Trantec S5

[sandall]

I've supplied aerobics headsets in the past where the transmitter was built into the headband., but on "Strictly" AFAIK all the transmitters are in pouches sewn into the dresses. On the other hand I was once in the front stalls for a Japanese version of Jesus Christ Superstar. He was heavily amplified (made obvious by a late fade up) & started right DSC in nothing but a loincloth, & no "big hair", but absolutely no sign of a cable - never did work out where his transmitter was.

[J Pearce]

I have worked on shows where mic and transmitter are fitted to wigs. It makes quick changes MUCH easier, but battery changes become more complicated.

[Wolf124]

17 minutes ago, J Pearce said:

I have worked on shows where mic and transmitter are fitted to wigs. It makes quick changes MUCH easier, but battery changes become more complicated.

Thanks. Is there any health and safety issues having a transmitter so close to the head for over 2 hours. I realise that there is probably more danger with a mobile phone but for normal use, probably not two hours. What type of transmitter were you using. I would have thought that most would be too heavy for practical use.

[J Pearce]

No H&S issues that I have been able to find. The transmission power is very small, and it is non-ionising.

I’ve seen it done with various transmitters, usually (but not always) the more modern types that use a small lithium based battery, which are lighter and smaller than PP3 or AA based transmitters. It needs a good wigs designer and wigs tech to make it work well.

[sunray]

5 hours ago, Wolf124 said:

Could that have been the source of his problems and why the kit came in for repair?

The rack contained a 1U mixer which had stopped working, nothing to do with the mics.

[paulears]

You would need to do the current OFCOM test to ensure compliance - it would almost certainly determine the risk small and managed - but the onus is on the operator to ensure the exposure is safe. I stuck 50mW in transmitting 100% duty cycle at 850MHz and the result was 'no further assessment is required' - so that seems OK?

[cedd]

15 hours ago, paulears said:

You would need to do the current OFCOM test to ensure compliance - it would almost certainly determine the risk small and managed - but the onus is on the operator to ensure the exposure is safe. I stuck 50mW in transmitting 100% duty cycle at 850MHz and the result was 'no further assessment is required' - so that seems OK?

 

Tricky one. Ofcom are never going to use the word "safe". They managed to do the Stewart Report - measuring cellular emissions near schools and hospitals, without ever using the word. All they'll do is quote ICNERP levels at you and tell you if it's lower than that. That calculator is useful, but it's slightly flawed for us in that it doesn't give results in the reactive near-field. If we're talking about head mounted mics then the skull is most definitely within that (8cm at 606MHz). It becomes far more complicated once we're that close. 
That said, the wavelength at 606MHz is 0.5M, so greater than the resonant frequency of the human skull. You have to get up to microwaves before we start getting to resonant frequencies, but of course with the higher frequency comes a smaller reactive near-field boundary, so that calculator starts to work for us again. At 2.4GHz the reactive near-field boundary is at 2cm, so only just through the skull. Wavelength then is 13cm, so arguably close to a cranial resonant frequency depending on which direction you measure (and the size of the person's brain!). 

As I say, it's complicated and nuanced. My gut feeling with it all is that when I'm putting a transmitter straight on somebody's head I opt for channel 38 over my 2.4GHz kit, as the longer wavelength worries me less. If I had to use 2.4GHz then I would, and I don't believe there's an issue there, but if the decision is within my hands then it's one that I take. 
It is also worth pointing out that most of these actors are going to finish the show and then not think twice about calling their mum for an hour, holding a more powerful transmitter (2W at 900MHz) straight up to their ear. 

[Wolf124]

Cedd- Talking about 2W at 900mhz transmitters, what is the current situation (if any) regarding interference from mobile phones with UHF radio mics? I haven't noticed anything recently but everyone was threatened with having their phones nailed to the flats if I caught any live ones backstage during a performance. Not that that would have stopped them, but the threat sounded good!!!

[sunray]

21 minutes ago, Wolf124 said:

Cedd- Talking about 2W at 900mhz transmitters, what is the current situation (if any) regarding interference from mobile phones with UHF radio mics? I haven't noticed anything recently but everyone was threatened with having their phones nailed to the flats if I caught any live ones backstage during a performance. Not that that would have stopped them, but the threat sounded good!!!

