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5 Mics In Channel 70


tom_the_LD

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Hi all,

 

I've just put in a semi-new radio mic system my church has bought. They've just bought 3 of the Sennheiser G3 ew112 sets to be used in conjunction with a Sennheiser ew100 G2 handheld and an original Sennheiser ew100 handheld - they want to use these in Channel 70, as that way you don't have to pay for a license!

 

Now, the Interweb seems to say that for any more than 4 radio mics you're going to need to get into either Channel 69 or Channel 38. However, I've used the online Audio Technica frequency calculator (http://ff.audiotechnica.com/cgi-bin/freqcompat.cgi) to check for intermodulation and it says these 5 frequencies are fine to use:

 

863.100

863.500

864.100

864.400

864.900

 

or even

 

863.100

863.600

863.900

864.500

864.900

 

Can anybody see why either of these sets wouldn't work?

 

I had originally tuned the G1 and G2 right up to 865.500 and 868.500, but then read that these freqencies are "reserved for other radio services and not to be used for radio microphones".

 

Apologies if I'm missing something obvious - I'm a lampy normally!

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Firstly, you can't mix different manufacturer's frequency plans - their kit is unique to them so their frequencies won't necessarily work with other manufacturer's equipment.

 

I have a distinct recollection that you could manage more than four channels in the deregulated (863.1 - 864.9MHz) band with G3 systems, but as you're using a mixture of G2 and G3, I think you'll be out of luck I'm afraid.

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It might work...

 

However, Sennheiser suggested only 4 simultaneous frequencies in the derestricted part of channel 70 for G1 and G2. The selectivity of those older radio systems wasn't as good.

Also, while intermod software can be useful, it helps to use the manufacturer's own version. You can use Senneheiser's Wireless System Manager with the G3s, and their Intermodulation and Frequency Management Software, but I'm not sure if it covers channel 70...

 

Have you tried these mics out yet?

 

Simon

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Hi Simon,

 

Thanks for the response.

 

I've got their IFMS software (SIFM) but it doesn't include the G3's - and I couldn't seem to find any other version of the software on the website! So thanks for that I shall look at it now.

 

Yes I've tried them out - but only on the tuning I later found out I couldn't use! I didn't realise at the time the top end was restricted - whatever it's restricted for!

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The snag is simply that the 5 frequencies that seem to fit are the centre frequencies, the actual band edges are 863 - 865 MHz. If you look at the 5 channels, they are spaced 400-500KHz apart, because each microphone 'spreads'.If you divide the bandwidth each one uses, you will find they extend over the band edges, so squeezing 5 channels in takes you out of the band. In fact, the actual bandwidth is less than 25KHz below the centre frequency, but artifacts do exist above and below - hence the usual greater spacing than the numbers indicate.

 

So it's quite likely you will get away with it. However - after the amount of money you just spent, is the license really a stumbling block? Surely getting away from the local DJ, disco and bingo can only be sensible?

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As you have bought the Kit, there is not a lot you can do, using Ch69 is out (or will be very shortly) and as you have found, 5 mics into Ch70 won't go.

I would see if you can return the new kit to your supplier and get a different freq range in it's place.

Ch70 will become very crowded shortly as all the people with unlicensed Ch69 kit find they can't use it and retune to Ch70.

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My memory was working for once. Over on the Sound on Sound forum, John Willett (the font of knowledge for all things Sennheiser) has said that you can get 6 intermod free frequencies working licence free in Ch.69 with G3 systems. He said that they're listed on Sennheiser UK's website but despite mooching around there I've yet to find them. I'm sure an email or call to Sennheiser would produce the goods.

 

I know that's not all that much help for your mixture of G1, G2 and G3, but for future reference, the possibility is there.

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I know that's not all that much help for your mixture of G1, G2 and G3, but for future reference, the possibility is there.

 

Sennheiser claim that 6 G3s will work on currently on channel 70. I think they expect you to connect them to Wireless Spectrum Manager (the software that replaced SIFM) and let it auto allocate the frequencies.

 

However a quick google comes up with

 

http://www.soundhire.co.uk/help-and-support/48-wireless-information/152-sennheiser-g3-ch-70-frequencies

 

From a random hire company's website.

 

What to do depends where you are. If you are in a place where interference from other channel 70 users is unlikely to be a problem then selling the G1 and G2 and buying 3 more G3 is probably the correct solution. Otherwise I'm afraid you'll either have to accept that you can't run more than 4 mics at once or sell everything and buy licensed channel 38 kit.

