Inexpensive long range audio transmission

[Dogoth]

A friend of mine has been tasked to connect 3 seperate P.A.s along a parade route so that when the Mayor gives some speech it will be heard simultaniously at all 3 locations (a second or so of latency is no problem). The problem arrises with his budget. It's just speech, so only mono intelligability is of concern here. The 3 placments are around 2000' apart.

 

He say's he can get authority to string a low voltage wire along a set of lamp posts that follow the whole parade route but that he doesn't have anywhere near that long of a piece of cable.

 

Question? is there a reliable RF transmission method anyone can think of? I was thinking of those directional IE transmission antennas (the coil around the PVC tube) but they are super costly to even rent (and 2000 feet?). I said that since CAT5 cable is so cheap (and has near perfect twists of it's pairs) that he might get away with sending a balanced signal that far. I thought I'd ask some of the more in depth engineers here if this is feasable? Would an impedence matching transformer at each end help? I've never delt with transmission of this distance before but I know that Telco does it all of the time. How far can you go between line amp/EQ devices?

 

Any help or suggestions would be appreciated.

 

Thanks in advance.

[jgthatsme]

Here's a design that might work. The transmitter and receiver can be picked up anywhere for pennies if not for free, and 2,000' of transmission cable should be well under $100.

 

[scarecrowbob]

Get a local radio station to treat it like a remote and the amplify their signal at the various points

[Craig Vecchione]

 

The city has police, fire, and other emergency services, right? Use a tac channel and standard receivers. Seems like a Mayor should be able to pull those strings. He might have to attend the Firemans and Police Fundraising Balls.

 

 

That's an illegal use. Post-9/11, that stuff is touchy and I wouldn't try to press the issue.

 

 

What is the actual budget here, JRBLE?

[Craig Vecchione]

 

Cities have lots of frequencies that are reserved for public use including parades, that are not assigned to specific emergency services. I know this for a fact because I've personally scanned them at the Rose Parade.

 

 

Then perhaps let us know to which frequencies you're actually referring. Tac's are not for this use, and the possibility if the OP being given transmitters that work on them is slim to none.

[srp72ee]

You really need to watch which frequencies you use.

 

One option would be to find a local business that has LICENSED "business band" radios that are frequency coordinated for the local area. Most the the walkie talkie radios have an external mic and headphone jack that you can connect into a mixer. Use only simplex frequencies (not through a repeater).

[BillESC]

Seems to me CB radios could do the job.

[kevinnem]

for this type of event we use FM broadcasting, by FM I mean the more comon undersating of the FM radio in your car, not the technique to send a single. By useing plain old FM radio , you can set up as many "pods" as you want, all you need is a FM tuner (20$ at a pawn shop), and a powered speaker. They can even run off an array of car batteries if you have to.

 

The trasmit power vaiers slightly between canada and the USA but you can get about 50 watts output, and still be classed as a "low power" user. Also, aslong as the you adhear to a few rule (no advertiseing, or policial messages ect). you are execpt form fees, and licenceing requirements.

 

However, in canada, true to canadaian form, you can to fill out a form(for CRTC) that says you are not going to be filling out a different form(for the CRTC).

 

in most cases you are not allowed to broad cast over 50 watss of effective reatated power (ie 50 in a sphere), .. if you use 25 watts, but a directionial antenna, then you still have 50 watts "effective". You are also alloowed to calculate in antenea and line loses.

 

having said taht , for a 3 hour event, who is goign to catch you if you are slightly over?

 

50 watts, easily trasmitted 10 KM in my "non optimal"/ real world tests.

[rwhealey]

If you can't figure out the radio stuff, mic cable isn't that much more expensive than Cat5. I'd say $120 for 1000 feet of Belden 8451. From what I've read a balanced line level signal shouldn't have any problems with 2000 feet.

