Paul Burridge wrote in message . ..
On 22 Mar 2004 22:01:47 -0800, (Tom Bruhns) wrote:

Of course, maybe you don't need such a high Q, Paul. Qu of 30 is
quite reasonable for small SMT RF inductors, at least the type I use.
In the following list, "series" means in series from the gate output
to the next gate input, in order, and "shunt" means shunt to ground at
that point. Anyway, try this (build it or SPICE it or RFSim99
it...add resistors to any simulation to account for the Qu. I'd
suggest 3 ohms series and 12k ohms shunt for each 1.8uH.)

Thanks, Tom. I've simulated the filter and posted the plot result to
abse. Looks promising. See if it meets your expectations....

Hmmm...I simulated it, and it looked fine to me. I don't do a.b.*
groups. I haven't actually built one; more pressing things to do.
But I expect it will work OK. It assumes no inductive coupling among
the coils. That's usually not too hard to get low enough in practice,
if you orient the coils properly.

BTW, check out Coil-Q inductors for commercial RF coils in small
shield cans with decent Q. 7mm square can, Qu around 100 for
inductances and frequencies in the neighborhood we're talking about
here.

On 23 Mar 2004 12:45:15 -0800, (Tom Bruhns) wrote:

Hmmm...I simulated it, and it looked fine to me. I don't do a.b.*
groups. I haven't actually built one; more pressing things to do.
But I expect it will work OK. It assumes no inductive coupling among
the coils. That's usually not too hard to get low enough in practice,
if you orient the coils properly.

BTW, check out Coil-Q inductors for commercial RF coils in small
shield cans with decent Q. 7mm square can, Qu around 100 for
inductances and frequencies in the neighborhood we're talking about
here.

Hey, give me a chance to keep up with your suggestions, will you? ;-)
I've only just today taken delivery of some powedered iron toroids you
tipped me off on (T37-10 for the time being) and am experimenting with
those at present. Moreover, I replaced the factory, miniature,
resistor-like inductors in my original 5X multiplier with hand-wound,
air-cored ones for better Q, and guess what? *Huge* difference!
Couldn't get a fifth *at all* before, as you may recall, but changing
the inductors for the higher Q construction really brought it on big
time! So much so I was convinced I'd made some fundamental mismeasure
with the test equipment settings. Eventually it dawned that there was
no error. The whole problem had been down to choice of coils - same
values alright, but very different Qs. I've you to thank most
sincerely for that revelation!
Though the transistor-based multiplier and buffer/amp now works great,
I'll still stick with your series filter solution as it saves on
transistors and other components too. Just one last query, Tom: in
your design between the ouput of the first inverter and the input to
the next, you have, in series, a 0-10pF variable cap and a 20uH coil.
Then you have your DC bias to the 2nd gate input and a 15pF cap
shunted to ground at the same point. What was the purpose of that 15pF
cap? Was it to provide an AC ground, bypassing the lower resistor (the
one from input to gnd) or was there some loading function involved
with it as well? Or was it intended to allow some independent control
over the signal voltage level to the 2nd inverter input?
Thanks again,

Paul

--

The BBC: Licensed at public expense to spread lies.

Paul,

It's a series resonant circuit. The inductor is obvious. The
capacitor is actually split between the one to ground at the gate
input and the one on the other side of the inductor. Since it's a
series circuit, the inductor and first cap can be swapped, of course;
that might make it more obvious. The gate's RF input impedance
(including a resistive part) and the bias resistors are in parallel
(AC-wise) with the cap to ground, and provide a certain amount of
damping -- lowering of the Q -- or the reason loaded Q is lower than
Qu of the inductor. Since the tuning cap is in series with that cap,
only part of the resonance voltage appears across it. Remember, in a
series-resonant circuit, the voltage across the inductor or capacitor
is much higher than the exciting voltage--that's where the voltage
step-up comes from that's needed in this case. Splitting the net
capacitance up this way lets you get a reasonably high loaded Q (to
reject the other harmonics better) and control the output voltage, and
provide the proper load at to the driving gate...as I recall, my
design goal was about 100 ohms at the fifth harmonic, and a much
higher impedance at the fundamental and the other harmonics. That
way, the driving gate doesn't dissipate much power trying to drive
those other harmonics into a heavy load, and only has to deliver
significant power at the fifth harmonic. -- You could just use a cap
from the gate input to ground, and an inductor to the driving gate's
output (and then do away with the bias resistors too...), but then you
can't so easily control the loaded Q.

