Frequency doubling: Is bandpass filtering needed?
 

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

Frequency doubling: Is bandpass filtering needed?
 

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/

Frequency doubling: Is bandpass filtering needed?
 

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

Frequency doubling: Is bandpass filtering needed?
 

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

Frequency doubling: Is bandpass filtering needed?
 

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

Frequency doubling: Is bandpass filtering needed?
 

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

Frequency doubling: Is bandpass filtering needed?
 

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

Frequency doubling: Is bandpass filtering needed?
 

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

Frequency doubling: Is bandpass filtering needed?
 

Scott wrote:
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?)....


Sure, but when you see how cable "professionals" handle stuff you'd get
the goose bumps. We don't have a cable subscription but a cable box down
the street. Often I see workers in the street and when walking the dogs
next day the lid on the green box is askew. Heck, often they didn't even
slide the lid all the way in, let alone lock it. Being a guy who can't
stand the sight of electronics just rotting and corroding away because
of neglect I always push it back on. Once the lid was completely off, it
rained and water was dripping from all the coaxes. This doesn't exactly
improve shielding effectiveness ;-)

--
Regards, Joerg

http://www.analogconsultants.com/

Frequency doubling: Is bandpass filtering needed?
 

Joerg wrote in :
Scott wrote:
Joerg wrote:

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?)....

Sure, but when you see how cable "professionals" handle stuff you'd get
the goose bumps. We don't have a cable subscription but a cable box down
the street. Often I see workers in the street and when walking the dogs
next day the lid on the green box is askew. Heck, often they didn't even
slide the lid all the way in, let alone lock it. Being a guy who can't
stand the sight of electronics just rotting and corroding away because
of neglect I always push it back on. Once the lid was completely off, it
rained and water was dripping from all the coaxes. This doesn't exactly
improve shielding effectiveness ;-)

The FCC *does* sometimes pursue interference and leakage complaints
against cable companies. It may take a while to get them moving, but
there are NOVs (Notice of Violation)s filed by the FCC against some
cable companies with more leakage than allowed.

A fair number of cable techs are hams, too, though not all. Calling the
cableco office and reporting interference, with a followup paper letter,
generally will get someone's attention.

Around here (Central Oklahoma, EM15gf in particular), it's the LED
traffic signals and the casino signs that put out hash. The traffic
signals are bad up around 2 meters, and there's one casino sign that was
taking everything from 40 (or 80) meters up through 2 meters.

HB content: I'm thinking of building one of the little receivers shown
at http://mikea.ath.cx/1-chip-rx.html/, just for hunting QRM. Note:
the second image has some editing performed on it to make some things a
little clearer; the first one is as it came off EDN.

--
Mike Andrews, W5EGO

Tired old sysadmin