Hmmm...

No, I don't believe I will have to read anything...

But, if you can't tell the difference between a white noise generator and an
osc giving a clean fundamental signal with greatly suppressed/filtered
harmonics (or even, non-existent harmonics), you may wish to read-up before
taking that project to the air...

John

"Ham op" wrote in message
...
White noise is a critical requirement of the Colpitts/Hartley oscillator
design.

Nothing new here!

You say you don't know why White noise is required. Better go read Terman or
other credible designers.

John Smith wrote:

Dave:

I have seen designs used which use a "white noise generator" at their osc.

Simply filter the freq you want from it and off you go...

John

"Dave Platt" wrote in message
...

In article nH6Ge.22103$HV1.10801@fed1read07,
Caveat Lector wrote:


Just out of curousity -- what modern Ham gear uses a Colpitts oscillator or
a swinging choke ??

I believe that a goodly percentage of fixed-frequency quartz crystal
oscillators use a Colpitts configuration in their feedback circuitry.
Pierce topologies are likely used, as well.

The L in such oscillators is the motional inductance of the crystal,
rather than the inductance of a wire-wound inductor, but the principle
is still the same.


Then why ask these questions on a 2005 Ham test ??

Because the circuits are still relevant, to either modern ham gear, or
to the older gear that many hams refurbish and use, or to both.


Maybe ask about a VCO or a crowbar circuit ??

VCOs require some form of positive feedback in order to oscillate.
This can be in a Colpitts configuration just as well as in any other.

Questions about a crowbar would certainly be relevant as well.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

John, I'm very serious when I say that 'white noise' is critical to
Colpitts/Hartley oscillator operation.

The feedback equation for oscillation requires a voltagecurrent gain
greater than 1 and a phase shift of 180 degrees [in simplified terms].

Starting conditions, in the absence of white noise, has zero input
voltage and hence zero output voltage and therefore no oscillation! The
presence of white noise provides the starting conditions, the Vin to be
amplified, and the tuned circuit, L and C, provides the frequency
discrimination, and the fundamental frequency of the oscillator. The
Capacitive voltage divider [Colpitts] or the Inductive voltage divider
[Hartley] provides the feedback factor. The active device, tube,
transistor, FET, etc. provides the gain and contributes to the phase shift.

White noise, frequency selectivity, gain greater than 1, and 180 degrees
phase shift are absolute requirements for an oscillator. In the absence
of any one there is NO oscillator. The white noise provides the starting
conditions for oscillation!!!

John Smith wrote:
Hmmm...

No, I don't believe I will have to read anything...

But, if you can't tell the difference between a white noise generator and an
osc giving a clean fundamental signal with greatly suppressed/filtered
harmonics (or even, non-existent harmonics), you may wish to read-up before
taking that project to the air...

John

Ham op:

Absolutely! Any amp is an oscillator, any oscillator is an amp... just depends
on how ya use it (mainly feedback.)

There is also the subjects of "thermal noise" and "quantum noise", both
contribute to the ease which with a circuit begins and sustains oscillations...

Well, unless the laws of physics have changed!

John

"Ham op" wrote in message
news
John, I'm very serious when I say that 'white noise' is critical to
Colpitts/Hartley oscillator operation.

The feedback equation for oscillation requires a voltagecurrent gain greater
than 1 and a phase shift of 180 degrees [in simplified terms].

Starting conditions, in the absence of white noise, has zero input voltage
and hence zero output voltage and therefore no oscillation! The presence of
white noise provides the starting conditions, the Vin to be amplified, and
the tuned circuit, L and C, provides the frequency discrimination, and the
fundamental frequency of the oscillator. The Capacitive voltage divider
[Colpitts] or the Inductive voltage divider [Hartley] provides the feedback
factor. The active device, tube, transistor, FET, etc. provides the gain and
contributes to the phase shift.

White noise, frequency selectivity, gain greater than 1, and 180 degrees
phase shift are absolute requirements for an oscillator. In the absence of
any one there is NO oscillator. The white noise provides the starting
conditions for oscillation!!!

John Smith wrote:
Hmmm...

No, I don't believe I will have to read anything...

But, if you can't tell the difference between a white noise generator and an
osc giving a clean fundamental signal with greatly suppressed/filtered
harmonics (or even, non-existent harmonics), you may wish to read-up before
taking that project to the air...

John