STL Crash Course?

I know a bit about the technical side of radio, but have to confess I am almost clueless when it comes to STLs. I'm looking to get some very basic questions answered:

1) They obviously have to be licensed, correct?

2) What are the power / frequency possibilities?

3) What's the maximum realistic distance a licensed STL would reach over moderately flat terrain or if you can get line-of-sight with the tower (& is it legal or advisable to put an STL antenna that high)?

4) I've heard it's possible to "repeat" STL signals to get to a transmitter. I assume both segments of the journey have to be licensed? What kind of signal quality loss can be expected in this relay system, especially if analog?

5) Are there maps similar to Radio-Locator to see STL signals already in use between your studio and your transmitter, or is this something a handy engineer builds for himself out of the numbers in the FCC database?

These are the questions that come to mind right now; if you want to point me to a "Dummies Guide To STLs" rather than answer in the forum, that's fine with me... I'm sure these questions are below-basic for most of the forum members here!

Thanks in advance for any help; we're tired of fighting with the one digital option available here to get our signal to our transmitter and are looking to "upgrade" to an STL, even if that means an analog STL. I'm just concerned about trying to get the signal from the studio to the transmitter about 20 miles (32 meters) away as the crow flies.

Google RF Licensing.They can give you all the details.Yes,they have to be licensed or you pay a big fine,if caught. 1st thing is to find a freq that would work.There is a place on the FCC site under wireless where you can plug in your tower co-ords and search for freq within a given milleage radius.Best left up to these guys,that's what they do.Plus you would have to file a 601,contact all the stations around you,etc,it's a pain in the ass..I sent you a PM..good luck

There is only one licensed band for STL's 944 to 951.5 mhz. You can use the unlicensed 5 ghz. data transmitters, but since they are unlicensed you have no protection against interference from some other user. The 5 ghz. links are more limited as to distance compared to the licensed band & more susceptible to fade from weather conditions. There are a variety of digital devices that can be used to send programing over dedicated telco/broadband links, even the internet, that are called "STL" links, but, generally, STL is taken to mean a radio link from studio to transmitter.

25~30 miles is a realistic limit for an STL hop (depending on your terrain, e.g., no mountain between your studio and the transmitter unless the transmitter is on top of that mountain). There are longer links, but they are major projects. Generally transmitters operate with between 10 and 20 watts, gain achieved with the directional STL antennas. There are "repeaters" for STL use, requiring the licensing of two different paths. Typical use may be to reach a site that is not line-of-site from the studio. One link to a high point, (such as the top of a tall building) then a second link to the transmitter from that high location.

In a lot of markets, the FCC database bears little relationship to what exists on the ground. So, that's why you use someone like RF licensing both to find a channel as well as take care of the required notifications.

While on the Google Machine, you might also wish to look up "Moseley SL9003Q Manual" in order to find and download the user manual for Moseley's ubiquitous digital audio STL.

In Appendix A: Path Evaluation Information you will find an in-depth discussion about such matters as selecting the proper path for your proposed STL shot and designing the system with the proper gains and losses.

I recall the manual for an older TFT STL as having a similarly-helpful discussion and tutorial.

Paul E. Burt, CE
Alert FM

NightAire,

If you must use a double hop on an analog STL system, the audio quality should be fine as long as the signal strength is high at both receive sites.
I'm assuming that you will be transmitting a composite stereo signal. A composite signal is more fragile than a mono signal at the same signal strength.
Wideband noise can creep into the signal if your signal strength isn't high enough.
Careful orientation of the transmit and receive dishes is very important.
Every fraction of a dB in received signal strength can make a big difference in the noise figure.
Good luck with your project.

This information is EXTREMELY helpful; thank you, everyone! I knew I could count on you guys.

Actually (& I should have clarified) this is a mono (music) signal for an AM. From what frankberry said, it sounds like needing only the one channel should make this even easier. I need to double-check topography, of course, but I think it's a pretty straight shot with minor elevations, at best.

(I DID get burned on topography once before, though: went & put a station on [as P.D.] in an itty-bitty town in the middle of nowhere. It was a 3kw licensed to a nearby town, but the tower was just a few miles out of town & just east of downtown... yet, as you drove INTO the town we were trying to hit, you started to lose the previously strong signal. The signal was TERRIBLE on main street, and improved again as you left town.

I asked the owners, long-time residents of the town, if there could be any hills between us and the tower. No, I was told, in no uncertain terms. How silly of me to suggest it! Yet, months later (after spending the money to move the FM antenna around to make sure we weren't putting a "null" over the city!) they came back to me with a topography map saying, "Gawl-lee! There IS a slow, but significant rise just east of town that drops back off before you get to the tower!" :

...So I know it CAN happen.)

Thank you, again, for all this information... FYI, we're currently running an ISDN (!!!) from the studio to the transmitter & using a hardware solution to compress & decompress the audio. We're using ISDN because the cable system doesn't have high-speed internet there, the phone system doesn't have DSL there, and there's no wireless internet available there.

We've had occasional drops since the beginning, sometimes chirping, hiccuping & muting in rapid-fire succession, sometimes going days or weeks without a blip. I don't remember the brand of our encoder / decoder, but it apparently doesn't have an adjustable bit-rate we could drop... & allegedly we're significantly under the 128kbps ceiling. The delay is negligible, maybe 250 ms... too long to monitor while talking on the air, but fast enough to monitor while producing. (I'm not aware of any ability to increase the buffer, either, which might at least reduce the drops.)

Another station in town uses this exact same setup with zero hiccups, apparently. Of course, their transmitter & studio are in different locations so they don't go through the same hops we do...

