Sunday, 4 December 2016

Noisy ESP8266

Having enjoyed a lot of success transmitting and having produced a usable VFO, I decided it was time to try using the new m0xpd / Kanga ESP8266 - DDS board in a receiving application. I soon discovered just how noisy the ESP8266 is.

Above, you see the new board sitting on top of my old Leslie 825. The Leslie is next to the bench, which is too full of work and other projects to host a little game like this - so the impromptu receiver has spilled out onto the nearest flat surface.

Next to the IoT processor and DDS is an early prototype of the Kanga / m0xpd HF receiver shield (it differs from the production versions sold as kits only in that the SA602 is a lovely old original DIL version, as opposed to the SOIC surface mount versions supplied on the PCBs of the kits).

The receiver shield is actually on top of the transmitter shield used in recent beacon exploits (which includes a buffer for the local oscillator signal for the receiver - an inheritance from the 'Occam's Micro' days - you can ignore that for the purposes of this story).

To the left of the receiver shield is a filter system, originally developed for the "Occam's Dirk" rig (that recently had a Dutch makeover), which provides switchable input and output filtering for 40 and 20m.

I fired up this little combo, with the ESP8266 - DDS board running the recently reported WiFi controlled VFO system.

The result was a working receiver, with tuning from my iPad, marred by a horrible clicking sound. 'Marred' is an understatement. I should say 'made un-usable'.

Here is a segment of the receiver shield schematic, including one point where I'm going to report a voltage...

I powered up the system with the antenna input connected to a dummy load and recorded the voltages at the point 'MEASURED HERE' in the schematic above (conveniently available on a header at the edge of the receiver shield). Here it is, (with apologies for the nasty oscilloscope screen photo), explaining the horrible clicking sound:

There are short clicks every 100ms, of amplitude reaching at least -300mV. Remembering that there is another active stage (at 0 dB gain) and then the final LM386 stage (at 46 dB gain) after this, you'll understand that the output is driven to saturation on its power rails every tenth of a second, making the 10Hz clicking, which dominates the output. The miracle is that it is possible to hear activity on the band at all against all this bad behaviour!

First of all, the origin: Remember that the ESP8266 is being asked to establish an access point in order to run my WiFi controlled VFO program. Well, every 100ms, the system comes to the end of its 'beacon interval' in servicing that access point and makes some wireless activity (such as broadcasting its SSID). It is that which is causing the noise - but how is it getting into my receiver?

I found (somewhat to my surprise) that the greater part of the noise wasn't being received via the SA602 (this discovery was made by removing the chip - the reason I was using the early prototype version of the shield with a DIL mixer - and grounding the input to the Op-Amp). Instead, the greater part of the noise is actually generated by the twin Op-Amp package, where it was being directly detected / demodulated to AF. Some little of this 'detection' is also happening in the LM386 - but the op-amp seems to be the greater culprit.

The receiver actually seems closer to usable (notice I say 'closer to usable' rather than 'usable') without the op-amp in circuit at all - just taking the output straight from the SA602 to the LM386 (just like the original Sudden). Some part of the clicking which remains is directly demodulated in the audio frequency circuitry (the LM386). In the shield (unlike some implementations of Sudden-inspired DC receivers) this is operated with an unbalanced input. This experience of a very hostile EM environment caused by the ESP8266 might occasion a re-think of the receiver shield design. The remaining part of the clicking appears to enter through the intended (i.e. tuned) RF input...

Either switching the input filter to the other band or (equivalently) switching the VFO to the other band causes a big drop (>20 dB) in the clicking amplitude.

All the above is pretty disappointing; the ESP8266 and a simple receiver are uncomfortable bedfellows. There needs to be some careful layout and some circuit re-design before a WiFi module and a simple DC receiver can sit next to each other easily. This isn't exactly news (noise problems have been reported before in trying to close-couple an ESP8266 and a 2m transceiver) but it sure puts the brakes on some plans I had for the next few weeks.

Finally, for something really wierd...

I re-programmed the ESP8266 with some code which just set the DDS frequency. No access point, no WiFi activity. Nothing. Just a quick set-up of the DDS on 40m and then just sit there in an endless loop, twiddling its thumbs.

The result?

You guessed it - exactly the same 10Hz noise!

The chip is still pumping out noise pollution, even when the code hasn't asked it to do anything fancy. I don't know if this is a failing of the IDE (I was using the Arduino IDE, and I don't know if the compiler doesn't turn off the WiFi resources if they've previously been turned on in an earlier program). I don't even know if it is POSSIBLE to turn off the WiFi resources (though I believe it is). All I know is that a piece of code written to evoke NO WiFi functionality at all is producing the massive noise fields around the device as are present due (presumably) to WiFi activity. Wierd.

