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freqs used by body microphones?

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justdan

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I'm listening to an undercover police operation going on tonight and it's clear that they've got a microphone on the good guy and are listening to him while talking with the bad guy(s). Any idea what frequency the mic may be transmitting on (or a range I can search)? It's not the local 800Mhz system the police are talking to each other on. I figure it might be some standard range, used in the US, but I dunno. Thought that since I'm a few miles away I might be able to pick it up and help fill in the gaps that I can't hear.

This is the exciting stuff in my book ... love to sit & listen in to the "goings on" :)

Thanks
Dan
 

KCChiefs9690

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justdan said:
I'm listening to an undercover police operation going on tonight and it's clear that they've got a microphone on the good guy and are listening to him while talking with the bad guy(s). Any idea what frequency the mic may be transmitting on (or a range I can search)? It's not the local 800Mhz system the police are talking to each other on. I figure it might be some standard range, used in the US, but I dunno. Thought that since I'm a few miles away I might be able to pick it up and help fill in the gaps that I can't hear.

This is the exciting stuff in my book ... love to sit & listen in to the "goings on" :)

Thanks
Dan
I'm not sure you will even be able to pick them up from a few miles away. They use EXTREMELY low power, and I don't believe there is a federally specified range that they need to be in, they can be any frequency the agency is licenced to, and in some cases a freq not licenced to them.
 

justdan

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Thanks for the info guys, much appreciated. I'll give it a shot & scan the ranges you mentioned for a bit ... couldn't hurt. If I had to guess, I think I'm about 4 miles away. If I don't pick him up, it'll just mean I have good reason to ask the wifey for a base antenna upgrade :)

Thanks again guys.
Dan
 

KE4ZNR

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justdan said:
Thanks for the info guys, much appreciated. I'll give it a shot & scan the ranges you mentioned for a bit ... couldn't hurt. If I had to guess, I think I'm about 4 miles away. If I don't pick him up, it'll just mean I have good reason to ask the wifey for a base antenna upgrade :)

Thanks again guys.
Dan
Dan-
I live right around the corner from ya and I know what you are monitoring as I am listening to the same thing :D unless you are in the exact same area (ie: within a 100 feet or so) you are not going to be able to monitor the body mic traffic from the Tac 6 activities...as others have said it is an extremly low power fm mic...feel free to join us in the NC forum!
gotta run-Foot chase in Raleigh!
Marshall KE4ZNR
 

justdan

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Hey Marshall, good to hear from ya.
Actually I've been listening to TAC8 but I did notice a while ago that something was going on TAC6 as well. I think they've been busier on TAC6 than 8 tonight ... probably ought to switch over to what you're listening to :)

-Dan
 

KE4ZNR

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justdan said:
Hey Marshall, good to hear from ya.
Actually I've been listening to TAC8 but I did notice a while ago that something was going on TAC6 as well. I think they've been busier on TAC6 than 8 tonight ... probably ought to switch over to what you're listening to :)

-Dan
Never mind you were right it was tac 8...that is what I get for my eyesight getting bad in my old age *grin* tac 6 was the High School football game activity I believe...
Now I gotta put the Cary 246T down and pick up the pro96 to do some VIPER digital monitoring!
Marshall KE4ZNR
 

Mick

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Bugs

In So. Calif. many PD's use the 154-155 MHz range in addition to the 171-173 MHz range. 39.06 is popular too.
 

radio10-8

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We use 173 mhz range and I have to tell you that you need to be 1 block or maybe 2 at the best with our equipment. We usually use these when we are in the next hotel room or similar.
 

nd5y

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KCChiefs9690 said:
I'm not sure you will even be able to pick them up from a few miles away. They use EXTREMELY low power, and I don't believe there is a federally specified range that they need to be in, they can be any frequency the agency is licenced to, and in some cases a freq not licenced to them.
This is from section 90.20. It also has conditions for the use of other low power, frequency hopping and spread spectrum stuff on the public safety pool frequencies.

(5) A Police licensee may use, without special authorization from the
Commission, any mobile service frequency between 40 and 952 MHz, listed
in paragraph (c)(3) of this section, for communications in connection with
physical surveillance, stakeouts, raids, and other such activities. Such use
shall be on a secondary basis to operations of licensees regularly authorized
on the assigned frequencies. The maximum output power that may be used
for such communications is 2 watts. Transmitters, operating under this provision
of the rules, shall be exempted from the station identification requirements
of § 90.425. Use of frequencies not designated by a ‘‘PP’’ in the coordinator
column of the frequency table in paragraph (c)(3) of this section, is conditional
on the approval of the coordinator corresponding to each frequency.

http://a257.g.akamaitech.net/7/257/2422/09nov20051500/edocket.access.gpo.gov/cfr_2005/octqtr/pdf/47cfr90.20.pdf
 

Audiodave1

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Hey Guys,
In my professional life I work with wireless mics alot so here's some hard information.

Wireless microphones are a tough target. 99% of wireles mics (WLM) transmit at 50mw or less, 20mw is more common to increase battery life.

They also generally use an an antenna that is a fraction of it's proper length, especially in the VHF band and usually have negative gain.

This can be compensated for on the RX end to some degree but the laws of physics work against us, most notable Inverse square law.

