03-03-2012, 02:25 PM
Thanks Al, no worries, I don't think the Mini-Circuits SBL1 is in production anymore but some NOS are still available, the nearest Mini-Circuits double balanced mixer that is still in production that I found is their ADE 1L, these are not expensive and are more or less the same spec as the SBL1 but with slightly less insertion loss. As regards matching the 50 ohm ports to valves I was thinking maybe for the A/F out port a simple A/F step up transformer to the cathode input of a simple grounded grid cascade twin triode, this would make the turns ratio on a homewound matching transformer a lot lower, I think maybe matching the 50 ohm R/F in port and Osc in port to the R/F amp and Osc might be reasonably straight forward, the idea of an R/F amp is to overcome to a certain extent the insertion loss of the passive mixer, Mini-Circuits do active versions of their double balanced mixers ie: buffered, but I am trying to keep whatever I eventually build to valves and diodes only. From what I can gather the impedance matching of the output port is the most criticall in preventing the mixer being out of balance ie: R/F and Osc breakthrough.
Lawrence.
Lawrence.
