I'm making a quick and dirty frequency "octupler" (x8) that uses a string of
three Mini-Circuits frequency doublers (AMK-2-13+, KC2-11+, KC2-19+) --
300-312.5MHz in, 2400-2500MHz output (the ISM band). I believe these are just
diode ring-based mixers hooked up and optimized to act as doublers; they have
an insertion loss of around 11dB. I have buffer amplifiers at the output of
each to make up for this loss, but I'm wondering... do I need to bother with
bandpass filters as well? Without them each doubler suppresses the
fundamental and 3rd harmonic by some 40-60dB (depends on input frequency); the
4th harmonic is suppressed by ~15dB. Is anything undesireable going to happen
if I just let everything through? That would mean that at the final (x8)
output, I'd still have plenty of lower frequencies around -- albeit pretty
well suppressed -- as well as some x12, x16, etc... but the x8 component
should still be the strongest by far.

For a diode ring-based mixer, it's not entirely clear to me whether or not
having some low-level "junk" to the RF input is all that bad. As a man once
said to me, "diode mixer RF ports like being driven by squares waves," so the
higher harmonics don't seem as though they'd matter much... but will the
lower-frequency signals tending to dither the exact turn-on point of the
diodes be deleterious?

---Joel

Joel Koltner wrote:
I'm making a quick and dirty frequency "octupler" (x8) that uses a string of
three Mini-Circuits frequency doublers (AMK-2-13+, KC2-11+, KC2-19+) --
300-312.5MHz in, 2400-2500MHz output (the ISM band). I believe these are just
diode ring-based mixers hooked up and optimized to act as doublers; they have
an insertion loss of around 11dB. I have buffer amplifiers at the output of
each to make up for this loss, but I'm wondering... do I need to bother with
bandpass filters as well? Without them each doubler suppresses the
fundamental and 3rd harmonic by some 40-60dB (depends on input frequency); the
4th harmonic is suppressed by ~15dB. Is anything undesireable going to happen
if I just let everything through? That would mean that at the final (x8)
output, I'd still have plenty of lower frequencies around -- albeit pretty
well suppressed -- as well as some x12, x16, etc... but the x8 component
should still be the strongest by far.

For a diode ring-based mixer, it's not entirely clear to me whether or not
having some low-level "junk" to the RF input is all that bad. As a man once
said to me, "diode mixer RF ports like being driven by squares waves," so the
higher harmonics don't seem as though they'd matter much... but will the
lower-frequency signals tending to dither the exact turn-on point of the
diodes be deleterious?


Yes, anything below the desired 8x frequency and anything above that
isn't a harmonic of it will cause spurious mixing products when your
intent is to drive the LO port of a DBM with it. What happens within
your octupler doesn't matter much as long as you filter the final output.

BTW, in the olden days we preferred 3x, 5x per stage. Two 3x stages
would give you 9x. The most brazen ones (not me) did a direct 7x or even
9x. We just drove transistors in class C real hard.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg wrote:


BTW, in the olden days we preferred 3x, 5x per stage. Two 3x stages
would give you 9x. The most brazen ones (not me) did a direct 7x or even
9x. We just drove transistors in class C real hard.

Or today, many of us just overdrive an untuned MMIC amplifier and filter
out the unwanted harmonics...

Scott
N0EDV

BTW, in the olden days we preferred 3x, 5x per stage. Two 3x stages would
give you 9x. The most brazen ones (not me) did a direct 7x or even 9x. We
just drove transistors in class C real hard.

Or today, many of us just overdrive an untuned MMIC amplifier and filter
out the unwanted harmonics...

Scott
N0EDV

And often have unwanted sometimes unfound parametric oscillations that have
nothing to do with harmonic content.

W4ZCB

Harold E. Johnson wrote:
BTW, in the olden days we preferred 3x, 5x per stage. Two 3x stages would
give you 9x. The most brazen ones (not me) did a direct 7x or even 9x. We
just drove transistors in class C real hard.
Or today, many of us just overdrive an untuned MMIC amplifier and filter
out the unwanted harmonics...

Scott
N0EDV

And often have unwanted sometimes unfound parametric oscillations that have
nothing to do with harmonic content.


If a huge drab-green truck stops in front of the house and folks in
fatigues and army boots hop off then the unfound oscillation has been
found ;-)

--
73, Joerg

Joerg wrote:
Harold E. Johnson wrote:
BTW, in the olden days we preferred 3x, 5x per stage. Two 3x stages
would give you 9x. The most brazen ones (not me) did a direct 7x or
even 9x. We just drove transistors in class C real hard.
Or today, many of us just overdrive an untuned MMIC amplifier and
filter out the unwanted harmonics...

Scott
N0EDV

And often have unwanted sometimes unfound parametric oscillations that
have nothing to do with harmonic content.


If a huge drab-green truck stops in front of the house and folks in
fatigues and army boots hop off then the unfound oscillation has been
found ;-)


Listening to all the "crap" on the bands these days, I doubt ANY truck
from the government would ever show up However, that being said, as
hams, we all need to make sure our "house is clean"...now about all that
other "crap"...has anyone else noticed all the interference these days
on 2M from other sources of "spurious junk"??? Examples: I pull up to
gas pumps and the squelch opens on my 2M radio...driving down the
Interstate, I pass semi trucks and get a static burst from the
speaker...Drive through town, listening to 145.19 and get static bursts
(this just happens to be a cable TV frequency...isn't the idea of cable
TV to keep the signals INSIDE the cable?)....

Scott
N0EDV

Harold E. Johnson wrote:
BTW, in the olden days we preferred 3x, 5x per stage. Two 3x stages would
give you 9x. The most brazen ones (not me) did a direct 7x or even 9x. We
just drove transistors in class C real hard.
Or today, many of us just overdrive an untuned MMIC amplifier and filter
out the unwanted harmonics...

Scott
N0EDV

And often have unwanted sometimes unfound parametric oscillations that have
nothing to do with harmonic content.

W4ZCB


Probably true, but the spectrum analyzer shows anything amiss fairly well

Scott

Scott wrote:


Or today, many of us just overdrive an untuned MMIC amplifier and filter
out the unwanted harmonics...

Scott
N0EDV


Or should I say, we filter to SELECT the harmonic we want....

Scott