EMRFD Message Archive 1038

Message Date From Subject
1038 2007-09-18 11:58:58 Ed Almos Low Noise 41 MHz Oscillator
I need to build a low noise crystal oscillator running at 41 MHz but
the oscillators chapter in EMRFD contains mostly Colpitts schematics.
Would this be the best circuit to use or should I go for something
like a one or two transistor Butler circuit? I will be using a third
overtone crystal and I need about 14dBm output (3,3V P-P)

Edward Almos HA6SST
1039 2007-09-18 13:15:19 Luiz Amaral Re: Low Noise 41 MHz Oscillator
√úlrich L. Rhode (from Rhode & Schwarz), at that time DL2LR, has many
articles and books that span this subject. For example,
http://www.pan-tex.net/usr/r/receivers/elrxtalosc.htm is a nice article and
the book Digital PLL Frequancy Synthesizers: Theory and Design.
Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1983 is excellent on the
matter (I'm searching for this book here in Brazil, but nothing so far).
Luiz - PY1LL / PY4LC

----- Original Message -----
1040 2007-09-18 22:08:20 jr_dakota Re: Low Noise 41 MHz Oscillator
Check out the Pic-A-Star project

They are using a Butler oscillator and a regular fundamental crystal
and grabbing the 5th or 7th overtone to create a stable low noise
clock for the DDS the project uses ... It's also got a
heater/stabilizer circuit so ,after a few minutes warmup it's solid as
a rock ... You should be able to retune it to grab the 3rd harmonic or
at least get some ideas

You can also learn a lot about radio and design just following the
1041 2007-09-19 05:47:34 Ed Almos Re: Low Noise 41 MHz Oscillator
Thank you for the replies so far.

The oscillator in the electroluminescent receiver operates at about 4
MHz so it is too low for my application. Also I am aware of the
Picastar project as I built one of their transceivers two years ago,
this is what gave me the idea of using the Butler oscillator.

The problem I have is that oscillators such as the Colpitts seem to be
used in HF oscillators and the Butler is used in VHF circuits. My
1043 2007-09-19 08:09:21 sm5glc Re: Low Noise 41 MHz Oscillator
I have built several low-noise crystal oscillators around this
frequency. The favourite is one published in QEX Nov/Dec 1999 "A
Stable, Low-Noise Crystal Oscillator for Microwave and Millimeter-Wave
Transverters" by John Stephensen KD6OZH. This is a modified
two-transistor Butler that easily adapts for locking to external
source i.e. GPS or similiar reference. Basic stability is very good too.

Or the one that Robert J Matthys do offer in "RF Design" march 1987,
the Harmonic Emitter Coupled Oscillator, I have tried this and it
seems very good. It is based on work by Driscoll but simplified and
improved. Matthys claims that his prototype oscillators at 20, 50 and
100 MHz all are better than 0.1 ppm and experimental measurements show
their short term stability to be better than any of the four other VHF
harmonic oscillators available.

Runner up is the Butler Emitter Follower with schottky diode limiter
as described by Mr Matthys in "RF Design" Magazine may/june 1983.

Other sources of information is the book "Oscillator Design & computer
Simulation" by Randall Rhea ISBN 1-8849-32-30-4 second ed. 1995.

It seems that all good designs do use a dedicated limiter i.e.
schottky diodes and a low noise amplifier rather than letting the
amplifier be driven into limitation.

A pretty thorough oscillator presentation is made in "Ham Radio"
Magazine march 1976 by rogwer Harris