DMR Interference on 435.350

Discussion in 'Satellite and Space Communications' started by K6LCS, Aug 27, 2018.

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  1. K6LCS

    K6LCS Premium Subscriber QRZ Page

    Recently there has been a DMR signal QRM'ing the AO-92 uplink on 435.350 or close by.

    Hotspots, repeaters, terrestrial simplex (anything not satellite) should not be in 145.8-146.0 or 435-438 by international bandplan. Please QSY these radios ASAP. Please pass this info around - thank you!

    - de AMSAT-NA
    W5PFG and K3RLD like this.
  2. K3RLD

    K3RLD Ham Member QRZ Page


    Not sure announcements are enough - there may need to be some local level detective work (in the south central US, perhaps?) to find the culprit.
    WE4B likes this.
  3. WD9EWK

    WD9EWK Ham Member QRZ Page

    And some leadership from ARRL and AMSAT, to get the word out about where the hotspots and similar system should - and should not - be located. More than just what is in the bandplans on bands like 70cm.

    Seeing comments encouraging all of us to e-mail operators of these systems is disappointing. We are self-policing, but I think that the "national association for amateur radio" and the main organization involved with building and launching satellites need to lead an effort like this. Otherwise, it could turn into lots of ham-vs-ham arguments, even if it can be shown that these systems are not supposed to be anywhere in the 435-438 MHz subband. Depending on where ARRL is in restructuring what was their Official Observers, they would be a good resource to bring into this situation. This is an extension of what I wrote about last year, related to the unattended stations squawking away on 145.825 MHz.

    Between Google searches and scouring a couple of web sites ( and, I found dozens of hotspots that are operating on the 435-438 MHz subband in the eastern USA. I even found a couple of systems that advertise that they operate on or very close to the 435.350 MHz uplink for AO-92. I have let AMSAT know about what I found.
    NJ4Y and KS1G like this.
  4. W9EXP

    W9EXP Ham Member QRZ Page

    Its no different than when I worked commercial repeaters its up to you locate the interference. So check your area.
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    Should be easy using a satellite.
  6. W5PFG

    W5PFG Ham Member QRZ Page

    It is. One of the members of our Satellite Operations Center team can aim the death-ray laser at the offending station during the next orbit. We have a SOC that makes the CIC in Wargames look like child's play. :D
    WD9EWK, NJ4Y and WE4B like this.
  7. K3RLD

    K3RLD Ham Member QRZ Page

    The only way to win, is not to play.
    W5SAT, NJ4Y, WE4B and 1 other person like this.
  8. N8HM

    N8HM Premium Subscriber QRZ Page

    With a linear transponder, you could analyze the Doppler shift of the signal and calculate its location. Locating a signal through its Doppler shift was actually first demonstrated on AMSAT-OSCAR 6 and lead to the Cospas-Sarsat system for locating distress beacons (one of many technologies pioneered using AMSAT satellites).

    Unfortunately, AO-92 is a single channel FM repeater with an AFC circuit, so both the FM capture effect and AFC circuit combine to make such an analysis impossible.
    WD9EWK, NJ4Y and WE4B like this.
  9. K3RLD

    K3RLD Ham Member QRZ Page

    What about XW-2F? You would only have "half" a pass to work with, but would that be enough?
    WD9EWK likes this.
  10. N8HM

    N8HM Premium Subscriber QRZ Page

    It's possible. If the offending signal is there, you could record the spectrum Doppler corrected for your location. I have no idea how to interpret the data though.

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