[time-nuts] tube GPS receivers

[Jim Lux]

On 6/22/13 3:28 PM, Magnus Danielson wrote:
> On 06/23/2013 12:04 AM, Jim Lux wrote:
>> I think that doing the PN code and correlator is something that could be
>> done with tubes (especially if you didn't want to go P-code).
>>
>> I suppose you could use a counter to record the changes in code phase as
>> you scan for the correlation peak, so that gets you your numeric code
>> phase.
>>
>> Getting doppler as a number for computation might be tricky, but you
>> could probably solve for the position and clock offset without using
>> doppler.
>>
>> Decoding the nav message at 50bps should be straight forward.
>
> All that is relatively trivial... compared to
>
>> Hmm. what about implementing the nav calculation as an analog computer.
>> ANalog multipliers were built using vacuum tubes.
>
> You will need more ummpf to do the trigonometry. If you go
> electromechanical you can do it, but it will be rough estimation
> regardless. CORDIC was made for these circumstances, to let a weak
> processing mechanism do navigation processing for airplanes. You could
> do CORDIC in tubes or relays. Bunch of transistors and diodes could make
> minor wonders in compactness.
>


electromechanical.. like omega receivers.  rotary transformers can do 
very high quality trig functions, but do you actually need trig 
functions assuming you're just solving for X,Y,Z,T.

Are you allowed to externally supply the almanac, in the form of a 
electromechanical system.  The satellites are in circular orbits and 
fairly stable, and with multiple satellites in the same plane.

You'd only need trig to convert X,Y,Z into lat/lon, and for us timenuts 
types, do you really need lat/lon? In fact, do you even need to solve 
for earth centered coordinates?  Why not work in inertial space (whether 
your receiver happens to be moving in a circle at 1 rev/24 hrs or flying 
in a plane at something else is sort of immaterial)


I envision something with a common shaft running at 1 rev/12 hours that 
drives N rotors (one for each satellite).  there's a small motor that 
sets the offset of the rotor relative to the shaft to account for small 
movements along the orbit plane.  That, plus some other transformers 
would give you X,Y, and Z for each satellite.


Actually, how bad would your time estimate be if you just assumed 
perfect circular orbits with no higher order corrections?