Radio Mic reception and channels

[pdherring]

All,

 

Hopefully I dont sound too silly asking these questions but this site seems to have the best advice around!

 

I have taken on the technical director role for my girlfriends dance/stage school, I have been having a massive nightmare with her radio microphones, they are not great devices but unfortunately neither me nor her have the money to replace these items.

 

She has 6 Gemini UF-2064 which if you are not aware are dual microphone diversity systems, so there is a total of 12 radio mics.

 

Firstly I have been having problems with channels, it is a 64 channel system and I have created a spreadsheet with the frequencies and have spread the channels out as best as I can with the most distance between each device but still I have problems with cross talk and hiss as the dancers/singers/actors move around. So my question is, is this the best way to set this system up, ie spreading the device frequencies out as much as possible!? if it is what can I do to help this situation.

 

Secondly the range of these devices is not great! They work perfectly when the theatre is empty but are terrible when we have an audience. For the last show I used a multicore and put the rack backstage, but I really REALLY dont want to do that again as I dont trust the users of the MICS at all and want to know when they have switched the mics off before they walk on stage. I am more that capable of opening the receivers up and removing the aerials etc but what would be the cheapest way of me extending the aerials either by running a couple of cables down to the stage front and adding a couple of aerials down there or putting some larger aerials at the back with the desk.

 

I know this is not an ideal solution but I really have very little money to spend as the group is run as a charity and therefore we rely heavily on donations.

 

Your advice and time on helping me make our next show a success would be very much appreciated.

 

Thanks

 

Pete

[pisquee]

If the mics are having problems with their radio signal reaching the recievers at the back of the hall, then having the receiver rack near the stage and running an audio multicore is the best solution. You should never trust the act with turning the transmitter packs on or off - you should battery them up and turn them on before the show, and if they have the facility to lock them so they can't be turned off with the power switch then this should be enabled, if not, the switch should be taped up so it can't be tampered with, or removed altogether.

 

Unfortunately, picking the frequencies for transmitting is more complicated than just spreading them out as much as possible, due to harmonics and other things (which I admit don't know much about.) This, I do know, has been asked about here before, so hopefully a search may help bring up the relevant topics. Is there a list provided by Gemini in the manual as to which freq combinations are known to work well together? If not, maybe have a look at websites for more reputable radio manufacturers and see if you can find lists for their gear and see if you can tune yours to those.

[pdherring]

Thanks so much for your prompt reply.

 

No there is not comparison of channels that work well together but harmonics explains why as hard as I try I can not get 12 good channels.

 

I have searched the web but cant find anything that seems to help me.

 

I agree that the users should not be allowed to 'play' but even threatening my girlfriend on them doesnt seem to help!! ** laughs out loud **

 

I may have to use the tape option as I have already looked at the removing the switch option.

 

Thanks

[Shez]

It's bad news on the frequency front I'm afraid. The frequencies they're programmed with aren't the standard shared UK frequencies so they only way you can legally use more than four channels at the same time is with a fixed site licence from JFMG. I suspect that even with one of those, you'll be lucky to get more than eight of them working together well.

 

The only frequencies you can use without a licence are between 863.1 and 864.9MHz. Within that range, you can usually get four channels working together. There's also a set of 14 frequencies available across the UK under a shared licence that live between 854.9 and 861.75MHz, but the number of those you can use together depends on the equipment itself - better kit will enable you to use more together.

 

When it comes to large numbers of radio mics, there just isn't a way of doing it cheaply.

[Russ83]

Sorry this isn't helping to answer your question but it is something you should be aware of.

 

The Gemini website has no useful information what-so-ever on your model, but as these wireless systems claim to be UHF then the frequencies you can use will depend on your licence. You can normally get 4 systems to work in the unlicensed band but if you are using more then you require a licence from JFMG/Ofcom.

 

Slightly off topic:- Gemini do have the manual for the UHF116 on their website and I find it interesting that none of their channels match up with the PMSE licence frequencies!! <_<

[pdherring]

Here is a copy of the manual if that helps anyone help me out any better <_< this isnt looking too good though!!!!

 

http://www.djstore.co.uk/manuals/gem/gemuf2064m.pdf

 

How can I work out the best channels to use out of the list in the manual!

 

Im wishing I hadnt asked now!! ** laughs out loud **

 

Thanks

 

Pete

[neilalexrose]

After a quick google for radio mic frequencies my first result was this document from Canford audio explaining a bit about radio=mic licenses and frequencies.

