What RF signal generator comes to mind? UK

[Richard]

I'm not an accomplished electronics person.

I was told that if it was designed right you could make a (2.0-2.5Mhz)
stabilized analogue VFO tune in very small increments, say 2 or 3 hz.
(Electronically stablized by varacters).

Say you wanted to base such a VFO on an analogue RF signal generator, does
anyone know what might be suitable?

I have been looking at what I beleive are stabilized analogue RF signal
generators, but they are quite expensive, (HP 8640A and 8640b) so I thinks
what I need is simply a good RF generator and I can add the stabilzation
circuitry myself. It is important that the basic oscillator is quality in
order to try for the 2 or 3 hz tuning steps.

Perhaps some of the older 1960's eqipment that is virtually obsolete would
be okay because the oscillator itself is a quality item. Maybe some
of the old Marconi stuff would do. Any peice of equipment come to mind?
TIA.

 

[Richard]

"Richard" <notty@emailo.com> wrote in message
news:2n57vuFt6topU1@uni-berlin.de...

I'm not an accomplished electronics person.

I was told that if it was designed right you could make a (2.0-2.5Mhz)
stabilized analogue VFO tune in very small increments, say 2 or 3 hz.
(Electronically stablized by varacters).

Say you wanted to base such a VFO on an analogue RF signal generator, does
anyone know what might be suitable?

I have been looking at what I beleive are stabilized analogue RF signal
generators, but they are quite expensive, (HP 8640A and 8640b) so I thinks
what I need is simply a good RF generator and I can add the stabilzation
circuitry myself. It is important that the basic oscillator is quality in
order to try for the 2 or 3 hz tuning steps.

Perhaps some of the older 1960's eqipment that is virtually obsolete would
be okay because the oscillator itself is a quality item. Maybe some
of the old Marconi stuff would do. Any peice of equipment come to mind?
TIA.

I'm not entirely certain whether quality analogue RF generators are tuned
with variable capacitors. I am assuming so. It's the tuning component that
has to be high quality so the frequency does not jump several hertz when
tuning, preventing say a 3 hz lock. I ask myself, can any analogue tuning
component, like a variable capacitor, actually change frequency in the 1, 2,
or 3 hertz range. Maybe for mechanical reasons it's not possible.

 

[Tweetldee]

"Richard" <notty@emailo.com> wrote in message
news:2n58juFsp6poU1@uni-berlin.de...

"Richard" <notty@emailo.com> wrote in message
news:2n57vuFt6topU1@uni-berlin.de...
I'm not an accomplished electronics person.

I was told that if it was designed right you could make a (2.0-2.5Mhz)
stabilized analogue VFO tune in very small increments, say 2 or 3 hz.
(Electronically stablized by varacters).

Say you wanted to base such a VFO on an analogue RF signal generator,
does
anyone know what might be suitable?

I have been looking at what I beleive are stabilized analogue RF signal
generators, but they are quite expensive, (HP 8640A and 8640b) so I
thinks
what I need is simply a good RF generator and I can add the stabilzation
circuitry myself. It is important that the basic oscillator is quality
in
order to try for the 2 or 3 hz tuning steps.

Perhaps some of the older 1960's eqipment that is virtually obsolete
would
be okay because the oscillator itself is a quality item. Maybe some
of the old Marconi stuff would do. Any peice of equipment come to mind?
TIA.

I'm not entirely certain whether quality analogue RF generators are tuned
with variable capacitors. I am assuming so. It's the tuning component that
has to be high quality so the frequency does not jump several hertz when
tuning, preventing say a 3 hz lock. I ask myself, can any analogue tuning
component, like a variable capacitor, actually change frequency in the 1,
2,
or 3 hertz range. Maybe for mechanical reasons it's not possible.

Yes, it's possible.. Your easiest approach will probably to put two or
three smaller capacitors across the main tuning capacitor. Tune the main
capacitor to approximately your desired frequency, then incrementally adjust
the smaller caps to get to your final frequency. The exact values of these
capacitors will, obviously, depend on the value of your main tuning element.
I would suggest that you start with a capacitor of around 10% of the value
of the main tuning element, and maybe another cap of 1% or 2% of the main
tuning cap. All would be in parallel with the main tuning cap.
A nasty side effect of this will be that you will upset the tuning range of
the system. IOW, your frequency dial will no longer be accurate unless you
redraw it.

