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. 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.
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.)
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. 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@earthlink.net>
To: towertalk <towertalk@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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