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Scott Dorsey Scott Dorsey is offline
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Default Wireless Microphone Systems

mcp6453 wrote:
For the second time, the FCC has eliminated the band used by my
Sennheiser EW series wireless mic. Supposedly there is a sliver of a
band that will allow it to continue working legally, but I haven't
confirmed that. My question is, if I decide to replace it, which band
should I consider? A 516-558, A1 470-516, or G 566-608? I'm inclined
toward none of the above. Other manufacturers have units that work in
other ranges in the US, but who knows when the FCC will sell that part
of the spectrum to the highest bidder?


So, what we can determine from previous actions:

1. Cellphone companies have an unlimited need for spectrum. Even as they
make individual cells smaller and smaller, the demands for aggregate
bandwidth are expanding constantly. No amount of capacity is enough
for them.

2. Cellphone users have very deep pockets. They are not unlimited the
way their demand is, but they are much deeper than those of other
spectrum users.

3. The current philosophy of the FCC is to sell spectrum space to the
highest bidder. People who do not pay for spectrum such as ISM band
users are treated without respect, and in fact many users of licensed
services have been forced to move into ISM bands as a consequence of
FCC neglect of non-cellphone services.

From these things, we can assume that all the spectrum is going away
sooner or later, all to be absorbed by cellphone services, and that we
can expect the decease of broadcast television and a future era where
people watch IPTV on their phones.

This being the case, the only future I see is with systems that are able
to co-exist with other services on shared noisy spectrum of poor quality.

There are some ISM band systems, and we used an inexpensive one at Worldcon
this year and it worked better than I expected. Of course, with these
systems, they work until they don't work and when they stop working you
have no recourse since you're using spectrum that was initially intended
as a dumping ground for waste emissions. But even Lectrosonics is now
selling a 900 MHz ISM band wireless kit. This is how desperate the situation
is getting.

I think the real future is going to lie with something like the Alteros
system, which uses spread-spectrum over a huge swath of 6GHz. Attenuation
in air is very high which reduces interference but also reduces range.
Directionality is very high (the human body is big enough to be a huge
baffle behind your antenna) so you need a bunch of receivers. The system
is not cheap, but it -is- reliable, mostly immune from interference since
walls and doors block the signal pretty effectively, and allows shared
frequencies between two adjacent auditoria. It will get cheaper.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."