UHF Band 70 Mic's - interference???

[DJ Jules]

I came across something odd on Friday night which I've played around with a bit today and can't find a reasonable answer for...

I have a Sennheiser Freeport wireless microphone set and I've recently bought a LD Systems Eco 2 Headset mic to use for kids parties. I tested the LD at home prior to taking it out with me on Fri and it worked flawlessly, but when I started using it on Friday night with the headset on and with the Sennheiser handheld Mic turned on as well (sometimes with me using it to talk to people on stage and at other times with one of the organisers using it for speeches) the LD kept cutting out.

At the time I put it down to the LD being faulty as it was new, but I had a play with this today and it's very odd...

The LD headset is hard programmed to Channel 4 (864.900Mhz according to the manual (http://www.ld-systems.com/202-1-ldwseco2bph.html?file=bGRlY29fZW5fZGVfZnJfZXNfcGxf aXRfMS5wZGY=)) and the Sennheiser set to channel 2 (863.700Mhz according to the manual (http://www.sennheiser.co.uk/sennheiser/products.nsf/resources/47B9BDF85EF1EFA1C12574330042CB30/$File/freeport_514013_0808_US.pdf)) so in theory the two shouldn't have interfered. Playing around at home though I've found that the Senny will make the LD cut out regardless of which channel it's set to (1 to 4 - 863.1, 863.7, 864.10 and 864.9Mhz respectively) when it's in either within about a metre of the transmitter or receiver or if it's in the line of sight between the transmitter and receiver. Previously with other band 70 devices I've found that the transmitters and receivers are more or less interchangable as they all seem to operate in a similar manner, but if I try and use the Senny Mic on the LD base station the base station will actually pick up on the Mic's transmissions regardless of which channel the Mic is set to - but only intermittently - it'll keep cutting in and out!

I'm not really expecting the Senny Mic to work reliably on the LD base station and vice versa, but I would expect to be able to use the Senny and LD mic's in the same area without interference from each other (as in theory it should be possible to operate up to 4 transmitter/receiver sets of either brand in the same area), but the Senny is utterly wiping out the transmissions from the LD.

Does anyone know the science behind what is going on here?? Bonus points if you know how to stop it happening too!?!

Thanks,

Julian

[Excalibur]

Does anyone know the science behind what is going on here??

No. But I have a sneaking suspicion. Bit of bedtime reading. (http://svconline.com/proav/audiovisual-equipment_10-wireless-microphone-problems/) Just because frequencies are separated by a seemingly large amount of Hertz, doesn't necessarily guarantee compatability.



Bonus points if you know how to stop it happening too!?!

Thanks,

Julian

Excalibur, nil points. :o

There may be some more pointers here (http://stakeholders.ofcom.org.uk/binaries/research/technology-research/sewm/finalreport.pdf), but be warned, it's 81 pages long. By page 7 I thought I'd read a couple of things which led me to believe that it may be an explanation for the problems described.

I'm not the person to give an explanation of why this problem opccurs, but I intend to Google it a bit more.

[super-hero]

I had a similar problem with LD and Sennheiser kit. Changed the frequencies and all was fine. But if that's not working for you, try to move the units further apart physically.

[CRAZY K]

No. But I have a sneaking suspicion. Bit of bedtime reading. (http://svconline.com/proav/audiovisual-equipment_10-wireless-microphone-problems/) Just because frequencies are separated by a seemingly large amount of Hertz, doesn't necessarily guarantee compatability.




Excalibur, nil points. :o

There may be some more pointers here (http://stakeholders.ofcom.org.uk/binaries/research/technology-research/sewm/finalreport.pdf), but be warned, it's 81 pages long. By page 7 I thought I'd read a couple of things which led me to believe that it may be an explanation for the problems described.

I'm not the person to give an explanation of why this problem opccurs, but I intend to Google it a bit more.

Sitting here waiting for a taxi to go on holiday I had a look through some of the technical notes:rolleyes:

I have a particular interest in this subject as I got ambushed down in Portsmouth in September--returning to a venue I played a year ago with the same Radio Mike ---my favoured JTS---and finding it kept cutting out for no reason despite being perfect the year before.:daft:

At home and subsequent gigs absolutely no problems.

