[TowerTalk] Telrex rotator with sychro

[jimlux]

On 11/21/18 8:00 PM, Hans Hammarquist via TowerTalk wrote:
>   Jim,
> 
> It is very easy to generate the V1, V2, V3 voltages if you want a receiver synchro to be set at a certain angles.

I'm thinking about the other direction - you have a synchro transmitter 
on the tower, and you want to measure it in the shack.



  You can even us a DC voltage for that. You just use the equations you 
show and replace the
> "cos(fline*2*pi*t)" with "1". It gets trickier to go the other way around as "C" not necessary is constant. You have to calculate that out of the know value of V1, V2, and V3.

An easy hack is to use the maximum of them (going from synchro to 
digital) or set one of them to max, and the other two at a fraction of max.


> 
> I'm sure there is an easy way to do that but it become a "little" easier if you first make a Scott-T transformation (see Wikipedia "Scott-T transformer) because your equations will be easier to reverse and calculation of "C" easier too.
> 
> C=(Vr^2*Vi^2)^1/2
> 
> theta=arctan(Vr/Vi)
> 
> When you finally are ready to implement your algorithm you have to make a synchronous rectification somewhere to get the value and the sign. You can do it before the A/D converter with a synchronous rectifier or probably with the software. (I would love to see a software that can do this. It should be possible.)

I was thinking more about just digitizing the AC waveform and 
calculating the amplitude by fitting a sine wave.

Or, it might be easier (I've not fooled with it yet) to turn each of the 
3 voltages into a complex number by "mixing" with cos/sin at the 
excitation frequency.



> 
> Regarding the precision there are a few things to keep in mind. It is very important that the output voltages are kept good. That means that the attenuation in the signal lines have to be the same. If one of them is off you will experience an error in your read-out. Therefore, the control cable has to be of a good quality with even wire thickness and resistance along the cable. You have to use five wires, two for th excitation and three for the return signals. You can not use a common wire for excitation and signals at that would introduce errors.
> 
> There are commercial IC-s around that will do this. 


Yes and they cost about $2000 for some reason. Probably a limited 
market. The last time I used them was in the late 90s, early 2000s, and 
when I checked last week, it hasn't changed much.  They're actually a 
thick film hybrid in a package that looks like a 24 or 28 pin DIP, but 
with a stainless steel can.


I know one application where a virtual sychro is virtually rotated and 
the "C" is adjusted until the V'1, V'2 and V'3 are as equal to the 
received signal as possible (leaving room for variations in an 
unbalanced attenuation). You notice that adjustment process as the 
output signal varies untill the readout stops at the correct value.
> 
> Who will be the first to make a Ham-type software to decode the sychro signal? I will be the first in line to get it.


> 
> 73 de,
> 
> Hans - N2JFS
>   
>   
> -----Original Message-----
> From: jimlux <jimlux at earthlink.net>
> To: towertalk <towertalk at contesting.com>
> Sent: Mon, Nov 19, 2018 10:14 am
> Subject: Re: [TowerTalk] Fwd: Telrex rotator
> 
> On 11/19/18 6:31 AM, Hans Hammarquist via TowerTalk wrote:
>> Hi Martin,
>>
>> Decoding the signals from a selsych is a "little" complex as it require you to do A/D convert all three signals at the same time, then do the mathematical quirk to calculate the angle out of that. Not impossible.
> 
> Assuming you don't need microdegree accuracy, and 1 degree is good
> enough, you don't actually need "precisely synchronized" sampling,
> ...
> 
> The voltage on each winding is:
> V1 = C* cos(theta)*cos(fline*2*pi*t)
> V2 = C* cos(theta+2pi/3) * cos(fline*2*pi*t)
> V3 = C* cos(theta+4pi/3) * cos(fline*2*pi*t)
> 
> 
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