I've been using Sony wireless for a couple of years now....never thought to check freq's before now. Was looking to get new units in view of the changing laws concerning the old freq's and after checking available bandwidth find that DC only has open 500-506. So have I been lucky in not having had any interference with my old units seeing as how everything is taken??? What do I do regarding new units? I'm guessing that operating on the same freq as someone that is assigned it is not legal....so if that's the case I may as well just keep the old ones and be illegal across the board and take my chances with interference??!!

What makes you think that only 500-506MHz is "open" in DC? If that were actually the case, most news media would be out of business, and there is abundant evidence contrary to that.

This Sennheiser USA - Headphones and Headsets - Microphones (http://12.148.18.149//) type in Washington DC and tell me what freq I should use??

When I do this the resulting chart shows 12 additional frequency ranges as vacant aside from the range you listed, mostly in the 700-800 range.

Have you not heard of this from the FCC???
· We prohibit the manufacture, import, sale, lease, offer for sale or lease, or shipment of
wireless microphones and other low power auxiliary stations intended for use in the 700 MHz
Band in the United States, effective upon the publication of the rules in the Federal Register,
and adopt related marketing and other requirements.
· We require that all low power auxiliary stations, including wireless microphones, cease
operations in the 700 MHz Band no later than June 12, 2010, one year from the end of the
DTV transition.2

My point is if I buy new units I am stuck using it with others already assigned to use those freq's. Just was wondering if it's a crap shoot as to what freq to get since it's all used up....

Nope. I stand corrected. I was just reporting on what the spreadsheet showed.

You learn something every day.

"Vacant" is not the only band that is usable. Note that a great many other channels show predicted signal levels way below -60dB (~200uV). If you are looking for absolutely clear spectrum you are chasing phantoms.

Well maybe not absolutely clear....but it sure would be nice to have a little wiggle room if I'm going to spend several thousand $$ on equipment!!

I figure my best bet is to find a section that is low power and a decent distance away from DC....

Not sure how the FCC Broadband plan is going to shake out yet, but when using Sennheiser's Frequency Finder, try changing the "Rad" setting (radius) if you know specifically what zip code you are operating in. I believe it defaults to 70 miles but if you shorten it to 20-30 miles, you'll find more vacant frequency ranges.

If you want (semi-assured) "wiggle room" then DON'T spend thousands of dollars on equipment with fixed frequency ranges. Instead, RENT equipment from a LOCAL vendor who keeps up with the neighborhood RF spectrum on a regular basis. They will know what they CAN rent and what customers bring back as unusable. If you don't use wireless microphones at least a few days every week, it may be cheaper as well, and directly billable to each production that needs that particular equipment.

If you use wireless mics every day then at the very least rent a few from the local vendor and see which ones you like in your price range AND which frequency bands the rental house finds successful in your city. You have a LOCAL question. Your local rental house is a FAR better resource for your question than asking here in a web forum with participants from around the planet.