As Peter says it could well be similar frequencies and is clearly some kind of incompatibility between the two systems, clearly not the venue if its a problem at home.

My issue may well be related to something different--possibly nearby Marine Craft/Royal Navy signals.

I would try and see if Sennheiser have a technical back up service--I would imagine their people would be able to help--I have an excellent LD mixer although I didnt know they were making radio mikes--again maybe try to pick their brains as well--seems that this is a very complex area---after I got to page 27 :D

[paulg]

You might not like the answer but that be intermodulation and it's a swine to sort out. Here is a good starting point (The wonderful Blue Room Forum~) http://www.blue-room.org.uk/index.php?showtopic=17557

You'll find that frequencies overlap (hence the gap between channel frequencies) and units also spill out signals to either side of their set frequency - some more than others. They also intermodulate with one another and this is the really complex bit. Manufacturers select components that don't intermodulate between their own particular product but that's as a far as it goes. Combining different types of radio systems is often a hassle and the intermod results can be very random. Been there, done it, chucked the lot and used single brand mics! I even had a faulty twin radio set that intermodulated with itself!!

Somewhere I have a calculator to work all this out but I can't find it right now and it tends to be manufacturer specific. There's a link to something similar at the bottom of the page. Anyway, you will find that cheaper systems (and fake ones) tend to spill out signals all over the place and hence tend to interfere more with one another. The cure is to stick to the same manufacturer and use the same, compatible receivers. From bitter experience, there are a few things you can do to reduce problems:


Reposition the receivers (further apart I'm afraid)
Tweek and experiment with the position of the receiver aerials
Check the cables connecting the receivers to the mixer (replace if they are made from low quality cable)
Don't let any connecting wires from either unit cross over each other or cross over the receivers or get close to aerials
Don't cover the receivers / aerials e.g. by putting them under a mixing desk where signals will bounce around
Move them away from other electromagnetic fields generated by power packs etc.


http://sennheiser.co.uk/uk/home_en.nsf/root/professional_wireless-microphone-systems_sifm-software

I really hope this helps!

[TONYTIGER]

You might not like the answer but that be intermodulation and it's a swine to sort out. Here is a good starting point (The wonderful Blue Room Forum~) http://www.blue-room.org.uk/index.php?showtopic=17557

You'll find that frequencies overlap (hence the gap between channel frequencies) and units also spill out signals to either side of their set frequency - some more than others. They also intermodulate with one another and this is the really complex bit. Manufacturers select components that don't intermodulate between their own particular product but that's as a far as it goes. Combining different types of radio systems is often a hassle and the intermod results can be very random. Been there, done it, chucked the lot and used single brand mics! I even had a faulty twin radio set that intermodulated with itself!!

Somewhere I have a calculator to work all this out but I can't find it right now and it tends to be manufacturer specific. There's a link to something similar at the bottom of the page. Anyway, you will find that cheaper systems (and fake ones) tend to spill out signals all over the place and hence tend to interfere more with one another. The cure is to stick to the same manufacturer and use the same, compatible receivers. From bitter experience, there are a few things you can do to reduce problems:


Reposition the receivers (further apart I'm afraid)
Tweek and experiment with the position of the receiver aerials
Check the cables connecting the receivers to the mixer (replace if they are made from low quality cable)
Don't let any connecting wires from either unit cross over each other or cross over the receivers or get close to aerials
Don't cover the receivers / aerials e.g. by putting them under a mixing desk where signals will bounce around
Move them away from other electromagnetic fields generated by power packs etc.


http://sennheiser.co.uk/uk/home_en.nsf/root/professional_wireless-microphone-systems_sifm-software

I really hope this helps!

Brilliant synopsis hit the nail on the head well done that man,i quite often use multi radio mics all sennheiser same model 2 hand held one head set never had a problem,add a freeport no go.

