Re: [AFMUG] C band 5G vs Radar Altimeters

Sun, 12 Dec 2021 15:17:22 -0800

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.
 
Sent: Sunday, December 12, 2021 1:57 PM
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.
 
Sent: Sunday, December 12, 2021 1:05 PM
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. 
 
Sent: Sunday, December 12, 2021 12:19 PM
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.

From: "Chuck McCown via AF" mailto:af@af.afmug.com
To: "AnimalFarm Microwave Users Group" mailto:af@af.afmug.com
Cc: "Chuck McCown" mailto:ch...@go-mtc.com
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:af...@ics-il.net wrote:


If radio altimeters have 200 MHz (which seems excessive), it seems equally excessive to be complaining about noise from 200 MHz away.

From: "Tim Hardy" mailto:thardy...@gmail.com
To: "AnimalFarm Microwave Users Group" mailto:af@af.afmug.com
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 <af@af.afmug.com> wrote:
 


--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
 
--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com

--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
 
--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com

--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com




-- 
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com

Reply via email to