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  • Why are airlines predicting doom and gloom about 5G?

    From Bill Horne@21:1/5 to All on Wed Jan 19 13:09:53 2022
    This is a multi-part message in MIME format.
    Tom,

    Please listen to the podcast available here <https://www.mondaq.com/unitedstates/telecoms-mobile-cable-communications/1151072/5g-deployment-and-radio-altimetersa-clash-of-industries-and-regulators-podcast?email_access=on>,
    and pass this along to any of the heavyweight techs in your ham club.

    Long story short: the aviation industry is hyping the possibility of
    dead bodies all over the place if the cellular carriers (which have paid
    big bucks to put 5G equipment in "C Band") don't stop and change their
    plans and go someplace else.

    Here's the point that I'm confused about: according to the podcast, the cellular authorizations go up to 3.98 GHz, and the aircraft altimeters
    that we're hearing all these dire warnings about are assigned to a range
    which starts at 4.2 GHz. I'm old-school, admittedly, but having 220 MHz
    of "guard" space between those two services seems adequate to me.

    Ergo, why the fuss?

    * Are the avionics salesmen trying to create a firestorm of fear that
    motivates airlines to buy brand new radar altimeters?
    * Do the old altimeters have substandard design?
    * Is the cellular industry choosing to ignore known risks?
    * Is it all a ploy by the cellular carriers to grab more spectrum for
    cheaper prices?

    I'm just waiting for the other shoe to drop, because there's something
    unsaid in this debate.

    Replies intended for publication should be sent to telecomdigestsubmissions@remove-this.telecom-digest.org <mailto:telecomdigestsubmissions@remove-this.telecom-digest.org?Subject="[telecom]">.

    Bill Horne
    Moderator, The Telecom Digest
    http://telecom-digest.org

    *****
    Interim moderator's response:

    The problem is that the FAA standards for altimeters required them to
    exclude signals from "more than 10%" away. That's 420 MHz of allowable
    sloop in the receiver. They made that standard in 1983 and never updated
    it. Many altimeters are better than that, but some apparently aren't, or
    aren't much better, so they can pick up signals from 3.8-3.98 GHz.

    So both sides are at least partly to blame. The FAA allowed crap
    altimeters to stay around too long, simply because there was no immediate
    need to do better. And the FCC discounted their concerns, because the
    actual risk is pretty small. Also, the FCC allowed the mobile base
    stations to operate at higher power levels than European ones can, and if
    they actually do run full power -- by no means certain, but the FAA has to
    take that into account -- then they might mess up the crap altimeters.

    Had they talked earlier, this could have been fixed quietly. Now it's two industries and their somewhat captive regulators flexing their muscles
    against each other.
    - Fred


    --
    I don't want to say that I'm old and worn out, but I'm never anywhere near the curb on trash day

    <html>
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    <p><font size="5">Tom, <br>
    </font> </p>
    <font size="5"> </font>
    <p><font size="5">Please listen to the podcast available <a
    moz-do-not-send="true" href="https://www.mondaq.com/unitedstates/telecoms-mobile-cable-communications/1151072/5g-deployment-and-radio-altimetersa-clash-of-industries-and-regulators-podcast?email_access=on">here</a>,
    and pass this along to any of the heavyweight techs in your ham
    club. <br>
    </font> </p>
    <font size="5"> </font>
    <p><font size="5">Long story short: the aviation industry is hyping
    the possibility of dead bodies all over the place if the
    cellular carriers (which have paid big bucks to put 5G equipment
    in "C Band") don't stop and change their plans and go someplace
    else. <br>
    </font> </p>
    <font size="5"> </font>
    <p><font size="5">Here's the point that I'm confused about:
    according to the podcast, the cellular authorizations go up to
    3.98 GHz, and the aircraft altimeters that we're hearing all
    these dire warnings about are assigned to a range which starts
    at 4.2 GHz. I'm old-school, admittedly, but having 220 MHz of
    "guard" space between those two services seems adequate to me. <br>
    </font> </p>
    <font size="5"> </font>
    <p><font size="5">Ergo, why the fuss? <br>
    </font></p>
    <ul>
    <li><font size="5">Are the avionics salesmen trying to create a
    firestorm of fear that motivates airlines to buy brand new
    radar altimeters? <br>
    </font></li>
    <li><font size="5">Do the old altimeters have substandard design?
    <br>
    </font></li>
    <li><font size="5">Is the cellular industry choosing to ignore
    known risks? <br>
    </font></li>
    <li><font size="5">Is it all a ploy by the cellular carriers to
    grab more spectrum for cheaper prices?<br>
    </font> </li>
    </ul>
    <font size="5"> </font>
    <p><font size="5">I'm just waiting for the other shoe to drop,
    because there's something unsaid in this debate.</font></p>
    <p><font size="5">Replies intended for publication should be sent to
    <a moz-do-not-send="true" href="mailto:telecomdigestsubmissions@remove-this.telecom-digest.org?Subject=&quot;[telecom]&quot;">telecomdigestsubmissions@telecom-digest.org</a>.<br>
    </font></p>
    <font size="5"> </font>
    <p><font size="5">Bill Horne<br>
    Moderator, The Telecom Digest<br>
    <a moz-do-not-send="true" href="http://telecom-digest.org"
    class="moz-txt-link-freetext">http://telecom-digest.org</a></font><br>
    </p>
    <pre class="moz-signature" cols="72">--
    I don't want to say that I'm old and worn out, but I'm never anywhere near the curb on trash day</pre>
    </body>
    </html>