[DJ Jules]

Thanks, I had a suspicion it was going to be something like this, but it's really interesting to read about the exact science behind it.

It doesn't really help solve the problem though... ;) I've come across no end of other Mic's and receiver units which look exactly like the Senny Freeport so I've always suspected that Sennheiser have bought in a relatively cheap wireless transmitter/receiver set, stuck their own insert into the Mic and badged it as their own. This probably confirms it - and confirms that the LD set isn't much better. As usual you get what you pay for....

So, my options in terms of resolving this (given that I usually have little or no ability to control the positioning of the receivers and/or transmitters and I'm doing pretty much everything that is going to cause problems (and the Senny/LD transmitters interfere with each other even in ideal conditions), my options are:

1. Buy a second Senny Freeport unit (which would mean going to Thomann as they're discontinued and no-one else seems to have any stock?)
2. Buy a second LD unit and ditch the Senny (which would be a massive shame as I love the sound from the Sennheiser mic, the LD - not so much).
3. Buy another single unit which operates in a different frequency band (2.4Ghz digital or licensed frequencies)
4. Buy a twin (or quad) channel set designed to operate together

Recommendations???

AKG do a 4 channel digital receiver with a handheld Mic and a Belt pack (and you can then add further Mic's/packs as required) under the DMS70 range. Has anyone used these?

There's also the Line6 Digital range

Or I know the cheaper Shure PG14 range work well together (and I can stretch to a pair of these with a SM58 and PG30 Mic/transmitter?)

What's my best approach?

Julian


Brilliant synopsis hit the nail on the head well done that man,

:agree:


I quite often use multi radio mics all sennheiser same model 2 hand held one head set never had a problem,add a freeport no go.

Let me guess though, all from the XSW or EW range (e.g. £300+ per set?)

Julian

[TONYTIGER]

Thanks, I had a suspicion it was going to be something like this, but it's really interesting to read about the exact science behind it.

It doesn't really help solve the problem though... ;) I've come across no end of other Mic's and receiver units which look exactly like the Senny Freeport so I've always suspected that Sennheiser have bought in a relatively cheap wireless transmitter/receiver set, stuck their own insert into the Mic and badged it as their own. This probably confirms it - and confirms that the LD set isn't much better. As usual you get what you pay for....

So, my options in terms of resolving this (given that I usually have little or no ability to control the positioning of the receivers and/or transmitters and I'm doing pretty much everything that is going to cause problems (and the Senny/LD transmitters interfere with each other even in ideal conditions), my options are:

1. Buy a second Senny Freeport unit (which would mean going to Thomann as they're discontinued and no-one else seems to have any stock?)
2. Buy a second LD unit and ditch the Senny (which would be a massive shame as I love the sound from the Sennheiser mic, the LD - not so much).
3. Buy another single unit which operates in a different frequency band (2.4Ghz digital or licensed frequencies)
4. Buy a twin (or quad) channel set designed to operate together

Recommendations???

AKG do a 4 channel digital receiver with a handheld Mic and a Belt pack (and you can then add further Mic's/packs as required) under the DMS70 range. Has anyone used these?

There's also the Line6 Digital range

Or I know the cheaper Shure PG14 range work well together (and I can stretch to a pair of these with a SM58 and PG30 Mic/transmitter?)

What's my best approach?

Julian



:agree:



Let me guess though, all from the XSW or EW range (e.g. £300+ per set?)

Julian

The Free Port model is really a Trantec they took it back so plenty available,just cheaper the line 6 range are very good Absolute music in Poole offer this range on line,and yes i use the EW range.

[DJ Jules]

The Free Port model is really a Trantec they took it back so plenty available,just cheaper the line 6 range are very good Absolute music in Poole offer this range on line,and yes i use the EW range.

Now you've said that I remember seeing it the other day and thinking "duh".

Problem solved... Bought a pair of AKG's, one handset, one headset since PMT did me a good deal (they beat Thomann on price so it can't be bad!)

Watch out for a brand new LD headset in the for sale section... ;)

Julian

[paulg]

You're right, the old EW range - bulletproof