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Setting up a 20km radius paging transmission signal coverage

  1. Sep 28, 2015 #1
    Hi,
    I am new in this forum and still can find my way around easily. Please forgive me if I have posted this in a wrong section. I need help from seniors in the field of wireless transmission. I have done a bit of research but not enough to justify any conclusion.
    I have a project to setup a LRS paging transmitter (TX7470 freedom transmitter) over a 20km coverage radius.
    The transmitter itself operates on 459.100 MHz frequency and has up to 2 miles radius signal coverage with its own antenna.
    It is a 2watts output transmitter that also has an option to use an indoor repeater that uses 2 watts output power and can add additional 2 miles radius signal coverage.
    The frequency range of both the transmitter and repeater (and pagers) is 420 - 470 MHz.

    I know I should be using a stalk array dipole antenna for this transmission but not 100% sure about this.

    My questions are then;

    1. What will be my effective mast height to transmit over 20km radius?
    2. What should be the length of the dipole antenna and the gain to make this possible?
    3. What angle should the stalks be to eliminate signal disruption?
    4. What is the permissible cable length and cable grade (specs) between antenna and transmitter to make this possible?

    The pagers to be used are 4line alphanumeric pagers.

    Please note that the location is in the woods. The tallest building is about 60ft tall. The buildings are sparsely distributed and very few building exist in the location.

    I will really appreciate all helpful inputs.

    Thank you.
     
  2. jcsd
  3. Sep 28, 2015 #2

    anorlunda

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    Are you located in the USA? If yes, then it sounds like you will need a FCC license. The FCC is likely to restrict the frequencies and power you use.
     
  4. Sep 28, 2015 #3
    No, not at all. I am located in Nigeria and I have checked up these frequency and bandwidth (459.100 on 12.5/25MHz bandwidth) with the NCC before going ahead. The frequency is not in the commercial frequencies of my region.

    Thanks.
     
  5. Sep 28, 2015 #4

    davenn

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    as high as possible to achieve reasonable line of sight from TX to any receive points
    foliage buildings etc will all attenuate the signal
    and wet foliage even more so

    300/459.100 = 0.653 metres (65.3 cm) for a wavelength, /2 = 32.7 cm for a 1/2 wave dipole
    a stacked phased array of 4 dipoles should give good coverage over a clear path

    stalks ?????

    depends on the cable. I wouldn't use less than LMR 400 which would be 4.5 dB loss over 50 metres @ 460 MHz
    my preference for installations I do is LDF4-50 which has an attenuation of 2.4dB / 50m @ 460 MHz


    Dave
     
  6. Sep 28, 2015 #5

    Baluncore

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    It all comes down to local topography. If you can put your transmitter on a hill that is visible throughout the area you may not need a significant mast or tower. If you have other hills and valleys you may find it very difficult to get good coverage. So are you on a flat plane without valleys or are you in the hills?
    The antenna may need to be omnidirectional which would be a vertical whip or array. Is the transmit site in the middle of the reception area?
    Use the least length of cable possible. If it needs a tall mast, use more expensive lower loss cable.
     
  7. Sep 28, 2015 #6

    davenn

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    thanks for the backup Baluncore :wink:
     
  8. Sep 29, 2015 #7

    Baluncore

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    As the provider of a free second opinion to the OP, I cannot let your answer sway mine without loss of the independence essential in a second opinion.

    But I do note that our opinions concur, which is very reassuring for me.

    It might also be reassuring to tadisa, if it was not for the fact that the 20 km range may be unobtainable due to topographic limitations.
     
  9. Sep 29, 2015 #8

    davenn

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    uh huh,
    2W TX for a 20k coverage, even with a good gain collinear array may still be "pushing the envelope" :wink:
     
    Last edited: Sep 29, 2015
  10. Sep 29, 2015 #9
    Okay sirs. I really appreciate these responses from you. Its really going a long way for sure.
    Since we use constant properties to design the length of our dipoles (@davenn) and topography and clear line of sight is a major factor, and since the height of antenna can increase signal strength of dipoles. Is it logical to:

    1. double my coverage radius to 400km to get effective signal penetration through the desired 200km coverage?
    i.e using a stack phased array designed for 400km coverage to gain effective coverage for 200km.

