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All is well in Engineering Radio Land, just very busy with typical projects. Nothing really note worthy, but there are some interesting things in the pipe line, which will be posted once those projects begin. Regarding myself, Hockey Season is in full swing.
My son (in blue) messing up somebody’s shot on goal. Good stuff.
I received an interesting question from occasional reader Gary over the weekend:
Have you ever heard of, or looked into, the “Max Headroom incident”?
Yes, I have heard of it, but never really thought about it that much. At that time, I was in California getting ready to ship out to Guam. I remember some brief news reports on it when it happened. After some reflection, I sent along this reply:
Good question. I have done a little bit of work at TV stations from time to time. In the mid to late 80’s, most television stations used 6 GHz analog microwave links between their studios and transmitters. These where unencrypted. Most often, these links used Microwave Associates gear, which had transmitter power output of about 3 watts into a rectangular wave guide. That was coupled, via elliptical wave guide into a 24 or 36 inch parabolic antenna. As you know, parabolic antennas have a main lobe and side lobes in their radiation pattern. The smaller the dish size, the broader the main lobe is and the further out the side lobes are. Since the Chicago studio to transmitter path was fairly short, I’d hazard a guess that they where using 24 inch antennas. In major markets, there was often a backup STL system on a different frequency (as the Wikipedia article indicates). Later on, most stations had a third backup via the cable company using either directly fed coax or fiber optic cable.
Since cutting into the transmission line of the microwave link at either side of the system would almost certainly fail, what I think happened is the perpetrators discovered (easy to do) the frequency of the 6 GHz link and over powered the normal signal at the receive antenna. This is possible if they used a much larger antenna and where located in either the main lobe or a side lobe of the receive antenna. If you recall, in the late 80’s C band satellite dishes where very popular. It would not be too difficult to repurpose one of these dishes for a 6 GHz antenna. Most C band dishes where 5-6 feet in diameter, which would give them much more gain than a 2 foot dish. They simply would have had to figure out a way to feed the dish with elliptical wave guide and adjust the focal length for 6 GHz. I’d bet there where dozens of C band dishes on Chicago roof tops.
Anyway, that is my theory.
I watched a few youtube clips of the event. The fact the video was noisy indicates some type of co-channel interference. I think there was no audio because they guessed the microwave audio subcarrier frequency wrong the first time. The second incident, there was audio. Whoever did to this had to have pretty good knowledge of television STL system. Wikipedia article here: https://en.wikipedia.org/wiki/Max_Headroom_broadcast_signal_intrusion
What do you guys think?
In other news, I have begun messing around with a few ideas on single ended tube audio amps and contemplating a DIY tapered transmission line speaker build. Actually, there is some pretty interesting software out there for speaker design which would be fun to play with.
I have also been messing about with room EQ Wizard, which I think I will do a separate post on.
That is all from here, hope that all of you are well.
Most professional audio facilities use differential audio or balanced audio within their plants.? The main reason for this is noise rejection, which was discovered by the early pioneers of wired telephony back in the late 1800’s.? Balanced audio is created by generating two audio signals that are 180 degrees out of phase using either a transformer or an active device.? These are usually labelled High and Low, + and – or something similar.? Those two audio signals are then transmitted across some distance and recombined at the far end, again by a transformer or some active device.
When an interfering signal is picked up, it is transmitted along both sides of the balanced audio circuit until the signals are recombined.? During the re-combining process, and common mode interference is cancelled out, as it becomes 180 degrees out of phase with itself during the re-combining process.
Differential signaling is used in analog audio, digital audio (AES/EBU), HDMI, Display Port, USB, Ethernet, POTS lines, ISDN, T-1/DS-1, E-1, etc. ? It is a fairly simple concept, but one of the basic building blocks in broadcast studios.
When a studio project was completed at a disused studio/transmitter site location, a certain amount of RFI was being induced on the studio microphones by the unassociated FM transmitter in the next room.? The problem with microphone level audio is the relatively low level of? microphone output, which requires a good deal of amplification.? The amplifiers in this console have active balanced inputs, which might not be exactly 180 degrees out of phase.? In this installation, microphone level audio was run about 20-25 feet on standard microphone cable then it was converted to Cat 6 cable before going into the console.? It may have been better to use the shielded Cat 6 cable for the longer runs as it likely has better common mode rejection than standard mic cable. Another option might have been Star Quad cable.? However, none of those things were done.