Ignoring the issue of licenses, which I won't go into right now, My reason for pointing you towards this document is that it will tell you the frequencies you need to tune your mics to on the 69 band and can purchase a licence for. As you have found out radiomics can be prone to inter-modulation if not tuned to the correctly spaced frequencies. On many radio mics these frequency's are pre-programmed and you just select a channel (1 - 16) on the pack. I assume from your description that you are manually tuning the frequencies. Best advice I can give to try and avoid intermodulation, is to tune your mics to these frequencies (854.900 855.275 855.900 856.175 856.575 857.625 857.950 858.200 858.650 860.400 860.900 861.200 861.550 861.7500) on the shared 69 band (this does assume you are using mics on the 69 band, and not unlicensed on another band)

 

Second issue of signal strength. Best thing to do is get hold of an appropriate ariel distribution amplifier, which will use external ariels which you can extend using co-axial cable of some sort, and place at discrete places on the stage - I'd usually put one downstage and one upstage. And yes the radio rack will probably have to be onstage. You may not like this, but as you have experienced, the further away the mics are from the receiver, the less chance of transmissions being picked up.

Also bear in mind that many things can affect RX signal. Everything from thick costumes to rather sweaty performers. There was a thread on here somewhere about one particularly large performer being a radio signal killer!

 

As has also been mentioned, no-body but you, or your designated sound assistant/radio-mic runner/no2 sound, should be turning radiomics on or off. Performers, chaperones, parents, untrained stage crew should never be given the responsibility of making sure mics are on and off. Mics are turned on at the Half when they are distributed, and turned off when they are collected at the end of the show. Lock the packs if they can be locked, tape up the on/off button if applicable. Do whatever it takes. Having toured as a no2 sound on a musical, I had to tell a few cast members off early in the tour, they were only trying to help. I would thank them and politely say that it's my job to make sure there mics are working. I only had to tell them once.

 

HTH

 

Neil

[Shez]

Gemini themselves are best placed to advise. Every manufacturer uses different design criteria which affects which frequencies will work together. If they've been sensible, each group of eight frequencies they list will work together. The last four frequencies in group eight may work together without needing a licence but for more than those four, you'll need to shell out.

[pdherring]

Neil,

 

Thanks ever so much for your reply!!!

 

I have attached a PDF above that contains the frequencies and I have only found 2 that match exactly with your list (although the others are only 0.050 - 0.075 out) so I assume that we will be ok to pick these frequencies instead.

 

As for the aerial distribution could this be a TV aerial distribution system and if so what kind of aerials would you use?? As I said cost is the main problem I have so I would love to know if it could be done with something this simple!

 

Thanks again

 

Pete

 

A concurrent post has been automatically merged from this point on.

 

Shez,

 

Thanks for your response!

 

I guess I will need to shell out on licensing but to be honest I want to just get it working before I shell out on licenses as if they are not fit for purpose then I will be left with no other option than to scrap the lot and have a big deep think!! Which will no doubt mean me shelling out!!! Why do we do this for the women we love!!! lmao

 

Thanks

 

Pete

[Shez]

if they are not fit for purpose then I will be left with no other option than to scrap the lot and have a big deep think!!

Some more food for thought - once we hit 2012, you won't be able to use more than four of them anyway as our lovely (ex?) government are selling off the bands that we've been using up until now so ch.69 (854 - 862MHz) will be occupied with mobile broadband or similar.

[neilalexrose]

I have only found 2 that match exactly with your list (although the others are only 0.050 - 0.075 out) so I assume that we will be ok to pick these frequencies instead.

 

As for the aerial distribution could this be a TV aerial distribution system and if so what kind of aerials would you use?? As I said cost is the main problem I have so I would love to know if it could be done with something this simple!

 

 

If only it were as simple as a commercial TV system. Unfortunately it isn't. The ariels themselves have to be tuned to the specific TV channel (channel 69 in this example), as does the receiver, and it ideally wants to be a diversity receiver using two ariels. (unless of course the gemini units you are using only have one aerial and not two on the receivers!). You may be better off hiring in the short term, especially as Shez points out, purchases may be a little wasted, with only a usable life of a year and a half!

 

 

Also worth a read is This document which goes back to basics of radio mic systems. Some googling of Radio mic Aerial Distribution amplifiers might be in order.

 

 

Neil

[Stan Hope-Streeter]

Oh dearie me....

 

There's nothing in the handbook to advise on any requirement for licencing. But it clearly states "complies with FCC Rules" and it's listed as the UK model - so hey, they must be OK to use.

