Ham radio nets served as social media, Sent from my iPhone
> On Dec 12, 2021, at 4:16 PM, Bill Prince <[email protected]> wrote: > > > A lot of things were different in the fifties. There was no internet. Car > transmissions were mostly manual. Modems were sub kilo-bit speeds. Phones had > round dials (and touch tone did not exist). > > > > bp > <part15sbs{at}gmail{dot}com> > On 12/12/2021 1:17 PM, Chuck McCown via AF wrote: >> But it was probably not developed in 1955. >> >> From: Bill Prince >> Sent: Sunday, December 12, 2021 1:57 PM >> To: [email protected] >> Subject: Re: [AFMUG] C band 5G vs Radar Altimeters >> >> Yet somehow the range-finding in my Mazda can figure out the distance to the >> car in front of me and adjust accordingly without a flat surface or using >> much bandwidth. >> >> >> >> bp >> <part15sbs{at}gmail{dot}com> >> On 12/12/2021 12:22 PM, Chuck McCown via AF wrote: >>> 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" mailto:[email protected] >>> To: "AnimalFarm Microwave Users Group" mailto:[email protected] >>> Cc: "Chuck McCown" mailto:[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 mailto:[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" mailto:[email protected] >>> To: "AnimalFarm Microwave Users Group" mailto:[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 >>> >>> >> -- >> 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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