12790	2016-05-04 15:58:15	lmeeny	Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Message	Date	From	Subject
Hello, I've designed a phasing network using the QuadNet software. There are 5 single pole all-pass filter stages in the I and Q paths respectively. I can calculate the 90 degree phase shift frequency of each stage. How do I determine at what frequencies to adjust the phasing network stages for maximum sideband suppression vs. frequency? Any suggestions appreciated. 73 Ed W2GHD
12796	2016-05-05 21:10:20	AD7ZU	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Hi Ed First determine the bandwidth of the signals you wish to optimize? 300hz - 3000hz? a 2700hz bandwidth suitable for SSB maybe CW but not other wider bandwidth modes a CW receiver with a 700hz or 1khz passband will not require 5 stages to get to 50db or greater opposite sideband suppression. but if you want 50db or greater across a 6Khz bandwidth 5 stages may be required. next go to the DESIGN tab in QuadNet and set the bandwidth parameters you wish to see. then go to the SUPPRESSION tab which will display a graph of the all pass network response. .. on the left notice the TUNE button which allows adjustment of each section individually while viewing the graph. this is a quick and visual way to optimize the parameters for each section to meet your design criteria. that's a quick and easy way using features in the QuadNet tool. also note that detectors, mixers, diplexers, and LO signals are not going to be perfect even when built with matched hand selected components and a precision layout so to achieve the kind of numbers shown in QuadNet (-65db) some phase and amplitude adjustment will be needed...somewhere after the mixer / detector and before the IQ signals are combined in a receiver. After IQ signals are generated but before combined in a transmitter. EMRFD has a proof in chapter 9 (i almost called it elegant) that only one adjustment point is required for amplitude and only one adjustment is required to correct the phase error anywhere in the IQ path. Chapter 9 also describes an op amp circuit that may be used to correct the amplitude and phase, however its my take after a brief look at the math involved that the phase correction will only be perfect at one frequency? any comment?? ... not the entire baseband. Additionally It will be challenging to accurately measure 50db or greater opposite sideband suppression across the baseband. hope that helps, Randy AD7ZU
12802	2016-05-07 15:17:26	kb1gmx	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
The way you view that is to insure the two all-pass networks maintain the closest to exactly 90 degrees difference between I and Q for the whole as mush as possible of your pass band. Keep in mind that is for the whole pass band and along side as well. For SSB make sure your wider than say 5khz or what you see is near band sputter from adjacent channels. The other part is if your all-pass were perfect then the preamps and the mixers and the LO I and Q will be the limiting factors. FYI A 5 pole network for the I and Q likely is overkill. The limiting factor is amplitude and also distortion presuming stages before and after the all pass were perfect. EMRFD give you the general patter and the math to calculate what level of phase and amplitude error will net what level of performance. from building several more than 43db is very hard to hear a difference and more than 50DB is hard to measure the difference. Allison
12804	2016-05-08 10:20:12	lmeeny	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Randy, I've followed the steps you so carefully explained, thank you. What I'm looking for is a technique as to what pots to adjust at what frequencies. I have an I/Q signal source and can apply the signals at whatever frequencies required. I sent an email to the guy who wrote the Quadnet program asking him if he could recommend an adjustment procedure. I'll forward his reply. Quadnet does provide the null frequencies. What puzzles me is that several of filter section break frequencies are an order of magnitude above the highest null. Thanks, Ed
12805	2016-05-08 12:42:15	AD7ZU	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Hi Ed, the important thing is to get a 90 degree phase shift between the sections. i agree with Allison's comment earlier that unless the bandwidth needed is very wide 5 sections is a lot. and that the allpass network error will likely not be the long pole.. there will be differences in the LO IQ signal phase, duty cycle, detectors/mixers, diplexers and whatever else is in front of the all pass network...there are many sources of error. you need only ONE adjustment for phase and ONE adjustment for amplitude in the entire chain. you may end up with far too many variables to ever get accurately aligned if you build this with pots in each allpass section at the very least only put pots in one lane. a cleaner approach is to hand select the caps first (all the same value). you can use a bridge circuit / audio generator / AC volt meter or if you have a rlc meter .. what is important is the phase difference so the cap values are less important than matching the values. If the all pass null is moved a few Hz but is 90 degrees from the opposite lane that is better than trying to precisely set the null frequency. ... actually if you have a big pile of 5% resistors just measure them until you find the values needed. The 3 section network in EMRFD R2 Pro is designed to maximize the use of standard value Rs and a single value Cs as I recall?? for SSB and CW a 3 or 4 section allpass network should perform well and I doubt you will hear any difference between a well aligned 3 section and a 5 secti
