There is a new variant, the 74LVC4066 which may compare favorably with the FST3253 and lookalikes. I have not got any of those, but using standard 4066's I have found that using the highest voltage it can stand works OK. You get both the lowest channel resistance and the highest dynamic range that way.
Of course, using old TTL's as drivers I had to resort to an open collector inverter with resistive load tied to +12V, but then playing tricks with a split load and a shunt capacitor, I got 50 % of Vdd with a large square wave superimposed. The new VLC devices may be worth the effort, if they can be found. They may overcome the frequency limitations of the old 4066's, which only work well enough on 7 MHz, 30 meters seems to be a bit too much for the old devices. The VLC's, being 5 volts devices with far less channel resistance, will not need any of such two voltage supply tricks. Regarding op amps, creativity does not need to be limited, just find a newer less noisy op amp that is pin compatible. I used TL084's on my design and on 40 meters they seem to be acceptable. Maybe the higher bands would do better with a less noisy op amp,..or an RF preamp with 6 or 10 dB gain and low enough NF. Perhaps a TL082 or a NE5532 could be pin compatible, I don't have their data sheets at hand now. And perhaps they won't do well with only 5 volts Vcc, that is something to make sure of, too. 73, Jose, CO2JA --- Neil McGrath wrote: > I chose the Soft66db because it was reasonably priced and there were > no surface mount components. I am fairly inexperienced with surface > mount construction and decided to stick with a circuit that I knew I > could build successfully. The experience has certainly whetted my > appetite for another SDR project and I may venture into the realms of > surface mount in the future. > > Neil > G7AQK > > --- In [email protected], "drmail377" <[EMAIL PROTECTED]> wrote: >> Hi Neil, >> >> Sometimes where there a lot of SMT parts like bypass caps, a kit >> manufacturer will include extras as they have a tendency to "jump" off >> the tweezers, never to be seen again. By now, I'm sure there's a whole >> Colony of SMT parts plotting against me somewhere in the shack! >> >> May I ask why you chose to build the Soft66B receiver? It seems like a >> dated design; a 4066 instead of an FST3253 for the QSD and relatively >> noisy LM358 op-amps. Wouldn't one of the recent Softrock kits have >> been a better choice both performance and price-wise? >> >> 73's David, WB4ONA
