December 2012
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The Continental D323C medium wave transmitter

I found a 1981 Continental Electronics equipment catalog at an old transmitter site. These finds are great if one is interested in history and looking at the way things used to be done.  This particular transmitter is a 2,000 KW (2,000,000 watt) medium wave unit:

Continental Electronics D323C, Circa 1981

Continental Electronics D323C, Circa 1981

I believe most units like this were destined for use by government broadcasters either the middle east or western Europe.  I know there were several 1,000 KW medium wave stations in West Germany at one time.   The Continental transmitter is basically two 1,000 KW units (323C) combined.  They used a modified version of Doherty modulation, that is called “Screen and Impedance,” which accurately describes how it works.  More information from the Continental Catalog can be found here: Continental D323C.  The tubes (or valves depending where you are located) used in the D323C were 4CW25000A tetrodes as modulators and IPA the final was a pair of X2159, which is an impressive tube.

EIMAC X-2159 water cooled power tetrode

EIMAC X-2159 water cooled power tetrode

The tube sat anode up.  The filament, grid and screen connections are underneath.  Cooling water was pumped through the two connections on the top at about 130 gallons per minute depending on the plate dissipation.  With a 30° C rise, that equals about 96,000 BTU per minute.  The D323C had a dissipation of 400,000 watts for the carrier tube and 240,000 watts for the peak tube (640 KW total) under 100% modulation.  That equals about 2 million BTU per hour.  Notice the lifting hook, this tube weight in at 175 pounds.  Tube date sheet here.

Continental no longer makes medium wave transmitters, their closest high powered broadcast product now is the 418/419 and 420 HF (shortwave) transmitters.  The 420D does a wimpy 500 KW using a solid state modulator section.

I remember in the early 1990’s when I was at the Harris plant in Quincy, they were working on a 1,000 KW solid state DX series AM transmitter for Saudi Arabia.  It had to be liquid cooled, which added another layer of complexity to an already complex system.

I don’t know if there is much call for 2 MW medium wave transmitters anymore as there are more efficient ways to reach remote populations and I can’t even imagine what the electric bill would be like.

Zonecasting; the Technical Details

I saw this a item many weeks ago, however, had not had time to look at it until now.  Geo Broadcasting Solutions has filed Petition for Rule Making (RM-11659) based on a system divides the coverage area of major stations into smaller zones allowing for ad targeting of specific audiences.  They have coined the term “Zone Casting” to describe the scheme. It is covered by two US issued patents filed by Lazer Spots, LLC: 20120014370 and 20110065377.  After a look at these two patents, it seems there are three possible ways to accomplish this Zone Casting Scheme:

  1. In the first described method, the main transmitter is broadcasting area wide and all the zone transmitters are muted.  An inaudible signal is transmitted to all units, the main transmitter is then muted and the zone transmitters turn on and transmit localized content.  After the local information is transmitted, the zone transmitters mute and the main transmitter resumes broadcasting.
  2. In the second described method, the main transmitter and the zone transmitters are broadcasting area wide information.  The main transmitter ceases broadcasting area wide information and the zone transmitters begin broadcasting localized information.  At the end of the localized information the main transmitter and zone transmitters transmit area wide information.
  3. In the third describe method, the main transmitter and zone transmitters are broadcasting wide area information with “capture ratio pattern.”  The main transmitter initiates an alteration, temporarily becoming a zone transmitter.  The zone transmitters then transmit localized content.  After the localized content, the main transmitter becomes a main transmitter again.

All of the transmitters are linked to the studio via digital STL systems, content for the zone transmitters is distributed via IP network.  The transmitter frequencies are synced with GPS, similar to FM on channel booster stations.  Method number three includes possibly switching the transmitter output to a lower gain and or lower height antenna.

Zone Broadcasting Conceptual Diagram

Zone Broadcasting Conceptual Diagram

Of the three methods, the first system will result in the fewest interference issues.  No matter which method is used, there will be interference issues between the zone transmitters and or the main transmitter where the signal strengths are equal and the audio is 180 degrees out of phase.  These can be moved around slightly by adding delay to the audio signal, but they will always be present.  More about Same Frequency Networks (SFN) and Synchronized FM signals can be found here.  While the zone transmitters are transmitting dissimilar localized information, standard capture effect rules apply.

The system has had limited testing in Salt Lake City, Utah (KDUT) and Avon Park, Florida (WWOJ), which according to the filing and comments, went well.

