For whatever reason, you need to bring high quality audio from one place in town (where your studio is) to another place (where your transmitter is). Maybe this is because Congress forced you to locate your transmitter in a weird place to meet bizarre distance standards between radio stations. Or maybe because you got a nice site on top of the mountain, but you want your studio to be in the middle of town. Whatever your needs, you were probably surprised to discover that just moving a signal from one point to another can easily cost you twice what your broadcast transmitter (which will reach everybody in your town) is costing. Below is a compendium of the options we have found over the years, ranging from crackpot to industry standard.

First of all- let's look at a few things that won't work:

Ordinary telephone lines:

The telephone company has a bunch of tricks that it used when it connects everyones phones to each other. They couldn’t possibly run a pair of wires from everyone’s house to everyone else’s house, so they use clever switching systems and they have figured out ways to run thousands of conversations over a single pair of wires. They do this by assigning each conversation a different channel consisting of a range of frequencies. My conversation with my aunt might be between 1,000,400 Hz and 1, 003,400 Hz,  and your conversation with your congressperson might be between 1,003, 500 Hz and 1,006, 500 Hz- and so on. Each conversation only gets a range of 3000 hertz to save space on the line, so the phone company puts on filters that cut out all the sound frequencies below 400 and above, 3,400. That is good enough to understand what your friend at the other end of the line is saying, but it does not really reproduce the sound of the music faithfully enough for radio. A great explanation, complete with a demonstration, of this is available at www.howthingswork.com   Another thing to keep in mind with any STL is whether it has the capacity to do stereo sound, which telephones obviously can not.

You might equalize the line yourself, and this is easy if you know how to check frequency response and have the stuff to do equalization, which is arcane telephone stuff.

Using a T1 line and an expensive CODEC made for the purpose is another and more popular way many full power FM broadcast stations get an STL from the phone company.  Depending on rates, a T1 might cost much less per month than an equalized line, but the CODEC will be pricey.

CB/ ham/ business band/two way radios:

First of all, all of these services are dedicated to two way communication between two or more individuals, not one way communication between your radio station and an audience. The very reason for the FCC to have authority over the airwaves is to make it so that two truckers don’t use the frequency for your radio station to gossip about smokies and foxy mommas- and vice versa. Transmissions in any form of two way radio  are limited to a minute or two from each side, taking turns. If you don’t follow those rules in ham, two way,  CB or any other radio, you will make a lot of people mad at you and it is not unlikely that they will try to track you down and shut off your radio, or report you to the FCC.

Secondly, these channels have the same bandwidth problem as the phone company. The phone company can put multiple wires going across country carrying everyone’s conversations, but there is only one electromagnetic spectrum so the channels are in even shorter supply so they tend to be even smaller in bandwidth. So again the sound is good enough to recognize human voice, but not good enough to reproduce music.

 And now some of the more straightforward options:

A long cable:

The simplest, and sometimes, this might be all you need. As the cable gets longer things get more complicated. First of all, the longer the wire, the more  it acts like an antenna and the more likely it is to pull in the signals of local radio stations (those damn radio stations)! When I built my first radio station, I did not understand any of this, so I used two ordinary pieces of phone wire with an RCA jack soldered to each end. This worked, but it also was a great antenna and it would pick up the local Golden Oldies station and for the first few months, below every song we played from Public Enemy to Crass, underneath at about a twentieth of the volume, there was Frank Sinatra or Bing Crosby!

So the first thing that you’d like is that the cable be shielded, meaning there are one or two inner conductors and then an outer conductor. The inside conductor is generally the hot, and the outer conductor is the ground, and it carries all the radio interference down to ground too. An even better cable has a hot and a neural inner conductor, and they together they are surrounded by a braided metal shield, which is connected to ground. The best is if you can have the whole line be “balanced.” When a line is balanced, there are special circuits at each end of the line which cancel out the noise that happens along it. As cables get longer than a few hundred feet,  the noise gets louder and the signal gets quieter. Amplifiers can help, but they amplify the noise too and eventually the noise adds up. 

Microwave:

This is the most common way for radio stations to move high quality audio, these days. The audio comes out of the mixing board, into an audio processor and into a microwave transmitter (typically five to twenty watts), and then up a cable and out a microwave dish. This dish is really carefully aimed at another identical dish, which needs to be in a direct line-of-sight with the studio. The dish on the other side goes down into the microwave receiver, coming out as audio. If the link is a composite type suitable for stereo, then the audio goes straight into your transmitter using a BNC connector and a short run of co-axial cable.  If the link is mono audio, then it goes into another audio processor, which then goes into the FM transmitter. As a broadcaster, you are entitled to use one of the frequencies in the special broadcaster STL band, in the 900 MHz range. To get a frequency, you call up a local frequency co-ordinator, and request a channel.  You can find a list of co-ordinators at WWW.SBE.ORG.  Then, you must file for a Broadcast Auxillary license on the agreed to channel.

