>From a white paper: Radar Altitude resolution is defined as where Bandwidth refers to the amount of linear frequency modulation in Hertz and c is the speed of light in meters per second. Specifications for Commercial Transport Altitude Accuracy found in industry document DO‐155 within 1.5 feet at or below 75ft of altitude and within 3 feet at or below 150 ft of altitude. These accuracy levels were determined from requirements for safety and smooth reliable performance for every landing under all visibility conditions.
The above calculation then reveals that to resolve 3ft of altitude range requires 164 MHz of modulation bandwidth. In order to reach 1.5 ft resolution would have required 328 MHz of operating bandwidth, but that is not available within the legal band. To reach 1.5 ft resolution requires “sub‐resolution” of the data by signal processing means. But this sub‐resolution is only possible with exceptionally high signal to noise ratios and over the flat surface of the runway at low altitudes. The total bandwidth is: 164MHz Resolution + 10MHz Multiple Altimeter Offset +15 MHz Frequency temperature stability results in a total 189MHz with the remaining 11 MHz of bandwidth reserved for 5.5 MHz wide “guard bands” at the band edges to assure that the minor sidebands created by the altimeter do not intrude on adjacent band users and similarly to avoid adjacent band users that might otherwise interfere with normal altimeter operations. From: Chuck McCown via AF Sent: Sunday, December 12, 2021 1:05 PM To: Mike Hammett ; AnimalFarm Microwave Users Group Cc: Chuck McCown Subject: Re: [AFMUG] C band 5G vs Radar Altimeters Start with every single airliner worldwide and probably every single military aircraft. This is a global system, global frequency allocation and brand new planes come with radar altimeters. From: Mike Hammett Sent: Sunday, December 12, 2021 12:19 PM To: AnimalFarm Microwave Users Group Cc: Chuck McCown Subject: Re: [AFMUG] C band 5G vs Radar Altimeters There can't be THAT many old planes in the air that have this automated landing system. Buy new receivers or install some filters. 5 MHz away? Okay. 10 MHz? Maybe. 200? Bugger off. They're not making new spectrum, so everyone (even incumbents) needs to move with the times. Just like the 30 MHz T1 microwave links out there. Put something else in the air more efficient. ----- Mike Hammett Intelligent Computing Solutions Midwest Internet Exchange The Brothers WISP -------------------------------------------------------------------------------- From: "Chuck McCown via AF" <[email protected]> To: "AnimalFarm Microwave Users Group" <[email protected]> Cc: "Chuck McCown" <[email protected]> Sent: Sunday, December 12, 2021 1:06:03 PM Subject: Re: [AFMUG] C band 5G vs Radar Altimeters Lots of old planes in the world. Lots of old front end filters too. And the system chirps the band to get a more sure return so it needs the bandwidth. It was designed to be robust, not to be spectrum efficient. Probably came out of WW2. Sent from my iPhone On Dec 12, 2021, at 11:45 AM, Mike Hammett <[email protected]> wrote: If radio altimeters have 200 MHz (which seems excessive), it seems equally excessive to be complaining about noise from 200 MHz away. ----- Mike Hammett Intelligent Computing Solutions Midwest Internet Exchange The Brothers WISP ------------------------------------------------------------------------------ From: "Tim Hardy" <[email protected]> To: "AnimalFarm Microwave Users Group" <[email protected]> Sent: Sunday, December 12, 2021 9:50:44 AM Subject: Re: [AFMUG] C band 5G vs Radar Altimeters Deja Vu all over again. Very similar to the OBE / adjacent channel concerns voiced in the 6 GHz unlicensed proceeding. The FCC’s total lack of understanding of receiver filtering in even current devices is astounding and its fairly clear that money / politics beats physics everyday. On Dec 11, 2021, at 3:59 PM, Chuck McCown via AF <[email protected]> wrote: I understand the issue now: https://youtu.be/942KXXmMJdY -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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