Western Electric was the manufacturing arm of Bell Telephone.? In their day, they made some really good equipment.? One such piece is the WE-111C repeat coil.? These can be configured for either 600/600 ohms, 600/150 ohms, 150/150 ohms,? or 300/300/300/300 ohms impedance ratios.? Since this is microphone level audio 150/150 ohms is the appropriate setting.
Over the years, I have found many of these transformers discarded at various transmitter sites and studios. There are five microphones feeding this console. I mounted five of these coils in a sturdy metal enclosure and wired them with RJ-45 jacks to be compatible with the Studio Hub wiring equipment used in this studio installation.? I also grounded each unit to a piece of copper strap, which is connected to a grounding lug on the side of the unit.
I swept the coils from 20Hz to 20kHz:
This shows a 0.4 dB difference from 20 to 20,000 Hertz, thus they are all nearly flat which is a pretty cool feat of engineering.? I would estimate the age of these transformers is between 50 to 60 years old.
These coils isolate each microphone from the microphone preamp in the console.? This completely eliminated the FM RFI and solved the problem.
Finishing up another studio build out in an unrated market. There are some engineers who think that small market work is beneath them. That is fine with me, I enjoy it.? Once again, creating a nice, functional, modern facility while not breaking the bank poses some challenges. ? I like to take sort of a minimalist simple approach while not compromising good engineering practice.? Another challenge is rebuilding an existing facility.? Each studio needed to be demoed one at a time with the stations playing hop scotch from studio to studio around the work.? There were four studios total plus the rack room.? There were also several other renovations going on at the same time as this project.
Looking at the overall facility, the client decided that one studio would be the main room where multiple guests could be seated, etc.? The other rooms would have guest microphones, but they are smaller rooms and limited to one guest each.? The smaller rooms have AudioArts Air4 consoles while the main studio has an R-55e.
The main studio had existing studio furniture that was in reasonable shape so we decided to reuse it.? While we had the studio ripped apart, the paint and carpet where updated.? The main microphone is an Electrovoice RE-20, the guest mics are Heil PR-20UT which are inexpensive and have excellent characteristics for a dynamic microphone.? Since this faces a fairly busy street, I put in some very basic DBX 286S mic processors with a little bit of downward expansion.? Adobe Audition is used for production.? I have also used Audacity which is available in both Windows and Linux flavors.? Acoustical wall treatments are coming soon.
The counter tops in the smaller studios were traded out with a local kitchen supply company.? We used Middle Atlantic BRK-12-22 racks with castors on them to install a limited amount of rack equipment.? Each one of these studios is nearly identical; a AudioArts Air4 console with JBL powered monitors.? The microphones in these studios are Heil PR-20UT with console supplied mic preamps.? These studios are used for WSRK, WDOS, WBKT and WKXZ.? All studios are off line when in automation, which means each can be used for production and other purposes.
We started the TOC from scratch. This area was occupied by a bunch of empty file cabinets previously. The original equipment racks where in Studio A.
A riser was installed from the racks straight up to the roof for the STL, monitor antenna and satellite dish transmission lines.? Everything is grounded with a star grounding system connected to the main building ground which consists of driven ground rods and the water main.? The STLs have Polyphaser IS-PT50HN lightning protection devices installed.
The racks are Middle Atlantic MRK 4031.? Since this building was built sometime in the mid 1800’s, the floors are a bit uneven (along with almost everything else), so a fair amount of shimming and leveling was needed to get these units bolted together.
Each rack has its own UPS in the bottom and they are all on separate breakers.
A manual transfer switch controls a dedicated electrical sub panel.? All of the racks and studios are powered from this sub panel.? Below the transfer switch is a NEMA L14-30 twist lock male receptacle for generator connections.
The total load about 18 amps.? The station is looking to trade out some generators for various transmitter sites.? I suggested that they get a couple of the portable Honda inverter generators, which are very good have excellent power regulation, frequency stabilization and fuel economy.
The existing Scott’s Studio 32 system was updated with new computers.? This is an interim step until a new automation system can be installed next year.? Each station has it’s own BT 8.2ss switcher which can select any studio to go on the air with.? That flexibility makes moving from studio to studio easy.? It also allows for all the stations to be simulcast, which is handy in the event of an emergency.
Punch blocks are mounted on plywood attached to the back wall.? We left extra space for a new phone system.