Geo-Broadcasting is applying to conduct a full test with WRMF in Palm Beach, FL.  The expected installation will include up to 22 zone transmitters.

Conceptually, tightly targeted advertising is not a bad idea.  Advertisers like it because they perceive a better return for their dollar.  The cost of such a system is not insignificant. Transmitter site leases run $1-2K per month, leased data lines, equipment, installation work, equipment shelters, etc will likely run several hundred thousand dollars or more.

If it gets approved by the FCC, it will be interesting to see how it works and whether or not the system is financially justifiable.


The Nautel NV-5 Transmitter

We are currently installing this sweet little transmitter:

Nautel NV-5 FM transmitter

Nautel NV-5 FM transmitter

Like its big brother, the NV-40 at WVPS, the NV-5 is a very cool transmitter.  I am a born sceptic, things like a touch screen displays tend to make me a little nervous, especially on a transmitter connected to a 350 feet tall steel tower right next to the transmitter building.  That is the one major difference between WVPS and this site; at Mount Mansfield there are many things between the transmitter and antenna, this place, not so much.  Even so,  Nautel makes a good product, so troubles are not expected.

The ground strap, AC power, remote control and composite audio connections were all made with out difficulty.  Result, new transmitter on the air:

Nautel NV-5 FM transmitter GUI

Nautel NV-5 FM transmitter GUI

This unit is analog only, but the information on the spectral display is still useful.  The GUI uses Linux with a touch screen, which is a neat feature.

Nautel NV-5 FM transmitter controller board

Nautel NV-5 FM transmitter controller board

In case the front panel GUI goes out, all transmitter controls can be accessed via push buttons on the remote control interface, which is the small board to the right.  The main controller board is on the left.

Part 15 Broadcasters

I am utterly amazed at the lengths that some people will go to to get on the air. Where there is a will, there is a way.  Part 15 refers to FCC Part 15 rules, which cover unlicensed operation. Such things as wireless microphones, cordless phones, garage door openers, WIFI, other intentional and unintentional RF generators like computers.  Subpart C deals with low power, unlicensed broadcasting.

There are several rules regarding unlicensed Part 15 broadcasting, the most often cited rules are 15.209, 15.219 and 15.239, which sets the signal strengths allowed for various frequencies.  For the FM band (88-108 MHz), the signal strength requirements are very straight forward;  it is 150 250 µV/m measured at 3 meters from the antenna. This results in about 200 foot radius from the radiator or antenna reception distance.  Slightly more can be gained by broadcasting in mono.

For the AM band (530-1,700 KHz) there are several different measurement criteria.  First, FCC 15.209 states that the signal strength for an unlicensed medium wave station shall not exceed the value of (24,000/F(KHz) which varies from a maximum 45 µV/m at 530 KHz to a maximum 14 µV/m at 1,700 KHz measured 30 meters from the antenna.

Medium Wave broadcasting lends itself well to power line transmission, also known as carrier current.  There used to be many carrier current college radio stations in the country as it was a very easy way to broadcast to a limited area without the expense of a license and large transmitter.   There are still some carrier current stations out there, but many have gone dark.  For carrier current stations, the signal strength requirements can be found in FCC 15.221, which states:

(a) Carrier current systems and transmitters employing a leaky coaxial cable as the radiating antenna may operate in the band 525–1705 KHz provided the field strength levels of the radiated emissions do not exceed 15 µV/m, as measured at a distance of 47,715/ (frequency in kHz) meters (equivalent to Λ/2Π) from the electric power line or the coaxial cable, respectively.


(b) As an alternative to the provisions in paragraph (a) of this section, intentional radiators used for the operation of an AM broadcast station on a college or university campus or on the campus of any other education institution may comply with the following:
(1) On the campus, the field strength of emissions appearing outside of this frequency band shall not exceed the general radiated emission limits shown in § 15.209 as measured from the radiating source. There is no limit on the field strength of emissions appearing within this frequency band, except that the provisions of § 15.5 continue to comply.
(2) At the perimeter of the campus, the field strength of any emissions, including those within the frequency band 525–1705 KHz, shall not exceed the general radiated emission in § 15.209.

Finally, there is Part 15.219, which states:

(a) The total input power to the final radio frequency stage (exclusive of filament or heater power) shall not exceed 100 milliwatts.
(b) The total length of the transmission line, antenna and ground lead (if used) shall not exceed 3 meters.