If you want to use varicaps, then you would use the same theory.. just use
varicaps with values that will allow you to get the frequency resolution
that you want.
--
Dave M
MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

 

[Richard]

"Tweetldee" <masondg4499@comcast99.net> wrote in message
news:7XiPc.213804$JR4.127960@attbi_s54...

"Richard" <notty@emailo.com> wrote in message
news:2n58juFsp6poU1@uni-berlin.de...

"Richard" <notty@emailo.com> wrote in message
news:2n57vuFt6topU1@uni-berlin.de...
I'm not an accomplished electronics person.

I was told that if it was designed right you could make a (2.0-2.5Mhz)
stabilized analogue VFO tune in very small increments, say 2 or 3 hz.
(Electronically stablized by varacters).

Say you wanted to base such a VFO on an analogue RF signal generator,
does
anyone know what might be suitable?

I have been looking at what I beleive are stabilized analogue RF
signal
generators, but they are quite expensive, (HP 8640A and 8640b) so I
thinks
what I need is simply a good RF generator and I can add the
stabilzation
circuitry myself. It is important that the basic oscillator is quality
in
order to try for the 2 or 3 hz tuning steps.

Perhaps some of the older 1960's eqipment that is virtually obsolete
would
be okay because the oscillator itself is a quality item. Maybe some
of the old Marconi stuff would do. Any peice of equipment come to
mind?
TIA.

I'm not entirely certain whether quality analogue RF generators are
tuned
with variable capacitors. I am assuming so. It's the tuning component
that
has to be high quality so the frequency does not jump several hertz when
tuning, preventing say a 3 hz lock. I ask myself, can any analogue
tuning
component, like a variable capacitor, actually change frequency in the
1,
2,
or 3 hertz range. Maybe for mechanical reasons it's not possible.


Yes, it's possible.. Your easiest approach will probably to put two or
three smaller capacitors across the main tuning capacitor. Tune the main
capacitor to approximately your desired frequency, then incrementally
adjust
the smaller caps to get to your final frequency. The exact values of
these
capacitors will, obviously, depend on the value of your main tuning
element.
I would suggest that you start with a capacitor of around 10% of the value
of the main tuning element, and maybe another cap of 1% or 2% of the main
tuning cap. All would be in parallel with the main tuning cap.
A nasty side effect of this will be that you will upset the tuning range
of
the system. IOW, your frequency dial will no longer be accurate unless
you
redraw it.

If you want to use varicaps, then you would use the same theory.. just
use
varicaps with values that will allow you to get the frequency resolution
that you want.

Yes thanks, that sounds the proper way to deal with the problem. This means
that the the bandspread capacitor is the key component, it is tasked with
giving a smooth frequency adjustment, not the main tuning capacitor.

And in fact I have two small-value capacitors that came from a wobbbulator.
They look to be very solidily built, I bet they would do. It's then just a
matter of choosing a good VFO/Osc circuit that offers a "clean" output. I
ether homebrew from scratch or try to get hold an oldish, cheap, but good RF
signal generator that has a pure output/low noise. Then I "bolt on" a
modern stabilizing circuit.

 

[mike]

Richard wrote:

I'm not an accomplished electronics person.

I was told that if it was designed right you could make a (2.0-2.5Mhz)
stabilized analogue VFO tune in very small increments, say 2 or 3 hz.
(Electronically stablized by varacters).

Say you wanted to base such a VFO on an analogue RF signal generator, does
anyone know what might be suitable?

I have been looking at what I beleive are stabilized analogue RF signal
generators, but they are quite expensive, (HP 8640A and 8640b) so I thinks
what I need is simply a good RF generator and I can add the stabilzation
circuitry myself. It is important that the basic oscillator is quality in
order to try for the 2 or 3 hz tuning steps.

Perhaps some of the older 1960's eqipment that is virtually obsolete would
be okay because the oscillator itself is a quality item. Maybe some
of the old Marconi stuff would do. Any peice of equipment come to mind?
TIA.

What are you trying to accomplish?
When I think 8640, I think microvolt outputs and heavy shielding so you
can actually use microvolt outputs.
How much FM can you stand on the signal? 2 Hz. steps sounds nice until
you discover that you've got 2KHz of incidental FM.
Once you start adding voltage
sensitive components, you also have to add voltage stabilization
components. Once you start adding circuitry to stabilize a piece
of equipment that's basically unsutiable for the task, you're asking
for grief.

The *best* commercial unit for the job is the one that pops un
unexpectedly at a great price...and meets your minimum specs.
If you go out looking for a specific item, you'll pay a LOT more.

All boils down to what you're trying to do with the result.
mike

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