Yes, you should generally consider more than just the inductance of a
coil. Q and self-resonant frequency are both generally important. At
high frequencies, coils are the least ideal of our linear passives:
Rs, Ls and Cs. Usually you can get by with ignoring the
non-idealities of film and composition resistors and the types of caps
usually used at RF, but inductors are a different story. It's good
preparation for working in the GHz range, where pretty much all
components have non-ideal performance.

Cheers,
Tom

Paul Burridge wrote in message . ..
On 23 Mar 2004 12:45:15 -0800, (Tom Bruhns) wrote:

Hmmm...I simulated it, and it looked fine to me. I don't do a.b.*
groups. I haven't actually built one; more pressing things to do.
But I expect it will work OK. It assumes no inductive coupling among
the coils. That's usually not too hard to get low enough in practice,
if you orient the coils properly.

BTW, check out Coil-Q inductors for commercial RF coils in small
shield cans with decent Q. 7mm square can, Qu around 100 for
inductances and frequencies in the neighborhood we're talking about
here.

Hey, give me a chance to keep up with your suggestions, will you? ;-)
I've only just today taken delivery of some powedered iron toroids you
tipped me off on (T37-10 for the time being) and am experimenting with
those at present. Moreover, I replaced the factory, miniature,
resistor-like inductors in my original 5X multiplier with hand-wound,
air-cored ones for better Q, and guess what? *Huge* difference!
Couldn't get a fifth *at all* before, as you may recall, but changing
the inductors for the higher Q construction really brought it on big
time! So much so I was convinced I'd made some fundamental mismeasure
with the test equipment settings. Eventually it dawned that there was
no error. The whole problem had been down to choice of coils - same
values alright, but very different Qs. I've you to thank most
sincerely for that revelation!
Though the transistor-based multiplier and buffer/amp now works great,
I'll still stick with your series filter solution as it saves on
transistors and other components too. Just one last query, Tom: in
your design between the ouput of the first inverter and the input to
the next, you have, in series, a 0-10pF variable cap and a 20uH coil.
Then you have your DC bias to the 2nd gate input and a 15pF cap
shunted to ground at the same point. What was the purpose of that 15pF
cap? Was it to provide an AC ground, bypassing the lower resistor (the
one from input to gnd) or was there some loading function involved
with it as well? Or was it intended to allow some independent control
over the signal voltage level to the 2nd inverter input?
Thanks again,

Paul

Paul,

It's a series resonant circuit. The inductor is obvious. The
capacitor is actually split between the one to ground at the gate
input and the one on the other side of the inductor. Since it's a
series circuit, the inductor and first cap can be swapped, of course;
that might make it more obvious. The gate's RF input impedance
(including a resistive part) and the bias resistors are in parallel
(AC-wise) with the cap to ground, and provide a certain amount of
damping -- lowering of the Q -- or the reason loaded Q is lower than
Qu of the inductor. Since the tuning cap is in series with that cap,
only part of the resonance voltage appears across it. Remember, in a
series-resonant circuit, the voltage across the inductor or capacitor
is much higher than the exciting voltage--that's where the voltage
step-up comes from that's needed in this case. Splitting the net
capacitance up this way lets you get a reasonably high loaded Q (to
reject the other harmonics better) and control the output voltage, and
provide the proper load at to the driving gate...as I recall, my
design goal was about 100 ohms at the fifth harmonic, and a much
higher impedance at the fundamental and the other harmonics. That
way, the driving gate doesn't dissipate much power trying to drive
those other harmonics into a heavy load, and only has to deliver
significant power at the fifth harmonic. -- You could just use a cap
from the gate input to ground, and an inductor to the driving gate's
output (and then do away with the bias resistors too...), but then you
can't so easily control the loaded Q.

