On 3/14/12 9:14 PM, J. Forster wrote:
On 3/14/12 8:07 PM, J. Forster wrote:
John
Like your thought. I seem to remember costas loops work like that to
recover the carrier.
Paul,
It recovers a bipolar signal to steer the local VCO as well as the
data..
It also needs a quadratue hybrid at the VCO frequency (although it might
be fairly easy to make a quadrature oscillator vat 60 kHz.)
One easy scheme is to make your VCO run at a multiple and divide down to
generate the two quadrature square waves.
Doesn't look like that works with the HP 117A. I don't know about other
receivers.
Had seen it in amsat many years ago. So perhaps an approach is to limit
if possible the incoming signal.
I'm not sure if it works properly with clipped (digital) dignals, off
hand.
Yes it will.
Not w/o a quadrature drive to the mixer/multiplier. A square wave,
multiplied by itself, has the same output as input.
Oh... I was assuming you had the two quadrature square waves (which are
just like the saturated LO for the mixer in RF land)
Though further simple dumb thought. A NE602 or SA602 or also teh 612
series. All the same mixer circuit (Or multiplier)will double the
incoming
frequency if you delay the incoming by 90 degrees I think.
Sine and Cosine are orthogonal. You need to do (Sine)*(Sine)
sin^2 (wt) = 1/2(1 - cos (2wt)
This is like the classic squaring technique to receive PN coded signals
without knowing the code. (it's used in some "codeless" GPS receivers..
you can retrieve frequency and phase)
A Costas Loop recovers the bit stream and the carrier frequency (from the
local VCO) from a BPSK. It is self syncronizing.
Yes.. but if you don't care about the bitstream, and you want simpler
hardware, squaring works. (especially if the modulator doesn't have good
carrier suppression)
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