A New Line of Transceivers ~ DifX

A New Definition of HAM!

 

HAM = Homebrew Avoidance Methodologies.

 

This posting undoubtedly will create a stir in the greater ham community and may give pause that  my advanced age is now affecting my mental faculties. What I am about to post is based on over 60 years of homebrew experience dating back to the early 1950's when I first dabbled with the CK722 in solid state circuits. Or perhaps there will be questions from some quarters is 60 years experience, one year of experience 60 times over? Or is it truly a progressive building of an experience base spanning 60 years that started with vacuum tubes and now involves amazing digital electronic building blocks packed into boards the size of postage stamps?

 

Many would think given my lengthy time at the bench, would I resist moving from the buggy whip to the new fangled automobile. What I will be sharing, while solely my view, is fully supported with the "why" I am taking the various positions.

 

A week doesn't go by (or maybe just a few days) where I get an email requesting help or asking questions by those who are new to homebrewing or maybe from homebrewer's not so experienced at soldering their fingers together.

I am aiming this post at a specific audience and as mentioned, to those newer to homebrewing and the boiled down "why" is that what I am describing of what not to do, makes it an uneven playing field against having early on successes. These HAM Tips are being provided perhaps as a substitute approach, in essence, saying you will save yourself a lot of grief by not undertaking certain methods to homebrewing a project. The journey as the Reverend Dobbs of GQRP SPRAT states is the important part --but the starting place is not the top of Mt. Everest!

 

 

Homebrew Avoidance Methodologies (HAM)

 

Since we now live in the "age of impatience" below are the avoidance subjects I will be covering. This is provided now, so you won't have to read any further and thus you can simply move on and revel in the view that my mind is totally gone.

1. Why not to build and use analog VFO's?
2. Why not to build and use the discrete (2N3904/2N3906) audio amplifier?
3. Why not to use the "prototype" bread boards?
4. Why not to build and use the Dishal Filters?
5. Why not to build "that really big project" without having built something small initially?

 

 

The Dreaded Analog VFO!

 



So OK for those who stuck with me this far let us take up subject Number 1, with me, and that is the non-use of Analog VFO's. Here come the arguments that with an analog VFO you have a link to the past and that there is so much satisfaction in finally getting one to exhale sine waves. Yes, there is the nostalgia trip and the idea of a connection with the past in how things used to be done. But for today's state of the art rigs they are barely "good enough".

 

It has even been suggested that I never have built an analog VFO or that I have never really built a VFO that was rock solid, didn't have warm up drift and didn't drift at all.  To those who think that, shown below is an example of an Analog VFO built by me. This did not happen in a span of two hours; but I started first by looking at all of the aspects that need to be covered to have a really solid VFO. Yes, I consulted DeMaw and Hayward and Hantchett (for those who don't know -- he was the guy from RCA, and his call sign W2YM. He built one of the first DGM VFO's). I read and reread the ARRL info on the mechanical side of building solid VFO's and even selected a VFO type that would afford the very best frequency generation characteristics as to stability and even considered the phase noise that incidentally could be generated. There was real engineering behind this project!

 

The VFO topology selected was the Hartley and the tank coil was wound on a ceramic form without any ferrite core, which has been installed in a captive cradle assembly. This was done so that the tank coil was solidly held but floating in air away from the any metal. Liberal use of coil dope [Gorilla Glue] was applied so that there was no movement of the windings. The enclosure was made of double sided PC Board and the method of construction had a metal cover that was solidly affixed to each corner as well as a center post. Thus you could flex the top cover and there was NO frequency change!!!! That said the bottom actual circuit board is single sided copper board so that there is no unwanted coupling through the small capacitance that would exist in the board given that you have two plates separated by a dielectric.

N6QW Homebrew Analog VFO

 

Hartley Oscillator

 



Multi-capacitors in parallel (NPO/COG and NPO Trimmers) were used to set the base frequency range of the VFO and a double bearing type variable capacitor was used for the incremental tuning. The main tuning cap was external to the box. [The black wire in the lower corner of the box connects to the variable capacitor.]  The multi-capacitor approach is to limit the circulating currents through any one capacitor so that there was no "heating" of individual capacitors which is a cause of drift.

To avoid loading of the VFO circuit I used a buffer/booster amp on the output  of the oscillator transistor and there were multiple outputs so that the main output drives a mixer circuit and one of the auxiliary outputs could furnish output to the frequency readout LCD. Still another output could feed a huff and puff stabilizer. The output stage was/is adjustable so that the appropriate drive level is provided to the mixer stage.

Voltage regulation is internal to the box for a reason. There would be some heat generated with the regulator and when the box is sealed up, in effect, you have a temperature controlled oven with a large external thermal mass (the enclosure). One approach for super critical applications is to have the VFO "hot" at all times even when the main rig is powered down. This eliminates the "turn on" drift.