Most variations on microwave are licensed. The advantage of using licensed bands is that they are licensed to you and only you, so they are less susceptible to interference. The disadvantage is that it is a pain in the neck to get a license. Some bands, such as 2.4 GHz, have power limits for equipment but are not licensed.

Conventional, analog radio broadcast microwave operates under FCC  rules in part 74 Subpart E. Most units are simple FM transmitters and  radios set up to operate in a band of frequencies reserved for radio  broadcast links.

Another variation of a microwave link is a private fixed point to point link.   FCC rules allow business and not-for-profit organizations to get these.  Links can be digital, analog, and can be in various frequency bands and channels have various bandwidths, all with more than adequate capacity for one way FM broadcast audio.  You might be able to score a used link from a local business or common carrier (telephone company). You might ask a local amateur radio or ham club to help license and rig it up.  Frequency coordination is through commercial service firms, and cost somewhat more than $200 per link.  If you get analog stuff good for the 952 band, it might operate very much like a regular broadcast FM microwave, but under this different category of license.

One more variant is digital broadcast transmitter links. Some stations buy expensive new digital links to operate in the same band under the same FCC rules as 1a. A digital link is more resistant to interference.

If it is not in a direct line of sight, you may need a second STL pair with another transmitter, receiver and pair of dishes, though the really clever can use other techniques like a large metal reflector, or a special bridge point that simply amplifies the signal it caught. Each time you put in another line of sight STL, it is referred to  as another “hop.”

We have seen equipment prices for single  hop full microwave systems go for between $3500  and $6000. Mono STLs are often quite a bit cheaper than stereo STLs. In fact, some STLs, to do stereo, are simply two mono STLs put together.

Another thing to keep in mid with STLs is that used STL units from before the early 1990s  are illegal to use by low power stations. This is because the standards for STLS were changed at that time, and new STLs had to comply with stricter standards. You can still see some for sale, and some were actually grandfathered in at the time of the rule change, so there are some out there that are still in service, but it is not legal to use them in a new installation. Consequently, the used market for STL systems is a little tougher for the buyer than with some other pieces of equipment.

Special phone company services: Some local phone companies provide special audio delivery systems for radio stations.  These generally involve the phone company setting up a box at the studio and a box at the transmitter. They then find a dry pair between the to points in the muddle of their phone wires in the streets between the studio and transmitter. In Philadelphia, Verizon  quoted a price for installation about $2100  plus a per mile fee between the two points, and about $120 per month charges after that.  In Fresno the installation was $1100, and the service cost $200 per month. The phone company generally charges a flat rate for installation based on the mileage between the two points, and then a monthly rate based on the quality of the signal, from 3000 Hz mono to 15,000 Hz stereo. The deal varies widely from town to town. The advantage of this is that if anything goes wrong, it is the phone company’s problem., not yours. Of course getting the phone company to fix a problem is not unlike getting them to fix something when there is a problem with your phones, only probably tougher.  Many radio stations use this, and the audio is generally really good.

CODECs

A CODEC is short for encoder/decoder. There are other companies that make different types of CODECS for different uses. Some of them use ordinary phone lines, some use souped up phone company services such as ISDN lines. 

CODECs  can get around the problem of phone line bandwidth, to some extent. If properly set up, an audio signal can be plugged directly into the CODEC. The CODEC can then digitize the audio by sampling it every few micro seconds, and then turning its values into the binary code of ones and zeroes.  Using clever compression techniques, the computer can send out the stream of ones and zeroes over the internet, and another computer can decode the ones and zeroes and reproduce the sounds through the speakers. It sounds like a lot of extra steps to go through, but amazingly, you can get much better sound from this technique than from the old analog technique that the phone company uses for regular voice. They are generally designed for intermittent use. They also often have a delay for encoding and decoding, so what is on the air is often a few seconds behind live.

Using a CODEC designed for intermittent use in a permanent, full time installation can raise several problems.

During the course of its use, conditions on the phone line often change over the course of the day ( as the sun shines on the wire, changing its physical and electrical length, As Squirrels run up and down the lines, etc) when this happens, the modems on each side have to renegotiate, and this eats in to your buffer. When you run out of buffer, you start to get dropouts, like you here on internet radio when bandwidth gets scarce.

Also, some of them may not be designed for use all the time, and could just plain overheat because their cooling systems were not designed with 24-7 use in mind.  A CODEC pair can cost between $2000-$3000 for POTS, or for ISDN.  Plus the ISDN or phone bill.

There is a relatively new product on the market that uses a broadband connection rather than ISDN or POTS.

It costs a lot more ( about $7000 plus the broadband bill each month),  but you do not need to be a computer expert to set it up and fix it if it breaks, and it comes with product support.  It is the Tele-link made by Energy-onix: you can see it at http://www.energy-onix.com/HTML/Catalog%20Sheets/TeleLink.html.If you have money for this, you probably have enough for a microwave- though this would be more cost effective if you need to make several hops for line-of-sight between the studio site and the transmitter site.

