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What range will we get with rx and tx but no antenna? (433MHz)

Discussion in 'Radio and Communications' started by Flyback, Jul 17, 2015.

  1. Flyback

    Flyback Well-Known Member

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    Hello,
    We wish to put an RF receiver and transmitter inside LED warning beacons on trucks. They will be used to receive data pertaining to which type of flash pattern they should be showing.
    There will be another receiver and transmitter in the truck cab, for the driver to communicate to the beacon with.
    We will use this receiver and transmitter….
    AM-HRR30-433 (£4.97) miniature receiver module datasheet:
    http://www.rfsolutions.co.uk/acatalog/info_AM_HRR30_433.html

    AM-RT5-433 (£5.71) Transmitter datasheet…
    http://www.rfsolutions.co.uk/acatalog/DS013-9%20AM-RTx.pdf

    ..these are said to be good for 50 metres when used with the lambda/4 antenna…

    FLEXI-M4-433 antenna datasheet (1/4 wave) (£3.95)
    http://www.rfsolutions.co.uk/acatalog/DS016-13_AM-HRR.pdf

    We do not want to use the antenna, what range do you think we will get without the antenna?
    In fact, instead of the proper antenna, we may just solder a 17cm bit of 7/0.2mm wire to the antenna pin.
    We will just leave the wire coiled into whatever position it ends up in, as it wont be perfect, but surely better than nothing? What range do you think we will get? (Its only 15 metres from truck cab to the warning beacon.)
     
  2. JimB

    JimB Super Moderator Most Helpful Member

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    If the transmitter and receiver were well screened so that there was no radiation leaking from the enclosure or from the power supply wiring, near zero.

    Contrary to popular opinion, "proper antennas" do not have magical properties. The main advantage of a proper antenna over a bit of wire is the physical structure.
    Your choice of 17cm of wire is fine, its physical disposition should be as straight and as far from other conducting objects as possible.
    For best performance you also need "the other half" of the dipole antenna, presumably the 0v line of the radio will be connected to one of the power wires to the LEDs.

    As for what range you will get from this, it is nearly impossible to say.
    It is possible to do some signal path loss calculations to predict the received signal level, but this only works for an unobstructed path. Mounted on a truck (big sheets of steel) the path loss is anyones guess.

    How are these beacons to be powered?
    Battery or from the truck (24v ?) supply?

    I vaguely remember a thread* here on ETO where something similar was discussed.
    It involved a low power UHF radio which worked well but was enclosed in a metal box. I will see if I can find it.

    JimB


    * On edit, here it is:
    http://www.electro-tech-online.com/...t-antenna-inside-alu-box.142517/#post-1195847
     
    Last edited: Jul 17, 2015
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  3. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    If they don't specify which antennae were used for this range , then assume they used their best offer , the 11dB Yagi. Thats 22dB total. A Rubber Ducky or coiled whip may get +3dB gain in the clear view horizontal direction at considerable loss in the vertical.

    But a coil at random will just bounce signals with echoes out of phase at many interference points at 1/2 wave lengths where reflections are equal amplitude but out of phase. These fading losses are common on WiFi in the home between floors. Dead spots in signal level are common.


    My guess if the coil is inside the truck in a plastic box is maybe a meter or so outside on average. Like Real Estate value, antenna location is of prime importance.
     
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  4. dave

    Dave New Member

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  5. Flyback

    Flyback Well-Known Member

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    thanks, becaons powered by truck battery, ie 12v or 24v

    I used one of these (below) years ago in effect just like a digital isolator, and just had a bit of wire hanging off the antenna pin.....I did 3 metres, to the other side of the room, but as you say, there was no big metal sheets in the room
    http://www.maplin.co.uk/p/quasar-am-super-heterodyne-receiver-433mhz-n66de

    Do you know of 2.4ghz rx/tx's which act like a digital isolator?....(ie we don't want all the embedded SPI or I2C etc). All the 2.4GHz ones I can find have embedded encoding etc.....we just want now a 2.4ghz one (as it has a smaller antenna) which works as does the one in post #1.

    You have deterred me from 433mhz as we will need the antenna and don't really have the room for it.
     