 

Did this VFO work and what was the performance? The VFO was set up to tune several hundred kHz around 5 MHz for use with a 20 Meter transceiver and 9 MHz IF. It did work and the drift (both turn on and long term) were typical for a 1960's/70's well built VFO. But here are the issues concerning this approach:

 

• It took several days to fabricate the parts and build the unit (no rapid prototyping here). McDonald's plastic straw coil forms are cute; but no where near what is needed for high end stability such as the process that was used. My tank coil took nearly 1/2 day to build!
• The tuning range was limited to several hundred kHz around 5 MHz. Frequency changing say to a 16 MHz VFO for use on 40 Meters would have been tenuous as I doubt the  level of frequency stability at 16 MHz would not be the same as 5 MHz. Taking that to 30 MHz for 15 Meter operation would be out of the question. The alternative is to have dual conversion and leave the VFO on 5 MHz. Now you have added an order of magnitude of complexity.
• Readout was a problem unless you employed some sort of counter that had offset functionality and if you went this far, then you are already 2/3 the way to a digital VFO. Mechanical Analog dials may get you 5 kHz or at best 1 kHz resolution
• While I used an Oren Elliot Products reduction drive on the double bearing variable capacitor (6:1) that still limited tuning in precise steps such as you would have digitally in going down to 10 Hz or 100 Hz.
• The physical size was almost larger than the rest of the rig components. So this type of VFO is not suited for a compact designs.
• The drift problems even though slight were still apparent.

 

An Arduino based digital VFO using the Si5351 can be built and functioning in two hours time and none of the problems described above are issues. The total cost is around $20 and I get a color display, wide frequency range coverage, selectable step rate and ultra super stable frequency generation of both the LO and BFO. My upper frequency limit is 200 MHz --try that with your LC VFO! The actual construction methodology can be less stringent which is another bonus. The physical size lends itself well to compact construction techniques.

 

Building a stable analog VFO only comes with experience, a well stocked junk box  and having test and measuring tools to peak and tweak the VFO for maximum performance. A digital VFO on the other hand using the Color TFT display has built in test features and functionality. This is a critical point -- a person new to homebrewing an analog VFO may be stuck when things are not going well. Whereas the digital VFO has less issues with parts, drift, setting ranges, circulating currents and on and on. So just move on and learn how to use the Arduino and Si5351. If I can do it so can you!

 

 

 

The Case of the Wimpy Audio Amp!

 

 

 

 

 

Shown above is the 2N3904/2N3906 complimentary pair audio amplifier as originally built for the Let's Build Something Project. This amp sucked in so far has having a room filling output. It was later modified to use the TIP31C/TIP32C combo in direct replacement of the 2N3904/2N3906. This dramatically changed the output level. The same arguments for not building this amp applies as with the Analog VFO. Yes it is retro cool and gives one a feeling of being connected to the soul of the rig BUT great care must be exercised in the build and having little experience building discrete audio amplifiers ties one hand behind your back.

 

 

This was the one circuit board aside from builders not following the three videos on how to build Double Balanced Mixers that caused the most heartburn in the project. Typically the builders ignored the layout suggested and just went off on their own and ended up with an amp suffering from squealing feedback. This amp can be a high gain circuit and thus circuit layout was critical. More often than not the haphazard builds had lead lengths that were too long. This puny amp also consumed too many parts. Being able to say you built it and it involved no IC's is not a substitute for a squealing amp with marginal performance.

 

 

A really major shortcoming is the output connections. In the design we used (from the Internet) one of the output connections is taken off of the 12VDC rail. This means you must use an isolated output connector or you risk shorting the 12 VDC rail to ground -- that will smoke things nicely. It is a bad design!!!!! There are other designs that are similar but avoid the 12 VDC rail as one of the output connections.

 

One might ask why we would use such a design and the answer goes back to the premise of the Let's Build Something project -- common parts, no (or very minimal) IC's and homebrew to the max.

 

My current favorite amp is the 2N3904 driving either an LM386 or LM380. There will be the hue and cry that the LM386 is too noisy --so is the 2N3904/2N3906 so that doesn't hold water. There are other IC's that will give around 1/2 watt out and there are even higher power complete amplifier boards  that can be had for a few bucks on eBay. Now we have room filling volume, no solder burns, no squeals and a much smaller footprint so important if you want a compact rig. The photo below shows such an amp from eBay with a single supply voltage of anywhere between 5 and 12 VDC and good for 18 Watts. The price is $1.99 and free shipping. Why would you want to build a tepid 2N3904/2N3906 audio amp that most likely will be noisy and subject to feedback? It is hard to make a case to build the wimpy amp.

 

 



Just Say No To Prototype Boards!