Yes, you should generally consider more than just the inductance of a
coil. Q and self-resonant frequency are both generally important. At
high frequencies, coils are the least ideal of our linear passives:
Rs, Ls and Cs. Usually you can get by with ignoring the
non-idealities of film and composition resistors and the types of caps
usually used at RF, but inductors are a different story. It's good
preparation for working in the GHz range, where pretty much all
components have non-ideal performance.

Cheers,
Tom

Paul Burridge wrote in message . ..
On 23 Mar 2004 12:45:15 -0800, (Tom Bruhns) wrote:

Hmmm...I simulated it, and it looked fine to me. I don't do a.b.*
groups. I haven't actually built one; more pressing things to do.
But I expect it will work OK. It assumes no inductive coupling among
the coils. That's usually not too hard to get low enough in practice,
if you orient the coils properly.

BTW, check out Coil-Q inductors for commercial RF coils in small
shield cans with decent Q. 7mm square can, Qu around 100 for
inductances and frequencies in the neighborhood we're talking about
here.

Hey, give me a chance to keep up with your suggestions, will you? ;-)
I've only just today taken delivery of some powedered iron toroids you
tipped me off on (T37-10 for the time being) and am experimenting with
those at present. Moreover, I replaced the factory, miniature,
resistor-like inductors in my original 5X multiplier with hand-wound,
air-cored ones for better Q, and guess what? *Huge* difference!
Couldn't get a fifth *at all* before, as you may recall, but changing
the inductors for the higher Q construction really brought it on big
time! So much so I was convinced I'd made some fundamental mismeasure
with the test equipment settings. Eventually it dawned that there was
no error. The whole problem had been down to choice of coils - same
values alright, but very different Qs. I've you to thank most
sincerely for that revelation!
Though the transistor-based multiplier and buffer/amp now works great,
I'll still stick with your series filter solution as it saves on
transistors and other components too. Just one last query, Tom: in
your design between the ouput of the first inverter and the input to
the next, you have, in series, a 0-10pF variable cap and a 20uH coil.
Then you have your DC bias to the 2nd gate input and a 15pF cap
shunted to ground at the same point. What was the purpose of that 15pF
cap? Was it to provide an AC ground, bypassing the lower resistor (the
one from input to gnd) or was there some loading function involved
with it as well? Or was it intended to allow some independent control
over the signal voltage level to the 2nd inverter input?
Thanks again,

Paul

On 23 Mar 2004 12:45:15 -0800, (Tom Bruhns) wrote:

Hmmm...I simulated it, and it looked fine to me. I don't do a.b.*
groups. I haven't actually built one; more pressing things to do.
But I expect it will work OK. It assumes no inductive coupling among
the coils. That's usually not too hard to get low enough in practice,
if you orient the coils properly.

BTW, check out Coil-Q inductors for commercial RF coils in small
shield cans with decent Q. 7mm square can, Qu around 100 for
inductances and frequencies in the neighborhood we're talking about
here.

Hey, give me a chance to keep up with your suggestions, will you? ;-)
I've only just today taken delivery of some powedered iron toroids you
tipped me off on (T37-10 for the time being) and am experimenting with
those at present. Moreover, I replaced the factory, miniature,
resistor-like inductors in my original 5X multiplier with hand-wound,
air-cored ones for better Q, and guess what? *Huge* difference!
Couldn't get a fifth *at all* before, as you may recall, but changing
the inductors for the higher Q construction really brought it on big
time! So much so I was convinced I'd made some fundamental mismeasure
with the test equipment settings. Eventually it dawned that there was
no error. The whole problem had been down to choice of coils - same
values alright, but very different Qs. I've you to thank most
sincerely for that revelation!
Though the transistor-based multiplier and buffer/amp now works great,
I'll still stick with your series filter solution as it saves on
transistors and other components too. Just one last query, Tom: in
your design between the ouput of the first inverter and the input to
the next, you have, in series, a 0-10pF variable cap and a 20uH coil.
Then you have your DC bias to the 2nd gate input and a 15pF cap
shunted to ground at the same point. What was the purpose of that 15pF
cap? Was it to provide an AC ground, bypassing the lower resistor (the
one from input to gnd) or was there some loading function involved
with it as well? Or was it intended to allow some independent control
over the signal voltage level to the 2nd inverter input?
Thanks again,

Paul

--

The BBC: Licensed at public expense to spread lies.

