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 or near 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-release/21165637/aopa-aviation-groups-seek-halt-to-fcc-spectrum-auction


                                    -Kristen (K6WX)

"Your eyes ... it's a day's work just looking into them" 
                                       Laurie Anderson

(--... ...--  -.. .  -.- -.... .-- -..-)

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