12806	2016-05-08 14:03:12	Bill Carver	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Have to disagree, Randy. A four section all-pass has FOUR frequency targets, each is adjusted at its designated frequency to produce precisely 90 degrees difference. When all four are set to the design values, then you get an equiripple phase error........where the deviation from quadrature is equally bad in between the adjustment frequencies. W7AAZ
12807	2016-05-10 12:01:07	lmeeny	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Randy, Thanks for the detailed reply. I realize 5 sections is overkill for 200 - 1800 Hz receiver tuning range but this design is a science project :-) I'm attempting to account for all the gain and phase errors in the chain to determine just how well I can do. The mixer is a Tayloe with hand selected integration capacitors matched to with 0.05%. No diplexers or mixer errors to contend with. The gain resistors in the phase shift circuit are center-tapped precision pairs. Over the frequency of interest the differential gain between the I and Q channels is less than 0.1%. As a first cut I adjusted the series resistor of each stage for 90 degrees +/- 1 degrees at each sections 1/2PIRC frequency for a 90 degree +/- 0.6 degree phase shift over the tuning range. If I understand you correctly I must disagree that a single adjustment for phase in the entire chain is adequate. A two pole phase shifter can do no better than a minimum suppression of -10dB or so. I agree that having 10 knobs to twiddle I may age a bit before finishing! ----------------------------------------------------------------------------- Bill, Thanks for tossing in you two cents worth :-) The more inputs the more I've learned. ----------------------------------------------------------------------------- If I can find an adjustment procedure for nulling the unwanted sideband, that is which pot at what frequency I'll post again. 73 Ed W2GHD
12809	2016-05-10 15:09:21	lmeeny	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Allison, Thanks for getting me started. I'm working on a science project ... just how much suppression can be achieved by hand selecting and matching components. with 3 all pass filters in each leg I hit about -40 dB last time around. I've preset the adjustment of each stage in the latest incarnation for a 90 +/- 1 degree degree delay at each filters 1/2PIR*C frequency. 73, Ed
12811	2016-05-10 15:56:17	bob_ledoux	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
When experimenting with QuadNet, I saw large theoretically possible attenuations, far beyond those that are practical. For example, I designed a two pair phase delay network with a bandwidth of 300 to 800 Hz. The calculated suppression was 67.6db for the unwanted sideband. But realistically, I might get 47db of suppression. So I was achieving about 20db less. Part of the loss is measurement. I don't have access to the tools that can measure L, C, or R values to within .1% The second issue is the parts themselves. voltage, current and change in signal strength. Back in the 1950's, when crystal filters were in their infancy, a number of manufacturers brought out phasing based SSB rigs. These systems often developed a reputation of being "touchy." They required considerable attention to keep the SSB functions running well. But they were less expensive to produce than the crystal lattice filters of the era, which required considerable effort to generate the proper frequency differences between the filter elements. Back in those days there was a small contingency of hams who built their crystal filters by taking surplus FT-243 cased filters and polishing them to the desired frequency. The technology of the day required similar processes for commercial equipment which was expensive. The development of crystal ladder filters made equipment less expensive and made it practical for amateurs to design their own filter systems. This of course also depended on the development of precise measurement equipment. While a filter constructed of L, C, or R elements is limited by the practical measurement and sources of variances in components, the crystal filter is much less subject to these limitations. With a simple RF oscillator and a frequency counter today's experimenter can easily select off a set of crystals within a few Hertz of each other. So measured variations of .0001% are practical. These practical limits, consistent with the nature of electronic components, is one reason phasing filter methods are not common at lower frequencies. The higher Q of crystals also plays a significant role in filter performance. This is my view as an experimenter. I'm certain that the older heads with professional credentials can offer an alternative view to my reality. bob-N7SUR