Paul Burridge wrote in message . ..
On 22 Mar 2004 22:01:47 -0800, (Tom Bruhns) wrote:

Of course, maybe you don't need such a high Q, Paul. Qu of 30 is
quite reasonable for small SMT RF inductors, at least the type I use.
In the following list, "series" means in series from the gate output
to the next gate input, in order, and "shunt" means shunt to ground at
that point. Anyway, try this (build it or SPICE it or RFSim99
it...add resistors to any simulation to account for the Qu. I'd
suggest 3 ohms series and 12k ohms shunt for each 1.8uH.)

Thanks, Tom. I've simulated the filter and posted the plot result to
abse. Looks promising. See if it meets your expectations....

Hmmm...I simulated it, and it looked fine to me. I don't do a.b.*
groups. I haven't actually built one; more pressing things to do.
But I expect it will work OK. It assumes no inductive coupling among
the coils. That's usually not too hard to get low enough in practice,
if you orient the coils properly.

BTW, check out Coil-Q inductors for commercial RF coils in small
shield cans with decent Q. 7mm square can, Qu around 100 for
inductances and frequencies in the neighborhood we're talking about
here.

On 22 Mar 2004 22:01:47 -0800, (Tom Bruhns) wrote:

[filter spec snipped]
It should give you enough voltage gain at 18MHz to drive the second
gate at the fifth harmonic, and should attenuate the third at least
50dB if you build it properly, even with low-ish Qu inductors. This
is rather a "hack" circuit, but works. The premise is that it's
easier to get three inductors all the same value than muck about
tuning the inductors. Make the 47pF, 45pF and 40pF caps variable and
you can peak up the response at your desired frequency. Your
simulation should show a reasonably flat bandpass characteristic,
centered at about 18MHz.

Thanks, Tom! You're even more indefatigable than I am, by the look of
it. I shall look into it...


--

The BBC: Licensed at public expense to spread lies.

On 22 Mar 2004 22:01:47 -0800, (Tom Bruhns) wrote:

Of course, maybe you don't need such a high Q, Paul. Qu of 30 is
quite reasonable for small SMT RF inductors, at least the type I use.
In the following list, "series" means in series from the gate output
to the next gate input, in order, and "shunt" means shunt to ground at
that point. Anyway, try this (build it or SPICE it or RFSim99
it...add resistors to any simulation to account for the Qu. I'd
suggest 3 ohms series and 12k ohms shunt for each 1.8uH.)

Thanks, Tom. I've simulated the filter and posted the plot result to
abse. Looks promising. See if it meets your expectations....

p.
--

The BBC: Licensed at public expense to spread lies.

Of course, maybe you don't need such a high Q, Paul. Qu of 30 is
quite reasonable for small SMT RF inductors, at least the type I use.
In the following list, "series" means in series from the gate output
to the next gate input, in order, and "shunt" means shunt to ground at
that point. Anyway, try this (build it or SPICE it or RFSim99
it...add resistors to any simulation to account for the Qu. I'd
suggest 3 ohms series and 12k ohms shunt for each 1.8uH.)

47pF series
1.8uH series
470pF shunt
45pF series
1.8uH shunt
3.3pF series
40pF shunt
1.8uH shunt
DC blocking cap series
high-value DC bias resistors, and the gate input (I assumed to be
about 4k net resistance to ground at the gate input, including the
bias resistors).

It should give you enough voltage gain at 18MHz to drive the second
gate at the fifth harmonic, and should attenuate the third at least
50dB if you build it properly, even with low-ish Qu inductors. This
is rather a "hack" circuit, but works. The premise is that it's
easier to get three inductors all the same value than muck about
tuning the inductors. Make the 47pF, 45pF and 40pF caps variable and
you can peak up the response at your desired frequency. Your
simulation should show a reasonably flat bandpass characteristic,
centered at about 18MHz.

Paul Burridge wrote in message . ..
Hi guys,

ISTR that one can improve Q in resonant tanks by having a low L-C
ratio. Or was it high L-C ratio. I can't remember but need to know.
Can any kind soul help me out? Thanks.

p.