Hello David, Yes, the "steam-gauge" altimeter that relies on the pressure altitude is verymuch still in use and is in fact required instrumentation for instrument flight, alongwith a requirement for biennial re-certification and calibration. With the advent of GPS, terrain avoidance displays are employed in an effort to reduce the incidents of CFIT (Controlled Flight into Terrain) but a number of aircraft still use the radar altimeter systems. I have experience with the radar altimeterin the approach segment of flight and personally I always found that instrumentuseless during the approach.... unless the approach inside the outer marker was"corn-field flat". 73, Kermit W9XA On Thursday, December 10, 2020, 8:27:10 AM CST, david davidsiddall-law. com <david@davidsiddall-law.com> wrote: Interesting, I thought that altimeters were purely mechanical devices. The auction is in progress, but the Commission has broad discretion to delay or condition licensing if it determines that this is a safety-of-life issue. $2.6 billion dollars already has been bid after just the first 5 rounds for the 3.700-3.980 GHz spectrum. The auction can be followed here:https://auctiondata.fcc.gov/public/projects/auction107. 73, Dave K3ZJ From: arrl-odv <arrl-odv-bounces@reflector.arrl.org> on behalf of Kermit Carlson via arrl-odv <arrl-odv@reflector.arrl.org> Reply-To: Kermit Carlson <w9xa@yahoo.com> Date: Thursday, December 10, 2020 at 9:06 AM To: Michael Ritz <w7vo@comcast.net>, Kristen McIntyre <kristen@alum.mit.edu> Cc: "arrl-odv@reflector.arrl.org" <arrl-odv@reflector.arrl.org> Subject: [arrl-odv:31463] Re: Aviation Groups Seek Halt to FCC Spectrum Auction | Aviation Pros Hello Mike and Kristen, I was cleaning out the garage this weekend, and did put two radar altimeters into the electronic waste stream. These were Bendix-King units that are basically range detecting 3.5-3.6 GHz CW units that use a processed swept doppler method to display the altitude on a panel mounted gauge. I seem to remember that they were simple non-locked cavity oscillators, they had impatt diodes oscillators with a diode mixer front end. This model is currently in use and similar newer systems are improved but the requirement for selectivity had not been demanding because it operates in a portion of the spectrum designated for radiolocation...... 73, Kermit W9XA On Wednesday, December 9, 2020, 9:37:20 PM CST, Kristen McIntyre <kristen@alum.mit.edu> wrote: My guess is that if there are cellular carriers in ornear the frequency range used by radar altimeters, they could easily interfere when flying over the towers. Probably S-band at 3.2 GHz. Those are strong signals and there might be enough energy to cause de-sensing. Radar altimeters are most common on helicopters which fly pretty low and need AGL altitude accuracy to avoid terrain. On Dec 9, 2020, at 3:11 PM, Michael Ritz <w7vo@comcast.net> wrote: I don't understand the issue. The FCC is supposed to be vacating others off those frequencies, meaning they have to go somewhere else. Is this a situation where the particular propagation of 3.5 GHz signals will affect wideband receivers used in the radar altimeters? I guess I don't know how they work..... 73; Mike W7VO On 12/09/2020 1:25 PM Kristen McIntyre <kristen@alum.mit.edu> wrote: Above our allocation, but it might be relevant to the ultimate disposition of that band. https://www.aviationpros.com/aircraft/business-general-aviation/press-releas... -Kristen (K6WX) "Your eyes ... it's a day's work just looking into them" Laurie Anderson (--... ...-- -.. . -.- -.... .-- -..-) _______________________________________________ arrl-odv mailing list arrl-odv@reflector.arrl.org https://reflector.arrl.org/mailman/listinfo/arrl-odv _______________________________________________ _______________________________________________ arrl-odv mailing list arrl-odv@reflector.arrl.org https://reflector.arrl.org/mailman/listinfo/arrl-odv