12812	2016-05-10 18:54:18	kb1gmx	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
If you only hit 40db with a 3 section all pass your doing it wrong. ;) I say that as there are already systems out there doing better with 3 stages. The miniR2 I have runs around 43-45db depending on where in the band it is. The limitation was not the all pass which I think can do better but combined mixer/preamp/hybrid imperfections. FYI the microR2 with only two sections dialed in does 36-37db. EMRFD has all the dirt on it and what is possible with 1 though 4 stages. Allison
12813	2016-05-10 19:12:26	kb1gmx	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
One comment on the fist phasing rigs. I have a HT37, classic phasing rig that I restored. After replacing the really poor wax-paper caps and the very drifty resistors I dialed it in and despite stories and the use of tubes it is stable. I can power it off and on and its were it was for sideband rejection. Granted even the 2Q4 needed help due to aging resistors and caps. The difference was modern carbon and metal film resistors, mylar and polyester film caps. The problem was the quality of the parts used not the basic scheme. Late 50s and early 60s parts were poor but comparison to those 20 years later and especially now. As to 1% and .1% parts SMT has been a boon for those. But a digital ohmmeter is still a good tool. Those with modern opamps, hard to beat. The thing is when you get to around 50db of suppression you have to remember that the offending signal is 100,000 time weaker! Its a thing with numbers is bigger may be better but does it need to be and does it sound good. Crystal filters are easy to make but good crystal filter that age well and have good shape factors with reasonable group delays are not at all easy to make. Most modern radios the opposing sideband rejection is not the filters result but the IF DSP doing phasing in software. The crystal filter in those radios keeps the clutter out of the IF where it can mix in unpleasant ways. Allison
12814	2016-05-11 11:27:07	AD7ZU	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Hi Ed, sounds like an interesting project. I have built 2 analog versions of a receiver also using the Tayloe detector. One with 2 sections, the other with 3 sections. I do not know the limit of the Tayloe circuit. I used hand selected parts both R's and C's. There will be differences in switching times and symmetry between on and off times in the switch and in the divider flops and a whole host of other subtle differences that accumulate error.. so at some point an error adjustment is required, and if there is an error adjustment required then all that precision isnt necessary..just tweek out the phase and amplitude error! the second version i built i used the circuit from EMRFD to add a small portion of the opposite lane to correct the phase error. My first take on that solution was that it was just wrong.. but after grinding through the arithmetic it is possible to completely null the phase error at one frequency in the passband...by my math. The amplitude and phase error correction interact with this circuit which means it needs some tedious tweeking. my measurement capability is limited but i could get it to where i could not hear the opposite sideband with more than 200uv at the input through 50db gain. In the 2 section design i added phase adjustments to each section and had similar results. again my measurement capability is limited. The point is that phase and amplitude errors are independent and therefore do not need multiple correction points. That is shown in EMRFD. i did those designs without the aid of quadnet... which is a great tool. one other feature in quadnet is the monte carlo which will allow you to see the calculated results when you provide a tolerance for the Rs and Cs. so.. i moved to a digital solution and used quickfilter technology qf1d512 fir and an audio codec. .. working on a transceiver version now that shares the phase shift and filtering between xmit and rx. ...when things get complicated is always wise to add more variables ;) Randy AD7ZU
12816	2016-05-11 16:50:13	Tayloe, Dan (Noki...	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
