"Paul Burridge" wrote in message
...
On Tue, 24 Feb 2004 12:30:12 -0700, Jim Thompson
wrote:

Aha! I just noted from Paul's post that "my" oscillator is called a
two-transistor Butler. Wonder when that was conceived? I've been
using the my direct-coupled version for 40 years.

Interesting. This is the type I've decided to build as the basis for
my next sweep generator attempt, since it's claimed the config is more
amenable to being pulled than most others (although I won't be
attempting to pull it anything like as much as my first abortive
attempt using a Cmos-based inverter). Do you find it's a reliable and
stable design, Jim? I assume if it wasn't you wouldn't still be using
it!

Why not use a VCO built from an LC oscillator? Its really easy to build one
with a single transistor that sweeps your band.

I built a simple one that looked like this:


+------+--------+-------+
| | | | /
| .-. C|L1 --- C1
--- | |R1 C| ---
C3 --- | | C| / |
| '-' | |
| | +-------+------o antenna
| | | |
___ | | |c --- C2
Vin o-|___|-+------+-----b| Q1 ---
R4 | | |e |
| | | |
| | | |
| | +-------+
| | |
| .-. .-.
--- | |R2 | | R3
C4 --- | | | |
| '-' '-'
| | |
+------+--------+

Q1 = 2N3904

L1 = 0.5uH
C1 = 20pF variable from 10pF to 80pF
C2 = 4.7pF
C3 = .22uF
C4 = 1uF
R1 = 47k
R2 = 10k
R3 = 1k
R4 = 100

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

I was able to sweep the band from 40MHz to 42MHz by first adjusting C1, then
changing Vin (with a pot) to vary the output frequency. I built it on a
solderless breadboard (!), and had no problems getting it to work. With your
newfound PCB skills, should be a snap to get something like this working. I
tested it by counting waveforms on my oscilloscope, so your mileage may
vary.

The resonant frequency is near

f0 = 1/2.pi.sqrt(L1Ct)

where Ct = C1 + C2||Cbe + Ca + Ccb

Cbe is the capacitance between base and emitter of Q1, which is varied with
base voltage; Ccb is the 'fixed' capacitance between emitter and base of Q1;
and, Ca is the capacitance of the wire antenna. I'm unsure about how to
calculate the power output of the thing, but I'm guessing its tiny. I was
able to sweep the FM band (using a 0.1uH inductor) pretty reliably, and it
knocked out radios in other parts of my house when I swept past them.

The Q of the inductor should be as good as you can make. You can buy highQ
inductors. At this value, an aircore is probably pretty good. Otherwise,
your resonator won't stay on frequency. It'll drift with temperature, and
probably the phase of the moon, as well.

Regards,
Bob Monsen

On Wed, 25 Feb 2004 19:47:49 GMT, "Robert C Monsen"
posted this:


"Paul Burridge" wrote in message

Interesting. This is the type I've decided to build as the basis for
my next sweep generator attempt, since it's claimed the config is more
amenable to being pulled than most others (although I won't be
attempting to pull it anything like as much as my first abortive
attempt using a Cmos-based inverter). Do you find it's a reliable and
stable design, Jim? I assume if it wasn't you wouldn't still be using
it!

Why not use a VCO built from an LC oscillator? Its really easy to build one
with a single transistor that sweeps your band.


Major problem with that idea is the fact that Paul has no way to
calibrate or adjust the VCO. That's why he wants to start with a crystal
oscillator. If it works, he won't have to calibrate it.

Jim

On Wed, 25 Feb 2004 19:47:49 GMT, "Robert C Monsen"
posted this:


"Paul Burridge" wrote in message

Interesting. This is the type I've decided to build as the basis for
my next sweep generator attempt, since it's claimed the config is more
amenable to being pulled than most others (although I won't be
attempting to pull it anything like as much as my first abortive
attempt using a Cmos-based inverter). Do you find it's a reliable and
stable design, Jim? I assume if it wasn't you wouldn't still be using
it!

Why not use a VCO built from an LC oscillator? Its really easy to build one
with a single transistor that sweeps your band.


Major problem with that idea is the fact that Paul has no way to
calibrate or adjust the VCO. That's why he wants to start with a crystal
oscillator. If it works, he won't have to calibrate it.

Jim

"James Meyer" wrote in message
...
On Wed, 25 Feb 2004 19:47:49 GMT, "Robert C Monsen"

posted this:


"Paul Burridge" wrote in message

Interesting. This is the type I've decided to build as the basis for
my next sweep generator attempt, since it's claimed the config is more
amenable to being pulled than most others (although I won't be
attempting to pull it anything like as much as my first abortive
attempt using a Cmos-based inverter). Do you find it's a reliable and
stable design, Jim? I assume if it wasn't you wouldn't still be using
it!

