RadioBanter - Frequency multiplication

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On Mon, 16 Feb 2004 11:40:18 -0500, " Uncle Peter"
wrote:

"Jim Thompson" wrote in message
.. .
On Mon, 16 Feb 2004 00:18:49 GMT, "W3JDR" wrote:

I would think a "W3JDR" would know that even harmonics are *much*
harder to obtain in nonlinear multipliers.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |

One would think a "PE" could give the man a civil answer.

---
Jim's not a civil engineer...

--
John Fields

Not really, Jim...unless you mean something special by "nonlinear
multipliers" like diodes/varactors which I suspect fall under your comment.
In the two-way radios of the 60's & early 80's before synthesizers, I
designed many a single stage multiplier of 2x or 3x, which were preferred
and sometimes 4x. They worked very well...using cap input coupling, to keep
the base Z low at the harmonics and keeping the conduction angle optimized
for output level. Also, the adjacent harmonics are easier to filter than
higher orders of multiplication (when that is a factor. Only a single
resonant circuit was required between stages.
The bottom line depends upon the spurious requirements. Then there are
always preferences for what we may have used in the past - and what the
application actually is.
Starting with a spectral comb(like a square wave or other pulse-type
waveform) and picking off the desired harmonic can also be very effective,
but again, it depends upon the specific application.
I did a synthesizer mixer with no tuned circuits to get from 40 MHz
crystal oscillator to 220MHz to mix down a VCO to an IF for the programmable
divider. Was really sweet! Did the same for what I believe was the very
first synthesized 2M hand held in 1973. A Motorola HT220. Even had the
Transmit VCO _ON_ yes _ON_ the TX frequency. Total current drain was 7ma.
Tx spurious (-70dBc) better than the original (-35-40dB) Still have it.

--
Steve N, K,9;d, c. i My email has no u's.

"Jim Thompson" wrote in message
...
On Mon, 16 Feb 2004 00:18:49 GMT, "W3JDR" wrote:

I think it boils down to something very practical:
...It becomes a matter of how close and how large the
undesired spectral components are compared to the desired spectral
components. ...
As an example, a x4 multiplier stage will have a desired output at Fin x
4,
and close-in undesired products at Fin x 3 and Fin x 5. ...
Joe, W3JDR

[snip]

I would think a "W3JDR" would know that even harmonics are *much*
harder to obtain in nonlinear multipliers.

...Jim Thompson

On Mon, 16 Feb 2004 10:19:49 -0700, Jim Thompson
wrote:

It depends on what your are starting from. If it's a sine wave, yes
even harmonics can be made from diode non-linearities.

The OP has a inverter-style XTAL oscillator, output very nearly
square.

A square wave is rich in odd harmonics, a perfect square wave has NO
even harmonics.

---
Starting with a perfect square wave at f1, bang the hell out of a diode
with it, and then bandpass it and the 3rd harmonic (f2) separately, then
mix them to get f1, f2, f1+f2, and f1-f2. Using a doubly balanced mixer
will get rid of f1 and f2, then notching out f1+f2 will leave f1-f2,
which will be 2f1, that non-existent second harmonic.

--
John Fields

See my previous post. What is your application? That would help get better
advise.

--
Steve N, K,9;d, c. i My email has no u's.

"Paul Burridge" wrote in message
...
On Sun, 15 Feb 2004 16:46:32 -0700, Jim Thompson
wrote:

On Sun, 15 Feb 2004 23:48:47 +0000, Paul Burridge
wrote:

What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

You ought to be able to answer that yourself... what's the spectral
roll-off of a square wave ??

I suppose it boils down to how much signal is left in the mush as the
harmonics get higher and higher. Knew I shoulda held on to that
spectrum analyser I used to have. :-(
I suppose that's the proper answer though: get the rise/fall times as
small and possible, measure the specral output and pick a suitable
harmonic with enough energy in it to set it 'comfortably' above the
noise floor?
--

The BBC: Licensed at public expense to spread lies.

" Starting with a perfect square wave at f1, bang the hell out of a diode
with it, and then bandpass it and the 3rd harmonic (f2) separately, then
mix them to get f1, f2, f1+f2, and f1-f2. Using a doubly balanced mixer
will get rid of f1 and f2, then notching out f1+f2 will leave f1-f2,
which will be 2f1, that non-existent second harmonic."

Oh yuchh...that sounds painful!
Why not just distort the symmetry of the square digitally (like drive it into an exclusive-or with a small delay on one input) to make a short impulse, then bandpass filter the output? Or staying in the purely digital domain, use same said exclusive-or and delay one of the two inputs by t/4 (t=period of input sq wave) and get a 2*F square wave out.

Joe
W3JDR

In article , Paul Burridge
writes:

What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

Paul, past state of the hardware art (past 60 years) indicates that
triplers are the practical maximum. Quintuplers have been done
but those are rare in described applications.

In 1955 I had hands-on experience with a septupler (7 x multiplier)
using a 2C39 and a cavity-tuned plate circuit at 1.8 GHz. That was
in a General Electric microwave radio relay terminal designed about
1950. Of nine terminals, two had to "QSY" to new crystal-controlled
microwave center frequencies for second-level contingency operation.
Difficult and fussy to do but was do-able...the crystal was also 7th
overtone in a vacuum tube oscillator but was followed by a buffer
stage feeding a tripler, another buffer, then the septupler which fed
another 2C39 as the pulse-modulated final for 12 W peak output at
1.8 GHz. [from memory and 35mm slides...big GE manual went to
recycle a long time ago] That's the only septupler application that
I am aware of...no doubt there are others, somewhere.

General Electric must have had some division/work-group with lots
of work in old frequency control methods. A local NTSC color sub-
carrier generator-regenerator made by GE had extensive use of
"locked oscillators" for frequency multiplication and division, but
mostly at frequencies lower than 7 MHz. Haven't come across any
practical hardware on locked oscillators except for two mentions in
older journals, trade papers. One of those used transistors as
active devices.

Doublers and quadruplers have been made using both diodes and
tube-or-transistor active devices. That's relatively easy with non-
square waveforms (distorted sinewaves); square waves have high
odd harmonic energy, low even harmonic energy.

Making practical, reproducible active multipliers in the home shop
is, practically, a trial-and-error process involving playing with cut-
off bias of the active device input, energy and harmonic content of
the source, and Q of the multiplier's output stage. In the past I've
made tripling-in-the-plate pentode crystal oscillators using
fundamental frequency quartz but those were highly dependent on
getting the highest impedance tuned plate circuit and needed
scope viewing to check output waveforms. Not very reproducible.
There's no "easy" way to do it that will "work every time" despite
the claims of many. :-)

Digital division IS straightforward up to about 1 GHz based on
such technology over the last 3 decades. That's why PLLs came
to prominence in frequency control techniques up to UHF.

Len Anderson
retired (from regular hours) electronic engineer person