[agedhorse]

 

for this type of event we use FM broadcasting, by FM I mean the more comon undersating of the FM radio in your car, not the technique to send a single. By useing plain old FM radio , you can set up as many "pods" as you want, all you need is a FM tuner (20$ at a pawn shop), and a powered speaker. They can even run off an array of car batteries if you have to. The trasmit power vaiers slightly between canada and the USA but you can get about 50 watts output, and still be classed as a "low power" user. Also, aslong as the you adhear to a few rule (no advertiseing, or policial messages ect). you are execpt form fees, and licenceing requirements. However, in canada, true to canadaian form, you can to fill out a form(for CRTC) that says you are not going to be filling out a different form(for the CRTC). in most cases you are not allowed to broad cast over 50 watss of effective reatated power (ie 50 in a sphere), .. if you use 25 watts, but a directionial antenna, then you still have 50 watts "effective". You are also alloowed to calculate in antenea and line loses. having said taht , for a 3 hour event, who is goign to catch you if you are slightly over? 50 watts, easily trasmitted 10 KM in my "non optimal"/ real world tests.

 

 

I think you will find that the process of negotiating the FCC is daunting and expensive for a single event. The reporting and conformance paperwork to do this legally is substantial, as well as the fees to complete such processes.

 

In fact, it may not be allowed at all, and if this is attached to a municipal event, there are deep pockets that the FCC can attach that would cause bigger grief down the road. They can be a big problem, and they have jurisdiction that you can't imagine.

[agedhorse]

Fore something like this, the usual solution is to contact a broadcast rental house that carries IFB equipment, These FM IFB systems typically run 3-5 watts, they are licensable, the rental house will assist with the paperwork, and you will typically be able to transmit ~1-3 miles with the proper antennas. The frequencies are allocated based on location and other licenses issues in that operating area.

 

You might give "Systems Wireless" a call, as a start.

[agedhorse]

 

If you can't figure out the radio stuff, mic cable isn't that much more expensive than Cat5. I'd say $120 for 1000 feet of Belden 8451. From what I've read a balanced line level signal shouldn't have any problems with 2000 feet.

 

 

When driving really long lines, special precautions must be taken. It can be done, but at 200o feet I would expect high current line drivers (and high stability) and output isolation networks to drive the distributed capacitance. Often large drivers and audio transformer isolation of the signal is pretty much essental.

[Special J]

I would see if there is a local radio station involved with the event. Talk to their engineers. Often radio stations will have FM transmitter/receiver set ups that they are already licensed to use. Most radio stations also can use carrier frequencies if you are able to get a signal to their station.

 

I did a 4th of July event every year with fireworks synced to music. There were 5 different sites on either side of a river with a barge in the middle where the fireworks were launched from. I had a CD on land which contained the fireworks music on one side and time-code to feed the fireworks launch computer on the other side. The time code would be transmitted via an FM transmitter with a large directional antenna to the barge. So essentially, I had the launch button. The music side was fed with a DA to the 5 different sites via telco lines which were ordered ahead of time. I don't remember how much the telco charged for dropping the lines (the client paid for it directly), but it wasn't cheap. I can say that it was always a good signal to all 5 sites, the farthest of which was probably a mile away from the source, as the crow flies. I'm not sure how far it had to travel down phone lines. I only a DA on my side driving it and IL-19 transformers on the other ends.

 

Honestly, it's one of the highest pressure gigs I ever did. There's about a 5 second delay between hitting play on the CD player and hearing the first mortars leave the tubes. FOOOMP. Seemed like an eternity. It was fun setting the receiver on the barge though. I would get a police boat to take me over there and then climb up the side of this huge barge with an FM reciever and omnidirectional antenna strapped to my back. If you think sound guys are crazy, you should spend some time with pyro guys. Dudes packing 4" mortar tubes with lit cigarettes hanging out of their mouths.

[RoadRanger]

Crazy thoughts - how about a conference call on cell phones? Steaming MP3 via wired/wireless internet?

[agedhorse]

If telephone lines are available at the sites, a hybrid used one direction at both ends would be viable too. A single hybrid at one end driving a conference call at the other 3 sites. A receive hybrid at each those lines would give you audio back ready to use. Audio quality would be ok, not stellar but with good hybrids certainly acceptable for that application.