 

Wow N6QW how can you be bashing prototype boards as shown below, when the very use of the boards suggests that their utility is in fact the ability to hook up a circuit without using any solder and have something working in minutes versus hours? C'mon Pete what is up?

 

 

 

 

 

Recently I received one of those emails that "your audio amp circuit doesn't work". As it turns out the amp was built on one these very same prototype boards. I then was asked to provide my voltage readings at various locations on my circuit.

 

 





 

I guess my first thought is "why am I doing this"; but in the true ham spirit I did. The reason I say this is that the homebrewer should have done this as a 1st step. As it turns out there was "0" volts on his collector of the 2N3904 and thus the reason for my circuit not working for him!!!!!!! 

 

There is fault with the homebrewer for not having a disciplined troubleshooting process to know what should be the voltages at various places in the circuit and the second problem is the fault of the prototype board in that it is easy to overlook wiring that must be supplied. The two rows along the right and left sides are not continuous but yet are intended to be the voltage rails. You have to "jumper" each grouping to have a continuity --an easy rookie mistake (or is it misteak). 

 

But more importantly here is my POX list for why not to use prototype boards:

 

1. While you have lots of holes at times it is not easy to make all of the connections.
2. It is hard to flow a circuit using the boards (ie lots of cross overs and opportunities for mistakes).
3. With repeated use, the contacts become flaky and that leads to intermittent circuits which are difficult to identify and you are left wondering what is the problem.
4. These boards do not provide a bottom ground plane so important for RF circuits. The boards are probably OK for making NE555 Flasher circuits but avoid them for RF circuits. So now I will get the hate mail that Mike, AA1TJ develops all of his amazing RF circuits using these boards. To that I would answer --Mike knows what he is doing and is well experienced. Most new to homebrewing do not have AA1TJ's skill set
5. In use for audio circuits the cross over mentioned in item 2 provides ripe conditions for hum and feedback.
6. Access points for voltage measures are not readily built in -- hard to fit a probe in the little holes.

In further response it is hard to beat Manhattan construction on a piece of single sided copper PC Board. You can flow the circuit, have an excellent ground plane, make connections short and direct and there is no fuzz that you have NOT connected voltage to the collector of the 2N3904. A ground plane is mandatory for RF circuits and the solid ground plane coupled with short direct connections mitigates against hum and feedback in audio circuits. So steel up your courage and throw out the prototype boards or give them to your grandkids with an NE555 flasher circuit. Unfortunately the grandkids will only be amused for about 30 seconds if that long.

 

 

 

The Dishappointing Dishal!

 

Several recent posts by me reflect my disfavor with the Dishal Crystal filter. What I got from the software resulted in an unsatisfactory filter. There just is no other way to sugar coat it. I actually built two Dishal Filters with one being a 6 pole and the second being a 4 pole. The six pole was a total bust and the plotted response curve looked nothing like the predicted curve.

The second filter was a four pole configuration and that seemed to be more successful --at least initially. The formal computer generated plot was based on the data that was supplied as input to the program. So if there was a problem with the input, the plot would have reflected that discontinuity. The plot from the "as built" filter matches the computer predicted plot in terms of general response shape for the four pole filter. That is significant in that had I made an error with the capacitor values or the matching network or in wiring the filter or in the test methodology the proof would have been in the plot I made. The plots matched!

 

So what conclusion can you draw? Is there a problem with the software since my evaluation is that the filter was actually too wide and the opposite sideband was slipping through? The capacitors were extremely close to those specified -- so what happened? I used great care in building the filter and the capacitors were premium quality high accuracy and less than 0.5 PF different than the specified values. I am left with a conclusion that there may be an error in the software that gives values for the caps that are wrong for the bandwidth specified.

 

I received some sharp criticism that I failed as an engineer to root out why my filter while looking like a Dishal was not a good filter. Frankly you cannot repeat the same exercise with nothing changed and expect to get a different result. Stay away from the Dishal software!

 

There are other filter design programs including the one from AADE and one in the EMRFD DVD. Frankly I have had better results using four highly matched crystals measured in a loaded state, using five 68 PF NPO couplings caps (for SSB) and in/out matching of 150 Ohms. The opposite sideband suppression is far better than the Dishal and the signal reports indicate it does the job on transmit.

 

 

 

The Art of a Non-Fake Deal: Start Small

 

I am amazed at how many homebrewer's tackle a very complex project as their first foray into the world of "rolling your own".  The fact that there was success may be attributed to pure luck but as often happens you end up with a non-working pile of parts. In a prior post I recommended starting with a project like the Michigan Mighty Mite which has only 7 parts --8 if you count the "one capacitor key click filter." What is amazing is that many new homebrewer's were not even successful with that project. If you can't do it with 7 parts what makes you think your odds would improve with 500 parts?

