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
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