Re: T41 Alternative VFO arrangement but will it work?
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I suggest checking the propagation delay through the inverter.? It will be somewhat temperature dependent but nearly constant in time for a particular device.? Constant in time means a different number of degrees in phase, depending on the frequency.? Analysis should show whether this is important or not. Andy KB3KX
On Monday, September 18, 2023 at 12:44:31 PM EDT, Harry Brash <harry.brash@...> wrote:
I was planning to convert my V10 system to run like V12 with two clocks phased 90 deg apart and was wondering what to do with the 74AC74s which are already mounted on the V10 QSD and QSE boards.
I¡¯m going to try a different system which may have some advantages over V12 or, of course, it may not work at all.
I am going to run two Si5351 clocks at the same frequency as in the V12 but I¡¯m not going to use phase control.? For that reason, the clocks can each run down to about 1MHz.? I am going to turn on invert on one clock so that the clocks are now 180 deg apart (they will be on the same PLL and there will be a PLL reset to sync them.
Both Si5351 clocks will run at twice the wanted output frequency and will each be divided by 2 by half a 74AC74 to give two output signals at the right frequency and separated by 90 deg ready to drive the demodulator and modulator in the QSD and QSE respectively.
The two clocks will tune down to about 500kHz which will allow top band to be included and they will probably still allow 6m at the other end.
I¡¯m about half way through modifying the QSD so if you think this won¡¯t work please explain why and save me some effort!!
One remaining issue is to sync the two divide by 2s so that their behaviour is predictable.? I think I have a simple solution.
Harry GM3RVL
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