 

But with only 7 parts you have a chance to develop some troubleshooting skills and things to look for when the completed circuit simply does not work. I think back to my earlier discussion about supplying the schematic with voltage measurements for the audio amplifier circuit. As a homebrewer the 1st thing you do even before applying power is to double check the wiring. Then if "no workie" take some voltage readings -- very likely neither was done by the person who emailed me.

 

You have this large pile of parts (that you paid $125 for) and nothing works --where do you start? This is where having a disciplined troubleshooting process can pay big dividends. But such a process is best developed in building your confidence by starting small -- and learning the how to do it.

 

 

Hope this was helpful -- keep in mind: separate the nostalgia from working circuits that are most easily implemented.

 

73's

Pete N6QW

 

 





A New Line of Transceivers ~ DifX

So What Do You Want To Build?

 

 

 

8/7/2017 Mikele, 9A3XZ has provided this video of two rigs he built and enables you to listen to a  Bitx40 and a DifX side by side.

 

 

 

 

 

73's

Pete N6QW





 



8/5/2017 I mentioned a new project in the text of this posting. Shown below  is a before and after photo of V.1 of the 20 Meter Shirt Pocket Transceiver.

 

Updates include:

1. Full 20 Meter Band Coverage versus only 100 kHz in the original VXO version
2. USB/LSB front panel selectable
3. Si5351 and Arduino Nano versus the Crystal Switched Heterodyne VXO
4. 1/2 inch high OLED versus crude Analog circular dial
5. Tune Function using a 988 Hz Pulsed Tone (you Bitx guys need one of these)
6. MOX switch
7. Homebrew 4.9152 MHs four pole filter --this really beats the Dishal or QER filters. Nice flat response with superb opposite sideband rejection
8. Smaller than the rig shown on the masthead.
9. Pout about 2 watts.

73's
Pete N6QW

2017 Updated Version of the 20 Meter Shirt Pocket Transceiver

 

Original Version I of the Shirt Pocket Transceiver

 

Compare the size of the new rig to the D-104 Microphone

 

 

Typically a week doesn't go by where  I receive emails inquiring about projects that I built several (or many) years ago. Much of this traffic is a  result of having posted about 125 You Tube videos and the subject matter of these video will spark a bit of interest which is followed by an email.

 

There was even a video I made on how to keep your feet dry while driving your Jeep Wrangler which suffers from a water intrusion problem. That one video had many hits (like 31,000) and even a few inquiries if I would manufacture the device that fixed the problem.

 

But fundamentally I think there is a desire today to return to our early ham radio roots where if you wanted to get on the air --you were faced with two problems: 1) there were no credit cards (or paypal) and 2) ICOM/Yaseu/Kenwood were yet to be in business. Thus to get on the air --you had to entirely build your own station -- everything was "homebrew". There is just something about the buzz you get when you can say " the rig on this end is homebrew". Which is often followed by "gee it sounds good for a homebrew radio!" Arrgh##$$$$!!!

 

Just yesterday (8/2)  I received an inquiry about the Let's Build Something (LBS) project that appeared in QRP Quarterly several years ago. Basically I was asked to create a special sub-channel on You Tube that collected all of the videos involving the LBS (to make easier for this person to look at all of the videos) and to provide a detailed parts list of all the parts need to build the project. I will do neither of these. If you want to build this project then you have to do some of the work! In fact the one major design criteria for the project was the use of all common parts that were readily available in most junk boxes. One fundamental axiom -- if you want to homebrew then you need a junk box!

 

The best piece of advice I can give if you want to homebrew a rig is to spend $59 and buy the Bitx40 kit from VU2ESE. The $59 gets you a nearly complete rig including being tested and the shipping to your QTH. Your homebrew contribution involves slapping it in a case and making any mods that are available on the Bitx reflector. For $59, you get all the parts, you get a tested board and you even get a digital VFO with LCD readout. Search on hfsigs.com for a link to his site. If you spend another $10 for expedited shipping you can have the kit in less than 3 days. My website has a tutorial on how to actually implement the Bitx40 project.

 

There is a bit of sound advice in this approach as taking on one of my projects for most hams new to home brewing, you simply do not have enough solder burns on your hands. You'll get there in time but there are many fundamental pitfalls to homebrewing a rig such as appears on the masthead. I didn't learn how to do that last week. My very first solid state transceiver was built in the early 1970's.

 

There was a lot of luck in getting that 1970's rig to work. Now today there is less luck involved as evidenced by the second version built just a few months ago. I also spend a lot of time learning about the techniques, processes and technology. That in itself is not a guarantee that everything will work the first time; but at least it gives a leg up on having no grounding in what it takes to build a rig. The very first thing I don't do is heat up the iron and start tack soldering  parts together. I also have learned to be skeptical about claimed results. My recent experience with the Dishal Filter bears testimony to that view.