The EAS monitor assignments are met with roof top yagi antennas.? I like drawings and diagrams, as the saying goes, a picture is worth a thousand words.? This is an image I created on Google Maps using the transmitter site coordinates for each of the EAS monitoring assignments.? That gives me good local aiming points for the various antennas needed.
Other drawings include a floor plan and block diagrams for each station.? I have a Viso template that I use for these.? I find that having these diagrams on hand in a book is very helpful in the event that somebody else needs to go to this station to work on things.
Finally, the wiring documentation which shows where each wire originates and terminates. Again, if I am not available and somebody else needs to do work here, this is very helpful. All the studios are laid out the same, so figure out one and then the rest falls into place.
There is still a little bit of clean up left and some old equipment to get rid of.? Otherwise, it’s a wrap.
Can a 50,000 watt AM station disappear from the airwaves and no one notice?
The answer is yes, if you live in the Albany, NY area.? WDCD, 1540 KHz, (formerly WPTR) has surrendered its license to the FCC last Friday, September 28, 2018.? Seventy years on the air and quite the legacy as a Top-40 station in the 60’s and 70’s.
Unfortunately, the station had fallen on hard times the last few years, being silent twice for long stretches of time.? In the end, I suppose it was simply time to pull the plug.
This was my first CE gig in the early 1990’s.? What I remember was, I had a lot of fun working there.
So long and thanks for the memories.
We have this certain transmitter which has been on the same tube since June 6, 2001.? Come to think of it, the transmitter itself has been on the air for the same amount of time without failure.? A testament to its designer…
According to my calculations, that is 151,691 hours or 17 years 3 months and 22 days.? The tube is the original EMIAC 4CX15000A that came with the transmitter.
I am a little nervous about turning it off to clean the cabinet.
We have a spare on the shelf for the eventual replacement of this tube, but I really want to see how long this thing will last.? This is also one of the last tube transmitters we have in main service.? There are several backup tube transmitters still around.
I found this video on YouTube about WEQX, Manchester, Vermont.? WEQX is a class B FM station with its tower located on Mount Equinox.? This gives the station a huge signal with a HAAT of 759 meters and 1,250 watts of power.? It comes in well south of Albany and while I am in the Albany area, I enjoy listening to it.
This piece is by CGTN, which one wonders how they ended up in Manchester, VT of all places.
The information below the video is also an interesting read. In part it goes into corporate ownership of radio in the US, stating:
In 1983, 90 percent of U.S. media was controlled by 50 corporations. Today, just six corporations control that 90 percent… Among the 10% (of radio stations) currently not controlled by those six corporations is an alternative rock station in the Green Mountains of Vermont.
That is misleading.? The “six corporations” they are referring to dates back an article published several years ago.? They are; Time Warner, Walt Disney, Viacom, News Corp, CBS and NBC/Universal.? As of this writing, none of those companies listed owns any radio stations.? Further, the media scene in general has become much more fragmented with the advent and greater acceptance of things like Pod Casting, YouTube and other social media.
There are three big radio station owners, which together own 1,613 radio stations. That represents approximately 14% of the licensed commercial AM and FM stations in the US. There are several medium sized owners; Entercom (237), Salem (118), Saga (108), Midwest (75), Forever (69), Beasley (63) and so on.? While iHeart (851), Cumulus (442),? and Townsquare (320) influence the way other station owners operate, by and large, the majority of radio stations in this country are still owned by small business owners.? Stations that are keeping it local continue to be noticed and hopefully rewarded with a successful business.
WEQX is certainly a unique station and it always has been.? In the late 90’s and early 00’s, I did some work for them at various times.? It was always fun and I enjoyed it.
I don’t know how things are in your neck of the woods, but here in the Northeastern US, our old copper TELCO networks are on their way out.? This is a problem for broadcasters who still rely on POTS lines (Plain Old Telephone Service) for transmitter remote controls, studio hot lines, etc.? The vast majority of my transmitter site access is through dial up remote controls.? There are a few locations that have web based remote controls, but to be honest; the phone part of my smart phone still gets a lot of use.? There are several locations where the old copper is just failing outright and not through a lack of effort by the repair techs.? Generally, the copper pairs get wet and develop a loud hum, which makes the remote control unit either hang up or become unresponsive to touch tone commands.
The best course of action is to get some type of VOIP line installed.? Here is the rub; many transmitter sites are nowhere near a cable system.? Several times, I have contacted the cable company to see if they will provide a VOIP phone line at a certain site.? The response is usually; sure, we can do that!? However, it will cost? you (insert some ridiculous amount of money) to extend the cable to your transmitter site.