    Last edited: Jul 17, 2015
  6. JimB

    JimB Super Moderator Most Helpful Member

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    Sorry, no, I do not know of any.

    JimB
     
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  7. JimB

    JimB Super Moderator Most Helpful Member

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    I presume these are beacons to indicate to drivers of lesser vehicles "Keep clear or you may get squashed", or some similar sentiment.
    Why would the flash pattern need to change?

    This sounds like adding complexity "just because we can"!

    JimB
     
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  8. Flyback

    Flyback Well-Known Member

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    my sentiments exactly, its pointless, but our marketing staff swear by it.
     
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  9. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    For every -20dB (lost) in antenna or fading, your range is reduced to 10% of ideal range. i.e. from say 100m to 10m.

    Fading losses of -20dB on average in the home are common. Deadspots of -30dB are possible. Shielding add more...
    Antenna transmission loss due to random coil +6 to -40 .

    i once design an antenna in this UHF range for small rockets and while spinning at 5 cps with nose cone ejected, the braided wire dipole spun out perfectly. It worked for the total flight time up to 50 mile altitude and down with a parachute to collect plasma experiment data. It worked perfectly until the lower atmosphere when the dipole ends was pointing towards the Telemetry building then there was a dead spot every half rotation. with clear line of site , using quad Helix tracking antenna and high power Tx.
     
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  10. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    Friis losses increase with carrier frequency, so lower f may be better. Consider a long coax wire with terminated end and length tuned for max radiation on the shield . Then test it with most of the length broadside to high gain Yagi Tx. It can be multiple wavelengths of 1/2 or near that used for max Return Loss.

    Even 75 Ohm coax with cheap F connector with proper impedance to a fixed wire outside would be far better, but must be tuned with SA.
     
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  11. Willen

    Willen Well-Known Member

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    Hi,
    I had tried dipole with my simple (found on internet) toy FM transmitter but same performance as a monopole. Maybe core thing is to match its impedance and making unbalanced signal to balance to feed the dipole. These two thing making my mind overloaded. How did you design and matched and got 50 miles? Wow!
     
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  12. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    dipole and monopole are not much different in your case because the monopole in theory has a couple dB gain if you have a perfect ground plane.
    The balun or CM choke gives a bit better isolation and output.

    My colleague designed the 10W transmitter and they had the best Receivers money can buy. I just designed the coiled spinning antenna using 1/4" braid flat rolled onto a plastic spool.

    When I used a directional coupler to measure return loss ( using diode and DMM ) I used waxed string to extend the dipole and snip to length for minimum mV on DMM. Then I was able to detect people walking within 10 m of the antenna by the reflected signals ( from a sig gen.) due to their causing reflections.
     
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  13. tunedwolf

    tunedwolf Well-Known Member

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    Why not just superimpose a serial bit stream on the power wire going to the beacons? It would be simpler, less expensive and much more reliable :)
     
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  14. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    Lower the frequency, the easier it gets from UHF to HF.

    Unless you want to go with 860~890 nm wavelength and use a custom remote control, good for 30m.
     
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  15. granddad

    granddad Active Member

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  16. alec_t

    alec_t Well-Known Member Most Helpful Member

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    I think I'd be swearing at the marketing staff! :D.
    Couldn't you just incorporate a variable pattern selector within the beacon, operated by a waterproofed/knockproof button accessible from outside the beacon?
     
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  17. Flyback

    Flyback Well-Known Member

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    Thanks Grandad I like that chip antenna, chap, and small.
     
  18. Willen

    Willen Well-Known Member

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  19. Flyback

    Flyback Well-Known Member

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    I think it may need a LC matching network with it, to take into account the small size...but that's no great bother.
     
  20. granddad

    granddad Active Member

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    Re Ceramic antenna... Sorry I don't have any tuning knowledge etc ... other than what you would find on the data sheet , I just hooked it up to the transceiver pin and it was a lot better than the 9" of wire i had before ! :rolleyes:
     
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  21. Willen

    Willen Well-Known Member

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    Hi Granddad,
    Seems an amazing integration! Wow! Being curious, if a tiny thing can do such better job then what to use long antennae!
     
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