 

I have a new transceiver on the work bench and this one is not so much new technology but more in the line of repackaging circuits to make a small rig even smaller. For those who have followed some of those 125 You Tube Videos, several years ago I built a 20 Meter Shirt Pocket SSB Transceiver. This new project takes aim at that former project; but with added capabilities in about the same size --yes the 1/2 size OLED display and the Si5351 are part of the mix.

 

Going back to yesterday's LBS email -- that project featured a building block approach where you started first with a direct conversion receiver (DCR) where almost all that was built initially was reused in the upgraded SSB transceiver. The simple idea --get the direct conversion receiver working and then advance to the more difficult sideband transceiver. By the way if you go to http://www.n6qw.com there is a link to the LBS project with all of the detail on how to build one.

 

Many new homebrewer's who undertook the LBS were unsuccessful, I might add, as they simply jumped right into the transceiver part thus bypassing the DCR. When things didn't work they emailed me with "your project sucks" or your design doesn't work. Ultimately those persons finally discovered that they had a wiring error, bad solder joints or failed to apply power to all parts of the circuit. These are rookie mistakes that are only overcome with practice, experience and starting small! It was important to build the DCR first!

 

 

Bill, N2CQR and I in our monthly podcasts (Bill, especially) have advocated building the Michigan Mighty Mite CW transmitter --about 8 parts total -- as a good place to start the home brew Odyssey. Yes even with 8 parts there were many learning failures as evidenced by emails that Bill and I received. But that project is a much better place to start than having limited experience or knowledge and undertaking a 500 part project and then trying to figure out the problem/issue why the board is inoperative.

 

 

But it all comes around to having a solid grounding in the basics before you undertake the complex. At the risk of being politically incorrect, those at the seat of our government should well understand this concept and tenet as applied to governance --and that is not Fake News! This comes back to the Bitx40 -- start there and learn all you can. Then and only then should you undertake an entirely scratch built rig.

 

 

73's

Pete N6QW

A New Line of Transceivers ~ DifX

Dissing the Dishal Filter

(AKA Ditching the Dishal Filter)

 

 

07/27/2017 ~ Updated with some additional data.

 

Several months ago I started a project that would use a filter designed using the Dishal method. I have finally concluded that it is time to say Basta. For those who claim they have a working filter I suggest you go back a fully evaluate what you really have.

 

A short review of my reasons for Dissing (Ditching) the Dishal. After resolving the issue that every time I downloaded the software my virus checker put the Dishal.exe file in quarantine (not a good sign) I started off with a 6 crystal filter. That did not end well! Then I shifted to a 4 crystal filter and the curve below is the result of the second effort. This is a real plot of my data and from what I see, it has the classic Dishal shape and far different than my plot of the failed six crystal filter. For reference purpose I have now added what the theoretical 4 Pole. Dishal Plot should result based on my data

Mind you I did all of the steps relative to measurements using the G3UUR oscillator and employed my SDR transceiver to measure the loaded frequency shift to 1 Hz. The crystals that were selected out of the large batch I purchased all were identical as to normal and loaded frequencies. I purchased precision close tolerance MLCC COG (NPO) caps so we had many factors in place when the filter was measured and built. Essentially I used selected 120 PF and 150 PF caps that read higher but where each value was identical --ie two higher reading 120 PF caps to get you close to the nominal 121.6 PF computed value. The same applied with my 150 PF caps.

 

 

N6QW's Plot of the 4 Pole Dishal Filter

 

4 Pole Filter Plot from Dishal

 

 



Based on this plot I installed the filter (11.5 MHz Cf [nominal]) in a working 40 Meter transceiver and should mention that I used a second external oscillator to accurately develop the BFO (USB/LSB) frequencies. Once these were determined then that data was used in the sketch. It was important that my four pole filter was installed in a known working transceiver so that the only variable was the Dishal Filter. That installation is shown in the photo below.

 

 

 

The next phase of testing was to tune across the band and just listen to what I heard. The first notable item was that received signals (LSB) seemed to have an unusual fidelity like in what the "Enhanced SSB Crowd" likes. There was no evidence of a pinched audio or that there was sideband cutting. It was like hi-fi. Next I shifted to USB and tuned away 3 kHz and boom I could copy the signal in USB. So that was most telling in that two things were happening: 1) The opposite sideband rejection was terrible and 2) that the filter was too wide. Now the hi-fi sound made sense.

 

Next I tried the rig on transmit (into a dummy load) and while in LSB tuned an outboard receiver to USB and there I was on USB (not quite as strong but definitely not 50 dB down). So throwing caution to the wind I connected my rig to an antenna (the worst I could be was to have a DSB signal).

In short order I found a very loud station in San Diego (200 miles away) and gave him a call. Boom he came back to me and reported "you sound absolutely terrific". I then asked if he could check my other sideband --and got a shocking answer (he was an extra class ham, newly minted) and he said I don't know how to do that. I thanked him and quickly said 73's. I already knew I had a DSB signal.