In the NC2030, two sections per side were used to cover the CW bandwidth. The clocking to the detector and the switching timing of the detector bus switch itself introduced phase errors so that a perfect 90 degree I-Q separation was not achieved. In addition, I noticed that when the detector caps are made larger in order to enhance out-of-band signal rejection, the roll off on one sideband is a bit different than the roll off on the other side, which caused an additional phase error effect. Thus, I put trimmer resistors on the two sections on one side to correct for these distortions. Envision the phase roll off on one side as if it were a straight line phase change with frequency (it is not straight, it is just easier to think of it that way). If the second side starts its straight line phase change descent after the first line, we can get a net phase constant difference between the two sides. We are shooting for something close to a 90 degree shift between these the straight line roll offs of the two sides. If the clocking source and the detector are not at a 90 degree difference, say 88 degrees instead, then the trimmers in the second side allow the straight line difference to be moved from a 90 degree difference to something different (92 degree?) to compensate for the fact that the source is 88 degree apart, not 90. Also, if the detector or the I/Q preamps introduce unequal frequency roll off (a frequency dependent small phase shift error) between I and Q, the slope of the second side can be changed such that it perhaps produces 92 degrees of shift at the low frequency end and perhaps 91.5 at the high frequency end to try to compensate for some of these additional frequency dependent phase changes. This form phase compensation is a bit different than what has been discussed since it not only can provide a constant phase difference, but is additionally able to vary the phase difference a bit over the frequency range if needed. I.e., the slope of the two lines can be adjusted so they are a bit different. This adjustment capability can also eliminate the need for high precision matched parts (i.e, the use of 10% caps and 5% resistors) since the scheme takes whatever slope the one side provides, and then matches the second side to it via trimmers to get the desired phase difference. This readily allows one section to use a 0.01 uF cap and the next section to use a 0.1 uF or even a 0.22 uF cap in order to keep the resistance low in that section for noise minimization purposes. Using surplus HP AC voltmeters that I find at hamfests (~$10, why would anyone want an AC only voltmeter?), I have no problem measuring opposite sideband suppression beyond 60 dB. For the frequency of interest that I was using (CW: ~200 to 800 Hz), I can get >50 dB across the audio band with a bit of interactive tweaking. This phase tweaking was also combined with the ability to tweak the gain of one of the two I/Q preamp stages. The biggest problem I have had lately in these measurements has been extraneous noise from my cell phone (it tends to be doing all kinds of things in the background), from my nearby Wi-Fi router and from the TV on the other side of the lab wall. Temporarily removal of power solves those issues. It seems pretty easy to trim phasing networks using two sections per side using a signal generator (8640B) and a HP AC voltmeter. I can see that adjusting three sections on a side would be pretty tough. - Dan, N7VE
12817	2016-05-11 19:00:03	bob_ledoux	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Dan makes the case for adjustment, and tuning by ear, rather than relying on high precision parts. The documents for the NC2030 transceiver remain available here: http://www.norcalqrp.org/nc2030.htm Pages 104 through 109 of the Assembly and Operation Manual discuss the adjustment for the best unwanted sideband attenuation. Pages following page 108 provide circuit operation principles. I've also found the Austin and Pacifccon presentations to be very informative. bob-N7SUR
12818	2016-05-11 19:12:07	AD7ZU	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Dan, very interesting comment: "In addition, I noticed that when the detector caps are made larger in order to enhance out-of-band signal rejection, the roll off on one sideband is a bit different than the roll off on the other side, which caused an additional phase error effect." is this due to the difference in reactance between sampling caps between the upper and lower sideband frequencies? or is this due to other factors in the detector op amp circuit? or internal op amp characteristics? Thanks, Randy AD7ZU
12819	2016-05-11 19:32:43	Tayloe, Dan (Noki...	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
I am not sure. I am not as mathematically inclined as others in the group. Ever played tennis or ping-pong? When I first observed this, my first thought was that it might be the electrical equivalent of “back spin”, helping the signal a little bit on one side, hurting it a little bit on the other. I have seen this effect over and over again. It is very repeatable. An HP AC voltmeter is your friend. I would never notice this “by ear”. Again, with a signal generator like my old 8640Bs, it is easy to see 60+ dB down on these phasing networks. When you get past 40 dB of opposite sideband attenuation, just crank in another 10, 20, or 30 dB of RF signal as needed. In my case I am looking at a small signal (200 mV?) at the other end of a 90 dB gain chain. In these tests I am not going to overload the front end. - Dan, N7VE
