Filtering TX from separate RX radio

Discussion in 'General Technical Questions and Answers' started by KE7RUX, Dec 9, 2020.

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  1. KE7RUX

    KE7RUX Ham Member QRZ Page

    Your suggestions on how to go about filtering out a single TX signal (my own) from an RX radio in the same shack or via handheld?

    For those of you who are wondering, this post is a result of my recent uptick in 2m simplex nets participation for emergency response; for the purpose of wanting to have the ability to hear someone with emergency traffic transmitting at the same time that I may be transmitting; (some of you call this Red Neck duplexing!:D)
    I would like to accomplish the same feat with handhelds as well for times that a quick "off the road" call comes through, and base/mobile stations are not reliable or plausible.
    I've briefly heard of Phase Cancelation methods to do the trick, but I know very little about it. 73
  2. W4HWD

    W4HWD Premium Subscriber QRZ Page

    How long-winded are your transmissions?
  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Two possible solutions:
    1. Buy radios that are single band. Commercial radios e.g. Motorola, Erickson, EF Johnson often have better selectivity than ham radios.
    2. Build narrow in-band bandpass filters for specific frequencies.
    3. Use minimum Tx power necessary

    Otherwise, I don't know of any other COTS solutions.
  4. K7JEM

    K7JEM Ham Member QRZ Page

    If you are transmitting on a simplex frequency, you can't simultaneously receive on the same frequency at the same location. There is no filtering or other method that will allow you to do that.
    WA0CBW, W4NNF and KC2RGW like this.
  5. WE4E

    WE4E Premium Subscriber QRZ Page

    Let go of the button after every sentence.
  6. N3HGB

    N3HGB Ham Member QRZ Page

    This is not physically possible.
  7. KB1CKT

    KB1CKT Ham Member QRZ Page

    On the same frequency? I don't think you can get the antennas far enough apart. Maybe if you used 100mW TX and antennas a mile apart; coax loss would help.

    Is this on 2m FM? Capture effect is going to trounce signals. SSB though might be plausible--but you have to get TX signal way down.

    Can you offset TX and RX? On 2m the bandpass filters used on repeater sites allow 600kHz separation--but they tend to be very large. Nothing wrong with using offset TX and RX. Some radios have a button for this, where it reverses the repeater, so as to listen to the input. In this case you'd have to be using the opposite setup that everyone else is using, and all would have to be on-board with this setup. If you could use a high end receiver, maybe a filter, and separate TX/RX antennas with lots of separation, it might work for you.
  8. AI5DH

    AI5DH Ham Member QRZ Page

    Simple answer. Not going to happen.
  9. KE7RUX

    KE7RUX Ham Member QRZ Page

    My long-windedness identifies as a ragchew
  10. KE7RUX

    KE7RUX Ham Member QRZ Page

    Okay; I don't understand how that would work for simplex.

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