Thus, there are several different ways to look at Low Power AM (LPAM) broadcasting.  In all cases, LPAM stations are not to be employed on the same frequency of an licensed AM station within its protected contour.  Part 15.219 appears at first to be contradictory to 15.209 which sets a specific signal strength value.  On reading the FCC’s recent NOUO and NOVs it appears the 15.219 is an exception and is left deliberately ambiguous, somewhat cryptically noting:

Another exception for some transmitters operating in the 510 kHz to 1705 kHz band is found in 47 C.F.R. S: 15.219. Specifically, Section 15.219(b) of the Rules states “the total length of the transmission line, antenna and ground lead (if used) shall not exceed 3 meters” (see 47 C.F.R. S: 15.219(b)).

From FCC EB-FIELDWR-12-00001143

Thus, from a technical and legal standpoint, which criteria will an FCC inspector use if they are looking at a possible violation with an unlicensed LPAM station?  In at least one case, it appears to be up to the inspecting officer.

With a well designed 3 meter (9.84 feet or 118 inches) vertical antenna and good ground system, it is very likely that a 100 mW station, particularly on the upper part of the AM band, could carry up to a mile or so, depending on the local ground conductivity.  There are several cases where multiple LPAM transmitters have been chained together, creating a SFN (Same Frequency Network) which covers a significant geographical area. This is a video showing two LPAM transmitters synchronized in Sioux Falls, SD.

Pretty amazing considering all the power lines and such.  Then of course, there is this, which shows that they might not be operating at 100 mW after all.  I don’t know at which point they began operating above the legal threshold, perhaps that video was taken during legal operation.

Even so, it is a very interesting concept, when one considers using a battery, solar panel, wireless LAN bridge and an AOIP device such as the Barix Extreamer to connect transmitters. There is one particular FCC certified transmitter that allows external synchronizing from a GPS source or by chaining the units together on a RS-485 buss. I have spent several days driving around and listening to static on 1,700 KHz, much to the annoyance of my wife and children.

There are several sources of information regarding LPAM broadcasting:

Those are just a few, if you know of others, leave them in the comments.  One thing to note:  If you are going to broadcast LPAM, make sure that you can demonstrate compliance with either 15.209 or 15.219.  Any type of unlicensed station that broadcasts with a regular schedule  over significant coverage area will be noticed.

If you are a licensed broadcaster and are concerned that a legally operating Part 15 station is going to cut into your market share, you are simply doing it wrong.

The Audioarts Air-4 Console

Aside from everything else, we have been working at WSBS, Great Barrington, MA installing a new Audioarts Air-4 console. WSBS is a small AM station (860 KHz, 2,500 watts day, 4 watts night) serving the Great Barrington area. They also have a 35 watt FM translator (W231AK) on 94.1 MHz which is highly directional.  During the day, the AM station has a much better signal than the translator.  After dark, the translator covers the down town area fairly well.  WSBS has been on the air since December 24th, 1957 (Happy 55th anniversary!), broadcasting from a non-directional tower just east of town on US Route 7.

The format could be termed full service, in the old tradition.  Music, professional sports, local news, network news and weather with coverage of special events like election night and so on.   The station does local very well, and as such, is profitable and has a great community presence.

WSBS control room console

WSBS control room console

The air studio console was this rather tired out Broadcast Audio unit from the early 1980’s.  It had certainly served its station well, but change was in the air, so to speak.  Actually, we were getting worried about continuing to service this unit, as parts had become scarce about ten years ago.

New WSBS control room console

New WSBS control room console

Thus, we moved the air studio to the production room temporarily and removed all the old equipment and furniture.  We installed an Audioarts AIR-4, which is a pretty cool little console.  The AIR-4 has four built in microphone preamps, a telco mix minus feed, two program busses selectable VU meters and so on.   The control room rebuild project included a new counter top, adding extra microphones, headphone amplifiers, cleaning up wiring rat’s nests, installing new monitor antennas, rewiring a good bit of the rack room and so forth.



It was a little more involved than we first thought, however, it came out pretty well:

WSBS Great Barrington, MA control room

WSBS Great Barrington, MA control room

The carpenter will be back next week, after Christmas to install the sides on the studio furniture under the counter top.  It is a small operation in a small market in Western Massachusetts, but they have a real, live station staff including two news reporters.  Hey, what a concept!  To be honest with you, it is a joy all its own to work at a real radio station, if only for a short while.