 

About 15 minutes worth of work I installed a filter from a Yaesu FT-101 (3.180 MHz Cf) and after repeating listening to my signal into a dummy load --there was no USB component. True it did not have the fidelity of the Dishal; but it was a real sideband filter.

 

Oh the 15 minutes -- 5 of it was to install the filter and load the code in the Pro-Mini --the other 10 minutes was to install the new paint job -- Juliano Blue V.2. You can just see the 3.180 MHz filter where the Dishal was installed.

 

The New Juliano Blue Rig!

 

I must challenge those who built a Dishal Filter -- have you looked at the Opposite Sideband Rejection both on receive and transmit? You might be surprised. Even my good friend Bill, N2CQR commented that he had less than sterling results using Dishal and he uses the AADE software or the Program in the EMRFD DVD.  While the purists want to say I built all of this rig, even the crystal filter, you may actually have a marginal filter in the rig if you use the Dishal method. If you are getting a lot of negative 40M SDR Police reports --you surely are getting a message about your filter.

 

By the way my local Home Depot was having a sale on spray paint and so look for some future rigs in  "Hot Pink" and "Cranberry" colors. I am reminded of Henry Ford who initially produced only black colored cars and when asked about other colors smartly said -- "you can have any color you want so long as it is black". Why do so many of the commercial rigs come only in black? Now I do know that the Hiberling PT-800A, (a $17K rig) did come in a sorta Juliano Blue --but not sure they are still being produced.

 

Final word -- the Dishal software has been exorcized from my computer. Based on my experience I would not recommend the use of the Dishal method. The results simply don't match what you hear once installed in a rig. I truly believe those who say they have built a successful Dishal Filter may need to revisit their data and re-evaluate the filter performance in a real rig.

 

73's

Pete N6QW

 



A New Line of Transceivers ~ DifX

A New Transceiver on the Air!

* Some updates added on 7/11, 7/12, 7/13, 7/14, 7/15, 7/16, 7/22



A New "Juliano Blue" in the Wings?



I frequently have several transceivers in work at any one time and eventually some event occurs that causes me to actually finish off one of the rigs. It was really hot this past weekend in SoCal and so that was the triggering event -- there is just something cool about working in a garage that is running a hot 90 degrees F or for those who use the " other standard " we're talking 32.2 Degrees C.

Here are some highlights of this DifX [Different from a Bitx]:

1. The size is 4X6 by 2 inches high. [For reference purposes the Bitx40 board is 25 square inches not including the display and controls.] I wouldn't call this micro-sized but Mini-Sized is probably OK. A bit of fudging here as I happened to have a 4X6X2 inch aluminum chassis that became the case enclosure. I bought this chassis years ago with the plan for a one "toob" CW transmitter --but who does CW anymore? To get more of a feel of the size of this power house look at the photo below and the relative size as compared to my venerable D-104 Microphone. This says a lot when your rig IS smaller than the Microphone.
   

   
2. For the most part the circuits used are ones applied by me in other projects although this is only the third time I have used MMIC amplifiers and seeing how well they work will now become the standard for me.
3. The rig operates on 20 Meters as that seems to offer plenty of activity (even DX) and there are less SDR police and old buzzard nets like on 40 Meters. Yes these are my contemporaries.
4. The main IF uses  a 9.0 MHz Crystal Filter from INRAD [Model 351] and the Bi-directional amplifiers used for the Rx RF Amp and Tx Pre-driver are two, diode steered and relay switched, AG-303-86G MMIC amplifiers. Going into this stage I used a 2 dB pad and this has really added to the overall stability. Lets face it --these are cramped quarters and lots of potential for unwanted feedback.
5. The Si5351 supplies the LO and BFO and the display is a 1 Inch Square Black and White OLED. Should mention OLED noise has not been a problem. The main Microcontroller is the Arduino Nano. A little detail here is that I provided clearance in the build so that a USB connector can be plugged into this board for any program changes without removing the Nano. A small but very important detail. The default step tuning rate is 100 Hz but additional selections via the encoder push button are 1 kHz, 10 kHz and 100 kHz. This approach gives plenty of flexibility to tune the entire 20 Meter Band,
   

   
6. The Bilateral IF Amplifiers are the 2N3904/2N3906 Plessey circuit and the RxTx Mixer is an ADE-1L as is the Product Detector / Balanced Modulator. ADE1-L = 4 dBm devices so set the output on the Si5351 to 2 ma. Note the 2N3904/2N3906 are SMD. The immediate photo below shows the Model #351 4 Pole Crystal Filter which had been in the rig for about a week. On 7/16 I replaced that with the GQRP 6 pole filter. This involved a bit of noodling and modification to the lower board and to the very top board of the three board sandwich. The GQRP Filter being taller than the Model #351, meant I had to add more spacing between the first and second boards. The top board which is the audio and microphone amplifiers had to have two electrolytic capacitor swapped out for one shorter ones. In one case a 330 Ufd was replaced with a shorter 220 in parallel with a 100 Ufd. It was a small nightmare but it is all back together and is a testament to a well stocked junk box, fifty years of building experience and throwing caution to the wind. BTW can tell the difference with the GQRP Filter. Much tighter skirts and actually more output!
   