Why not use a VCO built from an LC oscillator? Its really easy to build
one
with a single transistor that sweeps your band.


Major problem with that idea is the fact that Paul has no way to
calibrate or adjust the VCO. That's why he wants to start with a crystal
oscillator. If it works, he won't have to calibrate it.


I thought he wanted a VCO so he could sweep the range from 40.5MHz to 41MHz.
Using a frequency counter, it would be trivial to tune this circuit to start
wherever he wanted. Frequency counters are cheap on ebay:

http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=48 701

Using a crystal oscillator would obviously be better, but it sounds like he
is having trouble getting the range he needs out of it.

Regards,
Bob Monsen

Jim

"James Meyer" wrote in message
...
On Wed, 25 Feb 2004 19:47:49 GMT, "Robert C Monsen"

posted this:


"Paul Burridge" wrote in message

Interesting. This is the type I've decided to build as the basis for
my next sweep generator attempt, since it's claimed the config is more
amenable to being pulled than most others (although I won't be
attempting to pull it anything like as much as my first abortive
attempt using a Cmos-based inverter). Do you find it's a reliable and
stable design, Jim? I assume if it wasn't you wouldn't still be using
it!

Why not use a VCO built from an LC oscillator? Its really easy to build
one
with a single transistor that sweeps your band.


Major problem with that idea is the fact that Paul has no way to
calibrate or adjust the VCO. That's why he wants to start with a crystal
oscillator. If it works, he won't have to calibrate it.


I thought he wanted a VCO so he could sweep the range from 40.5MHz to 41MHz.
Using a frequency counter, it would be trivial to tune this circuit to start
wherever he wanted. Frequency counters are cheap on ebay:

http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=48 701

Using a crystal oscillator would obviously be better, but it sounds like he
is having trouble getting the range he needs out of it.

Regards,
Bob Monsen

Jim

On Thu, 26 Feb 2004 02:29:28 GMT, "Robert C Monsen"
wrote:

Using a crystal oscillator would obviously be better, but it sounds like he
is having trouble getting the range he needs out of it.

I'm mutiplying up and mixing down this time so getting enough spread
should be a piece of cake this time. The problem with your LC solution
is stability. This will be used for far field measurements at about an
eventual half-Watt output. I don't want to risk straying out of band,
but I do need to probe right up to the edges of it. The sweep
frequency will be controlled by a DC triangle generator voltage
applied to a varicap used as part of the crystal loading. I've
contrived it this way so I can carry out the mods on the filter
without having to keep going back and forth to the TX to vary the
output frequency. Yeah, maybe it's overkill but I've got the time
right now and nothing better to do. :-)

--

The BBC: Licensed at public expense to spread lies.

On Thu, 26 Feb 2004 02:29:28 GMT, "Robert C Monsen"
wrote:

Using a crystal oscillator would obviously be better, but it sounds like he
is having trouble getting the range he needs out of it.

I'm mutiplying up and mixing down this time so getting enough spread
should be a piece of cake this time. The problem with your LC solution
is stability. This will be used for far field measurements at about an
eventual half-Watt output. I don't want to risk straying out of band,
but I do need to probe right up to the edges of it. The sweep
frequency will be controlled by a DC triangle generator voltage
applied to a varicap used as part of the crystal loading. I've
contrived it this way so I can carry out the mods on the filter
without having to keep going back and forth to the TX to vary the
output frequency. Yeah, maybe it's overkill but I've got the time
right now and nothing better to do. :-)

--

The BBC: Licensed at public expense to spread lies.

"sweep" and "crystal controlled" seem to me to be mutually exclusive.
I once made a sweep generator for a specific job that used crystals
to generate frequency markers,(displayed on a scope). What
output/human interface are you
expecting?

"sweep" and "crystal controlled" seem to me to be mutually exclusive.
I once made a sweep generator for a specific job that used crystals
to generate frequency markers,(displayed on a scope). What
output/human interface are you
expecting?

On 27 Feb 2004 04:03:02 -0800, (GPG) wrote:

"sweep" and "crystal controlled" seem to me to be mutually exclusive.
I once made a sweep generator for a specific job that used crystals
to generate frequency markers,(displayed on a scope). What
output/human interface are you
expecting?

I've substituted a ceramic resonator for the usual crystal to get more
'pull' over it. At the moment it's working well and I'm getting stable
output from 3.46Mhz-3.58Mhz which I'm very pleased with. Next problem
is to oust the variable trimmer cap and replace with suitable
varactor(s) for better frequency control...

--

The BBC: Licensed at public expense to spread lies.