Who is using 2W at 900MHz?

[cedd]

Pretty much every GSM mobile phone going, at peak power.

https://www.4g.co.uk/4g-frequencies-uk-need-know/

They'd only be transmitting at that power if they were a long way away from the base station. I've always been struck by the irony of people complaining about a base station nearby on health grounds, when its presence is likely to reduce the transmit power of the device you hold against your head. 

Wolf124, my honest answer is that I don't know. I've not had any issues yet, but then again I only use my channel 65/70 stuff on chorus/company  - saving my channel 38 stuff for principals. Your biggest issue is likely to be receiver desense rather than anything else - stick enough RF up your aerials that's close enough to make it through the front end filtering and the receiver AGC will kick in, pulling back your own wanted signals too. If it's a bother then you could always look in to some simple bandpass filtering to remove it - a simple quarter wave stub would be a cheap and dirty solution, but you need a spectrum analyser/tracking generator to properly prune it. Other than that, as you've suggested, the most important thing is to make sure that your radio mic is the biggest signal that hits your receiver. Mitigations like no phones in wings and careful antenna placement can all help to make sure that's the case. 

You asked way back in the thread about where to start measuring your antenna lengths from. 
With the trantecs, given the case is metal, I've always taken it to be part of the rf shielding, and therefore have started measuring from the point the antenna left the metal case. Within the beltpack you can almost consider it like being inside a coax. That's been my theory anyway. I've got to be honest though, I've had a pack successfully finish a show with zero antenna and still had a usable signal from them. 

[Wolf124]

Thanks Cedd. I too ended up with two packs without antennae and still got a signal. Never found them and no idea what happened to them. Of course there's the usual batch of bent, folded or just where the h*ll has that been, antennae!!?? I also as mentioned way back, I have got antennae whose length bears little resemblance to that indicated by the standard formula for the frequency the pack is tuned to, so while I have the time, thought that I would check each one and fit with something that I know should be correct. Hence all the (sometimes repeated within the thread) questions. It doesn't help that I have acquired so many models covering so many frequencies, many of which are no longer available so these have been returned but I think that I have now got it covered and have decent separation between the frequencies. Time will tell. Thanks.

Edited December 29, 2021 by Wolf124

[sunray]

11 hours ago, cedd said:

Pretty much every GSM mobile phone going, at peak power.

 

 

 

What happened to the 400mW  limit placed on portable digital phones?

[cedd]

8 hours ago, sunray said:

What happened to the 400mW  limit placed on portable digital phones?

Struggling to find a reference to that. Do you have a link? I've always understood GSM to be 2W. Just tried checking Ofcom's documentation but it's less than clear and I'm supposed to be wrangling 2 small children in a soft play area today, not trying to unpick Ofcom's paperwork. I did however find a few articles from other sources including the British Medical Journal that mention 2W. That article is quite old though, so possibly out of date. 

Edited December 30, 2021 by cedd

[Wolf124]

Whoops. Sorry to have caused problems. Anyway, CPC have delivered the bits for me to experiment with. Just normal copper Flexi cable for now, but made up nicely. Now to test it with a 'proper' aerial and then test it's durability to destruction!!!

[sunray]

14 hours ago, cedd said:

Struggling to find a reference to that. Do you have a link? I've always understood GSM to be 2W. Just tried checking Ofcom's documentation but it's less than clear and I'm supposed to be wrangling 2 small children in a soft play area today, not trying to unpick Ofcom's paperwork. I did however find a few articles from other sources including the British Medical Journal that mention 2W. That article is quite old though, so possibly out of date. 

Going back to analogue the limit for portables was 4W and when digital was introduced it was supposed to be 400mW, certainly the early digitals didn't have the same coverage, where I was working I had the old analogue and the 2 bosses had digitals, they spent more time using mine than theirs.

Having written that, since my last post I've done a quick G search and it seems 2W is the norm and 300mW seems to be a typical low power setting.

 

Personally I find phones interfere with bits of kit like mixers more than desense radio mics.