Jock Cooper wrote in message ...
Hi everyone,
...
How do you diagnose a bad
oscillator circuit?

Roy offered some good advice. No need for me to try to duplicate it!
But I know there can be a lot of times you just don't see something
that would be obvious to someone else who has more experience. If you
can find someone locally to have a look at things, the answers might
come a lot quicker. Failing that, if there's a place you could put up
some pictures on the web, that might help.

Are you using known-good circuits? Sounds like you probably are,
given that you understand the differences among the various types of
circuits. But it might be good to get your hands on a book with a
bunch of circuit ideas in it, if you don't already have one (or more).

Cheers,
Tom

"Jock Cooper" wrote in message
...
Hi everyone,

I've been interested in radios and how they work since I was a kid --
I had a crystal radio kit and a RF-2200. Recently I started building
radios and have been having a blast. Please keep in mind that I
am very newbie.


[tale of woe deleted]

I'd start again with a simple Hartley oscillator using a tapped toroid (you
don't need a choke). Get the basic oscillator working (a scope helps) then
add a buffer stage.

Forget about getting the oscillator and front end tuning to track properly
at this stage, use separate capacitors. When you get the thing working
properly you can sort out the tracking.

73, Leon
--
Leon Heller, G1HSM

http://www.geocities.com/leon_heller

Hi Jock,
there is nothing you should apologize for. My recommendations:
1/ Do not use breadboards for RF. They are perfect for AF, good for
digital citcuits, but RF circuits sometimes work, more often not. And
keep the groundplane as big as possible. The "ugly", "rats-nest",
"dead bug" or "manhattan" style really seem to be far the best for RF
prototyping. Look at
http://w1.859.telia.com/~u85920178/blocks/deadbug_0.htm for more info.
2/ Get an oscilloscope covering at least three times your frequency
range. An add-on unit for your PC can turn it into an oscillscope and
spectrum analyzer for a fair price.
3/ Use the necessary tuning capacitors and their configuration to keep
the oscillator and input frequency near to each other at more than one
point. The configuration and formulae can be found in many books.
4/ Try the oscillator from
http://w1.859.telia.com/~u85920178/blocks/osc7m00.htm ,it should work
reliably in a wide frequency band.

BR from Ivan OK1SIP

Hi Jock,
there is nothing you should apologize for. My recommendations:
1/ Do not use breadboards for RF. They are perfect for AF, good for
digital citcuits, but RF circuits sometimes work, more often not. And
keep the groundplane as big as possible. The "ugly", "rats-nest",
"dead bug" or "manhattan" style really seem to be far the best for RF
prototyping. Look at
http://w1.859.telia.com/~u85920178/blocks/deadbug_0.htm for more info.
2/ Get an oscilloscope covering at least three times your frequency
range. An add-on unit for your PC can turn it into an oscillscope and
spectrum analyzer for a fair price.
3/ Use the necessary tuning capacitors and their configuration to keep
the oscillator and input frequency near to each other at more than one
point. The configuration and formulae can be found in many books.
4/ Try the oscillator from
http://w1.859.telia.com/~u85920178/blocks/osc7m00.htm ,it should work
reliably in a wide frequency band.

BR from Ivan OK1SIP

Jock Cooper writes:

Hi everyone,
[snip]

Thanks to everyone for the great and helpful suggestions. This sure
is a friendly group.

Since I just recently started all this tinkering, my junkbox is a
little low in some areas, notably NP0 capacitors.. I have a few in
values from 3.9 up to 47 and a few 100s but not else. So I've used
various other types when higher values are called for.. I'm planning
on picking up an assortment soon.

Also I have some copper clad non drilled pc boards, I'm going to try
to rebuild the oscillator (and radio) using the 'ugly' method;
although I'm a little afraid I'll make myself a tangled mess of
useless and stuck together parts. The main reason I use breadboards is
so that I can take parts in and out of the circuit quickly (ie I'm at
the stage where I'm curious about what happens when I take such and
such part out, or change its value etc).

I'd love to get a oscilloscope but my 'play' budget is mostly spent
for awhile. So I've been making due with an LCR and a little cheapo
DMM.

I did order the book _Experimental Methods in RF Design_ .. I've also
got a lot of good info from an old (well 1998) ARRL handbook I got
on Ebay.

Jock

Jock Cooper writes:

Hi everyone,
[snip]

Thanks to everyone for the great and helpful suggestions. This sure
is a friendly group.

Since I just recently started all this tinkering, my junkbox is a
little low in some areas, notably NP0 capacitors.. I have a few in
values from 3.9 up to 47 and a few 100s but not else. So I've used
various other types when higher values are called for.. I'm planning
on picking up an assortment soon.

Also I have some copper clad non drilled pc boards, I'm going to try
to rebuild the oscillator (and radio) using the 'ugly' method;
although I'm a little afraid I'll make myself a tangled mess of
useless and stuck together parts. The main reason I use breadboards is
so that I can take parts in and out of the circuit quickly (ie I'm at
the stage where I'm curious about what happens when I take such and
such part out, or change its value etc).

I'd love to get a oscilloscope but my 'play' budget is mostly spent
for awhile. So I've been making due with an LCR and a little cheapo
DMM.

I did order the book _Experimental Methods in RF Design_ .. I've also
got a lot of good info from an old (well 1998) ARRL handbook I got
on Ebay.

Jock

Jock Cooper wrote:

I tried numerous circuits and numerous types (Hartley, Colpitts etc) I
had found but I couldn't get any of them to start up.

Oh, that's easy. You're *trying* to build an oscillator; give up on
that goal and choose an easier one: try to build an amplifier. I mean,
really *want* to build a stable amplifier. Voila! An oscillator!!

Dana K6JQ

I tried numerous circuits and numerous types (Hartley, Colpitts etc) I
had found but I couldn't get any of them to start up.

Oh, that's easy. You're *trying* to build an oscillator; give up on
that goal and choose an easier one: try to build an amplifier. I mean,
really *want* to build a stable amplifier. Voila! An oscillator!!

I once built a power supply that oscillated above 150 MHz.
Unfortunately, I could never drop it into the 2-meter band.

--Myron.
--
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)

mcalhoun wrote:
I tried numerous circuits and numerous types (Hartley, Colpitts etc) I
had found but I couldn't get any of them to start up.

Oh, that's easy. You're *trying* to build an oscillator; give up on
that goal and choose an easier one: try to build an amplifier. I mean,
really *want* to build a stable amplifier. Voila! An oscillator!!

I once built a power supply that oscillated above 150 MHz.
Unfortunately, I could never drop it into the 2-meter band.


Heh. Of course a DC power supply is indistinguishable for
a 0Hz oscillator under the best of circumstances, right?

But, 150MHz. That's pretty special. What were you using
for a pass element(s) ?

Dana

mcalhoun wrote:
I tried numerous circuits and numerous types (Hartley, Colpitts etc) I
had found but I couldn't get any of them to start up.

Oh, that's easy. You're *trying* to build an oscillator; give up on
that goal and choose an easier one: try to build an amplifier. I mean,
really *want* to build a stable amplifier. Voila! An oscillator!!

I once built a power supply that oscillated above 150 MHz.
Unfortunately, I could never drop it into the 2-meter band.


Heh. Of course a DC power supply is indistinguishable for
a 0Hz oscillator under the best of circumstances, right?

But, 150MHz. That's pretty special. What were you using
for a pass element(s) ?

Dana