    So in practice will you permit me to assume like this...
    If a 200km radius coverage requires stacked phased array of 4 dipoles

    then...
    A 400km radius coverage would require stacked phased array of 8 dipoles arranged in phase ( i.e 90 degrees to each other using their mast plane as reference point)?

    2. Sir, kindly explain what "...32.7cm for a 0.5 wavelength dipole" means practically? (Do you mean there should be a distance of 32.7cm in-between each dipole midpoint on a dipole mast?)

    3. (the formal question No.3) At what angle should the folded dipoles be to each other with reference to their mast plane (if the 90 degrees I am assuming in question 1 above is wrong)?

    4. Will i need any form of signal amplifier in-between my transmitter and the antenna to achieve this coverage goal? Considering the cable length between transmitter and antenna (about 200m run in total) and the ratio of length to loss theory...

    Please forgive me for so many questions sir. Just trying to be as clear as I can. Getting this wrong the first time will be very costly for me.... if I can cover a radius of 195km steadily, then I am fine.

    Thank you sir.
    Regards.
     
  11. Sep 29, 2015 #10

    Baluncore

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    You were talking about 20 km which would be difficult.
    You have now changed that to 200km which will be impossible.
     
  12. Sep 29, 2015 #11

    davenn

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    200km ?? 400km ?? what happened to the 20km ?

    As Baluncore said, 200 and 400km isn't going to happen
     
  13. Sep 29, 2015 #12
    Uh..!!! Very sorry sirs.

    I mean 20km and 40km respectively I will repost if you don't mind.
     
  14. Sep 29, 2015 #13
    Okay sirs. I really appreciate these responses from you. Its really going a long way for sure.
    Since we use constant properties to design the length of our dipoles (@davenn) and topography and clear line of sight is a major factor, and since the height of antenna can increase signal strength of dipoles. Is it logical to:

    1. double my coverage radius to 40km to get effective signal penetration through the desired 20km coverage?
    i.e using a stack phased array designed for 40km coverage to gain effective coverage for 20km.

    So in practice will you permit me to assume like this...
    If a 20km radius coverage requires stacked phased array of 4 dipoles

    then...
    A 40km radius coverage would require stacked phased array of 8 dipoles arranged in phase ( i.e 90 degrees to each other using their mast plane as reference point)?

    2. Sir, kindly explain what "...32.7cm for a 0.5 wavelength dipole" means practically? (Do you mean there should be a distance of 32.7cm in-between each dipole midpoint on a dipole mast?)

    3. (the formal question No.3) At what angle should the folded dipoles be to each other with reference to their mast plane (if the 90 degrees I am assuming in question 1 above is wrong)?

    4. Will i need any form of signal amplifier in-between my transmitter and the antenna to achieve this coverage goal? Considering the cable length between transmitter and antenna (about 200m run in total) and the ratio of length to loss theory...

    Please forgive me for so many questions sir. Just trying to be as clear as I can. Getting this wrong the first time will be very costly for me.... if I can cover a radius of 18km steadily, then I am fine.

    Very sorry for the initial mistake.
    Thank you sir.
    Regards.
     
  15. Sep 29, 2015 #14

    davenn

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    OK

    seriously, for GOOD coverage over 20km,5W TX is almost a must even with the 4 dipole array
    and if you were wanting to double that to 40km, the really you should be looking at a minimum of 10W TX
     
  16. Sep 29, 2015 #15

    davenn

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    that's too difficult, easier just to use a power amplifier

    that's the length of a 1/2 wave dipole

    they will be stacked vertically polarised, above each other

    200m feedline seriously ? any reason you cannot 1/2 that distance ?
    then you will, even with 1/2 the distance need LDF5-50, the 7/8" cellflex from Andrews or other source
    eg http://www.pcs-electronics.com/professional-cellflex-coaxial-cable-connectors-p-1131.html

    we are now looking at a 10 - 20 W transmitter

    I really hope you have a huge budget !!


