Question on Transmitting between (174-178)VHF In USA Illegal

[troymelina]

Hi I have a question about transmitting on VHF frequency (174-178) I read it somewhere on the net stating that it’s illegal in the USA to transmit between that band. Is this true and if so why? Thanks

[Nand]

Channel 7 TV starts at 174 MHz. You would either interfere or be interfered with when you use this frequency. There is a nice chart with most TV channels in the ARRL Radio Amateur Handbook.

Actually, it is often illegal to transmit other places as well without a license for that frequency, not just the TV bands.

Nand.

[nc5p]

Some wireless mics operate on locally VACANT VHF high band tv channels. You need to coordinate (I think SBE does those frequencies) and get a license. Very few users (mostly churches and schools) ever bother to get a license for their mics.

Doug

[Tom in D.C.]

Systems houses (pro sound dealers; I work for one) provide wireless mics to users which do NOT operate on local active VHF TV channels between channels 7 and 13. Wireless mics do not operate on channels 2 through 6. Power of transmitters does not exceed 50 mW, or at least it's not supposed to. There are several dedicated channels around 169 mHz which are also used. The biggest problem on VHF is intermod which can usually be handled by purchasing a system with CTCSS. The CTCSS operates around 32 kHz, unlike LMR systems, so the tone is inaudible. Usually the intermod appears when the system transmitter is off; when it's on the signal captures the receiver and there is no intermod (again, I say "usually.")

On UHF the same theory applies, that being that you don't set up a wireless mic on an active TV channel. The mic mfrs all provide tech data on active channels for the whole USA and if you need to "clear" a channel you just telphone them for help. For whatever reason, licensing or wireless mics is virtually unheard of, rightly or wrongly. Transmissions on both bands are NFM which uses compandoring to get the required 15 kHz bandwidth. Current technology allows many systems to operate with power far under 50 mW, with 10 mw being a common power level.

Almost 100% of the wireless mic systems are analog, and can be intercepted by anyone with a suitable receiver; the processed audio can be heard just fine. If you set up an analog wireless mic system for your conference facility it can be monitored by anyone sitting out in the parking lot using a scanner. Digital systems are available and, so far, quite expensive. A major user of digital systems, for obvious reasons, is the NFL.

[mancow]

A different but similar question on the topic...

I have heard several times from varous sources (work of mouth) that law enforcement agencies can transmit from 148-174 with no licence as long as it's temporary, portable, causes no interference, and is limited to 5 watts or less.

Is this at all true? I swear I read this in some sort of FBI LEO publication in the Washburn University library years ago. I wish I had saved the article.


mancow

[dfc2]

This is the information I have been given as it applies to PD's using Radio Freq's. We can use ANY radio freq we need as long as it does not cause interfearance with another user and we use low power ( 5 Watts), and is used for Drug related investigations. they key was Drug investigatiosn. I have not heard of it being limited to VHF, but that would seem to be the best band to use at most times. This information came from both a rqadio shop and the head of a regional drug task force. but again this is still word of mouth, I have not read FCC regs on this.

Just my $0.02

DFC2

A different but similar question on the topic...

I have heard several times from varous sources (work of mouth) that law enforcement agencies can transmit from 148-174 with no licence as long as it's temporary, portable, causes no interference, and is limited to 5 watts or less.

Is this at all true? I swear I read this in some sort of FBI LEO publication in the Washburn University library years ago. I wish I had saved the article.


mancow

[mancow]

If I recall now, like you said, it wasn't limited to vhf. I think the article said it was 30 Mhz and above. I don't recall the drug investigation stipulation but I wouldn't doubt it.

Those odd band sabers sure are handy



mancow

[bud_mot]

Power of transmitters does not exceed 50 mW, or at least it's not supposed to.

Just to clarify, wireless mic TX's can be up to 250mW. I use several myself for critical situations. Most high quality units operate at 100mW.

The SBE does indeed coordinate wireless mic frequencies at some major events - notably NFL games. However, 99% of productions that use wireless are not coordinated whatsoever - especially feature films, documentaries, news, etc. Also, I would agree that 99% of wireless mic users are not licensed. It's simply not enforced and nearly everyone in the world of production is oblivious.

