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Thread: Whats your typical range using P25 handhelds?

  1. #1
    saberthree No Longer Registered

    Question Whats your typical range using P25 handhelds?

    Afternoon Gentleman, Just wanted to hear everyones feedback about their range and experience using P25 systems with their handhelds. I read a blog by N5FDL about his experience using P25 in the VHF band, and was basically saying he was able to get about 11 miles from his little experiment. It got me curious, so I looked for any P25 repeaters in my area..(theres only 5 publicly listed P25 Ham repeaters) I found one that was about 60 miles away, which is better than nothing. As I programmed in the freqs and nac code, I was being skeptical that this would even reach the repeater at all with only 2 watts of power. Anyway, long story short, I was able to send and receive from the repeater with no issues whatsoever when it came to the clarity and reception using P25 mode in UHF with only 2 watts of power. In fact, I ended up talking to K6LYE who owns the repeater and we had a conversation for about 20 minutes discussing his repeater and authorizing me to experiment with the TMS and other forms of digital signalling on his repeater. The cool part, is he gave me the option of experimenting with digital encryption like DES-OFB and AES-256 on his repeater, and will be programming it to become transparent. We all know that, its not legal to use HAM frequencies and use encryption, but him and I agreed on posting the keys on his repeater website, and that I should probably say the encryption keys in clear mode every 10 minutes to avoid any one having ideas that we are trying to have any bright ideas using crypto. Anyway, let me know your experiences, I wish I can perform this test with a VHF P25 radio, but unfortunately the closest P25 VHF repeater is about 200 miles away!!!


  2. #2
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    The range of the radios really dosnt depend on the mode of operation. P25 will have a small loss of range (about 3%) due to the digital signal being messed up due to noise creeping in on a weak signal but this is more than offset by the clarity of marginal signals that in analog may have lots of static and other types of noise on the signal. This does not mean that the transmitted signal covers 3% less distance it just means that the recoverable "audio" gets too low and noisy to be recognised by the P25 decoder.

    Any actual distance form unit to unit questions can only be answered by trial and error, its kind of like asking how big is too big? There are so many factors like height, obstructions, antennas, power, reciever sensitivity, frequency etc that there is no simple answer. No one can say 2watts UHF will talk 3 miles. A good example is to look at the absolutly garbage ranges listed for GMRS/FRS radios "30 miles" believe me if they talked 30 miles everyone would be using them and no-one would be buying systems, mobiles or portables and I would be out of work.

  3. #3
    saberthree No Longer Registered

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    Yeah, I was kinda surprised that I was able to get anything at all. I tried to make contact in analog, but the signal was too weak to understand anything at all, but I was able to key up the repeater. Im not sure how N5FDL performed his experiment or his test conditions, Ill have to ask him about that when I get the chance. Him and I talked about the UHF, he's curious now and wants to try it also, just gotta program his radio through CPS. Im excited that theres a P25 ham repeater that I can access to begin with since there's only 5 digital repeaters in the area. I been kinda experimenting also, by trying it in other cities in the area to get a rough idea, where I can and cannot get a signal, so far so good.

    I do want to eventually find someone with a digital handheld that I can perform tests with, but as far as Ham activities are concerned, I may as well be on another planet with the people around here. It does make it less boring experimenting with radios, since I'm around firearms all day, every day. I dont even shoot on my break anymore, I just pick up the radio and start talking to random people in the area. Eventually I would like to try to acquire a VHF digital radio, but gotta play the game and wait.

    I do agree on the garbage range they list on GMRS/FRS radios, its utter BS, and even then...most people dont care enough to even get a FCC license to use the GMRS. I ask people all the time about their GMRS radio, they just look at me like I'm speaking a different language when I ask them if they applied for a FCC license to use GMRS frequencies..."i just bought it at walmart and started using it" its even more sad, when I tell them you can use GMRS radios with some repeaters, which ends up with the conversation with the FCC license again.

    Myself, I'm still a newbie when it comes to commercial/ham radios, let alone some of the theory involved with propagation, antenna lengths and so on. The only experience I have with radios, is HF, VHF and satcom when I was a sniper 2 years ago, they program it for us...all I do is fill the crypto, set the frequencies, make sure the DTG is set right and start talking when I need to. So, if you have any advice or articles I can read, Im open to hearing them, or being pointed to the right direction.

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    Radio propogation is a very complex science. The best advice I can give for a starter is to look at the ARRL handbook and read anything relevent you find. There are tons of books and mathematical analisis formulas that describe the propgation and factors concerning how and under what conditions a signal will travel but unless your into higher math I suggest stay with the ham radio type texts untill your background aloows a better understanding of what is being discussed.

  5. #5
    saberthree No Longer Registered

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    Definitely not something you learn over night. I' try to look on the subject whenever I have free time. Its a very fascinating field, that makes me wish I'd went into communications specialty instead of combat arms. I'm not too terrible at math, Just been quite a long time. I haven't looked up any of the formulas yet, Im assuming its more complicated than ballistics. I should read up on it anyway, I will take the test for general license and maybe extra class down the road when I become more efficient at CW, and PSK. Thanks for the advice.

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    Happy to help feel free to ask if you get stuck.

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    One rule of thumb that I always go by is that the transmission technology/protocol can't defy the law's of physics. You always have to deal with path loss, reflections, refractions, HAAT, etc. and those all play in how far you can talk. Now yes the digital protocols do provide a lot cleaner reception where analog could be noisy at certain distances, but the radio still hears the same signal level no matter what the modulation factor is (with the exception of CDMA that by design thrives on noise).

  8. #8
    syntrx No Longer Registered

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    Digital LMR systems are designed to have the same usable range as analog systems, with any "coding gain" achieved by their digital format being used to obtain better audio quality at the fringes rather than for increasing the system's usable range.

    The reason for this is to avoid messing up the assumptions already used when planning spectrum use for analog systems, and thereby preventing digital systems from operating within the same bands.

  9. #9
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    Worst case if they can hear you use more power