A New Line of Transceivers ~ DifX

Transceiver Architecture 2.22

Have You Ever Wondered?

 

Arduinos and Si5351 PLL Clock Generators are inexpensive (well depends where you live); but for around $20 (US) you can purchase a ProMini and a si5351 Clock Generator. I have not seen many designs where two Arduino's and two PLL clock generators are employed. So why not? Yes you will hear from the lurking illuminati that you don't need to use two but has any one really explored the possibilities opened up by such an approach.

 

Let us think "Out of the Box" for a minute. Suppose we take a device like the Pro-Mini and loaded that with code so that CLK2 would provide the injection frequency for a second mixer in a dual conversion transceiver (the 1st conversion would be an up conversion to say 45 MHz).Thus the second conversion would be to the IF frequency and CLK0 would provide the BFO injection frequencies. You got that OK?

 

Now think for a minute of a two position switch mounted on the front panel so that one position would be to select USB, the second position would be for LSB. You might even have a second encoder with a PB so that by depressing the encoder push button you could have pass band tuning limited to the range of separation between the USB/LSB frequencies. Pretty cool.

 

Now about the second Arduino and PLL Clock Generator. Suppose that this time for the up-conversion we use the Si570 controlled by an Arduino Mega. The use of the Si570 would cure the gaff from the EMRFD Illuminati about phase noise and would use a true encoder and not a pot like in the Minima. I am thinking with the Mega you would have more digital and analog IO so that controlling band pass and low pass filters would be unencumbered by pin limitations. A bigger display (and more programming space in the Mega) would let you display to your hearts content. The two PLL Clock generators will also address the naysayers who complain about the spill over onto the third clock. The upper frequency limit of the Si570 is about 5X the Si5351 so other possibilities here.

 

So maybe it is time to add a few more Arduino's and PLL Clock generators in our rigs.

 

Pete N6QW

 



A New Line of Transceivers ~ DifX

Transceiver Architecture 2.21

 

We must look to the past often times to see the clarity of the way forward. I am reminded of something that Thomas Edison experienced. (Don't know if this is factual but may be more of an urban legend thrown in for good measure.)

 

It seems there was a major fire at his Menlo Park Laboratories and with that fire many of Edison's projects were burnt to a crisp. One of his assistants was lamenting to Edison about how terrible the situation was in that many of his projects were no more. Edison, ever the visionary, said this is actually good! The assistant could not believe what he heard --Edison chimed in -- "most of what burnt up didn't work and I just didn't have the heart to take it to the dump". The fire actually solved a problem for Edison --with the clutter removed he could focus on  more productive things.

 

So it is with all things Dishal! I had a ceremonial fire today and gone is all that wretched crap that didn't work and probably never would work. But with that fire, I have a new plan and I think a much better solution for the second filter. I am somewhat mad that I didn't noodle this before.

 

While I work the new approach the blog will be silent. But I am really jazzed that where I am headed will in effect be a super DifX.

 

June 12, 2017

73's

Pete, N6QW

 



A New Line of Transceivers ~ DifX

Transceiver Architecture 2.20

6/10/2017~ More on Dishal Dyslexia Part 2

There always has to be a reason why something as fundamental as 1 + 1 does not equal 2 and so it is with the results arising from building a Dishal Crystal Filter. So lets us take a few steps back and examine why 1 + 1 may not equal 2.

 

The Dishal software in large part requires the user to make some initial measurements outside of the software itself. Starting with the G3URR oscillator and my SDR receiver (capable of measuring to 1 Hz and verified by first locking on to WWV) I measured the crystals in the loaded and unloaded condition. Again the receiver is calibrated to be accurate to 1 Hz and the G3URR component values are 470 PF (NPO COG) in the Colpitts circuit and the load cap was 30 PF NPO COG. So the data was taken and crystals were found that were very close in frequency and thus were the basis for entering the data into the Dishal software. It is pretty automatic once you enter the data.

 

The Dishal software can be tweaked by factors such as the number of crystals and the ripple factor. Once these are selected then you get a plot of the filter. But the software also spits out the Filter Center Frequency, the values of the coupling capacitors and the impedance that must be matched to 50 Ohms. So far so good.

 

Now the problem is one of what BFO frequencies do you select. Starting with the predicted Center Frequency I chose BFO frequencies about 1.5 KHz above and below that value. This choice was one based on the stock of 9 MHz crystal Filters I have and the matching BFO crystals are just that -- 1.5 KHz above and below. That isn't gospel but merely a place to start. Those values were input to the Arduino Sketch. It became pretty obvious that those were not the right values.

