There is really great info on this page, and even more in the links at the bottom of it. While the page is about PTOs, the links often discuss their use in Direct Conversion Receivers. I really liked the Tin Ear receiver. And it was great to again come across the work of Alan Yates VK2ZAY. Alan very admirably admits that laziness caused him to use an LM386 audio amplifier in place of a more virtuous discrete transistor design.
https://qrpbuilder.com/pto_mechanism
I bought one of the qrpbuilder PTO kits and I will soon put it together. I have been having good results with a Glue Stick PTO and with a brass screw PTO form designed by Farhan and 3D printed for me by Dean KK4DAS.
LET'S GO PTO!
Why not dig up the one or two PTO articles in 73 in the sixties. I think there was one in QST then too. Real PTOs, so the knob doesn't move to and from the panel. Took skill. And probably worth it back then.
ReplyDeleteI seem to recall that spreading the winding linearized it, which is probably why Collins went with PTOs.
Non hamband receivers mostly had 2:1 tuning ranges until the digital synthesizer era. Impossible to linearize. Collins was radical, 500KHz per band,but extra cost for all those crystals.