   

7. The Audio amp is the LM386 driven by a 2N3904 and the Microphone Amp is a single 2N3904. The RC Shaping filter for the 988 Hz Square Wave Tone coming from the Arduino is also located on this board.
   

   
The next photo shows how the board was reworked and move slightly so all would fit back in the case. Note the use of the solder lugs to "collect" the board so it doesn't move and the add of the two smaller electrolytic capacitors so as the assemblies moved upward all of the boards would fit in the case.


8. The Power Output is 5 watts via a IRF510 and the driver is the 2N3904/2N3866 standard circuit from EMRFD.  This linear amp board is about 3.5 inches long and about 1.9 inches high and fits in the rear of the chassis box. The chassis is the heat sink. Note the shield between the driver and final stage and even the DC bias stage is behind the shield. Some additional bypass caps on the IRF510 have proven to add much to the stability.
   

   


9. Other features include USB/LSB, MOX and Tune (via a 988 Hz tone generated by the Arduino). I wonder why the Bitx40 aficionados have not added the "Tone Tune Up" to their radios? In time grasshopper, in time. Note on the display the words SSB XCVR --when you place the rig in the Tune mode the wording changes to TUNE and when the timing cycle is over it reverts back to SSB XCVR. There was a bit of trickery to make that happen and not something found on other currently popular radios. Note the size in comparison to the 1/2 used pencil.
   

   
10. The paint is standard Juliano Blue.

Some construction notes for this project. This is a really compact rig and even the install had to be sequenced so all circuits would fit in the enclosure and could be hooked up. Unless you have experience in building circuits in tight places, it is not recommend you replicate my approach. While the circuit pieces are modular, making them fit was a real challenge. One assembly consists of three stacked circuit boards with the bottom board being the IF, front end Mixer, PD/BM stages and the middle board is the MMIC bidirectional amplifiers and the top board is the Microphone and Audio Amplifier stages. The Driver and Final are on a separate board as is the Arduino.  From the photo below you can see it is pretty jam packed into the enclosure.

The OLED noise has not been an issue so check that box. BUT what has been a constant problem is the LEAD FREE SOLDER CRAP. That solder just does not stick and is a particular problem if you are using Manhattan construction. If you are doing ultrasonic wave soldering on 408 sized SMD parts --probably OK but not OK on an IRF510. Initially there was no output from the transmitter --yep a solder connection on the base of the 2N3866 just did not stick. You end up welding the parts and not flowing the solder. This new solder is real crap!!!!!!

The proof is in the pudding and my new rig just completed its first contact with WA7ND, Rick up in Bend, OR. The report was excellent and I was running the small outboard amp so the Pout was >100 watts. Forget that QRP crap and just move on. I have had a second contact on the rig with KD5CO, Chuck in downtown Texas. I couldn't resist an additional test with the second contact --yep two after burners and the Pout > 600 watts into my two element beam. Now this can be a DX machine. So this is proof that the rig is more than a one hit wonder. Today (7/11) I had a really great QSO with Jim, KA5BDO in New Mexico and he was very complimentary of how the rig sounded. He also suggested I use the Turner Dynamic Microphone for rag chews and the D-104 for DX chasing. You can see the new rig with the Turner Dynamic Microphone in the photo below. [That new rig IS small!] Just had a QSO with KH7XS, Bill out in Hawaii running 600 Watts -- another great report. This is a DX Machine in a mere 48 Cubic Inches.

This is one superb rig and lest you forget --it is a DifX! I can't fully express the joy in putting this rig on the air and to have real QSO's with this diminutive sized box. One asks could there be more features? With a bit of more effort on packaging and the add of one DPDT toggle switch, two band operation would be possible. The only adds would be a second Band Pass Filter and a second Low Pass Filter and of course the toggle switch. If I replaced the MOX switch with a band switch then no more panel space would be required. A 40/20 Meter rig would cover the bases or maybe the 20/15 Meter bands or even a 20/10 Meter rig when the sunspots kick back up. Maybe even a 40/17 Meter rig would be your cup of tea. It is merely some code changes to the sketch.

