I put up 11 pictures of recent progress on the two-stage transformer. I'm calling it a done deal for now, until I get around to final driver amplifier design and construction. The transformer design is now set with T1 primary at 18 turns 22 AWG bifilar, series connected. With the 4.5:1 T2 ratio, it's about 162:1 overall, so Z ratio about 26,000. Fed from my test circuit (in 25 R mode hookup), the output Z magnitude should be about 1 milliohm. After some study and design of the overall system using the 8568B and TG for dBQ display as I mentioned before, I have determined that a fixed output level around a mV is sufficient, so a modest amplifier is needed, rather than a much higher-powered one I had pictured before. The desired signal level is attainable without any amplifier, from the TG, which provides just a little over 0 dBm in 50 R, but I'll put in some gain to allow for more margin, and to reduce the driver (and hence output) Z a lot more, which also will drop the lower cutoff frequency to around 5-10 kHz.
The pictures are mostly self-explanatory, and I'll add lots of details next time. The main thing is to note the wide BW and good flatness, and the very low output Z that can take an almost dead short - me pressing a wad of copper mesh against the post and bushing as hard as I could without hurting my thumb - and dropping only about 10 dB, and still very flat at all frequencies. There is one oddity in the 1 dB/div picture. The dip around 7-8 MHz I believe is an artifact of the TG due to mismatch in the test circuit. Changing the cable length here moves it around in frequency. It should (hopefully) disappear after the amplifier is in the system.
BTW I probably should have made a new album for these, to avoid confusion with the older version and pictures. When I went to do the upload, I thought I could make a sub-folder inside, but could not figure it out.
Ed