[kurt meltzer]

The rules provision for unlicensed use of certain frequencies by law enforcement, which mancow and dfc2 are referring to, does in fact exist. There are some exceptions (please refer to 47CFR 90.19(3) for the full text), but essentially law enforcement may use any mobile service frequency allocated to public safety between 40-952 Mhz for communication in connection with physical surveillance, stakeouts, raids, and other such activities (it's not limited to drug cases) - without a license, and without identifying, provided power does not exceed 2 watts and that no interference results to any licensed users of the frequency. As a practical matter, the 2W limitation is often exceeded. Since comms are typically of short duration, and at infrequent intervals, and because the frequencies are carefully chosen, harmful interference to licensed users is virtually unheard of. Agencies employing this technique typically change the freq regularly to prevent it from becoming common knowledge among the monitoring public.

For many agencies, this makes a lot more sense than encyption, due to the cost and complexity of encryption and because virtually all of the available encryption schemes (other than digital) result in degragation of the recovered audio. This type of operation is very common, particularly in urban areas. BTW, operation is not limited only to mobile stations, and there is no limitation on antenna height (yes, there are even some low power repeaters being operated under this exception!).

[mancow]

Smooth!!!!!

Now I finally feel confident enough to proceed with a project I was thinking of


Thanks for the info

mancow

[DAL-COM]

Kurt, you have explained what I have seen here. There are vehicular repeater frequencies in use that do not appear on any agency licenses in the database. I really should get familiar with 47CFR90......
Bernard.

[CAPTLPOL]

The Police Call directories have that information in the text. That has been the case for many years. I have found some interesing frequencies back in the days before digital and trunked radio systems. However, having said that, I know of one agency that implemeted an 800 MHz digital radio system with some encryption for sensitive comms and yet several months later some officers were using some intersting frequencies on low power in the VHF band simplex on a sting operation. I thought that was pretty interesting, why go through the expense of such a system yet to have the old radios in use in the clear?

[nc5p]

why go through the expense of such a system yet to have the old radios in use in the clear?

It is not uncommon for larger police departments to go on operations far outside their radio system coverage areas. Case in point, APD vice unit participated in a raid on a house of ill-repute out in Tucumcari, which is closer to Amarillo, TX than Albuquerque. Don't know what radios they used on that assignment but you are down to talkaround on 800 or VHF which other agencies can interface to. Since these types of operations usually involve several departments the VHF route makes sense. I can also say that in many places the trunked system coverage stinks, especially if it is simulcast where you WILL have garbage audio in certain vicinities. The system engineers try to "tune" it into unpopulated areas but sometimes that is where the cops need to be. I can't blame them for keeping a few "old" radios around for such uses.

Doug

[abbylind]

We gave all ther old radios away Doug

Fowler

[Hightower]

I watched a TV show last year, and they breifly discused this. They were talking about big stadiums or amphitheaters (where people see large events like Metallica or Britney Spear), they do use a vacant TV channel for a few reasons. 1) Little or no possable interference 2) mics use a wider bandwidth (for best sound quality) than the normal 169Mhz freqs are designed/allocated for. These amphitheaters suppy the musicans with these wireless mics and other wireless linking equipment for the event. Every city has dead VHF and UHF channels and use them for this purpose sometimes.

They were discussing how they film "Sound Stage", which is a PBS program - only avaiable on the Hi-Def PBS channel in Chicago(WTTW 11-1). This Sound Stage is a varity of Musicans doing a concert usually with a full symphony orchestra - a new concert every few weeks ranging from rock to clasical music. I've seen some kick ass concerts, and its sometimes broadcast in 1080i Hi-def with 6.1 DTS surround sound. Pretty cool.

[Tom in D.C.]

Sorry but your information on touring companies, as they're known in the business, and wireless mics is completely out of date. Most of the touring companies use multi-channel wireless mic setups which come, usually, from SONY or Sennheiser, and are 900 mHz. The equipment is either brought in by the company or rented locally, subject to specific technical requirements and restrictions which are part of the concert contract. Wideband FM has nothing to do with the setups as all transmissions are, as noted above, narrowband with compression at the transmitter and restoration of the signal at the receiver, call "companding" sometimes. The days of using the "official" 169 mHz channels, and even the unused local VHF TV channels are over. The VHF stuff is now only used by those who don't know any better, because there is too much junk and intermod and many of the old VHF wireless sets don't have CTCSS. The common wireless mic stuff is now all on the unused UHF channels in the 500-800 mHz range.

[sglass]

but essentially law enforcement may use any mobile service frequency allocated to public safety between 40-952 Mhz for communication in connection with physical surveillance, stakeouts, raids, and other such activities (it's not limited to drug cases) -

ooneof the local pd's near me had 2 racks of icom

one rack of u-16s and othe rof h-16's


they used to use them when they were tryign to catch someone that they thought had a scanner.