2492	2008-12-12 02:16:44	David Brainerd	Differential squarewave drive for DBM
Message	Date	From	Subject
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 meters). Dave - WB6DHW <http://wb6dhw.com>
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 power. 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 source. 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 not-Q. 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
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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 measurements." 73, Wes w7zoi
2504	2008-12-13 18:03:13	Dave - WB6DHW	Re: Differential squarewave drive for DBM
Wes Hayward wrote: > 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 > measurements." > > 73, Wes > w7zoi > > > > Very interesting. What effect does LO level have on LO to RF isolation? Dave - WB6DHW <http://wb6dhw.com>
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, The articles
2534	2008-12-30 06:36:26	chris3trask	Differential squarewave drive for DBM
> > 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? > There is also some work by Tucker that appeared in a British journal in the 1950's. I have that and perhaps some others that address this. What is the complete reference for the Walker article? I may have that as well. Chris ,----------------------. 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
MCL recommends square wave drive for their mixers. 73, Leon -- Leon Heller Amateur radio call-sign G1HSM Yaesu FT-817ND transceiver Suzuki SV1000S motorcycle leon355@btinternet.com http://www.geocities.com/leon_heller