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Separating 315/433Mhz from 60hz

Discussion in 'Radio and Communications' started by Quantboy, Feb 18, 2016.

  1. Quantboy

    Quantboy New Member

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    I have an AC transformer - 24VAC @ 60hz (fed from 120VAC mains) that feeds a common set of power buss rails in a control assembly.

    On this 24VAC buss, we need to inject 315mhz RF from a 2400 baud transmitter (FSK/ASK) and the separate this 315 or 433 Mhz signal back off of the power buss further down the assembly in several locations.

    What is the best way to:

    1) couple the rf signal and inject it on the 60hz power buss? and
    2) what is the best way to pull off just the 315 or 433 mhz signal, but not the 60hz?

    I've considered using a high pass filter to just get the 300+ mhz freqs, and then a 60hz notch filter (will this pass the 315 mhz still???) in series to take off anything remaining... or a SAW as a bandpass filter -- but after a few attempts -- I'm not sure if I'm actually solving the problem -- or just throwing the RF hot enough where it's going thru the air instead of the power buss and working (intermittently) anyway.

    Any suggestions on circuits? What I could google? Recommended ways to get these signals in and out of the 60hz buss?

    Thanks in advance,

    Ted

    The transmitter/receivers are similar to: https://www.sparkfun.com/datasheets/Wireless/General/MO-SAWR.pdf (tx is a simple ASK w a SAW resonator)
    TX circuit is http://www.dx.com/p/315mhz-rf-transmitter-receiver-link-kit-green-236262#.VsZJQ-YT92M

    I also found IEC 61334, which standardizes a 2400 baud carrier over power lines - but this is more for "smart power meter" communication -- so I'm looking for a better / simplier / cheaper way to do it.
     
    Last edited: Feb 18, 2016
  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    On the left side of the schematic there are two 0.022uf high voltage capacitors. These pass very little 60hz and a large amount of high frequency.
    T2 inductance and the 1000pF cap resonate at the carrier frequency. (band pass filter)
    The transformer also isolates you from the power line. The primary to secondary breakdown voltage should be high.
    10k and 1000pF and two diodes are for over voltage protection.
    [​IMG]
    Search for "X-10 schematic" and "power line schematic"
     
    • Agree Agree x 1
  3. Quantboy

    Quantboy New Member

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    I'll wire wrap up a little circuit and give it a whirl.
    I guess I should be using two spectrum analyzers -- 1 for the 60hz range, and one for the carrier frequency range (315/433mhz).
    Thanks,
    Ted
     
  4. dave

    Dave New Member

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  5. Quantboy

    Quantboy New Member

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    Please excuse me still learning on this -- but if you were going to put this together -- where would you start in calculating wire wraps/ratio/gauge wire/core type for transformer and the selection of the values for X2 in the diagram (the inductors)?
    I realize I have to make a basic bandpass filter circuit like:
    [​IMG]


    BUT am very uncertain as to how to:
    - start designing the filter (component values)
    - transformer specs
    - C values
    - inductor values

    Would you recommend for 315Mhz?
    Would something like the below transformer work?
    http://www.mouser.com/ProductDetail...7Vqkz20l1pP-67xdHBZWMxUYG-Qs9wEQ-saAlTP8P8HAQ

    I have no problem wrapping my own air-core inductors -- I'm just not sure where to begin w the values.
     
  6. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Do you have a network analyzer. It will generate a scan from 50hz to 500mhz and you can see the filter's response.
    Because you frequency is much higher than the schematic I posted you should make the capacitors smaller. 650V to 1,000V.
    That transformer is for audio. Look for a "pulse" transformer.
    I would start out with SPICE. You can sweep the filter and easy change parts.
    ---edit----
    You could start out with a RF transformer much like in the front end of a FM radio.
     
  7. Les Jones

    Les Jones Well-Known Member

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    Hi Ron,
    I think you will have problems making an inductor to resonate with 1000 pf at 433 Mhz. It would need to be 0.135 nH (The reactance of a 1000 pf capacitor at 433 Mhz is 0.37 ohms. I do not think it is practical to transmit 433 Mhz over power lines. I have just looked up the frequency used by X-10 protocol to communicate over power lines. It is 120 Khz

    Les.
     
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    As others have said, you use a MUCH lower frequency for communication over mains wiring, UHF is totally unsuitable - you need VLF instead.
     
  9. Quantboy

    Quantboy New Member

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    Thank you very much to ALL -- I'm going to re-think the transmitter frequency and start back over.
    Any suggestions on where to start w a sample simple VLF circuit for transmitting simple serial data from a PIC chip?
     
  10. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    There's an X10 application note at MicroChip, it gives both hardware and software.
     
  11. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    I have used X-10 and power line modems. (20 to 200khz)
    I have not used RF on in home power lines. I have played with RF on large power lines. I don't remember what frequency(s) were used. My bad memory says there are carriers from 1mhz to 10mhz. I used to live near a large power line. I found many carriers all with ASCII data mostly numbers. (voltage, current, phase angle)
    Here is some reading.
    https://en.wikipedia.org/wiki/Power-line_communication
    ---edited---
    I made a quick filter for X-10 frequencies. You can see there is a small amount of gain at 130khz. You can see 140db of attenuation at 60hz.
    upload_2016-2-19_19-57-40.png
     
    Last edited: Feb 19, 2016
  12. Mikebits

    Mikebits Well-Known Member

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    I'm unclear on something, since your just wanting to transfer data over a wire, why do you need to use RF at all?
     
  13. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    To send data over "power line" wires, you need to get away form "60hz" and its harmonics.
    Any frequency above audio (20khz) will work. 100 to 500khz is common.
    Some companies use RF. I have used the AM band but I should not have.

    Before computers, the power line was high impedance at 20khz and above. So it is not hard to drive signals into the power line.
    With many computers and switching power supplies on line there are many filters that make for lower impedance, at high frequencies.
     
  14. Mikebits

    Mikebits Well-Known Member

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    Ok, I guess I did not word my question right. I know what RF is and I know about data transmission. What I meant to say, why not use something like a computer modem since it was designed to work over wire. 300 - 400 MHz across a power line would never work as the power line would look like a giant inductor. Also, to me when I think of RF I usually think in terms above VLF, albeit this is not correct. So to me, 200KHz is almost DC... :)
     

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