Guy Wire; a pseudonym

How much value should we place on commentary of someone who will not associate their name with their words?  One wonders more about the reason for anonymity than the opinions expressed by the author, or at least I do. I have been expressing and publishing my views fully and without reservations.  Being outspoken has almost certainly hurt my career and salary potential as a broadcast engineer.  I am okay with that, as every morning when I am shaving, I can look myself in the eye and be thankful for the person who I am.

For myself, until “Guy Wire” tells us who he or she is, there is no absolutely no credibility in those words.  It is a shame that Radio World chooses to publish this commentary.


Brazil: The place where they test tech before it is implemented

After extensive testing of Both HD Radio and DRM, the Secretary of the Ministry of Communications Electronic Communications, Genildo Lins, said the tests of the two technologies have had poor results, especially high power FM . The testing demonstrated the digital signal coverage is approximately 70% of the current analog signal. “The future of radio is digital, but that future is not yet. We are unable to make a decision on these results.”  A polite way of saying “This is not the digital radio we were hoping for.”

These are just a few brief excerpts of the FM HD Radio test reports from Sao Paulo.  The method of testing:

The transmission system was located in the center of the city of São Paulo. The signal HD Radio digital broadcast was extended hybrid mode combined with the analog signal in the air, with separation of 163.8 kHz from the carrier’s analog FM signal and the carriers of HD Radio digital signal in sub-upper and lower sidebands. The power used in transmitter for the analog signal was 27 kW, and for the digital signal of 1 kW. Attaching the FM and HD Radio systems in their respective transmission antennas, the power Isotropic Effectively Irradiated (EIRP) of the analog signal was 112.3 kW and the digital signal of 1.12 kW. Thus, the protection ratio (EIRP power ratio between the analog and digital signals) was 20 dB (sic). During the measurement campaign, two commercial FM receivers were used analysis of analog reception, both to verify their potential impacts on receiving due the introduction of the digital signal, as to assist in verifying the coverage area of the signal analog.

The results of this testing:

Checking the results on each route, the route R1 radial (southeast direction), the stretch P1 to P2, that extends to 10.88 km (7.3 miles) of distance from the transmitter, the audio decoding was 71.6% of the digital audio frames received, and in the remaining sections of the route were little digital coverage.

In radial route R2 (southwest direction) was decoding of digital audio throughout the stretch to P1 P2, which extends up to 10.7 km (6.6 miles) of distance from the transmitter. In the following passage (P2 P3), the first blend was 17 km (10.5 miles) from the station. Following the passage P3 to P4, 26.4 to 44.9 km (27.9 miles), there was only 21.8% decoding of digital audio frames received within that stretch. In the last section (P4 to P5), from 44.9 km, there was almost no coverage digital.

In R4 route (northwest), there was decoding of digital audio throughout the stretch P1 to P2, extending up to 11.8 km (7.3 miles) of distance from the transmitter. In the following passage (P2 P3), from 11.8 to 24.9 km, was 62.5% of decoding digital audio frames received within that stretch. Following the stretch from 24.9 to 47.5 km (29.5 miles), (P3 to P4) the percentage was 24.3%. In the last stretch, from 47.5 to 61.7 km (P4 to P5), no digital coverage.

In route R6 (northeast direction), the stretch up to 9.8 km (6 miles), (P1 to P2) was 74.7% decoding of audio frames. In the passage P2 to P3 from 9.8 km to 29.8 km (18 miles) of the station, there was audio decoding 100% of the received frames. Following the stretch from 29.8 to 45.3 km (28.1 miles) (P3 to P4), the percentage was 87.2%, and in the last stretch, from 45.3 to 60.9 km (P4 to P5), the percentage was 47.9%.

Routes shown on a map:


Using unbiased real world testing, HD Radio does not look so hot. One caveat; the digital carrier level is -20dBc. That being duly noted, results show a 112 KW EIRP analog station with a 1.12 KW digital carrier that is unusable 6 miles from the transmitter site in some areas.  It is almost hard to believe.  Original documents can be found on the Government of Brazil Ministry of Communications website (in Portuguese).  They are interesting reading, although you may need to parse them through the Google translator.

AM HD Radio (no surprise) and DRM have similar or worse results.

Thus the myth “Digital is better,” is called to question. I am not opposed to new technology, provided it works better than the technology it is replacing.

