I might be talking crazy talk here but...
I know often we talk about how to distribute audio to a remote network of transmitters. Many will use an FM Part 15 to distribute audio to part 15 AM transmitters, or use internet, etc. Suddenly, while answering Radioboy's blog this morning, I thought "Hey, why not a Marti unit?"
For those who don't know, a Marti is an FM transmitter that is used by commercial radio to broadcast from a remote location -- the high school basketball game, sale at the hardware store, grand opening at the super market, etc. They are sold in various frequencies, and they've been in use for probably 40 years or more. Marti units go way back to tube models, and of course there are modern solid state units as well. They're built like tanks and run on AC or 12 volts. Generally 20-40 watts depending on model or condition. They put out a very clear FM signal (not stereo) that is used for commercial broadcasting. I've used one in the biz since the 70's. I use one in my present day commercial radio broadcasting. It's presently putting out about 25 watts, we use a portable 1/4 wave antenna and get signal back to the station from up to about 10 miles out. We do much better with the yagi antenna, or if we can get some height. This could easily send a clear signal to an unlimited number of Part 15 transmitters within a ten mile or more radius with the right marti transmitting antenna. Although Marti units come with matching receivers -- all crystal controlled -- a typical $10 scanner from a thrift store will usually tune in Marti frequencies and can easily be used as the receiver at the part 15 transmitter. The one we use at work is on 161.700 MHz and 10 miles away my cheap Realistic scanner picks it up at home no problem.
Now that so many radio stations are moving to other types of ways to do their remotes (mostly internet) Marti units come up on the used market pretty cheap, especially the older ones from the 70's (no one wants to haul them around). They do require an FCC license but I believe that's a matter of filing out a form and sending in a filing fee. They're considered "RPU Units" (remote pick up). We have in a pinch used one to send audio to our commercial FM and AM transmitters from our studio when our STL or line to the AM was on the fritz. This makes a Marti an STL (studio-transmitter link). Obviously this would work, as it's done in commercial radio every day.
Plus a typical Marti has 4 inputs -- line and mic, so you could even feed remote transmitters and use the Marti as your mixer, too. Feed a computer into one channel, a mic into the other, and you're on! What you need is a Marti RPT-25. They're the least expensive right now it seems. I see they're all over ebay from a few bucks to a couple hundred depending on condtion. New ones are a couple thousand for a system. But simple receivers at remote locations could all receive the signal -- you could have a very solid way to feed a huge network of part 15's with minimal cost compared to other options!
Tim in Bovey
Seeing this interesting mention of Marti remote transmission system jostled a memory from just the other day when I stumbled across a real good article that talks about Marti...
http://bdcast.com/products/audio-data-links/marti
Back after hiatus. Blame Carl and his radio show 🙂
The Marti units seem very interesting. I had a similar idea earlier today to utilize unlicensed alternative bands with better distance to feed remote transmitters (i.e. spaced out transmitters blanketing an area or a transmitter over there in the next town).
Does anyone know the legality and licensing requirements for such Marti units? I don't think they are unlicensed.
I'm not a broadcast engineer, but this is what
I think...
Martis or similar units need to be licensed. Also -
they have to be frequency coordinated. That way
your transmission won't end up on somebody else's
newscast.
Many of us have tried to figure out how to legally feed,
install, and operate a Part 15 transmitter cluster.
It's sort of like the Holy Grail. It's out there. But where?
And how?
Bruce, DOGRADIO
part 15 ism band microwave thats how. over the internet with barix boxes is another way.
This will be a 3-part series of entries about various choices for setting up a point-to-point wireless relay to get your studio sound out to the transmitter.
Be sure to re-read Tim Bovey's opening post up at the top, because he has included a lot of details.
Recently Bill Baker of Information Stations Specialist (ISS) was a Low Power guest, and we learned that his company offers a "marti like" relay package operating in the 75 MHz region, including transmitter, receiver and assistance getting an FCC license.
http://www.theradiosource.com/about-us-contacts.htm
http://www.theradiosource.com/downloads/license-form-WAL.pdf
The list linked here shows the Auxiliary Frequencies (MARTI type frequencies) licensed between 25 and 75 MHz. Maybe there are some in your area.
http://www.theradiosource.com/downloads/license-form-WAL.pdf
Of course there are more such frequencies up higher in the VHF band, as Tim from Bovey said.
i was reluctant to post in this topic given how my posts lately have seem to veer off course of the regular topic but IIRC correctly in order to be licensed for an STL or RPU/Marti there has to be a master AM or FM station license that it is attached to. i do not believe you can get a stand alone marti or stl license without having a part 73 AM and/or FM license.
i could be wrong but i vaguely remeber such from the part 73 rules.
look for 1 watt FHSS 900 mhz ethernet extenders. they are NLOS and will be good with a pair of barix boxes and rangemaster.
I agree with Robert with his suggestion about utilizing Wireless technology - I've experimented a bit with it, but much more needs to be done. First, it's Part 15 as well (up to 1 watt with a 6db antenna is allowed under the rules) so no license required. 900 Mhz is not as line of sight as the higher frequencies, such as 2.4 or 5 Ghz, so you'll get greater range (which means in a practical sense that the antenna doesn't have to be mounted as high to get around obstructions). And the technology is relatively common and is available at reasonable prices new (with warranties).
I don't have any experience with Barix boxes. If all you're doing is using wireless to feed one transmitter, then you really don't need them. If you are attempting to synchronize multiple transmitters on the same frequency, then they're supposed to be a solution (but again, I can't speak to that).
kc8gpd is correct.
§ 74.432 Licensing requirements and procedures. (a) A license for a remote pickup station will be issued to: the licensee of an AM, FM, noncommercial FM, low power FM, TV, Class A TV, international broadcast or low power TV station; broadcast network-entity; or cable network-entity.
Me again.
There are options for wireless data and wireless audio. 900Mhz, 2.4Ghz, 5Ghz...
2.4Ghz is interference central.
5Ghz is commonly used in other fields for backhauling data for long hauls.
Looking at affordable solutions... Point-to-point wireless as digital - data.
Some units like those made by Ubiquity are really mature and reliable and have nice distances. Enough to reach other towns.
That's the only way I can see doing this. Mind you talking about permanent line of site style installations. For remote broadcasting on location, that's probably best with smartphone or similar cellular wireless.
The FCC Rule sited just above seems to rule-out Part 15 stations from holding an auxiliary license for remote transmission, but maybe we should look again.
What is a "broadcast network-entity?"
Is the Crow Network, with his array of affiliate stations a "broadcast network-entity?"
Radioboy Alan sure sounds like a "broadcast network-entity," but of course with his upcoming LPFM he'll definitely qualify for an auxiliary license.
Maybe I'm a "broadcast network-entity," with three AMs, FM, shortwave and three-streams on the interNET(WORK).
Today we'll check the FCC Definitions to see what we learn.
So much for my good idea.
§ 74.2 General definitions. Broadcast network-entity. A broadcast network-entity is an organization which produces programs available for simultaneous transmission by 10 or more affiliated broadcast stations and having distribution facilities or circuits available to such affiliated stations at least 12 hours each day.
Well, most of us do broadcast 12-hours a day or more. But do we have 10 affiliates?
It depends on the definition of "affiliate."
Can a Part 15 station be an affiliate by FCC definition?
Can a streaming station be an affiliate by FCC definition?
Take it from here. I've done my share.