[hpsdr] HORTON

[KD5NWA]

This one needs to be read carefully, fairly poor isolation between LO 
and out and RF IN and IF out,  and a lot of loss, might not a DDRM do better?

At 08:33 PM 6/10/2006, you wrote:
>***** High Performance Software Defined Radio Discussion List *****
>
>A FET array designed for use as a mixer should perform much better. Look at
>the Pergrine Semiconductor PE4140.
>
>73,
>
>John
>KD6OZH
>
>----- Original Message -----
>From: "Eric Blossom" <eb at comsec.com>
>To: <hpsdr at hpsdr.org>
>Sent: Saturday, June 10, 2006 20:02 UTC
>Subject: [hpsdr] HORTON
>
>
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> > I've been doing some thinking about HORTON.
> >
> > It seems to me that the biggest problem with getting the QSD to run
> > fast is finding switches/muxes that are fast enough.
> >
> > In my searching, the fastest CMOS FET mux I've come across to date
> > is the TI SN74CB3Q3253.
> > http://focus.ti.com/docs/prod/folders/print/sn74cb3q3253.html
> >
> > The problem with these isn't the "High-bandwidth data path (upto 500
>MHz)",
> > but rather it's the relatively slow speed at which you can switch
> > them.  According the specs, this part maxes out at 20 MHz, but perhaps
> > it could be pushed a bit past that.
> >
> > The ADG901 has a similar problem.  It's flat out past 1 GHz, but
> > the typical switching time is 4.7ns (worst case 7.75ns: 129 MHz).
> >
> > I'm interested in getting a QSD running at at least 100 MHz, but why
> > not try for 145 MHz while we're at it.
> >
> > To run at 100 MHz (passive radar application), the switches need to
> > work at 400 MHz.  You're feeding it quadrature LO at the center freq,
> > but the difference between I & Q is 90 degrees.
> >
> > Sythesizing the control of the switches shouldn't be a problem.  E.g.,
> > use a DDS to generate the I & Q LO, filter, run that into one of the
> > very nice ADI clock distribution parts (AD9511 and friends).  These
> > will give us differential LVPECL out.  A bit of LVPECL fanout
> > buffering and some AND/NAND ECL will generate the switch enable
> > signals, no problem (modulo level translation).  We should be able to
> > run this at 700 - 800 MHz, no problem.
> >
> > So, then we return to the original question: What's the fastest analog
> > switch we can find?
> >
> > Are there faster FETs available in technologies other than CMOS?
> > E.g., GaAs or SiGe?
> >
> > I don't think we need the signal path to be flat out past 150 MHz,
> > but we do need them to switch quickly ;)
> >
> >
> > Regarding the converter, the AD7762 (parallel) or AD7763 (serial) look
> > like a better fit than the AD7760.  The '62 and '63 sample at 625kS/s
> > (or lower, it's a delta-sigma part), with better dynamic range than
> > the 7760.
> >
> >
> > I'd like to end up with a system that contained 4 HORTONs, a board to
> > generate the quadrature LO and sample clock for all 4 HORTONs, and
> > some way to get it all back into the PC.
> >
> > Comments, suggestions, etc?
> >
> > Eric
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Cecil Bayona
KD5NWA
www.qrpradio.com

"Windows the worlds most successful software virus" 


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