Friday Funnies, Part something

Hey! Finals are over and I did pretty dern good. I’ll get my GPA sometime next week. Anyway, as a nod to my English 227 (Technical Writing) professor, this appears to the the state of things for those that did not take the class:

The neighborhood Mesh Network

Wireless IP Ethernet (802.11) technology has been around for a while.  Many know it as “WIFI” but you could also call it “WLAN” or something similar.  Like many other Ethernet technologies, WLAN relies on a spoke and hub connection system.  The hub being the wireless access point or router and the individual hosts (PC’s, tables, phones, etc) being the end point for each connection.  In a wired network, it is usually some type of switch that forms the center of the network data distribution system.

With a wireless mesh network or ad hoc network (802.11s), each wireless device can connect to any other wireless device within range.  In this type of peer to peer network, there is no central access point, although something can act as an internet gateway or there can be several gateways.    This type of topology functions much like the public network (AKA the internet), where there are many different paths to any one (major) destination.  If any one of those paths goes down, another route is quickly found.

This technology was developed by several vendors for military communications systems and for OLPC (One Laptop Per Child) programs in Africa and other places.    Each link acts to extend the boundaries of the network, thus the more users there are, the more useful the network becomes.

Wireless Mesh Network diagram

Wireless Mesh Network diagram

Advantages of mesh networking:

  • Networks are self forming; once the nodes are configured and can see other network nodes, the the network automatically forms
  • Networks are self healing; if one node drops off line, traffic is automatically routed to other nodes.  If the node comes back up, it is included back into the network
  • High fault tolerance; in areas where many nodes exist and can see each other, the failure of any single node does not effect the rest of the network
  • Low cost to deploy; mesh networks use standard off the shelf WLAN (802.11) devices.  Choice of software will dictate which hardware will work the best
  • Crowd sourced infrastructure; as each network node is owned by an individual, the cost and responsibility is shared among the community

Several specific routing protocols have been developed for the network side of the system.  Hazy Sighted Link State Routing Protocol (HSLS), BATMAN, OLSR  HWMP and others. These work well with the existing 802.11 a/b/g wireless network hardware currently available.

On the host side, a good IBSS capable wireless network adapter is needed, which many of the newer ones are.  Several of the software programs have lists of WLAN adapters that work with their software.  Open Garden is a free App for Windows, Mac OSX, Android, and they are working on an iOS version.  This leaves out certain devices like tablets and iPhones for now.

Since existing wireless adapter drivers do not yet support mesh networking, usually an additional piece of software is needed.  There are several interesting ones, including HSMM-MESH, which was developed by Amateur Radio operators.  Open source programs for Linux, Free BSD and other are available as well as commercial versions for Windows.

I was thinking that this might be useful for broadcast applications.  For obvious reasons, this type of system would work best in densely populated urban and suburban areas, which is exactly the type of area that LPFM licenses might be hard to come by.  For those who do not have the time or wherewithal to apply for an LPFM license, or for those that simply don’t get a license due to scarcity of available channels, this could be a great way to cover a neighborhood or section of a city.  The more people that participate in the mesh network, the stronger the network becomes.  Additionally, by using FCC type accepted part 15 FM and AM transmitters as broadcast nodes, carrier current transmitters and leaky coax systems, the presence of the mesh network can be advertized to potential listeners, including directions on how to take part.

Wireless mesh network example

Wireless mesh network example, courtesy of Meraka Institute

Wireless LAN bridges or broadband internet connections can act as a backbone between distant nodes.

For bandwidth efficiency sake, AOIP services should be limited to multicast addresses.

A good site with more wireless mesh network information is

Two sub-reddits on the subject: /r/meshnet and /r/darknetplan

Then there is project meshnet and the project meshnet wiki

Oh, by the way, go ahead and ask me what I have been learning about in school these days…

Oh, damn: la segunda parte

Emergency! The (AM) Transmitter keeps popping off the air and we can’t figure out why! YOU MUST HELP US!!1!!!


Some problems are easy to spot, difficult to fix

Some problems are easy to spot, difficult to fix

Well, with the ATU mounted about 1/4 inch away from the 90 degree, series excited tower, I wonder why.  It seemed to be especially problematic during rain, snow and ice storms.   When I asked how long this had been going on, I was told “About two years, ever since we put up the new tower!”

You don’t say.

We finally took care of this by moving the ATU back inside the shed after moving the transmitter to a different building.  The funny thing is, this was installed by a guy who had a BSEE.  I guess he must have been out sick the day they covered this in class.


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 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

Free counters!