[hpsdr] [CASMIR] Design Thoughts

[Ann & Sheldon Hands]

----- Original Message -----
From: "Lyle Johnson" <kk7p at wavecable.com>
To: "Alex" <harvilchuck at yahoo.com>
Cc: <hpsdr at hpsdr.org>
Sent: Saturday, May 27, 2006 6:57 PM
Subject: Re: [hpsdr] [CASMIR] Design Thoughts


> ***** High Performance Software Defined Radio Discussion List *****
> > I'll put into a picture later this weekend, but I'd like some gut
feelings from the group.
>
> I'd sure like to see something other than a DDS, especially for HF use.
>
> 73,
>
> Lyle KK7P
: http://lists.hpsdr.org/pipermail/hpsdr-hpsdr.org/
>

10 bit technolgy on current DDS parts has not proved easy to to tame from a
spur point of view. Both SDR-1000 and Star have had problems in this
respect. Even Pic A Star ,with the advantage of elvated noise floor by way
of a rf  pre-amp on 10/12 meters, needed carefull attention to screening  to
go some way to solving the problem.

Some members of the group have latterly been using the AD9951 14 bit DDS
from www.radioamatore.it/i0cg with good sucess. This uses an interesting
approach to gain a clean clock oscillator by selecting a harmonic of
typicaly a 100mhz Butler through a Toko 500mhz 2 or 3 chamber Helical
filter.(G4HGT shows a similar circuit in a 432MHz transveter in the UHF/VHF
DX Handbook) This system could use a variation of the KD6OZH osc (QEX
NOV/DEC 1999) locked back to Gibralter.

Apart from Synchronised parts for quadrature output one might use the G0BBL
approach (RADCOM July 2001 TT or pg82 Technical Topics Scrapbook 2000-2004).
This depicts a quadrature sytstem using 2xLO rather than 4x for his groups
Tayloe transceiver QRP2000 and a later version QRP2001 from 74HC or VHC
gates.

Shel CT1IZU









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