 

My next step was to disconnect CLK2 from the SBL-1 and in its place use my FeelTech signal generator to supply the BFO signals. Two cautions here with the first being that you crank down the output to 1.4 Volts PTP before connecting to the SBL-1 and second that you have a 10 NF cap between the FeelTech and the SBL-1. What I found was that the values that seemed to work were only  about 1 KHz away from the Cf. There is something wrong here.

 

A 1 KHz BFO would place the signal on the top of the pass band and not on the slope of the curve! Thus  1 + 1 is not 2. This bothered me and that is when the light bulb went on. Dishal is lying to me!!!! Well not entirely true but close to the truth (I must sound like Donald Trump.) Is this being taped?

 

This is when I tried something and this may provide an explanation for some of the crappy results I am seeing using Dishal. The first thing I did is to connect the radio to a dummy load so that no signals were incoming. Then I listened to the rig as I tuned the BFO (FeelTech) from about 2.5 kHz below the supposed Cf to about 2.5 kHz above and just listened -- I noted the change in the background noise and at one point heard a "null". Was this in fact the Center Frequency? I think it may be --tell me I am wrong. This value was close but different that the Dishal value. So I think my evaluation may have some validity. Using this value I added/subtracted 1300 Hz to set the frequencies. In looking at the location of +/- 1300 Hz this puts the frequencies about 3 dB down on the curve and so that may add some additional validity to my selection.

 

I have changed the Arduino sketch with the 1300 Hz values and will now await the 40M band to perk up so I can run some listening tests and get some reports on the transmitted signal. I very likely missed this part in the Dishal Tutorial (who reads that stuff anyway) but the setting of the BFO frequencies does indeed affect the filter performance.

 

Lurking here is the theoretical (Dishal Predictive Curve) versus what really results and that may be a shift of the Center Frequency because of imperfect components, stray capacitance, lead length and whether you have dandruff or AFF (Athlete's Foot Fungus). So many things could impact if indeed 1 + 1 = 2.

My Dishal experience has consumed way too much time and the results so far do not justify the effort. Despite what you may have read in all of the testimonials and the touted results --did those users actually install the filter in a radio and "air test it" and match their real world experience with what the curves may be telling them? I can only share what I have seen and so far it has not been pretty.

Pete N6QW

Dishal Dyslexia 

 

I am disappointed with the results from using the Dishal method where quite often what you get does not match the predictions or expectations. There are those reading this blog who are now quickly preparing a flaming response. There will be the usual comments: you didn't do it properly; or you did not make the measurements correctly or you built it in a haphazard manner or on and on.

 

 

My 6 pole filter sucks and is real crap. I then decided to build a four pole filter using four different crystals but ones from the same batch. I was very careful (again) to follow all of the steps and to double check the build, the test setup and the measurement process. The outcome was not unlike the six pole but  somewhat better. I did find that the skirt rejection was better than the six pole and closer to the predicted curve but installed in a radio sounded "not so good" when tuning across a signal. That to me is telling --how does it work in a rig.

 

So below are plots of the four pole filter responses both from the predicted value and the actual measured value. Using the FeelTech signal generator for the signal source and my Rigol scope for the detector. There was a 50 Ohm series resistor in the source end and a 50 Ohm termination resistor on the output side. The readings were taken as RMS readings.

 

Here is how I converted the Vrms data. First I multiplied the readings by 2.828 as this converts the readings to V Peak to Peak. I thought this would be useful to know and have as a matter of record the PTP readings. I then squared that PTP reading and divided that by 400. The 400 factor accounts for 50 Ohms and does in effect take the value back into RMS. The answer is in watts. If you multiply that by 1000 you now have milliwatts. Or you can simply take the squared value and multiply by 2.5 (1000/400). This answer is now in milliwatts. If you take 10 X LOG10 of this number you will have dBm. That is what I did. So find fault as you will; but the curve will represent the relative impact of the pass band and give you a prediction.

 

Here is my curve based on the measurement process. I took readings every 200 Hz. There might be some advantage at this point to repeat the test using 100 Hz data points. But this curve does look like the Dishal curve for the four pole filter. Installed in a radio I can say that on receive it does not sound that good.

 

 

 

The Dishal Predicted Curve!



