On 31 Mar 2008 at 4:18, drmail377 wrote: > Hi Jack, > > Do have a look at Dave WB6HDW's fine DDS SDR and filter kits. I see he > already posted a reply to you. If you want general coverage, then you > want to use a DDS (see detail below). Plus, you need to use > differential amplifiers on the QSD output instead of op-amps to reduce > the affect of antenna impedance changes. A purist might also want to > put a preamplifier/preselector on the front end of the radio to > further isolate the affects of changing antenna impedance on > performance. But many will argue that a preamp is not necessary and > may actually be harmful as the dynamic range of the QSD is > compromised. I don't believe the WB6HDW SDR has a preamp, but I think > it does use differential amplifiers. > No, it uses a regular OP amp. The circuit is basically a clone of the SoftRock with very high frequency dividors in the quadrature generator to handle the max frequency of the DDS and faster switches in the QSD.
Dave - WB6DHW <http://wb6dhw.com>
