Line 6 Digital Wireless Systems

[boswell]

Some advice please from the electronic guru's amongst you.

 

I'm connecting a CPC MP33750 lav mic 2 wire, imp <2K, 1.5V bias requirement into a Line 6 Tx, Zin 20K, Bias supply 5V. How do I calculate the best value of R required in the circuit shown below?

 

http://s86.photobuck...current=Mic.jpg

 

I've tried values from 2K2 to 10K and noticed no difference; they all seem to work equally well, but there must be an optimum value.

 

I've searched the net and found conflicting results, some say it should match the input impedance of the Tx, others say it is a potential divider to give the correct Bias voltage into the mic. So R=4K8 should give me approx 1.5V into the mic. What is the effect of increasing it to 10K or down to 1K? (apart from altering the voltage into the mic)

 

Help please

[mervaka]

could try 10k over 22k, or 4.7k over 10k?

[Lamplighter]

An interesing experience, last night I went to see an extremely polished performance of The Producers by one of our local groups. It was rather spoilt by crackling from the radiomics gradually getting worse as time went on. One character in particular was badly affected to the point where he lost his mic altogether. Enquireing after the show it transpired that it as Line 6 kit, with the receivers in the pit using the supplied whips as "paddles were not available" It was really a shame as a couple of the right aerials correctly positioned would have probably given a problem free show. Interestingly the operator felt it was more related to the way the character was wearing the kit. As he was in an ordinary suit and downstage when the worst of the problems occured I felt this to be unlikely. I think this well illustrated the problems of new technology where it is not totally understood by the user.

Brian

[boswell]

I've never found they crackle, they either work or they don't !

If you put a constant signal through a TX and then move until the signal path is sufficiently obstructed, it just cuts out.

Crackles to me means bad connections somewhere on the mic.

Or do you mean that the audio was cutting in and out and not crackling?

[Phill.Beynon]

An interesing experience, last night I went to see an extremely polished performance of The Producers by one of our local groups. It was rather spoilt by crackling from the radiomics gradually getting worse as time went on. One character in particular was badly affected to the point where he lost his mic altogether. Enquireing after the show it transpired that it as Line 6 kit, with the receivers in the pit using the supplied whips as "paddles were not available" It was really a shame as a couple of the right aerials correctly positioned would have probably given a problem free show. Interestingly the operator felt it was more related to the way the character was wearing the kit. As he was in an ordinary suit and downstage when the worst of the problems occured I felt this to be unlikely. I think this well illustrated the problems of new technology where it is not totally understood by the user.

Brian

 

Sounds more like sweating out or mechanical issues to me. Drop out on a line 6 yes, but radio crackles sound unlikely.

[Lamplighter]

Yes Phil, you are probably right. It developed a background hiss and crackling, akin to a VHF beltpack loosing its aerial.

Brian

[paulears]

I've not managed to get any hiss or crackles out of mine at all - they either work, or they don't. So I'd also assume it's a mic problem. I doubt we'll get any info as to what the mics being used actually were - so we're a bit stuck.

[ramdram]

For those in UK, and who read the Sunday Telegraph, you cannot have failed to read the headline on the front page ref. "Pupils at risk from wifi and mobile phones".

 

We know that Line 6 kit runs on the ISM band, so it may be that digital technology for radio mics as used by nippers dies on the vine before 2012. Perhaps it is just as well that "we" are naturally cautious before embracing new technology...certainly cautious about paying for it anyway. And, perhaps it is just as well that offers to mic up a whole panto of folk with this kit came to nothing? Even if nippers are "only" in the chorus does not mean they would be totally unaffected by a tx pack.

 

You could not ignore this new thinking in an RA now that we read of the concerns by "experts" on page one of the popular press. Ignorance being no defence in law of course.

 

Naturally there are no prizes for predicting that mobile phone and wifi router makers will protest and cite dozens of surveys, commissioned by themselves, ** laughs out loud **, that said technology is perfectly safe. There is concern too for the "new" type DECT cordless phones and even wireless baby monitors, so you can add that to the mix.

