Bad RF Environment

[André Boisvert]

Always keep in mind that your low power wireless mics are competing with other much higher power transmitters.

Besides the obvious 100 kW UHF TV transmitters there are now high power transmitters in the 700 MHz band.

So what works on the ground and in a shielded enviornment will not work the same way once you are high up in the air.

I don't know Seattle and can't exactly explain what you got but completely understand why you had problems up high.

In many areas Block 470 is NOT available for wireless microphones because channels are assigned to Land Mobile, including Public Safety. Since those transmitters are not always on you may find intermittent interference in that block. Also, should the local law enforcement track you down you won't like what they could do to you! (A/k/a "The grey bar hotel")

It is very convenient to run wireless but you are juggling very sharp knives!

I am very well known in the broadcast world with my statement "Bring lots of mic cable".

Bill Ruck

Wow, Bill. Several valuable posts on RF in one day. Many thanks.

[Marc Wielage]

In many areas Block 470 is NOT available for wireless microphones because channels are assigned to Land Mobile, including Public Safety.

That's also the case for part of Block 19. In LA, we lose a small piece of Block 19 to Police, and another piece to a local TV channel. But there's about 150 other channels available, and I've never had problems getting as many as 8 or 9 open frequencies without any problem. Sometimes, it does take a little work. On a couple of occasions, I suddenly started getting a spike after a certain time of day, requiring me to slide a few channels over. Not a big deal.

I agree, FreqFinder does add a lot of "peace of mind" in terms of intermod. With the local TV database added, it'll be even better, though realistically, nothing works better than a real sweep at the beginning of the day, especially on a location change. The difference here in LA between downtown, Hollywood, Burbank, and Culver City can be considerable, on block 19 and 21. 22 is a freeway mess from what I've seen recently, and I've stayed away from it in the last couple of years.

[Bill Ruck]

Regarding what is known as "T-Band".

There is this whole volume of Rules and Regulations that govern how all radio frequencies must be used. Although low power wireless microphone users have ignored The Rules they still apply. Officially they are Federal law Title 47.

For the official listing of "T-Band" frequencies and the cities where they exist, see

http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=ec44d364f141568a2895553fa7122006&rgn=div8&view=text&node=47:5.0.1.1.3.11.111.2&idno=47

That should lead you to Part 90.303.

A scan of those channels can be misleading because two-way systems are not always transmitting.

Also, the use of UHF TV channels for wireless microphones is regulated in another part of The Rules.

See Part 74 Subpart H Low Power Auxiliary Stations

http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=d2e545fb8fdaca66f65a0c41915e9b09&rgn=div5&view=text&node=47:4.0.1.1.3&idno=47#47:4.0.1.1.3.8

Note that I don't make The Rules; I have a hard enough time trying to understand The Rules; but no matter what they are THE RULES.

Bill Ruck

[Philip Perkins]

Tall buildings seem to invoke what I think of as "aircraft carrier" recording techniques. IE, expect there to be really massive RF present, and think in terms of the shortest cables and most RF resistant equipment you can use, and make sure your cable shields are very together. Sounds like a good day for a 416 on a short wire, balance line level to camera or better--no cam feed (cam mic for ref) and the mic directly to a recorder--as simple a path as possible.

phil p