Temporary, Bi-directional audio feed up to 1 km distance

[EventMan]

Can I please have people's thoughts, experiences on the following?

 

I am investigating how to get a two-way feed for a weekend rowing regatta. The rowing club would like to have the PA output at the start of the race fed to the PA at the finish line and, subsequently, the PA output at the finish line fed back to the PA at the start line - a distance of 900m. There is no line of sight at the moment, but this could be investigated by going up to the top of a building.

 

As I see it, there are three options:

1. Cat5e

2. RF

3. Mobile Internet

 

Does anyone have any experience of this sort of situation? The event is a charitable event (in Cheshire), so the aim would be for a robust, yet budget-friendly solution. Failing that they will have to use two-way radios to feed info between the two compères.

 

Thanks

 

Ian

[pete10uk]

I've used a wireless CCTV product called a VideoMitter Link

 

Yo technically speaking need to transmit video to stick with the licence but I've had it working 600-700m with dodgy line of sight. not the best audio bandwidth but it worked for a number of sporting events I did with 2 sites like yours. you'd need 2 sets for 2 way.

[EventMan]

Thanks for your input, Pete.

 

What sort of antenna did you manage to get away with?

 

Was the audio OK for speech?

[Owain]

4. Are the start and finish within range of premises with landline phones (and preferably with one of the premises having included calls) and use telephone balance units.

 

5. Use feeds from mobile radios earphone sockets into the PA.

 

You may not need bidirectional audio, just a unidirectional feed that can be reversed once competitors start approaching the finish. Thus 100 volt line (with intermediate speakers along the line if wanted) with an amp at each end, just don't have both amps feeding the line simultaneously. The 'transmitting' amp outputs 100V onto the long line and the "receiving" amp has a 100V-line level transformer on its input and local speakers on its output.

 

If land-based access is problematic don't ignore a battery-powered repeater on a boat halfway down the river.

 

 

 

 

[HilcrRWise]

No specifics as I haven't looked in to doing anything similar myself, however how about audio streaming over the internet?

[ninjadingle]

Came across this post from a few years back - why not go the cable route with a few reels of Cat5?

[sunray]

Came across this post from a few years back - why not go the cable route with a few reels of Cat5?

 

I have done this many times using cat 2 or cat 5 cable, it is very clean providing it's properly balanced and therefore does not need to be screened. Dropwire is nicest if it is all in the air but not for laying on the ground.

 

 

The controlling questions are always logistics ie: where to run it, public access for damage etc. Road crossings always seems to be the ball breaker for some reason.

 

Longest run to date has been 4Km using 9508 (8 pairs of 7/0.2 with overall screen) for stereo at 0dB, mic at -30dB (open mic confidence feedback), a cue light and intercom. It was 1000ft lengths, the joins were knotted once, wires stripped and twisted together and a single layer of pvc tape folded over (fairly typical for single day temporary service?). Hooked over trees and laid along the ground etc, intended to be there for a weekend but used for nearly a month without noticeable rain degratation and when we removed it we found BT had borrowed a couple of pairs for a temporary kilostream service too.

 

 

 

 

There are companies hiring out radio link kit but the cost of that for a day is likely to be a lot more that 3 boxes of cat 5. BTW the cheapest version of UTP CCA is adequate for sound quality at these short distances. If it is going to be used on a regular basis then I would suggest a flexible cable such as Belden 9502 (02 being number of pairs) which will stand much more of the repeated handling than cat5 will.

[EventMan]

I think the way to go will be over Cat5, although, for ease of deployment, an RF solution would be great.

 

Sadly, one site is in the middle of nowhere, so a landline option is out.

 

I'm not sure what the mobile signal is like at the two points, but that might be an option, as is the two-way radio suggestion (I have never listened to the audio output of a two-way through PA speakers, but have always assumed it would be a bit "thin"?).

 

Thanks for the suggestions so far - keep them coming!

[intyra]

I'd try to get my hands on some of the Ubiquiti AirMax kit and just do it all over IP. You could also use a couple of bonded 4G dongles but they're obviously less reliable.

 

The Comrex Access will let you send / receive audio over IP, and you can attach a 4G modem to them.

[EventMan]

I'd try to get my hands on some of the Ubiquiti AirMax kit and just do it all over IP

Thanks. This looks like a good option if we can get Line of Sight.

As a matter of interest, does anybody have any idea of how much data we would use with 8 hours of constant audio transmission over mobile data?

[Owain]

the two-way radio suggestion (I have never listened to the audio output of a two-way through PA speakers, but have always assumed it would be a bit "thin"?).

 

To put it politely

 

 

However if you can use an external headset microphone with a decent windshield at the transmitter end, and a suitably processed feed at the receiver end, you may cut out enough of the analogue/acoustic distortion in the setup for it to be tolerable.

 

Your local RAYNET may be able to help with radio comms for an event (but usually for passing messages, a remote PA feed is probably outside the terms of a amateur radio licence -- or indeed a business radio licence, although that doesn't stop the police using business radio licence for broadcasting applications).

 

 

[bruce]

 

As a matter of interest, does anybody have any idea of how much data we would use with 8 hours of constant audio transmission over mobile data?

 

Assume a 128k MP3 stream.

That’s 128 kilobits per second, which is around 60 megabytes an hour. So around half a gig of data for an 8 hour session. There will be a bit of overhead, but that’s the sort of order of magnitude.

 

 

If you can get line of sight, then the Ubiquiti kit is great, as is the equivalent from Engenius - and it costs very little.

 

.... but if you are planning to use mobile data, or public wifi, or anything like that, you should expect problems. I’ve lost count of the number of times I’ve gone to events where they’ve tested streaming over the site wifi and it’s been fine, but they had neglected to consider that it might be different when they had several thousand audience members in the vicinity, all chewing up some of the bandwidth or spectrum.

 

I’d be looking at either cable, or line-of-sight bridging on band C

[Jivemaster]

Can you consider a single telephone pair with two handsets so that the commentators can talk to each other. RS used to (may still) do 1000m reels of twin "bell wire".

[dbuckley]

Previous similar topic with recommendations.

[EventMan]

Thanks, Jivemaster, for reminding me that the word I was looking for is "Commentator", not "Compère" - I knew it wasn't the right word, but couldn't think of the right one (old age!). The idea is for the commentators' local PA feed to be replicated on the remote PA feed, and vice versa, so a simple phone line wouldn't cut the mustard, I imagine.

 

Thanks, Bruce, for the estimation of data usage, and the suggestion for Engenius; their prices are good.

 

One further question, assuming we go down the IP route, could a laptop at each end be used to convert the audio from the mixer to an IP protocol? I mean, have a feed from, say, the monitor output on the mixer to the mic socket on the laptop, and the headphone socket on the laptop connected to an input on the mixer, with the laptop acting as the audio to IP converter? Otherwise, there would be more expense to get the discrete kit.