And that's all the unsuspecting buyer ever needs to know ...

 

The people who sell this stuff, mainly to non-technical customers, really ought to be put up against a wall and shot.

 

-------------------

 

To the original poster:

 

Getting 12 mics to work together in the same band is technically quite tricky. This is due to what's known as "intermodulation" (not harmonics). You need to tune your radios to channels 1 - 8 in one of the "groups" on the France/UK List in the manual, which means you should get 8 that work together without interference. All you can do with the other 4 is pick frequencies in the gaps between them and hope for the best (don't use those 4 unless you have to).

 

Strictly speaking (as has been noted) you should be buying licences to use these radios. Fortunately the laws on this aren't generally enforced. But in a couple of years' time the officially sanctioned wavebands will be changed and most exsiting radio mics will be illegal anyway. At some point they will become unusable as the frequencies get taken over by other services.

 

So unfortunately, you're really on your own with this. Radio mics have become cheaply available in recent years, but really they are specialized items which require some expert knowledge to make the best use of, especially if you hope to have more than a few working together. The people who sell them, of course, don't want you to know this.

 

Sorry ...

[paulears]

Intermodulation is fairly complex to understand, but the one thing that rarely works (and then, it's just luck) is to spread them evenly. Intermod is troublesome because the actual electronics impact on it, as does the design specification. The actual amount of bandwidth each model of radio mic transmitter uses is different - so even if a Sennheiser on a spot frequency is replaced with a different make/model on the same frequency, there's no guarantee all will be well. The list of frequencies given by Neil won't necessarily work. Lots of very odd things happen when transmitters work together in the same space. If you want to get really confused - then this wiki entry is quite handy!

 

If a radio mic system causes problems, then before you do anything, get the receivers as close to the transmitters as you can. On a few occasions, I've had a receiver rack at the mix position from a previous show, and had another stage side that I'm actually using and it's very clear from the displays that solid channels from the stage side receivers would have been a serious problem if the receivers near me had been the ones in use! Sure - you can remote the antennas, but low loss coax suitable for the higher TV channels is really thick, really stiff and very difficult to manage - and even then, a 40m length is a pretty good attenuator. A few metres to get the aerials up high is fine, but long lengths are a real pain!

 

The other snag is that many of the budget systems simply were not designed to be used in multiples - they work fine as they are, but just don't have a good enough design to perform well in multi-channel systems.

[Bobbsy]

I'm afraid that Shez and Stan Hope-Streeter have just about summed it up. Your girlfriend has been "sold a pup" by Gemini and you have 12 mics that: A) need a relatively expensive license because they're not on the UK shared frequencies, B) will be difficult to use all together and C) won't be legal in the UK after 2012 anyway.

 

In terms of frequencies, unless Gemini can provide a lot more detail you're going to have to rely on trial and error. There are software programmes that can calculate frequency plans but you'll need to know things like FM deviation and bandwidth to use these effectively. Just for fun, why not try to contact Gemini and see if they have a UK frequency plan? If nothing else, we can all have a good laugh when you report back in here! Otherwise (assuming you're going to get a proper license) it might be worth calling JFMG. They've been helpful to me in the past by providing intermod free frequency plans for brands of gear they've encountered before and you might not be the only one in the UK stuck with this gear.

 

In terms of antenna distribution, it actually IS possible to use some TV stuff as long as you don't go for the cheapest. You'll need to get an antenna (or two for diversity) in the right band and splitters without too much loss at the top of the TV band. The other option (as already mentioned) is to move your receivers down near the stage and use a multicore to feed back to the mix position. You'll have to decide which works best for you.

 

Bob

[pdherring]

Guys,

 

I really want to thank you for all your help!

 

I guess I just need to keep trying different freq until I find some that work well together, I will certainly try to set the first eight packs to a bank of channels first and hope for the best then try to find another 4 channels that dont interfere with the first 8.

 

As for the question of aerials I have done some searching on here and found some people that have used TV style boosters (with the appropriate freq range) and sky coax running down to a pair of aerials. Obviously I would need two 6 channel boosters as each receiver has two diversity aerials.

 

My question is what would you guys use for aerials?? I certainly dont like the idea of TV stlye aerials as I have seen in other posts as the different halls or theatres we work in would make my life hell trying to hide these aerials.

 

I really do appreciate your time with a budget radio mic novice. Oh how I wish she had spent more money initially!

 

Thanks

 

Pete