[hpsdr] HORTON

[John B. Stephensen]

There are also high-performance Gilbert-cell mixers, such as the LT5512 and
LT5517. These often eliminate the need for an LO amplifer as they contain an
LO limiter.

Good DBMs for UHF and VHF are the Mini-Circuits
SYM-30DHW/SYM30-DMHW/SYM30-DLHW series that each operate over 5-3000 MHz.

73,
John
KD6OZH

----- Original Message ----- 
From: "KD5NWA" <kd5nwa at cox.net>
To: "Eric Blossom" <eb at comsec.com>
Cc: <hpsdr at hpsdr.org>
Sent: Saturday, June 10, 2006 20:09 UTC
Subject: Re: [hpsdr] HORTON


> ***** High Performance Software Defined Radio Discussion List *****
>
> The switch time is the killer, most FET switches can handle 100's of
> MHz but are slow at switching which makes them unusable.
>
> Give consideration to using a Doubly Balanced Diode Mixer, they are
> inexpensive, and good to GHz frequencies. They have a 6dB loss but
> that can be made up in the pre-amp.
>
> At 03:02 PM 6/10/2006, you wrote:
> >***** 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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