EMRFD Message Archive 2492
Message Date From Subject 2492 2008-12-12 02:16:44 David Brainerd Differential squarewave drive for DBM On my UHFSDR board, I am driving the LO inputs of the ADE-2ASK DBM
differentially from the Q and not Q outputs of a PECL flip flop. I
measure just under .5V P-P on the squarewave drive(.25 on each
output). The works out to 7 dBm average power. But, I don't know how
that will affect the DBM verses a 7 dBm sinewave which would have a
higher peak voltage. It seems to work, although we have seen
increased carrier feed through on 440 MHz(about 30 dB higher than on 2
Dave - WB6DHW
2496 2008-12-12 22:27:30 timshoppa Re: Differential squarewave drive for DBM 2498 2008-12-12 22:27:30 Glen Leinweber Differential squarewave drive for DBM Dave asks about square-wave driving a DBM diode mixer
from PECL digital output Q and not-Q...
No matter HOW you drive the L.O. port, you'll measure
about 0.5v p-p at the DBM's L.O. input. You're really
measuring the DBM's internal diode forward voltage.
You'd really rather want to know - how much current
flows thru a diode that's ON?
All the literature I've seen says to set up drive levels this
way: Your signal source should have a 50-ohm source
resistance - loaded with 50 ohms, the load should receive
+7 dBm signal power. Then you substitute the mixer for
that 50 ohm load. The mixer is actually a very non-linear
load, but on average will absorb roughly similar +7 dBm
Set up this way, I'd say diode current is likely 10mA
or less. You'd want to add a resistive pad between PECL
outputs and L.O. port to achieve similar diode current.
You could try a similar setup to the accepted method,
modified considering a square wave source, measuring
with a good 'scope that can resolve the square wave
voltage. The 'scope should have a 50 ohm input
termination. Come up with any kind of resistive pad
between PECL outputs and the 50 ohm resistor load
at the 'scope. Choose a resistive pad so that about
0.7v peak voltage (1.4v peak-to-peak) is measured
at the 'scope. The peak voltage of a conventional
sine wave source should similarly be about 0.7v. Or
a 50 ohm RF power meter should indicate 5 mW.
(+7 dBm) for either a squarewave or a sinewave
For a similar setup to yours, I've tried a resistive
pad of this type: a simple series resistor between
ECL output and DBM L.O. input. My DBM had
floating, fully differential LO input, so I used a series
resistor on Q and another similar series resistor on
Rick once pointed out that driving with square waves
can be fraught with transient trouble, especially where the
path from mixer to L.O. signal source is a significant part
of a wavelength. Reflections can cause screwy
waveforms, and wildly varying mixer diode current.
The non-linear source, and non-linear DBM load can
also cause wacky transients.
For your VHF case, the PECL outputs should be VERY
close to the mixer's L.O. port.
My attempts at SPICE simulations show wild transients
using square wave drive, mostly due to diode reverse
recovery time (trr). Even sine wave sources produce some
transients. These transients might be hard to observe on
a 'scope. Makes me wonder how a mixer manages to
"mix" at all!
2500 2008-12-12 22:27:46 leon Heller Re: Differential squarewave drive for DBM ----- Original Message -----
2502 2008-12-13 14:41:15 Wes Hayward Differential squarewave drive for DBM Hi all,
In connection with one of the current threads, I did some measurements
and put them up as a file. The file title is "Diode ring mixer
2504 2008-12-13 18:03:13 Dave - WB6DHW Re: Differential squarewave drive for DBM Wes Hayward wrote:
> Hi all,Very interesting. What effect does LO level have on LO to RF isolation?
> In connection with one of the current threads, I did some measurements
> and put them up as a file. The file title is "Diode ring mixer
> 73, Wes
Dave - WB6DHW
2530 2008-12-29 08:43:23 timshoppa Differential squarewave drive for DBM 2531 2008-12-29 09:56:09 Wes Hayward Differential squarewave drive for DBM Hi Tim,
2534 2008-12-30 06:36:26 chris3trask Differential squarewave drive for DBM >There is also some work by Tucker that appeared in a British
> Many books reference H.P. Walker's 1976 article "Sources of
> Intermodulation in Diode-Ring Mixers" where he shows results for
> intermodulation and some quote him as saying that with square wave
> drive, that the same intermod can be achieved with a factor of 15
> less LO drive. But I've never seen Walker's actual article, is it
> maybe out there on the net somewhere, or maybe on the EMRFD CD-ROM?
journal in the 1950's. I have that and perhaps some others that
What is the complete reference for the Walker article? I may
have that as well.
,----------------------. High Performance Mixers and
/ What's all this \ Amplifiers for RF Communications
/ extinct stuff, anyhow? /
\ _______,--------------' Chris Trask / N7ZWY
2538 2008-12-30 10:38:40 Wes Hayward Differential squarewave drive for DBM Hi Chris,
Good to see you in here.
The paper is:
Walker, H.P., "Sources of Intermodulati
2546 2008-12-30 12:14:03 leon Heller Re: Differential squarewave drive for DBM