Re: [Discuss-gnuradio] Implementing Dicke switching

[Matt Ettus]

Marcus Leech wrote:


>
> In order to do this, I need to know which samples correspond to "sky"
> and which samples correspond to
> "calibration source" as I'm processing them.  One thought I had was to
> synthesize a pair of identical channels,
> one called "Sky" and the other called "Calibration", and have the code
> that flips the hardware switch set
> a multiplier on each of these channels to either 0 or 1.  That is:
>
>    when the hardware is switched to "Sky":
>
>    skychan *= 1.0
>    calibchan *= 0.0
>
>    when the hardware is switched to "Calib":
>
>    skychan *= 0.0
>    calibchan *= 1.0
>
> With the two channels being low-pass filtered separately, then one is
> subtracted from the other to produce a
> synchronously-detected result.
>
> How can I make sure that the chanels are properly synchronized with
> the hardware state of the switch?
>

Once inband signalling is done, this shouldn't be hard at all.  In the
mean time, here is what I would suggest --

Dicke switches have typically used rates in the low hundreds of Hz, with
a 50% duty cycle.  My understanding is that is not necessary, and was
only done to make things easier with the electronics of the time.  I
think I would switch at a much lower rate, 1 Hz or less, and probably
use a calibration duty cycle on the order of 10%.  This way you can
easily throw out some samples on either side of the switch time without
having to worry too much.

Matt