12820	2016-05-12 08:58:42	lmeeny	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Roger & Dan, I must eat a some crow Roger! In spite of it being right in front of me I never looked in detail at the direct conversion sections of EMFRD instead relying on other sources. Having spent time (trying to) absorb the details I understand more of where you're coming from. I will agree that a single amplitude and a single phase adjustment will do given the assumption that the totals of amplitude and phase errors of over the audio frequency range of interest are small. Let's just say that in order to make them small I'm into overkill Hi Hi. To answer my own question of how to adjust the 5 section I/Q phase shifter my best bet is to adjust each section at its' 90 degree shift frequency then leave it alone. Incorporating Dan's phase adjustment technique in his previous note is a better way to go. With regard to using small value integration capacitors in the Tayloe mixer. Simulations I'd done showed me the affect of phase shifts over the audio range of frequencies if larger value capacitors were used. I'm using a relatively small value capacitor, 0.22 uF to minimize this affect. Again, Thanks for making me actually think. These forums continue to be a great source of information. Ed W2GHD
12821	2016-05-12 13:27:50	Tayloe, Dan (Noki...	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
My thought on making the detection caps larger was that I was getting wideband large signal rejection for free for my I and Q pre-amps, which helps blocking and perhaps IP3 performance. Thus, I was trying to play with the roll-off cap across the feedback resistor on the pre-amp op-amp and the detection caps to get as tight as possible. The differences in the roll off in the two sides creates frequency dependent phase differences. Matching here would really help, but I usually just relied on adjustments in the phasing strips to kind of patch things up. I really like Rick’s simple discrete pre-amp stages from a cost point of view. I was using a much more expensive low noise op-amp with rail-to-rail output in order to squeeze a bit more dynamic range out of a current conservative (given a switching supply) 3v receiver supply rail. The inherent front end detector bandpass filtering helped make the use of a 3v supply rail (rather than a 12v, +/-12v, +/-18v rail) a bit more tolerable as well to other large signals elsewhere on the band. I was also cheating big time using ceramic SMT caps rather than larger, more stable Mylar or polyester caps for the detectors, phasing, and R/C filtering. The use of 50v SMT caps in a 3v circuit helped reduce some of the problems that modern ceramic caps have with the C changing (a lot?) based on the applied voltage. I used so many caps in the design that they had to be small and cheap to keep costs down. I think I was able to get away with it in the end, all thought it was still an awful lot of parts. - Dan, N7VE
12822	2016-05-12 16:22:15	AD7ZU	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
must admit i find myself obsessing over the opposite sb suppression subtleties and every time there is a discussion here there is some new sometimes esoteric piece of info that comes to light and i file away and use later. the detector circuit is simple, elegant, easy to build, uses cheap readily available parts, and performs exceptionally well .. even my bench breadboard receivers (no enclosure, rats nest wiring) would put some receivers i used in my early days to shame. my latest .. isn't too concerned with power consumption as batteries are getting very good these days. .. the codec alone probably consumes more power than the entire nc2030 receive chain.. and its a "low power" part. at some point after all the trade offs it is good enough Randy AD7ZU
12823	2016-05-12 18:24:42	kb1gmx	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
As someone that build more than a few from simple passive second order to full out higher order image reject receivers a hint. A perfect all pass can be screwed by a lousy preamp or a messed up mixer or a 90degree system that has error with increasing frequency. If there was one thing I could say is its a system. The math only works at the system level. I did the lets chase the magic 60db or more thing. Then I built and listened to many actual radios of lesser performance on a contesting weekend. Guess what, even if you had 60db, the spurs, splatter, and trash coming off the transmitters in the band will still be heard, maybe better. Balancing the overload performance, gain and in band and out band is the system problem and not limited to the all pass. Even a "lowly" MicroR2 can hear that. Oddly all the limits of a uR2 at maybe 37DB are just as endemic on my Triton and Eagle, since its often the other guy, not everyone on 40 runs clean or knows how to. When I say over 45-47db is very good build it and listen. But at that level the hybrid or whatever has to be also as good and the mixers and their amplitude balance and phase must be as good. The system is only as good as the weakest link and oddly often that not the all pass network though it could be. A good system can be done but its often inconsistent with wide tuning. The variables that need to be controlled are not limited to the all pass. So if your doing a 4th or 5th order network then getting the widest band width that gives good suppression is desirable over a narrow one. The out of channel stuff can be handled by a good audio filter. You need one anyway. The interesting thing is the early systems were build and still in use and still show the as built numbers. I have a few filter based radios that can't say that due to crystals ageing. Allison
