds in a separate ground rod outside and connects the TELCO equipment to that.  That defeats the concept of single point grounds and should be fixed ASAP.

Electrical services entrances also can act like big lightning antennas.  Normally, pole mounted transformers will filter some of this energy out.  Internal electrical distribution systems can also add impedance, thus act as inadvertent filters for lightning.  In most mountain top transmitter sites, however, some type of power line surge protection is needed.

LEA series surge protector

Inside view of LEA surge suppressor

There are two types, series and parallel.  Parallel types are the least expensive and least intensive to install.  They are usually found mounted next to or on the service panel and fed with their own breakers.  They usually have some type of MOV or similar device that acts as a crowbar across the AC mains, conducting spikes to ground.  Series types go in between the service entrance and the main panel.  They include a large inductor designed to force spikes off into shunts.  A series type protector offers more complete protection than a parallel.

How expensive is online radio these days?

iphone 3GSI read a very good and interesting post on James Critland’s blog.  He is somewhat concerned about the trend for mobile wireless providers to no longer offer unlimited data service for a flat fee.  I find it interesting that all of these companies seemed to have reached the same conclusions at the same time.  But anyway…

The general surmise of James’ post is that the average person will not be able to afford online radio through a 3 or 4G device because of the limited minutes available and the additional charges incurred.  (35 quid is about $50.00) To make that meaningful to a US audience, I decided to redo some of James’ math.

Iphones are primarily serviced through ATT.  ATT has two different data plans that are coupled with voice plans in a bundle.  For example, a 450 minute voice plan and a 200 Mb data plan will cost $55.00.  At 900 minute voice plan with a 2 Gb data plan will run $85.00.

Here are a few interesting tid bits and some good math:

  • A 64 kbps stream runs 7.68 kb per second, or 460 kb per minute (1 kilo bit per second = 0.12 kilo bytes)
  • 1 hour of online listening equals 27,640 k bytes of data transfered
  • The 200 Mb plan cost $15.00 with voice plan, the 2 Gb plan cost $25.00 with voice plan
  • The 200 Mb plan would allow for 7 hours of listen time if no other data use occurred
  • The 2 Gb plan would allow for 72 hours of listen time if no other data use occurred
  • Beyond those data transfer amounts, extra charges are incurred

Almost 50% of the time spent listening to all radio source (terrestrial, satellite, online) is in the car.   The average person in the US listens to radio about 3 hours per day, or 90 hours per month.  Half of that time would be 45 hours or so.

Clearly, anyone who is more than a casual listener of online radio will need the 2 Gb plan.  However, given the paucity of entertainment available from traditional radio sources, this is not an outlandish amount to pay.  I remember in the 70’s when folks were saying cable TV would never catch on.

Blanketing Interference and RFI

Blanketing interference refers to the phenomena of receiving radio signals on devices not designed to do so.  In broadcast radio, this is defined for AM stations in part 73.88 as:

The licensee of each broadcast station is required to satisfy all reasonable complaints of blanketing interference within the 1 V/m contour.

And for FM stations, it is part 73.318:

Areas adjacent to the transmitting antenna that receive a signal with a strength of 115 dBu (562 mV/m) or greater will be assumed to be blanketed.

Any interference to any device with that signal contour is blanketing interference.  73.318 further states that:

permittees or licensees who either (1) commence program tests, or (2) replace their antennas, or (3) request facilities modifications and are issued a new construction permit must satisfy all complaints of blanketing interference which are received by the station during a one year period.

I have always taken a more pragmatic approach to interference complaints.  Rather than pass the buck and tell the home owner or business owner that it is not our (the radio station’s) problem, I’d go and try to help them out.  Generally speaking, the interference problems are close to the transmitter site, so on the next trip to that site, I would bring RFI filters and my 25 years of RF experience and solve the problem.  I would like to think this help the station’s and the company’s imagine in the community.

Most of the problems are pretty easily solved, although once in a while, I have come on some head scratchers.  An AM station playing on the outlets in a guys garage, the mic cords on a church PA system, and an off switch on a blender, off all things.  The Bare Naked Ladies had a line in the song Light up my Yard: “we can dance to the radio station that plays in our teeth.”

What I have found is start with the simple stuff first, check the ground on the electrical service entrance panel.  One might be surprised to find it disconnected, corroded or missing completely.  More than one occasion, I have fixed all of the RFI problems with a simple turn of the screw holding the ground wire to the grounding electrode.  In my experience, this is the most common single failure point.  A disconnected ground will cause the entire neutral wiring system to act like a giant AM antenna, with all sorts of bad outcomes.

RFI suppression ferrite

RFI suppression ferrite

Most often, telephone answering machines, cordless phones and other devices powered by wall warts are suspect.  Those devices do not have a path to ground.  A few turns of all the wires coming and going from said device around a ferrite core such as a snap on TDK RFI EMI filter available from Mouser will take care of it.  Mouser has several different versions available.

Occasionally, one needs to put on a detective hat and do some foot work.  Mast mount TV antenna preamps can cause untold heartache and problems.  One such incident involved the second harmonic of an FM station falling exactly on channel 11’s audio frequency.  This was affecting several houses in a one block area.  I finally found the problem at one of the complaintent’s house when I pulled the TV out and found the preamp power supply.  Unplugging it made all the problems go away (I hate Radio Shack).

Usually process of elimination will discover the problem and thereby reveal a solution.  The aforementioned church incident was discovered after I began unplugging microphone cords from the back of the Mackie mixer in the choir loft.  It turns out several mic lines were plugged into the back of the mixer, unused and unterminated, creating a large long receiving antenna on the cable shield, which happened to be aligned perfectly to pick up RF from an AM station.

Move AM stations to channel 5 and 6

It might happen, at least according to Commissioner Clyburn, they aren’t saying no right away.  According to her prepared statement:

I believe it is time that we consider the fate of Channels 5 and 6 as they relate to current radio service. These channels have proven difficult for television broadcasting, and I have a hard time imagining that they would fare much better as additional spectrum for mobile broadband use. This spectrum is not well suited for digital transmissions. It certainly is possible that this spectrum could be used for LPFM, expanded NCE use, and AM broadcasters.

That would, indeed, be an interesting development, if it were allowed to happen.  Of course, there are quite a few hurdles to get over, even if it gets the FCC’s nod, which is a long shot to say the least.  There would likely be some type of congressional “input” into the matter, which could stall things for years if not forever, depending on which way the money flows and which one of our wonderful congressional representatives can be bought and sold.

  1. Getting new radios on the market with the expanded FM band (77 through 87 MHz) will take some time.  Thankfully, unlike HD radio, no licensing fees will be required.  Manufactures simply need to increase the frequency range down.  It might take several years, but it would happen eventually, as is the case with expanded AM band radios, which are universal now.
  2. Existing AM stations should be given the option to move, those that stay on the AM band will get the option to improve their facilities or go non-directional as the interference contours allow.
  3. Those that choose to abandon AM need to surrender their AM license before commencing broadcasting on FM, none of this expanded band crap where they were supposed to surrender licenses after five years and never did.
  4. Those that choose to abandon the AM band also will not be assured the same theoretical coverage areas they had on the AM band.
  5. AM migrants should not have to compete in an auction.

Indeed, if LPFMs get a boost in the process, all the better.  It might actually give radio the shot in the arm it needs, add a good deal of local competition and satisfy several needs.

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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