 

 





 

 

 

 

 

So what do you do now? You have the filter, it looks like the prediction but does not sound too good. There are opportunities for changing things. One change: make the bandwidth less. I set it at 2.5 kHz so it would have that "hi fi" or enhanced SSB sound. A filter at 2.3 KHz night be a better choice, and doing so will change the cap values and the matching transformer. So before I do that I want to do some more testing with the current configuration.

 

This now  begs the questions: Why did the 6 pole shoot craps and Why the 4 Pole while looking like the prediction not sound so good? Maybe the sounding not so good is that the bandwidth has been opened up and I am used to hearing like about 2.1 kHz. Stay tuned.

 

 

73's

Pete N6QW



The LM373 Transceiver ~ Three weeks on the air.

The LM373 Transceiver - What a Rig!

The LM373 is a Real Gem!

6/7/2017 ~ New Video of the LM373 Transceiver!

 

 

6/6/2017 ~ Added >10 dB Attenuator to handle super strong signals. It is a "T Type" controlled by a small relay with the Series arms being 33 Ohms and the Parallel arm being 22 Ohms. A switch on the front panel controls the In/Out. Kind of amazing --with the pad Out of the circuit you can hear the noise on the signal and with it In --the noise drops like a rock. Good affirmation about RF amplifier stages and their contribution to noise. The Pad/Relay was mounted on a small circuit board which was soldered vertically to the main board.

 



 

 

 The panel mounted toggle switch that selects Pad In/Out is located below the volume control and above the earphone jack. This is a solution to the strong signal overload.

 

73's

Pete N6QW

 

 

Every so often the planets align and you end up with a really nice rig. No nice is not the right word but the correct terminology is that you end up with a Superb Rig. I have fully documented the building of the LM373 Rig at http://www.n6qw.com/LM373.html

 

Frequently I joke that I have two boxes of electronic projects with a giant box containing rigs/projects that worked once, or ones that don't work or ones that will never work (the 6 Pole Dishal Filter is in this group). Then I have a smaller box of rigs/projects that work very well. The LM373 Rig is definitely in that box.

 

Rigs can look good --or can even be called pretty; but how do they work is the real test. Typically the unofficial criteria is how do they sound on the other end, can they work DX , how do they receive, and for those who lurk the bands with their SDR store bought radios with 72 inch screens is there any energy below 200 Hz or above 2800 Hz. This latter criteria seems to be the one that is the most controversial with those of us who homebrew their rigs.

 

So now I would like to share some LM373 Performance information. With IRF510 for a final it will put out in excess of 5 watts (6-8 can be easily had). With my intermediate amp it will do >110 watts and with the SB200 in line following the intermediate amp it will do 700 watts (easily). Couple that with a 2 element beam (which I will talk more about a bit later) and you can break pile ups --which I have. Stations have been worked running QRP and most of the stations worked at 110 watts and of course stations worked at high power. Interestingly about 1/3 of the DX stations were worked running the 110 watts -- the beam antenna is a great field leveler.

 

Now how does it sound -- I get frequent rave comments about the audio (subjective from non SDR monitors). Punchy and articulate are frequent descriptors --kind of amazing since the audio stage is a single 2N3904 that was modeled in LT Spice. There have been no reports about spurs, lack of sideband suppression or pinched sounding. All this from a homebrew rig!

 

On the receive side it hears really well and that has been a frequent question from the other end after hearing the transmit side. Well I have found the hearing part an interesting aspect of the rig. The LM373 has built in AGC Circuitry and the data sheets include suggestions for making this adjustable versus fixed values. That will be a further experiment.

 

In W5BAA's design he used a second LM373 as the receiver mixer stage and riding along with that is that you do get some gain from that stage since it is an active (versus passive) mixer. In my rig I used an SBL-1 as the mixer stage which as a passive mixer (non-gain) does have a conversion loss. Ahead of the SBL-1, I added a single manually adjustable gain stage. Mind you the manually adjustable is a trim pot on the circuit board. My original intent was to set it for about 10 dB and forget it. Well I have found that on really strong signals and with the beam down the throat of the station that the rig will overload. Crank back that trim pot ( 2 to 3 dB of gain) and everything clears right up without any other adjustments. This does not happen all of the time --just on the rock crushing signals and sometimes I do see those kinds of signals. With the beam moving off the signal heading this clears up the signal too. So I smile as I now know the beam is doing its job!

