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Author Topic: Digital Wireless IMD (Sennheiser 6000 vs. Axient Digital)  (Read 951 times)

Dan Currie

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Re: Digital Wireless IMD (Sennheiser 6000 vs. Axient Digital)
« Reply #10 on: May 08, 2018, 09:11:46 am »

That is correct, Sennheiser 6000 series is 'intermodulation free' because of extremely linear rf amps and the use of rf isolators in all transmitters.
I'm not absolutely sure whether the Shure Axient Digital is also using isolators, but I don't think they have them...

The quick test I did was a worst case scenario with the packs as close together as they could get.  The next question would be does it affect rf performance.  In the case of the AD the answer is no.  If someone around the Detroit area has a 6000 series available I would be more than happy to do a direct A/B comparison.     
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Diogo Nunes Pereira

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Re: Digital Wireless IMD (Sennheiser 6000 vs. Axient Digital)
« Reply #11 on: May 09, 2018, 04:32:05 pm »

Not moving, Rather spread out, akin to a fully deviated FM signal. Presuming highly linear gain stages, if there is any mixing of of signals, it will result in an overall rise in the noise floor, not defined carriers experienced with typical FM systems.

That was my understanding also, and what I would expect: a raise in the noise floor... but upon measurement, and as the scans/screenshots show, you can see defined carriers caused from the digital transmitters in close proximity.

At 20mW (true, in a low ceiling, very bunker-like stretch of a warehouse) it does seem to me the power of the IMD products can't be disregarded, and the equipment profile in WWB6 for Axient Digital (ULXD and QLXD also) does disregard IMD, at least in the "more frequencies" scheme. Having 4 Tx as close as I did aren't common practice fortunately.

That is correct, Sennheiser 6000 series is 'intermodulation free' because of extremely linear rf amps and the use of rf isolators in all transmitters.
I'm not absolutely sure whether the Shure Axient Digital is also using isolators, but I don't think they have them...

This makes sense... circulators probabilly are key to their design.

The quick test I did was a worst case scenario with the packs as close together as they could get.  The next question would be does it affect rf performance.  In the case of the AD the answer is no.  If someone around the Detroit area has a 6000 series available I would be more than happy to do a direct A/B comparison.     

During my tests, while producing intermod at a given frequency and then firing the transmitter allocatted to that same frequency didn't seem to impact the audio/link-quality. Receiver still reported 5 stars quality and sounded good. Range would still be an issue of course... I get the part where physics are still physics ;)
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Diogo Nunes Pereira
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Jason Glass

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Re: Digital Wireless IMD (Sennheiser 6000 vs. Axient Digital)
« Reply #12 on: May 10, 2018, 05:44:50 pm »

I was speaking to a Sennheiser rep last week at a trade show here in the UK and he too mentioned about 6000 being intermod-free. He said that they were using isolators on the RF output to ensure nothing got ďback up emí ď (Dadís army quote for anybody this side of the Atlantic).
I was actually looking at the G4 EW100ís in the 1.8GHz frequencies and he said these had the same isolators as the 6000 because there was space on board due to the higher frequencies and therefore smaller component sizes.
Iím seriously considering buying some of these G4 systems to move me away from 2.4GHz (which Iím currently using with Line6, so the prospect of simply spacing my channels by 600KHz is quite appealing.
Isolators such as these are precisely why Lectrosonics products from the last decade or so can operate at 100 mW in close proximity and not kludge the noise floor. It's also why their freq blocks have such narrow tuning bandwidth. It's extremely difficult to engineer isolators with wide bandwidth and small size at UHF freqs.

Sent from my Nexus 5 using Tapatalk
« Last Edit: May 11, 2018, 10:46:02 am by Jason Glass »
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Lyle Williams

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Re: Digital Wireless IMD (Sennheiser 6000 vs. Axient Digital)
« Reply #13 on: May 11, 2018, 07:44:12 am »

Not moving, Rather spread out, akin to a fully deviated FM signal. Presuming highly linear gain stages, if there is any mixing of of signals, it will result in an overall rise in the noise floor, not defined carriers experienced with typical FM systems.

I remember struggling to find the right word to cover both DSSS and other schemes.  Moving wasn't quite the word I was after, but I worried about wording my answer in a way that was only meaningful to someone who already "got it".
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