[hpsdr] Odyssey Active QSD Rev. A Schematic

[Steven Bible]

Hi Ahti,

Thanks for your analysis.

Phil H. alerted me that I may not want to drive it from two overlapping 90
degree square waves.  Is the Johnson counter appropriate?

Also, Bob N4HY alerted me to the circuits on the HPSDR SVN by Phil C.  So I
will study them as well.

73,

- Steve, N7HPR
 (n7hpr at tapr.org)


> -----Original Message-----
> From: Ahti Aintila [mailto:oh2rz.sdr at gmail.com]
> Sent: Friday, September 29, 2006 1:26 AM
> To: Steven Bible
> Cc: hpsdr at hpsdr.org
> Subject: Re: [hpsdr] Odyssey Active QSD Rev. A Schematic
>
>
> Steve (and the Gang),
>
> It seems to me that your circuit should work as such. Here are  just
> few comments to be taken with a grain of salt, because I am an analog
> designer from the vacuume tube era:
> 1. Keep the extra component pads for easy changes during the prototyping.
> 2. 74HC74 may be too slow for 42.76 MHz, try 74LVC74A.
> 3. According to my quick checking of truth tables, maybe, Q-Clock is
> leading 90° to I-Clock. It should be opposite. In any case, it is just
> a matter of reversing the output wires.
> 4. R5 and R7 should match the input impedance to 50 ohm. The exact
> value depends on the actual duty cycle of the sampling pulses, the
> internal resistance of the switches and the values of R6, R3, R8, R21,
> R18, R23. Possibly some of these resistors should be removed in the
> final design. Hoever, due to any parasitic coupling of switching
> spikes and internal capacitances of the semiconductor components and
> circuit board traces, maybe that R5 and R7 are partly or totally
> tranferred after the swithes to the places of R3, R8 and R18, R23
> respectively. R6 and R21 may be unnecessary.
> 5. It is useful to have the output capacitances C4 and C16 for
> improving the filtering of the  transients that may get coupled in due
> to the eventual unbalance of the 0.01µF capacitors.
> 6. If the common and/or differential mode components in the output I
> and Q signals are problems, output coupling capacitors may be used.
>
> I hope, these comments help.
> Good luck and 73,
> Ahti OH2RZ
>
>
> On 29/09/06, Steven Bible <srbible at earthlink.net> wrote:
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> >
> >
> > Gang,
> >
> > Here it is, revision A version of the schematic using Ahti's
> active QSD circuit connected to a TI Codec.  The TI codec will be
> connected to a dsPIC33FJ256GP710.
> >
> > You will notice that I added some extra components and labeled
> them with ? values.  These parts are just a guess as to weither
> they are needed or not.  I thought to place the foot prints for
> prototyping purposes.  However, I do know the circuit well, so
> I'll allow the group to comment.  If they are not needed at all,
> I'll removing them.
> >
> > Comments please.
> >
> > - Steve N7HPR
> >
> >
> > \r\n- Steve\r\n  (n7hpr at tapr.org)\r\n
> >
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> >
> >


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