It doesn't seem to be related to temps, time of day, moisture, etc. The phone company has found bad cards at the downtown office, out near our transmitter, and on and on, and each time it is "fixed," usually not too long after, here we go again.

I talked to the owner about good ole equalized phone lines, but he says the phone company is now all-digital and would just basically be doing what we're already doing... and then he said last time he had to equalize the "equalized" phone line himself! Seems like if they're dropping us now, they'd be dropping us then... and of course there's the monthly cost of a twisted pair vs the one-time expense of STL equipment.

I've threatened to string up kite twine and paper cups (lower fidelity, but fewer drops!), but he & I BOTH would rather look into other, more professional options.

Here's a useful on-line program to analyze your path:

http://kb9mwr.dyndns.org/n9zia/path.main.cgi

A new Marti 20 watt transmitter/receiver system would run around $3,600. For $2600 you can get a rebuilt used Marti pair, see here: http://www.rpu-stl.com/srs_003.htm. The older Marti STL-10's are common on the used market--the above site is a good place to go to get them rebuilt inexpensively. The STL-10's are generally very reliable once rebuilt.

Allow about $1,600 for a pair of antennas (e.g. miniflector receive, Marti 4' on transmit), plus cable for another $1,000, and you can have a complete system for around $5~6 K. Don't know what you are paying for the ISDN, but suspect the system would pay for itself very quickly.

By the way, if you want to see what will work, despite terrain--put in the following coordinates & elevations for an AM station's path into the terrain profile program:

Transmit: 39-25-07.3 N , 081-28-37.4 W Receive: 39-22-49.3 N , 081-11-35.4 W
The transmit antenna is 15 meters AG, the receive antenna 60 meters, there's a Scala PR450U on the transmit end and a Marti SC-48 for receive antenna.

This station was using an FM subcarrier to feed what then became the second hop STL from the receive location down to the AM site in the valley. Substantial improvement in audio quality and reliability.

Barix Instreamers are $350 now. Exstreamers are under $200. We have been using these reliably over IP for years.

This is a quality stereo feed. You can use them in mono which will use less data. If you use brtp with mp3 protocol (although any format works with brtp) there will be so little delay you won't notice it live.

We feed a stereo program from Indianapolis to Fort Wayne with Barix. We listen to the return over phone and there is more delay on the phone than on the feed over ip.

I am a big fan of real live stl systems.

When you talk a 30 mile hop (a double hop?) and the proper dishes to make it work it seems self defeating. We have a 35 mile path 400 feet on one end and 160 feet on the other. It works but is not the blockbuster signal I like to see. $15k in an install is nothing.

If you seek equipment George Marti and crew are still rebuilding and selling Marti gear. I got a different link for Marti but google it if you have trouble. http://www.rpu-stl.com/srs_008.htm

Consider looking at ip delivery as it bypasses line of sight issues. The only other consideration is the ned to dsl at the transmitter site. Cheap old any kind of dsl will work for receive.

"RF Licensing" is one company that seems to actually "get it" when it comes to the real world. Another major coordination company (wish I could say who it is) doesn't have a clue. They've suggested frequencies/paths that were completely unworkable. Just because it's pointed in a different direction from a co-channel STL doesn't make it work. Have to take into account building and terrain scatter too.

Have noticed that the Moseley 6000 analog STL is no longer being sold.

If you build your own STL system, you own it & there is no ongoing costs. Granted, if it goes down, you have to fix it, but assuming good equipment and properly installed antennas, not a likely event.

If you use an ISDN or an IP based system, you are nothing but a tenant on someone's system. If it goes out, you wait while they fix it.

As a side note, I have a composite STL hop that is 26 miles, (actually 2--one program feed to our other station and one to a booster in the same town). Cost about 7K, 8 foot receive dish, 6 ft. transmit, but is rock steady, no fades. Pair of rebuilt 606's.

You may want to invest in the NAB Broadcast Engineering Handbook. A valuable resource that covers this and many other areas quite well.

You may want to invest in the NAB Broadcast Engineering Handbook. A valuable resource that covers this and many other areas quite well.

TomT said:

Here's a useful on-line program to analyze your path:

http://kb9mwr.dyndns.org/n9zia/path.main.cgi

A new Marti 20 watt transmitter/receiver system would run around $3,600. For $2600 you can get a rebuilt used Marti pair, see here: http://www.rpu-stl.com/srs_003.htm. The older Marti STL-10's are common on the used market--the above site is a good place to go to get them rebuilt inexpensively. The STL-10's are generally very reliable once rebuilt.

Allow about $1,600 for a pair of antennas (e.g. miniflector receive, Marti 4' on transmit), plus cable for another $1,000, and you can have a complete system for around $5~6 K. Don't know what you are paying for the ISDN, but suspect the system would pay for itself very quickly.

By the way, if you want to see what will work, despite terrain--put in the following coordinates & elevations for an AM station's path into the terrain profile program:

Transmit: 39-25-07.3 N , 081-28-37.4 W Receive: 39-22-49.3 N , 081-11-35.4 W
The transmit antenna is 15 meters AG, the receive antenna 60 meters, there's a Scala PR450U on the transmit end and a Marti SC-48 for receive antenna.

This station was using an FM subcarrier to feed what then became the second hop STL from the receive location down to the AM site in the valley. Substantial improvement in audio quality and reliability.

Click to expand...

I know this is an old thread. But isn't that the wrong antenna for use on the 950 STL band? Maybe just a typo as the part numbers are similar, PR-450 vs PR-950. Just hate seeing incorrect info that someone may use to make an expensive mistake.