Previously, I described the HF antenna analyser project I’m building, from Beric Dunn K6BEZ’
schematics
and Arduino firmware, listed the costs of the components (around £50 in May 2014) and where I obtained them. In this article, I’ll show the veroboard layouts I’ve designed, and start with the construction. All resources, pictures and files for this project are available from the project GitHub repository.

Please contact me if you have any questions about the analyser and the plans shown here, I’d love to hear from anyone building it!

Errata

First, a correction and apology – the pin strips I chose for connecting the Arduino and DDS module are fine for connecting chips with thin pins, but are unfortunately too small for the thicker pins of the Arduino and DDS module. If you started buying components based on the previous post, I’m sorry for the mistake – I only spotted it when plugging the boards in. I’ve replaced them with sockets made from “springy” Dual-In-Line chip sockets – these are not ideal: the boards connect into them, but I’m not satisfied with their security. I’ll be looking for suitable, cheap replacements. You’ll see the changes throughout the rest of the article.

Power distribution

Also in the previous article I mentioned small changes I’d made to the original design – I omitted that I’m powering the Arduino Micro with 7-9v via its VIN input, rather than its 5.5v pin (I think this is a power output, rather than power input?) – the Arduino Micro page states:

Power

The Arduino Micro can be powered via the micro USB connection or with an external power supply. The power source is selected automatically.

External (non-USB) power can come either from a DC power supply or battery. Leads from a battery or DC power supply can be connected to the Gnd and Vin pins.

The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.

The power pins are as follows:

  • VIN. The input voltage to the Arduino board when it’s using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin.
  • 5V. The regulated power supply used to power the microcontroller and other components on the board. This can come either from VIN via an on-board regulator, or be supplied by USB or another regulated 5V supply.
  • 3V. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
  • ⏚ Ground pins.

Construction Time!

OK, let’s start!

Firstly, prepare a piece of veroboard, 38 strips x 31 holes, 96mm x 81mm, 2.54mm hole spacing. Farnell sell a 121.92mm x 101.6mm 41 tracks x 44 holes board that can be cut to fit.

Carefully mark where you’ll cut tracks in the places shown by the red X’s in the diagram below, check them, then cut with a spot face cutter (or drill bit).

Here, I’ve used the solid tracks at the top (which I’ll later cut off), and the solid tracks cut from the bottom of the board as a guide to where to place track cut marks. I’ve marked the cuts with a CD marker pen before checking, then cutting.

I’ve placed mounting holes in the four corners of the board.

Clean the board by lightly sanding it with fine sandpaper to aid soldering, then check that you do NOT have continuity across each of the track cuts.

Here’s the board with tracks cut, mounting holes drilled and the top solid strip still attached.

Now it’s time to add all the wire jumpers, IC holder and pin strips for the Arduino Micro and DDS Module. Use CD marker pen first to mark these out on the component side of the board.

Here’s the board layout:

The DDS Module goes at the top left, with its trimmer at the top and crystal at the bottom. The Arduino Micro goes at the bottom left of the board, so that its USB socket can protrude through the case. The PSU is at the bottom right, and the SWR bridge circuitry is at the top right, connecting to the antenna UHF socket (the type that takes a PL-259 plug – feel free to change this to a 50 Ohm BNC socket). Power comes in via a barrel socket and switch.

When the wires, test pins and pin strips are done, the board should look like this:

Now would be a good time to check the continuity of the ground and +5v connections. Check that ground is connected to all the components connected by the purple tracks here:

Check that +5v is connected to all the components connected by the purple tracks here:

If all is OK, now add the components for the PSU: the electrolytic capacitors, 7805 and 7809 voltage regulators at the bottom right. Take note that in the layout diagrams, the square pin of the electrolytic capacitors is negative. The In/Ground/Out connections of the voltage regulators can be found here [PDF 78xx datasheet].

After fitting the PSU components, and connecting a 9V battery to the +V IN and GND IN pins on the right of the board, you should have a board like this:

Measuring the voltage between the GND test pin (between the DDS module and Arduino), and the +5V test pin, I had 5.02V, and between that GND and the +9V test pin near the Arduino Micro pin strip, I had 7.02V – which is fine, it’s within the 6-20V given in the Arduino Micro page – with a 12V DC wall adapter, I expect to have a nice, smooth 9V. Be careful with the GND test pin next to the +9V test pin – I added the one between DDS and Arduino because the one next to the +9V test pin is very close to GND, and you don’t want to accidentally short them out!

Next, add the rest of the components in the top right of the board forming the SWR bridge. Solder the diodes in last so they don’t get overheated, and remember to get them the right way round: the end with the line is the cathode, and matches the line in the diode circuit symbol. Take care with the C1 electrolytic capacitor – the square pin on the layout diagram is negative. I couldn’t find 5K Ohm resistors, so made them out of a pair of 10K Ohm resistors in parallel, mounted on their end next to each other. Add the R12 resistor on the left of the Arduino Micro.

When done, the board should look like:

Some detail on the SWR bridge components, in case the layout isn’t clear:

Connect the scan LED on long wires, as it’ll need to fit into a hole in the case (I used a LED mounting clip). Connect the power (I’m using a 9V battery for now) and antenna connector (I’m using a longish piece of RG174 cable from a previous project). When finished, the board will look like this (with the original pin strips replaced with homebrew ones made from “springy” Dual-In-Line chip sockets):

After adding the Arduino Micro and DDS module boards, the analyser looks like this:

Firmware

The firmware then needs loading into the Arduino Micro. I’m using version 1.0.5 of the Arduino programming software. I’ve made a few changes to Beric’s original firmware:

  • Added the “Scan in Progress” LED control.
  • Made the Arduino’s inbuilt LED pulse slowly when it’s waiting for serial input, as a way of showing that it’s working.
  • Fixed a bug in the reporting of the stop frequency in the ? report.

Testing

After uploading the firmware, and starting the Serial Monitor at 57600 baud, you should be able to issue commands to the analyser, and test that the DDS module is generating a signal at the RF test pin. I connected the analyser output to a 50 Ohm dummy load, and started a sweep at a low frequency (my old scope doesn’t handle high frequencies), and observed:

Next….

I haven’t covered testing the SWR bridge circuit yet, so that’s next. The “Scan in Progress” LED isn’t working; don’t know why yet. Also, I’ll finish off the construction, cover the software used to drive the analyser, showing SWR graphs, and hopefully give some background on what’s being measured here, and how you can use the analyser to adjust your antenna.

Acknowledgements

Thanks to Rick Murray for VeroDes, a very nice Windows program that I used to draw the board / track / continuity layout diagrams in these articles.

Advertisements