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I don't know about G3 but the peak deviation on G2 is +/-48kHz so 864.975 would go at least 23kHz out of the legal band on any peaks--and that's assuming "perfect" filtering.

 

A tiny bit of RF theory for those not familiar with it: FM transmitters (and pretty well all radio mics are FM) don't just sit on the specified centre frequency. What's actually transmitted is a range of frequencies varying with the level of the audio signal--the higher the level, the wider the variation. On Sennheiser G2 equipment, a peak audio signal will send the radio frequency 48kHz above the centre frequency and 48kHz below the nominal frequency. The legal top end of the licence free frequencies is 865MHz...and a peak audio signal when the selected TX frequency is set to 864.975MHz would go to 865.023MHz--assuming everything is perfect. The reality is that no electronic filter is perfect so the problem is probably a bit bigger than that.

 

Besides legality, this is also an issue for receivers. Although 863.1 and 863.5 look 400kHz apart--but each of those go +/-48kHz, so the end result is that, when both transmitters peak at the same time, the "guard band" is down to about 300kHz. This might be fine on receivers with good filters or might cause problems on cheaper ones. And all this is before we get into IM problems...but that would be a different lesson!

 

Bob

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If the issue is staying licence free, would you not be best sticking to 4 Ch 70 mics, then 1 of either 2.4GHz or VHF kit? I know there's a couple of other threads going on about the Line 6 offerings in theatre settings, but I've used the XD-V30 lav version in church setting alongside Senn G2's, and they compare very favourably in terms of sound quality and reception (which was the reason I tried them - neither VHF or UHF reception was reliable, 2.4GHz was rock solid). Think what others have said about returning the Senn's and finding an alternative might be the way ahead.

 

Alan

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However a quick google comes up with

 

http://www.soundhire.co.uk/help-and-support/48-wireless-information/152-sennheiser-g3-ch-70-frequencies

 

From a random hire company's website.

 

There's your answer. Using the information from that website set up the G3's to 863.100, 863.400 and 863.750.

 

Set the G2 to Bank 8 channel 3 (864.300) and set the other Sennheiser to Bank 8 channel 4 (864.900).

 

Give it a go, there's a good chance that it will work.

 

David

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Give it a go, there's a good chance that it will work.

 

Again, it might work, but having had problems getting four G1 or G2 systems to play nicely in the ISM band, I would be pleasantly suprised to see this mixture cohabiting without some squabbles. Sennheiser only make the 6 unit claim for G3.

 

Overall, though, relying on a channel 70 solution is somewhat problematic...

 

Simon

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Thanks for all the responses guys. I'll go back in and have a play with some frequencies and see if I can get a solution. Other than that, they've said to put one of the G3's on the same frequency as the G1 handheld, as the two won't be used together - or not in a situation when a workaround isn't possible.

 

For those that are just saying "return the sennheiser kit" what would be the good in that? The G3's are designed to work in either Channel 38, Channel 70 and I think Channel 69 too. So saying to return it is daft!

 

There's no point sticking to VHF kit as it doesn't work well at all in the church in question - which is why they've gone for high quality UHF this time.

 

The church is in a fairly remote situation not close to any other buildings which will be using radio mics so I don't think interference will be a problem.

 

I'll try some of the frequencies suggested and see if I get anywhere I've also written down:

 

863.100, 863.400, 863.700 (that's the piece of paper I have for the 6 frequencies) for the G3's

864.200 and 864.200 for the G1 and the G2 (both using G1 receivers though)

 

Thanks for all the help, and to Bobbsy too for the very informative post.

 

I shall keep you updated on what happens!

 

Thanks once again for all the help guys. Really is appreciated.

 

Another quick ones whilst I remember - I assume the best way to check for intermod and dropouts is to have them all transmitting, and go through the desk channels one by one (muting and unmuting) and check there's no nasty suprises in there?

 

Unfortunately I can't seem to get the sennheiser software to play ball propely. It only has the 300's and 500's in there, not the 100's from the G3 series and complains that they're not connected!

 

 

Thanks again,

 

 

Tom

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Another quick ones whilst I remember - I assume the best way to check for intermod and dropouts is to have them all transmitting, and go through the desk channels one by one (muting and unmuting) and check there's no nasty suprises in there?

That's a start. You will need people walking around the stage with all the TXs open, and any other electronic kit on. The cast will absorb the signal, the kit may interfere.

 

You wouldn't believe how long it took to find that the thing causing dropouts here was the colour oscillator crystal in a BBC Micro!

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