So - I have a working, WiFi tuned HF receiver running. It is just ruined at present by some nasty 10Hz clicking, which makes it just about worthless. I don't know if it can be fixed.

It has certainly put a dent in my enthusiasm for the ESP8266.

...-.- de m0xpd

Sunday, 27 November 2016

A WiFi-Controlled VFO

Now that I have placed a DDS on a board with Wireless connectivity, it is only obvious to set it up as an AP Web Server and allow remote control via a 'soft' user interface...

When I first started to play with the AD9850 DDS, I made some beacons and wrote the Kanga VFO demonstrator code (as application code to support the Kanga / m0xpd DDS shield). Well, now I've produced this new internet savvy AD9834 DDS board, I've followed the same pattern; I've done the beacon thing and now - in this post - I'm covering the VFO. Only, of course, this VFO won't have physical knobs and buttons like its predecessor. Understand, it could have all the physical controls if you wanted it to - but that's not the point. Instead...

When  the new code fires up, the ESP8266 sets itself up as an access point and offers a new wireless network:

which you can join from any phone, tablet, computer or similar wireless enabled device. This will provide the interface to the VFO. The network name 'm0xpd Kanga DDS 94TD' is formed of a generic part ('m0xpd Kanga DDS') and a four character index associated with the particular board (such that two VFOs in the same area could operate independently).

Opening a browser and going to the VFO's 'web page' will open the simple control interface seen below, which reports the frequency at which the oscillator is running, offers 'buttons' to adjust the frequency and 'buttons' to change band:

The picture above is a photo of my iPad mini screen, controlling the VFO. I've added the red annotations to make it clearer for you.

The web page is generated entirely by the m0xpd / Kanga ESP8266 - AD9834 board - the iPad is just interpreting it (as HTML).

Clicking on any of the 'Adjust Freq' hyperlinks will cause the VFO frequency to change according to the label. Clicking on any of the 'Select Band' hyperlinks has the obvious effect.

All this is rather dynamic and needs a video to demonstrate (which I haven't provided) - so here are some rather dull 'stills' of the system on 40 metres

and 80 metres...

And here's a 'sniff' of the requests received from the web page of sequential increments and decrements in frequency whilst on 80m, along with the resulting frequencies...

This code will be released as an application 'demo' for the new m0xpd / Kanga ESP8266 - AD9834 board (along with a multi-mode beacon).

Of course, the demo code above is intended only as an illustration of what is possible. The rather dry web page could be replaced by an application, written specifically to control a different piece of VFO code, etc.. This is just a start point - but it sure gets me thinking...

There are other exciting opportunities to be exploited via this access point - watch this space!

...-.- de m0xpd

Friday, 25 November 2016

Occam Going Dutch

Kees, pa5cw, has produced a new variant of my 'Occam's Dirk' software for a multi-band CW transceiver.

'Occam's Dirk' was a multi-band development of the original 'Occam's Microcontroller' concept, adding automated 'CQ' calls and one or two other little refinements (like RiT, VFO A/B, etc). The original 'Dirk' was presented with an Si5351 in the RF generating role (as I wanted to try using the then new Kanga / m0xpd Si5351 shield).

Kees has decided to revert to the AD9850 DDS for his version of the code, which makes the architecture similar to that introduced in my 'Kanga VFO' demo software (and elsewhere).

Kees has also added some new functionality: the means to change keyer speed using a voltage input to A0, most conveniently generated by a potentiometer. The original code had speed change as a software function under the menu system - which works, but isn't immediately accessible for a quick change.

I've always built keyers into my software (and provided both a paddle and a straight key input) but - if I'm honest - I've seldom used these keyers in anger. Here at the shack, I usually drive all my rigs (via their straight key input) from the old faithful "Funky Keyer", which has its own physical speed control. Thus, menu-based speed adjustment of the software was never a big handicap for me. But Kees' approach certainly is convenient (at the expense of one knob).

Any of you interested in trying Kees' code can find it here on the Occam's Software page. I haven't tried running it - but I have confirmed that it compiles correctly.

Many thanks to Kees for sharing his work,
...-.- de m0xpd

Saturday, 19 November 2016

SNA Junior

I have (finally) got round to building my own instance of DuWayne, KV4QB's prize-winning Scalar Network Analyser Jr:

and a great little instrument it is too!

DuWayne and I have been corresponding for a couple of years, sharing mutual interests. I was pleased to be able to give his work a shout in both the printed and  'spoken' version of my talk at this year's Four Days in May event in Dayton and - more importantly - to catch up with the man in person for a quick eyeball QSO. I also got a PCB for SNA Jr, which has been sitting on the bench for months - until last week.