And now some things that can work if you are clever.

Broadband and computers

Prometheus Radio Project and the PhillyIMC, are working on developing a suite of free software that can turn any two cheap old PCs into a Studio Transmitter Link CODEC.  To make this work, you need computers at both ends, with good soundcards that you can plug an 1/8 inch headphone jack into. You also need DSL, cable, satellite or some other form of good internet connection at both ends. Your station will probably want broadband in the studio anyway, in order to hook computers up to for downloading programming and other general business- so adding dsl at least on that side is not much of an added cost.  A 56k modem on an ordinary phone line will work in a total pinch, but eventually it will probably jam up and you will not be able to set the data rate high enough to sound good. Definitely not recommended  with 56k modems.

The STL committee of Prometheus, in partnership with Phillyimc.org, has put a lot of time into developing a set of computer programs that do this job. You can learn more about them at:

Non- standard  broadcast microwave links

If you are a low power fm licensee, you need to use “type verifgied equipment.” Type verificication is a new, looser standard than the old “type accepted” and “type certified” standards from the FCC, but it is still a standard. In type verification, the manufacturer must test the transmitter on testing equipment and submit the results to the fcc. Once the equipment has received the OK from the FCC, it is standard practice to charge quite a bit more for it, even though it is the same equipment, to defray the costs of attaining  “type verified “ status.

There are studio transmitter links  available from other countries. They often offer comparable equipment at a fraction of the price for type verified  equipment. If you are a LPFM licensee, you can not use this equipment. If you are purchasing equipment advertised as a studio transmitter link from an other country, you should confirm that t uses frequencies that are legal  for this use in the united states. Some equipment that has been advertised on the web wasw actually designed to work on some of the frequencies which were empty in that country, but are allocated to ham radio, RPU or other uses in the US.

Dry pairs:

A dry pair is a phone line with no dial tone on it.  They are often used  by alarm companies and other services. They are not filtered in the same way that phone lines are-m in fact, they are not processed at all, so when the phone company rents you a pair of these they are basically giving you an unused pair of wires threaded along with all the rest of their wires through their right-of-way on everyones property in your town. It is often very difficult to figure out how to get these, because when you call the phone company no one will have any idea what you are talking about.  You may need to amplify your signal You would need to talk to your local phone company about the exact parameters. Many phone companies have different names for different services like this- sometimes they are required by regulations to seell these things, but they do not like to because they are not very profitable. Sometimes people buy these services and then use them to provide their own broadband DSL.  For more about this option, see:

Cringler article

Wireless Microphone:

If you just need to go a few  hundred feet, you may find that a wireless microphone might work for you. These things really don’t go very far, but if you need to get from  your studio to the roof of the building next door, it might do the trick.

Remote Pick-up Unit

A remote Pick-up Unit, or RPU, is a device that broadcasters use when they want to do a live remote broadcast from a used car dealership or a cheezey night club promotion. They use the frequencies around 450 MHz, and involve directional antennas that are aimed from the remote site back to the main studio. They have generally have enough bandwidth and power to deliver broadcast quality audio.  They are intended for intermittent use. Sometimes, broadcast stations have been known to use RPUs for months or even years at a time as a temporary studio transmitter link, when there other link has gone down. In some areas this might not cause too much problem, where there is not too much competition for these frequencies, but local broadcasters could be upset if someone monopolized tone of these channels on a permanent basis. The rules for use of these frequencies specify that you can use one of them for 720 hours per year, though of course if you have a frequency agile model you could probably switch frequencies indefinitely and stay within the letter of the law. This method is definitely not recommended, but could be useful in a pinch for temporary use.

Infrared Beam

In some places, infrared equipment can be used to move signals around for limited distances. Infrared is extra sensitive to humidity and rain, so it is not as reliable in bad weather conditions.

Fiber optics: 

Many towns and college campuses have built fiber optic networks for their communications needs. If there is some fiber kicking around between the locations of your studio and transmitter, it should be trivially easy for the engineers who maintain it to figure out how to connect you up with a high quality  connection. Of course we at Prometheus  have no idea how you would do such a thing, so your big trick will be convincing the school, city government or the engineer in charge that they want to do this for you...

Cable systems:

If you happen to have a good relationship with the local cable system (as many public access tv stations do), it is also probably fairly trivial for their engineers to provide you with a high quality signal between two points on the cable system.

Glossary:

radio frequency

n. Abbr. RF

1.         The frequency of the waves transmitted by a specific radio station.

2.         A frequency in the range within which radio waves may be transmitted, from about 3 kilohertz to about 300,000 megahertz.

bandwidth

n.

1.         The numerical difference between the upper and lower frequencies of a band of electromagnetic radiation, especially an assigned range of radio