 

The solution to the infrequent overload can take many forms and two of those would be to make the AGC a panel control as shown in the LM373 Data Sheets or add a 10 dB attenuator (a simple  relay with a 10 dB pad on one side of the contacts) as I did with the KWM-4. The attenuator would be easy to implement right on the 2N3904 Rx RF Amp Board. This has perhaps a better approach as the engagement is a simple toggle switch versus a panel mounted pot.  So this whole discussion boils down to that the receiver is sensitive and can be too sensitive if upstream there is not some signal limiting for extremely strong signals. A more elaborate AGC would also 'save the day'.

 

Now how does it work with DX -- well my DX standard is the European / VK-ZL path. I have worked the following pre-fixes S51 (Slovenia), EA3 (Spain), E51(Cook Island), LU1 (Argentina), XE1(Mexico), ZL1(New Zealand) and 9Y4 (Caribbean). Mind you that so far I have made 50 contacts total with the rig and 15% have been DX.

 

Sides have been added to the case (painted black) and now I am working on a top cover. One possible top cover might be a sheet of 1/8 thick Lexan plastic so you can the "innards" another is a metal cover with a speaker built into the cover. Still noodling that piece.

 



 

 

 



There is just something about being able to work DX stations (some running Flex 6700's) and to have them say nice signal --all from a homebrew rig using 1970's technology.

 

73's

Pete N6QW

A New Line of Transceivers ~ DifX

Transceiver Architecture 2.19

6/4/2017 ~ The Dishal Saga continues.

Bob, N7SUR shared his Dishal experience (he was very successful) and in his configuration he has a TIA amp ahead and following the filter. He is also using a AD9850 signal source. I added a front end amplifier and the results improved somewhat. This added about 15 dB of improvement. The real test would be to add an amplifier on the back end and make another run. But NOT THERE yet but better than earlier. The theory about amplification is that the scope may not be detecting the lower signal levels (masked by noise) and with a boost this enable better readings.

73's
Pete N6QW



6/3/2017 ~ More Listening Test with New BFO Frequencies

(BTW only 1 kHz below/above the apparent Center Frequency --what does that tell you?)

 

 

 

The Dishal Filter must be on par with Fake News!

 

73's

Pete N6QW





Four weeks of work and this is what you get --not very satisfied!!!!  Several blog posts ago I mentioned about Method #1 which simply is finding 6 crystals that are no more than 50 Hertz spread among any of the crystals, use 150 PF NPO caps and build a ladder filter. Assume the Zin/out to be 150 Ohms and get on with life. I would bet that approach would have netted a much better filter. If you are considering the Dishal approach opt for Method #1.

 

 

 

 

73's

Pete N6QW



A New Line of Transceivers ~ DifX

Transceiver Architecture 2.18

The Final Filter

 

6/3/2017 ~ A definition of Covfefe: Running the same exact test on the same piece of crap will change the outcome!

 

My question is why is there only about 25 dB difference is the peak response and the rejection? The bandwidth looks about 2.2 kHz but the ultimate rejection looks poor. I would feel better about the results if there was say a 45 dB difference in the peak response. The shape looks fairly flat but not within 0.2 dB as predicted by Dishal for a 127 Ohm termination. I can only reflect that what we have going here with the Dishal approach is much like the touted Gas mileage is indeed YMMV!

 

Pete N6QW

 



 

6/1/2017

 

I have received a private email from someone who knows and they have shared that my disappointing results with the Dishal Filter possibly is linked to Covfefe. I surely hope not but this malady may be affecting a lot of electronic failures from now on and for the foreseeable future.

 

Shown below is a second data run which is not inconsistent with the 1st run. The results are disappointing. I wouldn't call this a very good filter.

 



 

Pete N6QW

 



5/31/17

 

The filter is built and this may be the last one I ever build. Talk about wasted man hours. I will now begin some characterizations tests. Getting to the precision caps was a lot of effort and without the AADE LC meter this would have been impossible. I have added a plot of the response and now need to go back and do some fine tuning  of the caps.

To use a crass common vernacular term --this was a real "ball buster"! I am not satisfied with the result. This was a lot of effort for a curve that looks no better than picking 6 close crystals and using 150 PF caps in a ladder configuration. One has to ask why go through the agony?

 

73's

Pete N6QW



The above plot is with the data converted to dBm. No resemblance to the Dishal curve but we now have a baseline for "Twizzling" the caps. I am not all that hopeful that this will dramatically improve.
The BW looks like about 2.4 kHz but not enough data points to look at the 60 dB points. I only scanned about 5 kHz at every 100 Hz point. More points and maybe at 50 Hz increments would have further defined the curve. But this is a starting point.



 

I am so glad that my brain works while I sleep as that often keeps me out of trouble or at least may minimize some downstream trouble.

