Frequency Doubling Mixers... evaluation...
ka7...@uugate.wa7slg.ampr.org
These mixers are the ones consisting of back-to-back diodes, with the LO
at 1/2 the desired LO frequency is applied to one end, and the RF and IF
signals are extracted from the other, or something similar.
I have heard that the characteristics of this type of mixer as similar
to those of a singly-balanced diode mixer (i.e. very poor intrinsic port
isolation, not really great dynamic range, etc.)
The advantage of this type of mixer (obviously) is seen particularly
in microwave applications where it might be awkward to come up with an
LO on-frequency...
Any comments on this would be appreciated.
<Clint>
koe...@skyfox.usask.ca
Frequency doubling mixers are really just normal double balanced mixers with
the same signal applied to the RF and LO ports. The output is the sum (i.e.,
2x the frequency) and difference (zero - DC) as in normal DBM's. The ones
manufactured for frequency doubler use are just ones selected to give
better than normal performance. I've used normal DBM's as doublers and
they work nearly as well.
Jim, VE5FP
Alan Bloom
: Frequency doubling mixers are really just normal double balanced mixers with
And they work even better if the RF and LO ports are fed 90 degrees out of
phase. (No DC component on the output.)
AL N1AL
Richard Karlquist
>koe...@skyfox.usask.ca wrote:
>
>: Frequency doubling mixers are really just normal double balanced mixers with
>: the same signal applied to the RF and LO ports. The output is the sum (i.e.,
>: 2x the frequency) and difference (zero - DC) as in normal DBM's. The ones
>: manufactured for frequency doubler use are just ones selected to give
>: better than normal performance. I've used normal DBM's as doublers and
>: they work nearly as well.
Not necessarily. Some frequency doublers use a full-wave rectifier topology.
That type of topology allows unlimited (except for diode ratings) drive
power. If you use a DBM as a doubler by driving both ports, the output
power stops increasing when the total drive power is in the neighborhood
of the rated LO power for the DBM as a mixer.
>
>And they work even better if the RF and LO ports are fed 90 degrees out of
>phase. (No DC component on the output.)
>
>AL N1AL
>
Yes, this is true. The input impedance is much better behaved and you
can drive the mixer somewhat harder (maybe 6 db) before it starts to saturate.
On the other hand, it is more susceptible to AM to PM conversion.
If you instead drive the ports in phase, be sure to short out the DC output current
with an RF choke.
Rick N6RK
rka...@scd.hp.com
Fred McKenzie
> I've used normal DBM's as doublers and
> they work nearly as well.
Jim-
Do you think they would work with square wave, rather than sine wave
signals? I've been looking for a simple doubler from 24 MHz square wave
to 48 MHz (sine wave OK). So far, what I've tried works better for odd
harmonics!
73, Fred, K4DII
Alan Bloom
: > I've used normal DBM's as doublers and
: > they work nearly as well.
: Do you think they would work with square wave, rather than sine wave
: signals? I've been looking for a simple doubler from 24 MHz square wave
: to 48 MHz (sine wave OK). So far, what I've tried works better for odd
: harmonics!
With a square wave, you have to feed the two ports 90 degrees out of phase.
Otherwise, you just get pure DC at the output (theoretically, anyway).
AL N1AL
David Tiller
: Could someone tell me about the performance of a "frequency-doubling mixer"?
: These mixers are the ones consisting of back-to-back diodes, with the LO
: at 1/2 the desired LO frequency is applied to one end, and the RF and IF
: signals are extracted from the other, or something similar.
Another type I was just reading about is a varactor diode multiplier.
Basically:
RF at F0 -> Attenuator -> Varactor Diode -> Filter at n * F0 -> RF out
The cool thing is that there's no power supply involved! I can give you
the reference to the book if you want - email me if you'd like it.
--
David Tiller | Network Administrator | Voice: (804) 752-3710 |
dti...@rmc.edu | n2kau/4 | Randolph-Macon College| Fax: (804) 752-7231 |
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koe...@skyfox.usask.ca
I'd try out a standard DBM as a doubler using some proper lab
equipment. I connected a signal generator (50 MHz) to an old
HP 10514A DBM. With the input signal at +10 dBm, the output at
100 MHz was down 12 dB (about what would be expected) and the
50 MHz fundamental was down 45 dB relative to the input. Not bad!
I didn't look at higher harmonics.
Jim, VE5FP