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  1. #1
    Join Date
    Aug 2007

    Default VHF (78MHz) VS UHF (468 Mhz) what is the difference

    The police in my area use both 78MHz VHF and 468 MHZ UHF. What is the difference? Does VHF have a longer range? I,m sort of thinking about getting a CB (with emergency/police channel scan) for each one. Why the 2 different frequecies? I suppose I will need 2 different kind of radios and anntennas?

  2. #2
    Lead Foot
    Join Date
    Dec 2006

    Default Re: VHF (78MHz) VS UHF (468 Mhz) what is the difference

    Chances are their old system is 78 MHz and they have moved or in the process of moving to 468.

    There are a number of factors of different frequency ranges, but in general:

    Lower frequency is less likely to be blocked by objects (light is very high frequency radio and is easily blocked for example)
    Lower frequency is more likely to bend (it will follow a wire, where as higher freqs in the gigahertz range need coaxial cable and waveguides (and radar horns!) to make them get to the antenna)
    Lower frequency in general needs more power to transmit
    Higher frequency can carry more information (higher bandwidth).
    Higher frequencies are more generally available, while low ones have mostly been reserved for specific uses.

    Now in the case of the police, they may have only had a few analog channels on their old VHF system. The extra bandwidth of their UHF system probably allows them doezens of analog channels, some digital data chanels for laptops, or even a digital trunking system where even the voice is digital.

    Plus, you don't need 10-foot long antennas and 100-watt transmitters on every police car.

    In the case of, say, CB vs FRS, they are very different. CB may actually be better for range because it is 5 watt but needs a huge antenna. FRS can fit in your pocket but is only a half watt, and more easily blocked by surroundings. I actually use MURS radios (another free radio band that never caught on) which is about halfway between the two, when skiing for example because it does a much better job going through trees than FRS. But FRS can run off of two AA's, and offers newer technology like PL tones (the subchannel) so you can filter others out.

  3. #3
    Join Date
    May 2006
    Olive Branch, MS


    VHF doesn't require more power, if anything, it should require less power because it is not as affected by line of sight. UHF systems typically use less power because more repeaters are required to cover a given area, which allows a single repeater or mobile unit to use less power to communicate between each other since the distance between units is reduced. An area that used maybe 1-2 VHF repeaters may have to install 6-7 to get the same coverage. VHF would transmit at a higher power (100-150 watts or so) just to ensure that the one site maintained adequate coverage over the entire area. That's because you might have a mobile unit trying to talk to a repeater that's 20-30 miles away or more. With a UHF system, the distance is probably less than half that on average.

    It also has nothing to do with bandwidth. I can make a given channel as wide as I want to, within reason of course. Old VHF/UHF channel spacing was usually 25 KHz, but it has been reduced to 12.5 KHz in most areas over the past 30 years or so as technology has improved in order to allow for more efficient use of spectrum. It mainly depends on the mode being used for transmission, FM (which is what 'analog' voice systems use) is a "wide" mode compared to AM. Since aviation still uses AM for voice, there has been a push to further reduce the channel size to 8.33 KHz. Digital voice modes are probably somewhere between FM and AM.

    The move to UHF (450-700-800/900 MHz) is motivated because of interference to other radio systems due to atmospheric propagation. VHF has the potential to travel further distances due to surface ducting and atmospheric skip. As a result, a given VHF frequency may not be able to be reused over a very large range (100 mile radius or more). Frequency coordination isn't as critical and it allows more re-use of the same frequency within a smaller area.

    That said, in rural areas, VHF is still more prevalent because of its ability to cover longer distances.

  4. #4
    Speed Demon
    Join Date
    Dec 2006
    Baltimore City


    I don't think 78 mghz is being used for police dispatching....
    I doubt that its any police radio activity there...78 mghz I think is in the tv band I 'think' and right before the fm radio band we use in our cars. Its also wide fm I'm sure..
    Not very likely that police radio is in there, I could be wrong but, nothing I have ever heard of....

    Nice information on this page fellas....

  5. #5
    Good Citizen
    Join Date
    Sep 2005
    Victoria BC


    78 Mhz is used in Europe and I think Australia.



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