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Gilbertd :)
I wonder if you could cast your expert ear over the following recording?
http://www.lard.me.uk/nastynoise.wav

Something really horrible is interfering with our work radio repeater. It's located in a Farm Yard with adjoining works yard and joinery shop, so there's loads to go at and I can't think of anyone with more experience who might be able to narrow it down a little bit!

I can't stretch to £350 a day and free F1 tickets but I could manage a pint :)

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That's a data transmitter, very strong and on the same frequency by the sound of it. Is this a licensed system? If it is, I suggest you contact Ofcom (0207 981 3131) and get someone out to see where it's coming from (although you'd best check that your licence is current and you haven't let it lapse so the frequency has been re-allocated....).

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Thanks! That has eliminated a huge amount of dicking about!
Our system is licensed and current - I'll check the paperwork tomorrow but I think it's a Technically Assigned license. Our supplier (Zycomm) have checked the list of license allocations and there's nothing in our area on our frequency.

I'll head down to the repeater tomorrow, and check over the config before calling Ofcom just in case it's an embarassing own goal.
Not that I've made any changes recently, but you never know! I might ask a local Amateur to listen in on our freq and see if he can get any clues to help out. My initial guess would be taxis, the problems seem to start slowly in the morning, ramp up by mid day and last until late at night.

Again, thanks a lot. This is causing our radios to be pretty much inoperable for large periods of the day and that causes us a lot of Health and Safety type implications quite apart from the general PITA.

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Yes, it will be Technically Assigned. Data can be used by taxis for handing out jobs but that tends to be in short bursts as it needs a handshake back from the other end. There's also digital business radio which digitises the speech and sends that as data. Advantage is that you get two voice channels for one radio channel as it either uses time division multiplex or frequency division multiplex depending on who made it. If you drop me a PM with the postcode (or better still, the NGR) of your base station, I'll run a check and see if there's been anything recently licensed in your area. It may be a new system where whoever programmed the system suffered a dyslexic keyboard and got it wrong. Shame it's not in my area, it'd make a change from pirates causing interference to aircraft and interference to the mobile networks.

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That's DMR. Anyone got shiny new Mototrbo radios recently?

Incidentally I no longer work for a Mototrbo dealer, having packed it in last week to go and deal with blue-light services instead.

It's a nice clean signal, and a .wav file, so maybe I can footer about a bit and run it through DSD and see if I can get anything decoding.

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I wondered if you'd pop up. It sounds like it's just idling with no traffic on it. You can usually hear when a Mototrbo is carrying traffic. Probably set up with a ridiculously long hang time if it does drop occasionally. I monitored one recently that was being used by the parking wardens in one of the London Boroughs. 80 handportables on it, each with GPS location turned on. In two hours the carrier dropped twice for less than a second each time. The co-channel user 4kms away wasn't best impressed.

Blue light? Maybe they are doing something different your side of the border but down here they are dropping the Airwave Tetra system very shortly and going over to using 4G instead.

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I've got one of these http://hamradiostore.co.uk/aor-ar-dv1-digital-voice-receiver.html out in the van. Works really well on off air Mototrbo signals and has a built in SD card slot to record received signals to. Not sure if I could copy the audio to an SD card and play it back though as I've never tried it (or read that far into the manual).

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Not sure what they're doing but I don't think 4G is a goer for a patch that covers from the M8 down to the borders and everything west of Dumfries...

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Wonder if you could play that sample back through your test set, and tune the radio to it?

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I can record more if it's useful.. For that one I just used a recording app on my phone, a radio and a quiet room. Is the quality good enough to read it into your kit? I'm not sure if that sample had the header because I was using a "Skip Silence" feature but whoever it is is transmitting regularly enough for me to wait about.

We're using 75 Hytera 7 series handhelds with a repeater and two channels. The kit is about 3 years old and this interference started at about Christmas time so maybe it was a shiny new Mtrbo present for someone :)

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Hmm, the plot thickens.
http://www.lard.me.uk/Interference.mp4

I wonder if our repeater is buggered :(

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Hytera PD7xx ought to be digital (they can be used for analogue).

That video looks like your repeater is just sending normal beacon bursts.

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They're used as digital, certainly. One of the sets in the video is programmed to receive on analogue so we can hear what is busying up the repeater. The video shows short bursts, sometimes they're a couple of minutes long and we can't transmit because it's using both channels. I'm chasing our radio supplier.

Oh, Ofcom say our channel is shared but there shouldn't be anyone nearby.

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It's a shared channel but the nearest user on it is just outside Hunmanby, near Filey, so not exactly on your doorstep. But, as Gordon says, it's transmitting and what you are hearing is the data it is sending rather than what it is receiving off air. It will use both channels as there aren't really two channels, just two virtual channels within the one radio channel.

Get Zycomm over to have a look first as it is starting to look like what we'd call an own goal.

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Yep, I'm with you on that. I think there's a problem with the repeater, but I can't quite understand what on earth it thinks it is doing but I'm loathe to call OFCOM unless we're sure there's an external problem.

Thanks again!

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Okay, right digital repeaters are a bit different from analogue. With analogue repeaters you basically have a transmitter and a receiver in a box (often these are just two mobile radios), wired together. When the receiver hears a signal, the squelch opens and that keys the transmitter. You can do various neat tricks to share that repeater, like having it decode and retransmit different subaudible signalling tones (although I struggle with the idea of 110.9Hz as "subaudible" since it's about the same frequency as an open A string on a guitar).

Digital works rather differently, mostly because of how the two timeslots work. When your portable transmits, it'll listen to see if the repeater is transmitting first. If it isn't, it'll send a burst of data to wake the repeater up. If you're very out of range of the repeater, you'll see the LED on top blink a couple of times before you get the BEEEEEP tone warning you it can't transmit.

Once the repeater is up, it sends a string of timing pulses (the buzzing noise). When your radio wants to transmit, it picks a pulse and starts working in sync with that. It only transmits on every second pulse, so you get the two timeslots (two "channels" per frequency). Every so often when no-one is using it, the repeater will fire up and send a burst of beacon data so that the radios can check they're still in range. This isn't very useful on a single-repeater system but if you've got several of them it will help your radios pick the strongest signal to listen to.

Now here's where the troubleshooting begins. If you've got a repeater, you've got a strong local signal transmitted from the repeater, and much weaker signals from the portables. If you're having interference from another site, it's far more likely that it's on the frequency that the repeater receives on, than transmits on - it's going to be far easier to step all over the relatively weak signal from the portables, especially if you've got a nice big aerial up high outside.

So to track it down, try programming one of your radios to listen on the same frequency that the repeater does, on analogue, carrier squelch, so that you hear anything that pops up.

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But, with the nearest user being over 35km away, it would need to be sending the same colour code to cause the repeater to wake up in the first place. It's always possible that the other user has a mobile in use in the area I suppose. It's a very old licence so they may well have recently changed to a digital system and their supplier has just picked a colour code at random. But if that was the case, then I would expect the audio to be heard as well. Suppose we'll have to wait and see what Zycomm have to say.

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Is it actually waking the repeater though, or just doubling over the local signal? Bear in mind that the repeater will transmit every ten seconds or so anyway.

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While I was away, we had someone from Zycom come up and have a look. They're sure that the repeater is actually being hit by multiple requests from radios to log in with the Smart Despatch software. They reckon there's a network problem which is preventing the login acknowlegement being sent back to the mobile and that causes multiple retries. I'm not convinced it's network, but I'll have to eliminate it before we can do much else.