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  • From John Levine@21:1/5 to malQRMassimilation@gmail.com on Thu Jan 20 17:26:44 2022
    It appears that Bill Horne <malQRMassimilation@gmail.com> said:
    Ergo, why the fuss?

    * Are the avionics salesmen trying to create a firestorm of fear that
    motivates airlines to buy brand new radar altimeters?

    To some degree, but a lot of it is "everything was fine until you guys
    showed up" and the FAA doesn't understand radios very well. The first
    study of interference with identified equipment only showed up a
    couple of weeks ago, after years of duelling press releases.

    * Do the old altimeters have substandard design?

    Definitely.

    * Is the cellular industry choosing to ignore known risks?

    It depends on your definition of known risks. There are duelling studies,
    the risks look pretty low to me, particularly if the telcos limit power
    in cells near runways which would not be a big deal.

    * Is it all a ploy by the cellular carriers to grab more spectrum for
    cheaper prices?

    Check how much they paid for C-band in the spectrum auction and you'll know
    the answer to that one. Heck, no. But they may end up paying a lot more
    if they're stuck with the cost of replacing every 30 year old altimiter
    in the country.

    R's,
    John

    --- SoupGate-Win32 v1.05
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  • From Dave Platt@21:1/5 to All on Thu Jan 20 12:15:49 2022
    Here's the point that I'm confused about: according to the podcast, the >cellular authorizations go up to 3.98 GHz, and the aircraft altimeters
    that we're hearing all these dire warnings about are assigned to a range >which starts at 4.2 GHz. I'm old-school, admittedly, but having 220 MHz
    of "guard" space between those two services seems adequate to me.

    Interim moderator's response:

    The problem is that the FAA standards for altimeters required them to
    exclude signals from "more than 10%" away. That's 420 MHz of allowable
    sloop in the receiver. They made that standard in 1983 and never updated
    it. Many altimeters are better than that, but some apparently aren't, or >aren't much better, so they can pick up signals from 3.8-3.98 GHz.

    There's a graphic showing that portion of the spectrum in the article
    at:

    https://www.aviationtoday.com/2021/12/23/faa-issues-new-radar-altimeter-5g-c-band-risk-assessment-request-aviation-industry/

    The "Typical RA filter tolerance mask" as shown there (without a dB
    scale, alas) is quite broad, and the 5G emission strength shown is
    quite high (higher than the radar-altimeter emissions, and far
    higher than the satellite signals previously used in that part of
    C band). I haven't found a document yet which shows the actual
    emissions strengths and masks with an accurate scale.

    My guess is that the problem with some altimeters may be one of
    "desense" (de-sensitization). If the altimeter receiver doesn't have
    sharp filters before its first active gain/detector stage, the
    out-of-band signal can saturate the gain stage, and this reduces the
    gain for the desired in-band signals. In effect, the radar
    reflections "go away" when the altimeter enters the area on which 5G
    emissions are strong. To use an audio analogy: you can't hear the
    piccolo, when the bass guitarist has cranked the volume up to 20 and
    the amplifier is clipping and the speaker cones is being driven to its
    limit. Filtering at a later point in the chain, after the point of
    amplifier clipping, doesn't help.

    It's also possible in principle for multiple, strong out-of-band
    signals to mix (heterodyne) inside the receiver, creating spurious
    signal products inside the altimeter bandwidth and "confusing" the
    altimeter.

    It's surely possible to build altimeters with the necessary filtering,
    and to replace existing altimeters with better ones, but that will
    take a long time and cost a pretty penny.

    There seem to be two issues here in the US which are making this
    problem more severe than in Europe: the authorized 5G C-band emission
    limits are higher, and the C-band antennas here aren't required to
    have a "down-tilt" pattern to limit their emissions to mostly "below
    the horizon". So, when a plane is in its landing pattern (which is
    where you'd most want the altimeter to be working correctly) it will
    enter the area where the altimeter is most likely to be overloaded
    by strong C-band 5G signals.

    --- SoupGate-Win32 v1.05
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