my 500kc PTO in progress

[KL7AJ]

oops...more better oscope shot......

[KL7AJ]

By the way, that waveform is taken right off the oscillator tank......no buffering or filtering.

Despite being one of the OLDEST oscillator configurations, I've ended up using the Armstrong oscillator for every VFO. There's something elegant, primitive, and "un-touchy" about the Armstrong oscillator. I think the fact that no DC passes through the tank circuit has something to do with this.

Eric

[K5UOS]

HI Don:

I have a nice collection of Minicircuits DBM modules. I'm going to be using a pretty strong local oscillator....+27 dbm, which will give me lots of dynamic range. For the audio section, I'm going to use three stages of OP-37 op amps...each stage using Salen-Key low-pass filtering....I like running multiple stages at relatively low gain...this allows me to build very sharp cutoff filters.

My next revision is going to make this an !/Q receiver, so I can do coherent detection .

Eric

I was going to offer you some of my MCL mixers. I have some level 10 and lots or level 7 of different models.

But you look like you are set.

Oscillators are the most fun thing about radio to me. With a few components and some solid mechanical construction one can build a circuit that can oscillate at millions (and millions) of cyles per second with a clean and frequency stable output.

BTW...I am partial to Colpitts but have been using more and more Hartley.

Good project! Real homebrew!

73, K5UOS

[KL7AJ]

I was going to offer you some of my MCL mixers. I have some level 10 and lots or level 7 of different models.

But you look like you are set.

Oscillators are the most fun thing about radio to me. With a few components and some solid mechanical construction one can build a circuit that can oscillate at millions (and millions) of cyles per second with a clean and frequency stable output.

BTW...I am partial to Colpitts but have been using more and more Hartley.

Good project! Real homebrew!

73, K5UOS

Hi Donald:

Thanks for the great offer! Well, don't lose track of those mixers....some folk in my electronics class might end up needing them. Minicircuits charges a fortune on shipping to AK!

Eric

[G3TXQ]

As someone who has now stripped and rebuilt four Ten-Tec PTOs, I can confirm that a successful PTO mechanical design which is smooth and avoids backlash is not trivial; I still have the scars - physical and mental

Steve G3TXQ

[AF6LJ]

That's way cool Eric.
Love to see the rest of the project as it matures.

[KL7AJ]

Well, my initial cook-in, bench test, revealed that after 24 hours, it drifted a mere 700 Hz! Not TOO shabby for an unbuffered, non temperature-compensated oscillator, with a 2n2222! The mechanical backlash is only a few hertz, so I think I got the mechanical artistry figured out.

My PTO runs on 5 volts. If I put a 5 terminal regulator in the case to drop it from the 12volt supply that runs everything else, I'll probably get enough heat to have some oven-action going...which should make the drift even less, after a short warm-up time.

One of the art forms of VFO design I learned a while back, is that it's easier to keep a VFO consistently warm than consistently cool. No big revelation here.

Stay tuned~

Eric

[K9STH]

Just add an old Hallicrafters "damp chaser" to keep everything warm!

Glen, K9STH

[KL7AJ]

I got one o them....Just wont fit in the box...HI!

Eric