12824	2016-05-12 20:03:30	iq_rx	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Hi All, I'm enjoying reading this thread, lots of ideas being kicked around here. I'd like to make one small correction: regarding "Rick's simple discrete pre-amp stages." I've used that circuit again and again, simulated, analyzed and measured it extensively to make sure it's not the weak point in a receiver, and modified it when it is, and published the circuitry in at least a dozen different places. But I can't take credit for it. I used a different topology in my earlier instrumentation receivers and learned of that simple discrete pre-amp stage from QST articles that Roy Lewallen and Wes Hayward published. So I credit them with introducing that particular circuit to the amateur receiver community. Each of them claims to have seen it somewhere else even earlier. Keep up the good work everyone. This is interesting work, and has been since Mike Villard and others were playing with it more than 65 years ago. Best Regards, Rick KK7B
12825	2016-05-12 20:32:53	farhanbox@gmail.c...	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
was it described even before roy's optimized transceiver? btw the preamp works pretty well into the rf range as well. the half mill bias current limits its signal handling capacity. higher current will lead to proportionalty lower inpuy impedance. however, bob kopksi described a way to increase the signal handling capability. if we imagine a 10ma bias, the input impedance looking into the preamp would be 2.6 ohms. a series resistor of 47 ohms would take the impedance up to 50 ohms. this would be noisy but it would have a pretty decent distortion characteratics. the noise increase would be due to the loss in the 47 ohms resistor. nothing the transistor can do to stem it. - f
12826	2016-05-13 14:01:47	kb1gmx	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
That circuit was a point where I have to hit the books and the bench and test in the crunch proof 6M TRX. There is a balance point for gain its low currents, for impedance its .5mA, and for signal handling its gain. I ended up going higher to 1ma (25ohms) as that had minimal impact on noise. Then by lowering the load resistance you get to a higher overload point with a trade for gain. Since that part of the system was not noise figure limited (hybrid single conversion with VHF IF) and the down converter (from 6M to 36mhz) made for the gain and NF (high current LNA). It works for that application. It was a balancing act. I'd consider 10mA rather extreme as something in the 1 (25ohm) or 2(13ohm) mA range is easier to deal with as the noise impact is not really that great. Another approach is using a boosted JFET common gate (CP665 or similar are still available) at high currents. In all cases you have to know where to stop. The limiting factor usually ends up at a preceding stage or the mixer itself. In the end its no more gain than needed to insure noise factor balanced against how big a signal you can handle in later stages. The all pass networks have a useful voltage swing of about 6V for a 12V system. If you can run at 24 or 30V or better +- 15V that greater voltage before compression/limiting/clipping is moved. The curve I've never seen is output voltage for a fixed level input over frequency range. Fixing one problem helps but there are many variables, they all interact. Allison
12887	2016-05-31 09:12:32	IEN	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
I am looking at the schematic of NC2030 V1.3. and noted transformer T2 and associated componets and I ask how it works in rejecting AM stations.- Regards. LU5DNM norberto.modanesi@gmail.com San Nicolás ----- Original Message -----
12889	2016-05-31 14:56:53	Tayloe, Dan (Noki...	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
T2 and the associated parts were not used in the final kit. It has been a long time I did this. I recall some read of EMRFD that LO in the input could unbalance the detector and encourage out of band AM detection. This was an attempt to null out the LO on the input from the internal LO clocking. I am not sure if that “unbalance” concern actually applies to this switching mixer, as opposed to a regular diode mixer. On the first prototype build, it “seemed” to improve AM rejection, but it did not in any of the later builds. Just ignore this portion of the schematic. Dan, N7VE
12890	2016-05-31 15:22:50	IEN	Re: Adjusting IQ Phasing Network in Direct Conversion r\Receiver
Thanks Dan for your answer. norberto.modanesi@gmail.com San Nicolás ----- Original Message -----