The Answer to Ailing Copper

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; 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
Unlimited $4.25 $0.00 $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:

Diagram of LAN extensions to various transmitter sites
Diagram of LAN extensions to various transmitter sites

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.

Burk Autopilot, DOS version

We have been doing work at a particular radio station for a few years now. Every time I go there, I look at this… thing:

Burk DOS Autopilot/CDL running on Windows 98
Burk DOS Autopilot/CDL running on Windows 98

It is a very old PC running Windows 98 and Burk Autopilot/CDL 4.6 for DOS.  The auto pilot program is running from a windows DOS prompt and seems to be working okay; my concern is about the age of the hardware and the potential for failure.  The Autopilot is what controls the AM station’s power levels, which vary from 1,000 watts daytime, to 4 watts night time.  We have all read about AM stations fined by the FCC for running daytime power levels at night.  Failure of the ancient autopilot computer could lead to exactly this scenario.

I attempted to purchase the newer, Windows XP version of Autopilot, only to be told “that item is not in this year’s budget.”  Apparently, it was not in the budget for following year, or the one after that.  Thus, when the hard drive on the old Windoze 98 machine began making a terrible grinding noise, I knew the end was near.  I made an attempt to run the Autopilot from a Windows XP DOS prompt, at which time I was informed: “The program cannot start or run due to incompatibility with 64 bit versions of windows…” GAK!  I kind of knew this already.

I began day dreaming about running a DOS virtual machine inside of a Ubuntu or Lubuntu operating system.  Then I found a DOS emulator program for Linux called “DOSemu” which looked like exactly what the doctor ordered.  Using the carcases of several old HP desktop computers, I came up with one working PC that had two organic serial ports.  This is actually not a bad unit, as it has a 1.6 GHz dual core processor and 2 GB RAM.  On this machine, I loaded the 32 bit version of Ubuntu 12.04 desktop.  Naturally, the original Autopilot/CDL 4.6 disks were nowhere to be found so I had to copy the directory off of the old computer.  It was also understood that this project was simply going to suck.  Therefore, the superannuated Windoze 98 machine had no network interface nor any USB ports.  My only option was to copy the files unto a 3 1/2 inch floppy disk.  Fortunately, I have a USB 3 1/2 floppy drive, which I was able to use to copy the files onto the new computer into the /home/ARC16 directory.

Downloading and setting up Dosemu was fairly straight forward.  There were a few configuration steps that needed to be completed before the Autopilot software would work and communicate with the ARC-16 remote control:

  • In the DOSemu configuration file, the hardware serial port needs to be configure to work with the DOS emulator.  This is located at /etc/dosemu/doseum.conf.  The default conf file has all of the serial ports commented out.  Remove the comment and change the serial port source:  $_com1 = “/dev/ttyS0” or $_com2 = “/dev/ttyS1”  The serial ports available can be determined by the following terminal command: dmesg | grep tty  The output should look something like this:

    paul@engineeringIII:~$ dmesg | grep tty
    [ 0.000000] console [tty0] enabled
    [ 37.531286] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
    [ 37.532138] 0000:04:00.3: ttyS1 at I/O 0x1020 (irq = 3) is a 16550A
    [16206.667112] usb 2-1.3: pl2303 converter now attached to ttyUSB0

    For USB to serial port converters, the serial port source may look something like this: $_com1 = “/dev/ttyUSB0”

  • The DOS emulator time can be synced to Linux time by: $_timemode = “linux” This is great because Linux can be synced to a NTP source, meaning Autopilot time will always be correct.
  • The logged on user that will be running the DOS emulator needs to be added to the “dialout” group.  This can be done by sudo adduser [user name] dialout.  This will allow the Autopilot software access to the comm port.
  • The DOS autoexec.bat file should be edited so that Burk autopilot loads automatically when DOSemu is started.  DOSemu automatically assigns the D drive to the Linux home directory.  Thus, simply adding:

    CD ARC16

    to the end of the autoexec.bat file will start the ARC16 program automatically when the DOSemu program is started.

  • DOSemu can then be added to the Ubuntu desktop startup.

The results:

DOS autopilot running on Linux machine
DOS autopilot running on Linux machine

Burk Autopilot/CDL (DOS version) running on a Linux (Ubuntu 12.04.4) machine.  The stupid thing will probably run forever now.

This computer is also used to program the satellite receivers, which are located at the transmitter site.  Thus, there are several manuals and program clocks stored in the documents folder.  I also installed the x11VNC server program, so that the computer desktop can be logged into remotely from the studio over the LAN link.

I noticed that the DOSemu program hits the processor fairly hard, with one core running about 45% most of the time.  That should be fine, as this machine is used very infrequently for other tasks.

Temperature Sensor for Burk Remote Control

As a part of the re-wiring of a transmitter site, I realized that the site needed a temperature sensor.  I believe it is important for any remote transmitter site to have a temperature sensor, too many things can go wrong at a transmitter site.

I recall one incident at WGNA-FM in Albany, NY were a ventilation fan failed on a hot summer day.  The Harris HT-10 transmitter stayed on the air while the temperature climbed through 160 degrees inside the building, finally shutting down when the solid state driver module failed.  This site had a temperature sensor and a live operator taking transmitter readings every three hours.  They faithfully logged the temperature increase in three hour increments but didn’t call anyone until the station went off.  When I arrived there, it was so hot inside the building the I couldn’t touch a metal surface.

For the present day project, I looked at the Burk BTU-4, which seemed a little pricey.  After doing a bit of quick research, I found the National Semiconductor LM34 a good alternative.  This unit puts out 10 mv/degree F, which can be directly calibrated to a metering input of a ACR-16 using the lin scale.   I checked the accuracy by using a piece of melting ice, it was right on.  The design and implementation is very simple:

LM34 temperature sensor
LM34 temperature sensor

The LM34 is available in TO-46 or TO-92 case.  I bypassed the V+ with a 0.01uf capacitor.  It should be mounted in a small box with the case of the LM34 mounted on a metal cover or heat sink.  The TO-46 version, the case is ground.  It can be run on any voltage from +5 to +30 VDC, I used +5 because I had a little wall wart with the right voltage.  The wire is any type of balanced audio wire like Belden 8459, etc.  The LM34 cost 4 dollars, the rest of the parts were laying around.  It took about 15 minutes to create.

The site is air conditioned, therefore I set the remote control to alarm if the temperature goes above 85 degrees F inside the building.