LAN extensions to the transmitter site are a useful for a number of reasons.? More and more transmitters are equipped with web interfaces as are processors, UPSs, transmitter remote controls, security cameras,? etc.? LAN extensions can also be used for backup audio in case of STL failure.? Finally,? an inexpensive ATA (Analog Telephone Adaptor) and DID line can replace a POTS line for a lot less money.? One example; voip.ms has the following plans as of this writing:
|Plan type||Per month per DID number (USD)||Incoming call rate (USD) per minute||Outgoing call rate (USD) per minute|
|Per minute||$0.85||$0.01 (USA)||$0.009|
|Toll Free (800)||$0.99||$0.019||$0.009|
Any of those plans surely beats the standard TELCO rate of $40-50 per month per line.
Design criteria for a wireless LAN system needs to take into account bandwidth, latency and reliability.? Each VOIP phone call takes anywhere from 28-87 Kbps depending on the protocol being used.? If the wireless LAN is being used for other things such as back up STL service, access to various GUI’s, etc then the total bandwidth of all those services need to be considered as well.? Do not forget ethernet broadcast traffic such as DHCP requests, ARP, SMB, etc which can also take up a fair amount of bandwidth.
For LAN extensions, I have been using a variety of equipment.? The older Moseley 900 MHz LAN links still work, but are slow in general.? The Ubiquiti gear has proven to be both inexpensive yet reliable, a rarity to be sure.? There are several links to various transmitter sites running on various types of Ubiquiti gear, usually without problem.? One simply needs to remember to log into the web interface once in a while and make sure that both ends have all the firmware updates installed.? They are cheap enough that a couple of spares can be kept on the shelf.
The following diagram shows how I replaced all of the copper pots lines at various transmitter sites with VOIP:
List of equipment:
|Nomenclature||Amount||Use||New or used|
|Ubiquiti Rocket M5||3||AP and station units||New|
|Ubiquiti AirMax 5G-2090 90 degree sector antenna||1||AP point to multi-point antenna||New|
|Ubiquiti Rocket Dish 5G-30||2||Station antennas||New|
|Ubiquiti ETH-SP-G2||3||Lightning protection||New|
|Trastector ALPU PTP INJ||6||Lightning protection out door units||New|
|Cambium PTP-250||2||Point to Point link||Existing/Used|
|Motorola Canopy 900DA PCDD||1||AP point to multi point||Existing/Used|
|Motorola Canopy 900DA PCDD||2||Station||Existing/Used|
|Microwave Filter #18486 diplexer||3||Diplexer 900 MHz ISM band and 944-952 STL band||Existing/Used|
|Cisco SPA122 ATA||9||Dial tone for remote controls||New|
The main studio location has the gateway to the outside world. This system is on a separate subnet from the automation and office networks. From that location a point-to-multipoint system connects to the three closest transmitter sites.? This setup uses the Ubiquiti Rocket M5’s with various antenna configurations.? Then, from one FM transmitter site, there is an existing 5.8 GHz path to another set of transmitter sites.? This uses Cambium PTP-250s.
The next hop rides on the STL system, using Motorola Canopy 900 MHz radios and Microwave Filter Company #18486 dilpexers.? These are long paths and the 900 MHz systems work well enough for this purpose.? The main cost savings comes from reusing the existing STL system antennas which negates the cost of tower crews to put up new antennas and or rent on the tower for another antenna.
There is a smaller sub system many miles away that is connected to the outside world through the cable company at the AM transmitter site.? Unfortunately, due to the distances between the main studio and those three stations, there was no line of site shots to these sites available on any frequency.
When installing the 5.8 GHz systems, I made sure to use the UV rated, shielded cable, shielded RJ-45 connectors and Lightning Protection Units (LPUs).? Short cuts taken when installing this equipment eventually come back in the form of downed links and radio heads destroyed by lightning.
Regardless, I was able to eliminate seven POTS phone lines plus extended dial tone service to two sites that previously did not have it before.? In addition to that, all of the transmitter sites now have Internet access, which can be useful for other reasons.? All in all, the cost savings is about $310.00 per month or $3,720.00 per year.
I am currently finishing an interesting project involving putting up two translators on a diplexed AM tower which also holds a mobile phone/data tenant as well.? All-in-all, this seems to be a very efficient use of vertical real estate.