 

I happen to have a set of 4 brand new, sitting on the shelf looking for a new home.

[Craig Vecchione]

 

By tactical channels, I didn't mean police tactical for SWAT and such. I meant municipal channels that are not the normal public safety dispatch.

 

 

You misused the term, hence the confusion.

[kevinnem]

 

I think you will find that the process of negotiating the FCC is daunting and expensive for a single event. The reporting and conformance paperwork to do this legally is substantial, as well as the fees to complete such processes. In fact, it may not be allowed at all, and if this is attached to a municipal event, there are deep pockets that the FCC can attach that would cause bigger grief down the road. They can be a big problem, and they have jurisdiction that you can't imagine.

 

 

I Am not aware of the deatils involved with the FCC - but the equivilate organisation for me is called "industy canada". There is no negotiaion in volved, if you quilifi under the low power FM tasmition guideline, you are garrenteed a liecence. They will tell you what freqancy you get. The process to get the liecence for setting up this system is quite easy, and straight forward. There are no fees, and the people that I delt with where very freindly, and agreeable.

 

The CONTENT you broadcast is handled as a seprate issue with CRTC (in canada).

 

Kev.

[Craig Vecchione]

 

please cite the City Code, State Code or FCC regulations that restrict the use of frequencies dedicated to municipal channels from being used by parade participants or officials for any purpose. Sorry if I don't take your word for it, since based on what I've heard over my scanner, they can pretty much use it for any purpose they see fit.

 

 

It's pretty simple; the OP isn't an "official", and isn't licensed. The FCC requires licenses for the frequencies we're discussing. Unlicenced use is illegal. I hope this clears it up for you.

[agedhorse]

 

I Am not aware of the deatils involved with the FCC - but the equivilate organisation for me is called "industy canada". There is no negotiaion in volved, if you quilifi under the low power FM tasmition guideline, you are garrenteed a liecence. They will tell you what freqancy you get. The process to get the liecence for setting up this system is quite easy, and straight forward. There are no fees, and the people that I delt with where very freindly, and agreeable. Kev.

 

 

Though I haven't delt with Canada's "industy Canada" organization, I can't believe it's any easier or cheaper to navigate than our FCC, which is VERY restrictive. There's a lot more to it than what you describe Kevin, maybe Canada is easier but my past dealings with your Hydro dept. folks lead me to believe otherwise.

 

Here's some information that makes for interesting reading.

 

http://www.ic.gc.ca/eic/site/smt-gst.nsf/vwapj/ric40e.pdf/$FILE/ric40e.pdf

 

http://en.wikipedia.org/wiki/Low-power_broadcasting

 

and... here's what can happen when you run afoul:

 

http://www.fcc.gov/Bureaus/Miscellaneous/Orders/fcc95333.txt

[Gordon Sound]

Check some surplus places for 2 conductor w/ shield cable and run a balanced line.

here is a place that sells 500 ft spools for $39.99

https://www.fairradio.com/catalog.php?mode=viewitem&item=1310

Another option i have used is old steel feild phone wire w/ a 70 volt line and 1/4 watt transformer taps fed to a 10 K pot. a 50 watt 70 volt amp should work. https://www.fairradio.com/catalog.php?mode=viewitem&item=6550

Other options include cat 5 baluns but I think they are only good to 200 ft

[Dogoth]

Thanks to Everyone for your recomendations. I'll let my buddy look at these posts and decide what he wants to do. I'm aware that the FCC is not someone who we want to get directly involved here (the proverbial bucket-O-worms). The idea of renting some High quality radio sets from someone who has already dealt with the FCC is probably the best and most cost effective way IMHO (I can't imagin the cost being more than the T&M for a hardwired solution (although I'm sure there'll be a big security deposit :>). This is what I'll recommend. We'll se what he says.

 

Once again, Thanks to all.

 

J.R.

[agedhorse]

The T&M for installing arial runs is substantial, including the lift rental cost.