Inverse square law states that a transmitted signal from a unity gain or less antenna drops off at a rate of 6 Decibels per doubling of distance referenced to 1 meter (this applies to sound we hear also),
(Increasing the power output or a 20mw WLM to 40mw gains us 3dB, halfing it we loose 3dB of radiated power)

A bodypack microphone usually has the antenna against a persons body which contributes 8-12dB of loss in itself.
This is a bit frequency dependent, VHF being better, UHF worse.

On the receive end we can add gain or a band specific antenna but the bigger factor will end up being the radio receivers noise floor and the local noise floor of the radio band we are monitoring.

Why does it work for the person using the WL system?

Quality professional microphone receivers have very sharp filtering on the receive end. They do not listen beyond the band capabilities of the transmitters they are used with which greatly improves the receiver performance (and immunity from strong out of band RF)
Add to that a 3-6dB preamp on a proper length antenna and life is good. To further improve performance amplified yagi antenna systems are available (from the WLM manufacturer) which can provide up to 20dB of gain (with less than 1dB of background additional noise in the process) SPECIFIC to the operating range of the microphones.

This again is done with a band limited preamp unlike most of those we use for radio monitoring.

WL mics are a tough but monitorable target if you know where to look and have decent equipment. If you hear an operation clearly you are likely close to the action, for better or worse......

The provided link further up in the thread lists the most likely RX ranges for PS use.
The entertainment world generally uperates from about 550-806Mhz, Around the DTV stations of course. Steps are .025
Sennheiser has a great reference for wireless frequencies in their Tech library as does Shure.

I just wanted to throw some details out there that are applicable since I had some time,

Dave
 
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radio10-8

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Thanks, Dave that was great info and explains why I had so much trouble trying to listen to WLM at rock concerts... I thought maybe I could single out a WLM on a guitar or singer and hear just that mic.
 

loumaag

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Dave, this topic comes up from time to time, from both new scanner hobbyists and old hands. You seem to have a pretty good handle on the subject. Why don't you put together a page for the RR Wiki. If there is not an appropriate major page to link from I am sure that Mike can fix that for you. Think about it and if you are concerned about the actual putting together of the page, give me a PM and I can either help with that or point you to the right spot, but you have the knowledge, not me.

Now that I think about it, you could just update/add to the Cordless Mic page referenced above.
 
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Audiodave1

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radio10-8 said:
Thanks, Dave that was great info and explains why I had so much trouble trying to listen to WLM at rock concerts... I thought maybe I could single out a WLM on a guitar or singer and hear just that mic.
It's fun to try! and yes, you could with a little work.

The most popular wireless on tours these days are made by Shure, look up their UHF-R series. The other most pupular ones would be the older Shure UHF (A,B,C)'s. Sennheiser 3000 series and Lectrosonics (Series?) are also very popular but it falls off quickly after that.

Touring acts will change WLM freq's in most every city but look at the software on those sites and check the venue city HDTV channel plan and look between those channels.

Also note that WLM's are WFM signals. (at least the pro ones are)

More interesting to listen to are the In Ear Monitors (IEM's) which will have a mix of what that artist wants to hear in their glorified wireless headphones. Check the freq's of the Shure PSM600 and 700. Usually they live in the 530-650 range. 100mw output + whatever gain from the antenna transmitting to them. Not all artists use them but many rock / top40 bands do. Each member using them will have their own mix taylored to what and who they need to hear (other singers, instruments, crowd noise etc)

Stages are a sea of RF these days with some pretty advanes RF going on.
A few tours I was on had really nice HP RF spectrum analyzers rack mounted side stage for the RF tech to use and monitor prior to the performance. We would hope to not need then during the performance....

Dave
 

edweirdFL

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When I've seen used police in car video equipment show up on the popular auction site, with wireless mics, they were most commonly the VHF model Azdens. Pro-sumer type stuff. I've not seen the specialized body pack mic's anywhere but a Monitoring Times Convention years ago, and they could be setup for most any freq, with very low power.

The commercial wireless mic gear I use and see used at the meetings, conventions, conferences, and video tapings is predominantly UHF band, set for unused TV channels in the specific locale, like Audiodave1 said above. One of the makers, Sennheiser or Shure has a web page where you can enter a zipcode, and it will give you a chart of suggested open channels to use. I've used this when figuring out what to set a mic for, and then used the scanner to listen to the channel for awhile to verify it's clear. The rental gear usually has a label on the receiver indicating what freq or channel the tech set it up for.

Ed
 
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I ran across some body wires and premises bugs that were operating in the 70 MHz area and those and some other surveillance gear was operating in the 600-800 MHz area. No UHF TV in the area and nothing licensed either and it was normally quiet RF wise there so it was a great place to hide plus few scanners covered those areas. Certainly nothing your normal criminal would pick up at wal-mart to keep track of the local cops.
 

Audiodave1

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yep, the 72 and 75Mhz bands can be a good place to hide since there are strict restrictions on power output levels in those bands. No 100w repeaters to deal with for sure!

I believe most industrial services are limited to 3w or so and simplex only. I wonder if anyone even uses that band anymore? Hmmm....

Dave
 
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