 

When I awoke the other morning I got a message from my brain about the effect of stray capacitance and the design of my compact board. The pads as cut are 0.5 inches by 0.5 inches and there is a pad to pad capacitance as well as a pad to ground plane capacitance. So I took my handy AADE LC meter and measured away. Boom the pad to pad capacitance is in the range of 3 PF and fairly consistent from pad to pad and the pad to ground is higher in the range of 4 PF. So those values are in parallel with what I am soldering to the board. Thus I need to re-look at the values I have chosen for the caps and this may negate the need to have trimmers installed.

 

It may take a day or two but this is a precision crystal filter and thus will need to rethink the install. There has also been traffic on the illuminati reflectors about capacitor Q and how this impacts the use of caps in various tuned circuits. I purchased precision MLCC 1% caps so I am not starting in a deep hole for those who will be quick to email me about the Q of capacitors. I have been advised accordingly so am aware of this concern. Thanks Greg.

 

 

73's

Pete N6QW

A New Line of Transceivers ~ DifX

Transceiver Architecture ~ 2.17

[For more info on the LM373 SSB Transceiver see http://www.n6qw.com/LM373.html)




Reworked Color Display for the Dual Conversion DifX

 

The Crystal Filter Build Out

 

5/25/2017 ~ Where "Noodling" pays big dividends.

 

Yesterday I made a "linear layout" of the six pole crystal filter and the result was a series of 11 pads where the crystals and caps would be installed and that assembly was about 6 inches long. This is an unwieldy dimension to handle inside of a compact radio. Then I spotted a photo of an 8 pole filter as used in the Elecraft rigs and saw how they had compacted the build. So that led me to think a smaller footprint. I now have come up with a compact version that get the footprint down to something like 2 (or 3)" X 4" inches --much more accommodating. I also had concerns about signal leakage between the sections of the compact layout and think that can be fixed by the addition of a shield between the sections. See my "noodling" sketch below. (I are not an artist and barely an engineer!)

 



 

I have already created the design for the compact board in G Simple and have the dxf file ready to cut a board on my CNC Mill. I will add a photo of the cut board when I am done.

 



 

Noteworthy I have received an email about my capacitor selection process and a link to a video about polarity of capacitors and the stability of capacitors. Hopefully the extra $$$ I spent for the 1% caps and the NPO criteria will abate some of these well founded concerns. I will also exercise caution in NOT applying too much heat to the caps during the soldering process.

 

73's

Pete N6QW

 

 

5/24/2017

 

The caps arrived today and I also measured the 150 PF NPO caps I had in stock. One of values needed (4 places) was 151.2 PF. Using my AADE LC meter, I measured 13 caps and here are the results.

 



The results of this test shows that of the 9 caps we have nailed down 5 of them. The two 115.4 PF I think will be asy to achieve with the 100 PF NPO I bought and the 15 PF trimmer. The 430 PF that were to be the basis of the 437.1 PF are so small I can hardly see them so I may have to invoke a work around.

 

I also designed the PC board and it is about 5 inches long and 3 inches wide. There may be a way to compact this but for this 1st run it will be linear. Hope to cut the board tomorrow and start soldering in crystals and caps.

 

73's

Pete N6QW

 

I have been awaiting the delivery of some 1% caps and they will be arriving in the next couple of days so in the meantime I will flesh out the circuit board for the crystal filter. So let us examine what is required. My Dishal filter for the 6 Crystal Filter has a total of nine capacitors and they are as follows: 

 

• 2 X 151.2 PF
• 2 X 437.1 PF
• 2 X 115.4 PF
• 2 X 151.2 PF
• 1 X 156.8 PF

Noteworthy is that we really only have 4 values of capacitors including 4 caps of the same value. The precision caps I ordered are 100 PF, and 430 PF and these are 1% and NPO AND Surface Mount. I have a bag of 150 PF NPO caps which I will measure to find values all below 150 PF. (Hopefully finding four that are all below 150 PF but close in value. I have an AADE LC meter and that is my measurement tool.

 

The PC Board will require a total of 11 Pads to accommodate the crystals and the caps. To get me exactly on the values needed I will make the pads large so that there room for the 15PF  air variable trimmer caps in addition to the fixed value ones and the crystals. Playing with these parts before I cut any pads is critical to the final assembly. Thus 437.1PF = 430 PF + 0-15 PF Trimmer

 

I will add to this posting with the layout of the crystal board after I get it laid out.

 

73's

Pete N6QW