    Just an observation I have so far .....
    you seem to lack the experience to carry out a project of this magnitude ??

    Dave
     
  17. Sep 29, 2015 #16
    Yes sir. I can try cut the cable length to 120 - 130m meters but the antenna may not be in the middle of coverage region anymore.
    You are right. I lack the experience to calculate the RF design criterias to get what i really need.
    But I have the experience to integrate all the components assuming I am going to get them shipped in ready for integration without fiddling or tuning anything complex.

    I am a system integrator, not really an RF engineer.

    If I know the exact following, I can integrated perfectly...

    1. the type of amplifier to get me a 10 - 20W inline boast from my 2W paging transmitter (remaining this one to be resolved)
    2. the exact antenna type and configuration to use (you solved this)
    3. the exact cable grade (you also solved this)
    4. and most importantly, an experienced mentor to lead me through (and i really believe I have you guys for this one)

    Trust me sir when i say this. Even the people to sell me antenna could not figure out my need when I explain to them what I want. The same thing I explained to you.
    The engineers that are suppose to rig the antenna for me here hasn't gotten back to me since 5 days ago. I call them everyday to ask if they have gotten the type of antenna I can use. They are still not coming up till today... (One of them even said it is an impossible project...). I came to know that a stack array dipole will be the best to use from personal research.

    Now, with your mentoring, I am better informed and I know exactly what I need to achieve something very close and realistic (maybe 15 km coverage radius guarantied).

    I am your scholar now. This is your project, your brainwork but I run this errand for you. I take all the responsibility for failure if it does fail. In my 8 years of integration experience, I have never failed. I have had tougher challenges than this one though...

    To be very honest with you sir, all the credit goes to you if the project is successful. I am just a systems integrator (and really not the genius type).

    So just take me as I am. But I am glad I have an eye to check my moves and a voice I can trust without any reservation.

    Thank you sir.
     
  18. Sep 29, 2015 #17
    What about an Agilent 8447E RF power amplifier? It's rated at 15W, but I'm not sure if that's output power or total power used.. It gives a 22dB gain, so you may need to limit your transmit power somehow.

    FCC rules exist for good reasons. Just because they don't cover your area legally doesn't mean you should totally ignore them.
    You need to consider why they exist before breaking them.

    Don't forget you are likely in a much lower noise environment than the U.S. With a lower noise floor (which you should measure if you can) it may be you don't need as much signal. Of course without any regulations, the noise floor may be higher in your band.

    If you really need to get this right the first time, you should hire an experienced RF engineer. You need to discuss lots of issues you probably haven't considered, such as corrosion, terrain, and what your communication needs are needs are. There may be simpler solutions. Police, fire, and rescue regularly use systems similar to this and there may already exist a system you can modify for your needs.
     
  19. Sep 29, 2015 #18
    Thanks you sir. I appreciate your contribution. As I said earlier, I am still awaiting the response of the RF engineers here. I just want to get details from parallel reliable source. I am going to call in again to the NCC to have them check their records again for these frequencies and request for any documented floor data if they have.

    But at Least I know what to expect from any incoming recommendation.

    The system is only to send paged text. No voice or radio to radio comms.

    Its is strictly paging transmitter messages to 4line alphanumeric pagers...

    Thanks....

    Regards.
     
  20. Sep 29, 2015 #19

    Baluncore

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    tadisa. You have not yet identified the topography of the service area. Are you on a flat plane? Does it have trees?
    Do you have valleys? How deep are the valleys? Do you have hills? How high are the hills? How many hills?
    Will you put the transmitter on a hill?
     
  21. Sep 29, 2015 #20

    jim hardy

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    skeptic2 posted in conversations :
    i put it here for continuity.
     
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