The SNA board finally bubbled up to the top of the pile and I looked around for the bits I needed to complete it. Perhaps I should explain (to those of you who don't know) what's involved...

DuWayne's baby uses an AD9850 in one of our familiar modules to generate RF, under the control of an Arduino NANO. You can read on DuWayne's blog how the SNA Jr is the descendant of earlier experiments in which an Si5351 was used as the signal source.

In the SNA Jr, the output from the DDS is fed to the device under test and the returned signal is observed in a detector system. DuWayne has 'history' in using simple diode detectors in this role (and I was praising kv4qb for this minimalist approach in my talk at Dayton) - again, you can read about this lineage. However, the SNA Jr now replaces the earlier simple diode detector with a fancy AD8307 detector, in the well-known Wes Hayward, w7zoi, circuit. This gives superior performance in terms of dynamic range and 'linearity'. Also, with the availability of cheap AD8307s (of dubious parentage) from China, this option is also becoming attractive for cheapskates like me! [I have some Chinese AD8307s on order and will report back on performance when the slow boat docks.]

You can't see the detector in the photo above, because it lurks under the screen - so here's another shot (with apologies for my wayward handling of some of the SMT devices):

The detector is supposed to be enclosed in a screening can, which I haven't made yet - so final performance will be better than I'm going to show you below.

The DDS RF source and measurement of the RF level returned from the device under test are all under the control of the little Arduino NANO, which runs a sketch provided by DuWayne. This sketch compiled for me under Arduino 1.6.12. The user interface is provided through just a rotary encoder and the 1.8 inch TFT screen.

I found I had everything needed to build SNA Jr in the 'junk box' - except the screen and a spare NANO, so these were quickly ordered through usual suppliers.

The result, as you see above, was simple to put together and works very well.

DuWayne's software offers a number of options, including a 'signal generator' mode, in which the output of the DDS module is set at a single frequency, whilst the returned RF amplitude is displayed numerically and on a bar display (useful when the numerical display is flicking between two values). This mode is illustrated in the graphic below, which shows the system driving a simple switched attenuator, seen in the graphic, with and without 20dB of attenuation switched in (two 10 dB stages).

I'm sure the (in)accuracy of the -20dB step is down to my cheapskate attenuator (with its low tolerance resistors, lack of screening etc.), rather than SNA Jr.

Another, more important series of modes sets the DDS module generating RF sweeps, which result in graphical displays. These are illustrated below, in which I've contrived a test of the low pass filter which has been conditioning the output of the 'connected beacon' (Blogs passim) on 30m.

SNA Jr can also be used with various 'attachments' such as a 40dB tap (with which DuWayne's software allows it to function as an RF Power Meter) or a Return Loss Bridge, with which it can perform SWR Scans.

Here's a scan looking into my (g5rv) antenna, with (right) and without (left) the Made-from-Junk 'Deluxe' Versa Tuner II switching in tuning appropriate for operation at the CW end of 40m...

As you see from my additional labeling in the graphic above, the scan was set up to run from 6 to 8 MHz. I reported an equivalent measurement on my own system (originally reported here) in one of my slides at FDIM (although it was presented in terms of Reflection Coefficient, rather than SWR)...

There's even more to SNA Jr - it can even locate minima to impersonate a dip meter (but I haven't been able to try this yet).

I said at the beginning of this post that SNA Jr is 'prize winning'. DuWayne won the 'Best in Show' award at  the homebrew competition at FDIM (which is no mean feat, given the very high standard of the submissions I saw there, in several widely different categories). The prize was well-deserved.

The project was written up in QRP Quarterly (vol 57(3)  pp 22:25, July 2016) :

which is nice to read. But the best thing to do is to get the information from DuWayne's blog and build an SNA Jr for yourself  - or take the inspiration to build something similar.

Great fun - thanks, DuWayne.

...-.- de m0xpd

Saturday, 12 November 2016

ESP8266 Production PCB

The first sample of the production version of the PCB for the ESP8266 / DDS system arrived a couple of weeks ago.

As you see, it follows the plans established in the earlier prototypes, with the surface mount components already fitted (such that tyros don't need to face the challenge of dealing with these pesky little things).

I've been detained by work and by a short break up in M-land, where I stayed on the banks of the River Nith, playing at being mm0xpd/p. However, now I'm home, I've stuffed the new board - this time with the intended 1/8th Watt resistors:

I set her up for a quick test yesterday morning, programming the ESP8266 with my beacon code and plugging a Kanga / m0xpd TX shield on top of the new PCB. Here are the WSPR spots accumulated on 30m in the first thirty minutes (from 09:00 GMT):

Looks like things are working FB.