The translators are W250CC and W245DA which are using a NICOM BKG-77/2 two bay 3/4 wave spaced antenna mounted at 53 meters AGL.? The translators use a Shively 2640-04/2 filter/diplexor which as a broad band input port in addition to the translator input ports.? Since these translator signals are only 1 MHz apart, the higher power Shively filter was installed because it has better rejection characteristics.? The broadband input port allows the NICOM antenna to be used as a back up for any of the three FM stations; WKBE 107.1, WNYQ 101.7, or WFFG 100.3.? Two transmitter sites for those stations are mountain top locations which are very difficult to get to in the winter time.? Having a backup site available takes some of the pressure off during storms or other emergencies.
The NICOM FM antenna was mounted on the tower when W250CC went on the air in October of 2016.? When it was installed, the base impedances for both AM stations were measured.? For some reason, WENU 1410 KHz seems to be more sensitive to any changes on the tower, thus the WENU ATU needed a slight touch up.? When working on diplexed AM systems, it is also important to make sure that both trap filters, which are parallel resonant LC circuits, are tuned for maximum rejection of the other signal.? During this particular installation, nothing was added to the tower and no change in the base impedance for either station was noted.
As a condition of the construction permit, measurement of spurious emissions of all stations sharing the common antenna needed to be completed to ensure compliance with FCC 73.317(b) and 73.317(d).? I made careful measurements of the potential intermod products between the two translator frequencies.? This measurement was completed with my TTI PSA6005 spectrum analyzer.
The primary concern here is mixing products between the two transmitters. Both transmitter are BW TXT-600 with low pass filters before the output connector. There are three frequencies of interest;
That, plus harmonic measurements out to seven or eight harmonics of the fundamental frequency should be enough to demonstrate compliance with FCC out of band emissions standards. Being that this site has LTE carriers, it is very important to measure the harmonics in those bands. Mobil data systems often use receiver pre-amps, which can amplify harmonics from the FM band and make them look out of compliance. Having a base set of reading to fall back on is always the best course in case the “out of tolerance” condition gets report to the FCC.
Measurements on these frequencies must meet the emissions standards outlined in FCC 73.317 (d), which states:
Any emission appearing on a frequency removed from the carrier by more than 600 kHz must be attenuated at least 43 + 10 Log10 (Power, in watts) dB below the level of the unmodulated carrier, or 80 dB, whichever is the lesser attenuation.
Harmonic frequencies to be measured:
|Harmonics for 96.9 MHz fundamental||Harmonics for 97.9 MHz fundamental||Comments|
|678.3*||685.3*||US LTE Band 71|
|775.2*||783.2*||US LTE Band 5|
|872.1*||881.1*||US LTE Band 5|
*Frequencies that fall within the mobile data LTE bands. Traces where recorded and saved for these frequencies.
All of that information, once compiled is attached to the FCC form 350-FM, which, once filed grants Program Test Authority.
I was at the WEBE transmitter site recently and took the time to look over transmitter we installed last year:
Overall, I would say that this transmitter has been very reliable.? We had to install a UPS for the exciter and HD Radio exporter, but that is not a big deal. During the first power outage, the exciter went dark first. It took longer for the transmitter controller board to lose power, in the interim the controller turned the transmitter power all the way up. When the generator came on line 10 seconds later, the transmitter returned to operation at 41.5 KW. This, in turn, caused one of the other field engineers to freak out and nearly lose his mind (stay away from the brown acid, FYI).
I installed the UPS a few days later.
Transmitter power output is 35.3 KW, which is getting into the semi-serious range. The reflected power goes up when it gets warm out and goes down in colder weather.? Over the winter, it was running about 50 watts.? Even at 138 watts, that represents 0.004% reflected power. The TPO forward goes to the 6 bay, 1/2 wave spaced antenna side mounted, 470 feet (143 meters) AGL. The station covers pretty well.
Overall, I would give the liquid cooling system an A grade. The transmitter still dumps a fair amount of heat into the room from the RF combiners and PA power supplies. Most of the heat, however, ends up outdoors. Previously, we had two Bard 5 ton AC units running almost full time. Now, only one AC unit cycles on and off except for the hottest days of the year. Outside temperature when this picture was taken was 81 degrees F (27.2 C).
Next year, we will have to send a sample of the coolant off to be analyzed.
I have had good experiences with the GatesAir FLX/FAX series transmitters. I would recommend this to a friend.