One of the guys from a Shure has given a great presentation a number of times on intermod. He has a spectrum analyzer and proceeds to move a couple of belt packs closer together, then with three. Looking at the spectrum analyzer you can see the intermod products. He shows that if you pick channels at random, you may get problems. Also, if you use the tools provided by the manufacturer (wireless workbench in this case), you will get channels that are not going to put intermod products on top of other active frequencies. Sent from my iPad using Tapatalk HD
Just wondering about these .....I have 2 of the Sennheiser EW300 units each with 2 body backs which I run in mono. I have them next to each other in a rack with the antennas to the front and I have had zero problems and love them. I have the chance to purchase one more with one pack used but new condition and was wondering whether if I decide to add one more system if I need to think about getting one of those antenna combiner / distributer thingies. Is it really necessary at this point and in fact why would it be necessary at all? ... Benefits etc....
Deb.. this thread got real technical, real quick. FWIW - We have 4 PSM units and a Carvin EM900 in the rack with no intermod (so far) - all with front mount antennas, located on stage as band does not have FOH person.We did look at the extra expense of antenna combination options, talked to a few folks who [basically] concluded that over the range in question, being stage located, not being mixed/xmitted from FOH, that we should need the extra equipment expense. So far that has been proven to be correct.YMMV.
Thanks Steve…ironically I just posted my comment as yours was posting too. I did get rather overwhelmed with the info being provided but I respect everyones knowledge and experience here so I never want to sound unappreciative.Good to know you are not having issues going this route...
Ok, I did some calculations and the intermod performance of a properly combined single antenna IS better than separate antennas, given the way sound people are likely to deploy those antennas. Ie, close together and without crossed polarisation.Rough calculations here on intermod product strength from two 30mW signals for B-band gear I have here seem to be about 1uW with the ZAPD-21 as a passive combiner. Separate antennas yield worse performance until you get about 5m antenna separation. A BNC-T is simply dreadful, maybe 100x worse than the passive combiner.A circulator will be better than the ZAPD-21, but not hugely better. Maybe 6-10dB?How much do we care about a millionth of a watt interference as long as it is out-of-band relative to our gear?(But I stand corrected. :-) )
Last I checked, 6-10dB is a big deal.
(RF-wise, this issue is about as big a deal as two people with mobile phones sitting next to each other on a bus....)
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