I had a nice time working CW, PSK-31 and even a little SSB on my TS-480 yesterday, so the station was out of commission for beacon operation for most of the day. But I turned the beacon back on in the evening and let it run overnight.

Here are the accumulated 24 hours of spots on 30m ...

(It looks even better as I write, 'cos I'm also down to Stewart, w4mo in Venice, FL - but you've got to draw the line somewhere).

I hope it won't be long before Kanga can offer the new board as a kit to anybody interested in playing similar games.

...-.- de m0xpd

Sunday, 4 September 2016

New ESP8266 Board

Kanga UK and I have been developing a new board and I can bring you some pictures of the first engineering sample...

You can well see it is an engineering sample, because I'm squeezing the wrong size packages into locations (quarter Watt resistors where eighth Watt components should be, etc) and using a mishmash of different component types, but you'll forgive me, I'm sure.

The new design presents the Expressif ESP8266 device on an Arduino-sized board, supported by a full USB programming interface and power supply.

I should be careful to explain - this is not a "shield". It does not sit on top of an Arduino. It REPLACES the Arduino. It IS the processor - and a whole bunch more...

Of course, there's all the interfacing headers you'll need to connect it to other expansion devices ("shields") from the Arduino ecosystem. This is nothing new - it is already available in commercial platforms out there, such as the WeMos D1 R2 (indeed, I made this new board largely compatible with WeMos' digital I/O pin allocations).

Of more relevance to fellow amateurs, this new board includes a DDS system, capable of generating stable, controllable RF, using the AD9834 device.

You have here a powerful processor - significantly more capable than that on (e.g.) the basic Arduino UNO - with a full, on-board DDS system. All with access to the advantages of the Internet (time servers, geolocation, remote control, ...). All on one little board.

The overall architecture is seen in the image below...

The output from the DDS module is taken to the header on the upper left hand edge of the board in the orientation of the photo above - which is the m0xpd RF bus I've defined previously for other shields. This facilitates the first application for the new board: to implement a beacon system, using the Kanga/m0xpd Sudden Transmitter shield, which can simply plug on top of the new board to make a complete beacon assembly.

The USB interface is implemented using a genuine FTDI chip, with the hope that interface problems should be minimised. However, I've just had all sorts of problems after upgrading the operating system of my MacBook Air to El Capitan, after which it seems incapable of operating reliably with ANY external peripheral - not just the FTDI devices.

The new board has flexible power supply options. It can be powered off the USB connection. It can derive power from the 5V supply from the Sudden Tx shield in the beacon application described above or it can be powered through the d.c. power jack visible at bottom left of the photo.

Of course - the collaboration with Kanga signals that this board - or the final production version - may soon be available for purchase as a kit. With the experience of the m0xpd Si5351 shield, we have discovered that many Kanga customers are not great fans of surface mount technology. Accordingly, this system has been designed with the intention that key SMD elements could be delivered pre-fitted...

leaving the kit buyer to fit only thru-hole components, one large voltage regulator and the ESP8266 module itself.

Here, finally, is the engineering sample, plugged into a Sudden Tx shield (itself a prototype) for the very first time to run my beacon code as a "stack"...

The little OLED display on the breadboard at bottom right is there just as a sign of life.

Although not so good these last two or three days, when it has been harder to burst far out of Europe, the same technology has been running WSPR and QRSS all over the globe for the past couple of weeks, as recent posts testify.

I hope that this new board might tempt some more radio hams to look toward the ESP8266 and the"Internet of Things" for inspiration and fun.

...-.- de m0xpd

Wednesday, 24 August 2016

USB Mini Breakouts

If, like me, you ever fool around with USB hardware and choose to do so in the context of solderless breadboards, you might well need a little breakout board for one of the several types of socket - in my present case the USB mini-B receptacle.

There are, of course, lots of lovely commercial ways to scratch this itch, available - for example - on our favourite auction site...

but I wanted one now, rather than in a day or two's time (or longer, if it had to take the slow boat).

Of course, I'd been getting by with the usual solution of a butchered cable with a type A plug at one end and some pins on the end of bare tails I'd made at the other...

but I wanted to get rid of this 'trailing wire' and fit a neat socket.

I had some surface mount mini-B receptacles in the junk box and noticed that the connector pitch was close enough to the 0.95mm spaced pads on one side of a 10-pad SOT23 DIL carrier...

So, with a little judicious bending of the outer pair of pins, a 5-way strip of male header pins and some solder, I soon had my own USB mini breakout...

Here it is in action on the beacon...

I don't think I'll even bother to order any from the Far East - they're too easy to make!

...-.- de m0xpd