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.

Working with rigid transmission line

Installing transmitters requires a multitude of skills; understanding the electrical code, basic wiring, RF theory and even aesthetics play some part in a good installation.  Working with rigid transmission line is a bit like working with plumbing (and is often called that). Rigid transmission line is often used within the transmitter plant to connect to a four port coax switch, test load, backup transmitter and so on.  Sometimes it is used outside to go up the tower to the antenna, however, such use has been mostly supplanted by Heliax type flexible coax.

We completed  a moderate upgrade to a station in Albany; installing a coax switch, test load and backup transmitter.  I thought it would be interesting to document the rigid line work required to complete this installation.  The TPO at this installation is about 5.5 KW including the HD carriers.  The backup transmitter is a Nautel VS-1, analog only.

This site uses 1 5/8 inch transmission line.  That line is good for most installation up to about 10-15 Kilowatts TPO.  Beyond that, 3 inch line should be used for TPO’s up to about 30 Kilowatts or so.  Even though the transmission lines themselves are rated to handle much more power, often times reflected power will create nodes along the line where the forward power and reflected power are in phase.  This can create hot spots and if the reflected power gets high enough, flash overs.

Milwaukee portable band saw
Milwaukee portable band saw

Working with rigid line requires a little bit of patience, careful measurements and some special tools.  Since the line itself is expensive and the transmission line lengthener has yet to be invented, I tend to use the “measure twice and cut once” methodology.   For cutting, I have this nice portable band saw and table.  This particular tool has saved me hours if not days of work at various sites.  I have used it to cut not just coaxial line and cables, but unistrut, threaded rod, copper pipe, coolant line, conduit, wire trays, etc.  If you are doing any type of metal work that involves cutting, this tool is highly recommended.

Milwaukee 6230N Band Saw with cutting table
Milwaukee 6230N Band Saw with cutting table

Next point is how long to cut the line pieces and still accommodate field flanges and inter-bay line anchors (AKA bullets)?  The inner conductor is always going to be sorter than the outer conductor by some amount.   Below is a chart with the dimensions of various types of rigid coaxial cables.

Length cut chart for various sizes of rigid coaxial cables

When working with 1 5/8 inch rigid coax, for example, the outer conductor is cut 0.187 inches (0.47 cm) shorter than measured distance to accommodate the field flange. The inner conductor is cut 0.438 inches (1.11 cm) shorter (dimension “D” in the above diagram) than the outer conductor to accommodate the inter bay anchors. These are per side, so the inner conductor will actually be 0.876 inches (2.22 cm) shorter than the outer conductor.  Incidentally, I find it is easier to work in metric as it is much easier to measure out 2.22 CM than to try and convert 0.876 inches to some fraction commonly found on a tape measure.  For this reason, I always have a metric ruler in my tool kit.

Altronic air cooled 20 KW test load
1 5/8 inch rigid coax run to Altronic air cooled 20 KW test load
1 5/8 inch rigid coax and 4 port coax switch mounted in top of Middle Atlantic Rack
1 5/8 inch rigid coax and 4 port coax switch mounted in top of Middle Atlantic Rack

The next step is de-burring.  This is really critical at high power levels.  I use a copper de-burring tool commonly used by plumbers and electricians.  One could also use a round or rat tail file to de-bur.  The grace of clamp on field flanges is they have some small amount of play in how far onto the rigid line they are clamped.  This can be used to offset any small measurement errors and make the installation look good.

Happy New Year!

After a bit of reflection and a few good conversations over the New Year’s Holiday, I decided that I should continue my work on this blog.  I would like to thank all those that have stuck by and waited.  I have received numerous emails and messages off line, all of which have been read and appreciated.

Since the abrupt stoppage last July, which was absolutely necessary for me, many things have happened within the business.  Fortunately, during the hiatus, I was still taking pictures.  After sorting through them, here are a few interesting things that happened:

At one of our client’s AM transmitter sites in Albany, NY a 2.6 Million Watt solar system has been installed.

WROW-AM Steel mounting poles on antenna array field
WROW-AM Steel mounting poles on antenna array field

This project required many steel mounting posts be driven into the ground around the AM towers.  I don’t even know how many, but I would hazard a guess of over three hundred.  Each one of those mounting posts was hand dug down a depth of 6-10 inches to look for ground wires.  Where ever a ground wire was found, it was moved out of the way before the post was set.

WROW-AM ground wire moved out of way
WROW-AM ground wire moved out of way

Basically the solar array covers about 1/2 of the antenna array field.  All of the steel mounting hardware is tied into the ground system, making, what I am sure is a pretty large above ground counterpoise.

WROW-AM solar panel mounting hardware
WROW-AM solar panel mounting hardware

View from the south looking north:

Solar Array installed on WROW antenna array, Glenmont, NY
Solar Array installed on WROW antenna array, Glenmont, NY

View from the north, outside of the transmitter building, looking south:

Solar Array installed on WROW antenna array, Glenmont, NY

Power company interface and disconnect:

Solar Array utility company disconnect, Glenmont, NY
Solar Array utility company disconnect, Glenmont, NY

The utility company had to upgrade the transmission lines to the nearest substation to handle the additional power produced by the solar system. All in all, it was a fun project to watch happen.

At a certain studio building, which is over 150 years old, the roof needed to be replaced.  This required that the 3.2 meter satellite dish and non-penetrating roof mount be moved out of the way while that section of the roof was worked on.

3.2 meter satellite dish

Dish ready to move, all of the concrete ballast removed and taken down from roof.  The roofing contractors constructed a  caddy and the entire dish and mount was slid forward onto the area in front of it.  Since the front part of the roof was not reinforced to hold up the satellite dish, we did not reballast the mount and the XDS receivers ran off of the streaming audio for a couple of days until the dish was put back in its original position.

3.2 meter satellite dish ready to move
3.2 meter satellite dish ready to move

A couple of other studio projects have been underway in various places.  Pictures to follow…

One of our clients sold their radio stations to another one of our clients.

There has also been a bankruptcy of a major radio company here in the good ol’ US of A.  Something that was not unexpected, however, the ramifications of which are still being decided on in various board rooms.  One of the issues as contractors is whether or not we will get paid for our work.  All things considered, it could be much worse.

Learned a valuable lesson about mice chewed wires on generator battery chargers.  I noticed that the battery charger seemed to be dead, therefore, I reached down to make sure the AC plug was in all the way.  A loud pop and flash followed and this was the result:

Arc burns, right hand
Arc burns, right hand

My hand felt a bit warm for a while.  The fourth digit suffered some minor burns.  There is at least one guy I know that would be threatening a lawsuit right now.  Me, not so much…  All of the high voltage stuff we work on; power supplies that can go to 25 KV, and a simple 120 VAC plug is the thing that gets me.

The return of the rotary phase maker.

Rotary phase maker, Kay Industies T-10000-A

Mechanically derived 3rd phase used when the old tube type transmitter cannot be converted to single phase service.

Those are just a few of the things I have been working on.  I will generate some posts on current projects underway.  Those projects include a 2 KW FM transmitter installation, another studio project, repair work on a Harris Z16HD transmitter, etc

It is good to be back!