While it may not be possible for readers of this blog to build this project in a very tight space like this 48 cubic inch chassis box -- this is a worthy transceiver project that could be successfully built on an albeit larger scale (or box). That said the smallest SSB transceiver I have ever built was 33.3% the size of this rig --16 cubic inches. Virtually all of the circuits used in the rig have been previously published on this very blog (or articles in QRP Quarterly) so the module schematics are no mystery. If some one would like the Arduino sketch send me an email to the address on my QRZ.com page.

 

Block Diagram and Some Schematics



 

 









The Finished Rig~ Another Successful DifX!

 



As of 7/15 I have made over a dozen contacts with this DifX rig and am very pleased with the signal reports I have received. Only one negative SDR police report regarding opposite sideband suppression being only 40 dB down. Opposite sideband suppression could be improved with a different filter but  a commercial 9.0 MHz Filter I have might not fit in this build. On 7/16, I did replace the 4 pole filter with the 6 pole GQRP filter so we now have a better filter in the rig.  The signal quality is much better on receive and I am sure likewise on transmit.

73's
Pete N6QW

A New Line of Transceivers ~ DifX

Homebrewing a Chassis, Cases and Enclosures

Make your Rig Look as good as it Sounds!

 

There is just something about a rig that has that finished look when it has a painted case. Yes, it is something that came out of your garage or workshop but there is no reason why it can't look "finished". Long ago I adopted "Juliano Blue" and perhaps there was an unconscious bent to that decision based on my very early solid state experiments with the distinctively Blue CK722 transistor. Go Blue!

 

Of late I am not satisfied with a project unless it resides in a Blue Case --a Juliano Blue Case. So how do you get to the point of homebrewing a chassis, cases or enclosures. The first part is the right tools --no you don't need a $250 K CNC mill but for about $50 you can purchase a bench type metal break from Harbor Freight.

When I bought mine about 10 years ag they could be had for about $25. The type I have is 18 Inches long. The next thing you need is some stout metal bars in various lengths. The tool from Harbor Freight comes with an 18 inch bending bar. By using smaller bending bars in the 4, 6 and 8 inch range you now have a box break where you can easily make 6 X 8 inch chassis boxes -- thus the smaller bending bars.

 

For a chassis I make it in three pieces. Two pieces are "L" shaped and the final piece is the to cover. The two "L" shaped pieces are formed with ears so you can bolt/fasten to the pieces. Fastening also include "pop riveting". Two Chassis' are shown below one is a general purpose chassis and the other was one made for a transmitter power supply. Believe it or not most of the materials are galvanized metal available from Home Depot. The power supply chassis shows the "L" structure of the pieces and make for a very rigid chassis. The Sheet metal is very inexpensive and with a couple of homebrew chassis bulds you will recover the cost of the metal break.


 



 

 

 

In the photo above there is a trick to making these "L" section and it all has to do with the sequence of the bends. Excellent measuring skills are needed to pull this off and laying out the bends and cuts has to be done carefully. this is even extended to when the metal is in a flat state and that is when I actually drilled the holes. I have a stock of manila folders and so my first step is to make the part out of the manila folder stock. This in essence is a template. The first pieces bent are the top and bottom lips which are about 1/2 inch wide. At the location of the bend line I cut a 45 degree angle of material to the bend line on both the top and bottom sections. This when this is bent at a 90 degree ange the pieces meet up perfectly. Both sections are identical only in one of the pieces the end section is bent up at 90 degrees at each end. This is where the smaller bending bars come into play. Essentially an end of the bending bar is placed perpendicular to the bend line and the larger piece is bent upward. For normal operation the bending bar is "C Clamped" to the bed of the metal break and so with the smaller bars you can make boxes. the following two photos give a bit more detail of what is described here.

 

 

 

Now I would like to spend some time on how I build cases using angle stock readily available from Home Depot. The metal plate can be ordered from a company called "On Line Metals"

 

 

 

 

 

Yes this is an old project when I actually built analog VFO's as evidenced by the National Velvet Vernier. As soon as I started using the Si5351 I gave this rig away since I didn't want any evidence in my shack of an analog VFO. The aluminum angle stock makes for a very rigid structure and you can easily screw sheet metal to the sides and top.

 

 

 

 

 

 

The next critical issue is one of materials. Use what you have or think out of the box (enclosure). Sheet metal (versus aluminum) is readily available and inexpensive. Home Depot is a good source. I also have used single sided copper PC Board which often can be had a really good price. ABC Fab up in New Hampshire (eBay) sells various packages of boards. Recently I bought 18 pieces of 4X6 inch heavy duty board for about $1 a board --delivered. I also bought some 8.5 Inch by 12 inch board from the same source and two of my rigs have that for a base plate. One ham shared he found a source for large square tin cans which he cut open and flattened. Also check out computer shops as you can often find CD/DVD units which are defunct but its the case you want. Cookie tins are another great case source. So open your mind to the possibilities.

 

Oh --it is not a real case unless it is painted Juliano Blue!!!!!!

 

73's

Pete N6QW