 

Those who read up on the subject will know that some manufacturers are offering RM kit operating in the 5GHz band, which does not imply automatically it will be twice as harmful but it is definitely something to be aware of.

 

Can you imagine the legal furore if the parents of naturally dim children start blaming the phone and wifi router makers, not to mention schools etc etc. if their issue don't get a degree? How can manufacturers prove the kit did NOT cause the problem.

 

It almost makes you wish you had trained to be a lawyer...almost.

[Tom Baldwin]

And if you read the whole article in the Telegraph, you'll see that bureaucrats are calling for rules restricting use, and serious health organisations aren't.

 

What insane risk assessment would disregard WHO et al in favour of a bunch of people who aren't health professionals?

[Simon Lewis]

The committee is composed of 84 MPs and politicians from member states, and

its vice-chairman is Lord Prescott, the former Deputy Prime Minister.

 

Forgive me if I smile wryly at this point ;-)

[ramdram]

Indeed yes the bureaucrats are on the case, ** laughs out loud **, so if we get new rules and regs from Brussels we'll know whose will prevailed. I got the impression that it was an arse covering exercise, what with the mention that "we" had not acted quickly enough on the asbestosis or tobacco risks in years gone by.

 

And, ref the business of bureaucrats v "expert's advice...who passes legislation...certainly not experts.

 

Wry smiles are smack on target.

[chelgrian]

And, ref the business of bureaucrats v "expert's advice...who passes legislation...certainly not experts.

 

Wry smiles are smack on target.

 

Ah well the the telcos can turn off all the MPs mobile phones and see how they like it before the law is quickly and smartly filed under B for bin.

[themadhippy]

Ah well the the telcos can turn off all the MPs mobile phones and see how they like it before the law is quickly and smartly filed under B for bin.

Dont be silly,they'll claim parliamentary privilege and be exempt,not that theres any need ,there so thick skinned they could have a picnic at Fukushima and not be affected

[Shez]

Good luck prising the teenagers' phones out of their hands...

[fliggygeek]

I've had a chance to try them out into a proper system this morning and results are encouraging and slightly odd.

 

As Rob mentioned the wifi - I've discovered some handy info. I can sit with a mic right next to this laptop and wi-fi is unaffected. Put the mics near the router and wi-fi clogs up and distant wif-fi devices drop off the network. No idea why, but I'm not having any problems with this rather 'troublesome' laptop.

 

 

As regards the Wifi access point proximity, have a think about the system in use. Each device on wifi uses bandwidth, all in a set channel, (or in a really expensive setup, a few different set channels). From what I read, the Line6 systems use frequency hopping systems to combat inteference. This is a technology used by the RC (Radio Control) Models community for a couple of years now, involving the transmitter and receiver being sync'd up and from then on, jumping randomly around in a set band of RF, but doign it together, in order that even if you have a microwave going, the chances of being on the exact same channel as the microwave for more than a millisecond is almost nil. Audio, form what I hear, using 4 hopping channel sets per device, will have a higher chance of hitting channels that are in use. using 12 of these, 48 channels of frequency hopping will severely affect anything that is on static channels.

 

Wifi is a different system, it depends totally on the integrity if its packets, if one is not transmitted correctly, it retransmits it. it is also based on static channels. with the two technologies acting together, wifi just retransmits the packets of data that are intefered with by the microphones. It slows the system down a bit, but not too much. at the router end, I suspect that because of the amount of packets trying to be read by the router, (traffic) it makes lots of errors when its packets get intefered with, meaning it sends a lot back to get retransmitted. at high signal levels, its fine, the computer just resends them, I suspect that the wireless drivers are configured that if the wireless strength is less than good, it looks at the amount of packets rejected and if its over a threshold it says the connection is dead. this might be why the connection is dropping off.

 

End result is that the microphones, with which the dropped packets are not necessarily needed, work fine, but the wifi is impeded.

 

PS, I'm a 19 year old IT Consultant and Lighting tech, think about how many years of experience I have in the industry and please flame me if ive made an error. A mistake pointed out to me is valuable experience gained.