Message	Date	From	Subject
3025	2009-05-13 06:24:00	w1kilofoxtrot	Buffer amplifier distortion
I'm suffering from extreme brain fade, and I'm looking for a clue. I've built a 14 MHz VFO for my R2T2 'Pro' project. (Colpitts, J-FET, Varactor tuning)It's working fairly well. I built up a buffer amp from the 2004 Handbook, and it didn't work. (Fig 14.17) I saw a similar buffer in EMRFD, and it mostly fixed the problems, since it included the proper biasing the first circuit lacked. It's the buffer in Fig 6.151. (The 10K from the first base to ground was omitted in the HB version.) My version outputs a sine wave that has a look more like a sawtooth. That is, the rising slope is different than the falling slope. I don't have my spectrum analyzer available, so I'm trying to figure out what I might have done wrong. The component values all seem correct, so the big variable is the transformer, I guess. If anyone has been through this, and can offer suggestions, I'd be obliged. As soon as it's clean, the T2Pro will be ready for testing! 73, Steve W1KF
3031	2009-05-14 00:21:01	Vaclav Peroutka	Re:[emrfd] Buffer amplifier distortion
> > My version outputs a sine wave that has a look more like a sawtooth. > Hi Steve, on amp's input the sine is ok ? You take the signal from LC tank ? Does your amp work in linear region ? If nothing helps, use ouput LC low pass filter. But this way you do not solve the problem, you just cure the symptoms. 73, Vasek
3134	2009-05-27 06:31:38	w1kilofoxtrot	Re: Buffer amplifier distortion

I'm suffering from extreme brain fade, and I'm looking for a clue.

I've built a 14 MHz VFO for my R2T2 'Pro' project. (Colpitts, J-FET, Varactor tuning)It's working fairly well. I built up a buffer amp from the 2004 Handbook, and it didn't work. (Fig 14.17) I saw a similar buffer in EMRFD, and it mostly fixed the problems, since it included the proper biasing the first circuit lacked. It's the buffer in Fig 6.151. (The 10K from the first base to ground was omitted in the HB version.)

My version outputs a sine wave that has a look more like a sawtooth. That is, the rising slope is different than the falling slope. I don't have my spectrum analyzer available, so I'm trying to figure out what I might have done wrong. The component values all seem correct, so the big variable is the transformer, I guess.

If anyone has been through this, and can offer suggestions, I'd be obliged. As soon as it's clean, the T2Pro will be ready for testing!

73,
Steve
W1KF