Tuesday, September 21, 2021

Resistive tap built with sharpie PCB etch

I'm keen not to burn out the input to the spectrum analyser. It's 50 ohms in with a maximum of +30dBm. The solution is to transmit into a dummy load and sample the signal with a resistive tap.

A good candidate for a simple PCB and I used Paul Taylor, VK3HN's, technique of drawing resist on the board with a sharpie. Components are all soldered on to the top of the board so laying them out to figure out where the tracks go is easy.

Here's the circuit and the components for the board:


I cleaned the board to remove fingerprints with Isopropyl Alcohol - is that the best thing to use? Using components to lay out the board, tracks were drawn with a standard sharpie. I didn't go to much trouble and could probably have filled in more of the board with earth plane to minimise the amount of copper to be etched.


In to a small bath of Ferric Chloride. While gently rocking we had a magnitude 6 earthquake which was fun. It took about 20 minutes to clear the copper.


After washing under water the etch looks great.


Steel wool was used to rub off the sharpie ink. 


Here's the completed board. 


I've got some more of the nice board edge mounting SMA sockets coming so had to make do with a panel mount for the tap output.

What should I use to protect the copper? I think Paul just tins the whole board but maybe there's a spray lacquer that would still allow solder modifications but prevent oxidation.

Sunday, September 12, 2021

An OWON XSA815-TG Spectrum Analyser for the bench

I've wanted to try a spectrum analyser for many years but they've been prohibitively expensive. Just as oscilloscopes have come down in price, spectrum analysers are also getting cheaper. I bought an OWON XSA815-TG Spectrum Analyser from Banggood for just under US$1,000.

This one is good to 1.5GHz which should be plenty for my use.

So far, I'm really impressed. It's very easy to use - easier than many CROs. Certainly easier than the TinySA. Here it is showing the local FM broadcast band:


Here is a signal from a 2m FM hand held (received off air):


Here is the tracking generator in operation showing a 9MHz low pass filter:

There is lots to learn but I feel that after a CRO, a spectrum analyser is a wonderful piece of test equipment that is now within financial range of some of us lucky hobbyists.

The terrible interference I often see on 40m has just returned. Here's how it looks on the IC-7300:


I tried plugging the antenna into the spectrum analyser in the hope of seeing the overall noise but I'm not:


I think I need to play with attenuation and gain to see what's going on. Much to learn!

Here's the output of my recent Si5351 WSPR transmitter with a fairly poor low pass filter after it. Those second and particularly third harmonics look pretty big.



Tuesday, September 07, 2021

Simple WSPR Beacon using Si5351 and ESP8266 NTP for time sync

Wanting to play with a simple WSPR Beacon in the house where I can't receive GPS for time synchronisation, I've hacked together a beacon using an Si5351 oscillator and an ESP8266 board that joins my Wifi and gets the time from an NTP server.

Here's the rig:


It starts off by joining Wifi, then requests the time from time.nist.gov. Next it figures out how many seconds to wait before the next 2 minute slot and delays that long. The WSPR signal is transmitted followed by a 10 second delay before requesting the time again. Assuming the NTP server replies, WSPR transmission is every second 2 minute slot.

The Si5351 generates a square wave into 5cm of wire and there's massive hum on the signal presumably due to the USB power. Here's how it looks decoding off air:

I got this going using a WeMos D1 R2 board which is basically an ESP8266 on an Arduino style board. I tried to use an ESP32 but for some reason (possibly power voltage) I couldn't get it to talk to the Si5351 although it could see it on the I2C bus.

Just a toy really but might be useful for something. The source code is here.

I'm using Arduino 1.8.15 and the following libraries are installed:

  • Etherkit JTEncode 1.3.1
  • Adafruit Si5351 1.2.1
  • Other libraries for UDP were bundled with the board, in my case LOLIN(WeMos) D1 R1

Wednesday, September 01, 2021

ZM-4 Z-match antenna tuner kit review

Years ago I built the AM-2 Z-Match antenna tuner and found that it could match pretty much any old bit of wire thrown outside. I melted the polyvaricons by running WSPR one day but they were easily replaced.

There's a German made evolution of this design with more robust variable capacitors and a larger toroid that claims to handle up to 15W.


The ZM-4 kit is available from QRP-Shop for 98 Euros. It came with an English manual but it helps to view it in colour here.

Nice spread out circuit board for easy construction.

Unfortunately a couple of component labels are missing from the board’s silk screening.


Instructions fairly clear but I started off reversing the direction of winding on the main toroid. 

It says wind to the right but neglected to say the winding should start on the bottom of the loop. At one point it says to wind over the red wire, but there’s no red wire. (I now see that it's red in the colour instruction manual).

The BNC connectors have substantial thermal mass and my little soldering iron struggled to heat the earth pins to melt temperature.

The metal case is great but it would be wonderful if the front and back panels were pre-drilled. My metal work skills are not great and I found the front and back plates to be quite hard aluminium to drill safely.


Great to see metric units with no comment.

When assembling the front and rear panels, have the circuit board close by as a guide. The instructions don’t suggest switches and plugs in the order they are on the panel and I ended up enlarging a hole that I shouldn’t have by mistake.

The kit comes with two banana sockets which I replaced with terminals so that a wire can be directly connected.

Some of the wiring, in particular the links from the panel switches down to the board is pretty tedious. I guess the solution would be a PCB behind the panel to handle that wiring but extra cost would be added by this.

Only after wiring up front and back panels did I realise that you need to slide the board in to the bottom of the case before connecting the panel wiring. I should have tried fitting the case before this but also the instructions should have mentioned it.

I unscrewed the BNC connectors and luckily had enough length of wire to the switches to be able to lift the panel out of the way and slide the board in to the lower part of the case which I had already lined with gaffer tape to try to minimise likelihood of shorts to the case as warned in the manual.

Hooked up to an end fed wire with a short counterpoise the Z-Match was able to get an excellent match by playing around with the additional capacitance switches and rocking back and forth between the variable capacitors.

Z-Matches are a versatile antenna tuner although I understand they can be lossy. This kit is well done but the switch wiring and panel metalwork takes some effort. When boxed up it's a compact and strong little tuner that will work well for portable QRP operation.

Wednesday, August 25, 2021

WSPR Watch app updated with better graphs

WSPR Watch is a free app for iOS that displays data pulled from WSPRnet.org. Originally I wrote my own code to draw charts of reception data but my clumsy attempts were pretty simple. Recently I started using the excellent Charts library and this has opened up all sorts of improvements. For a little while, the app lost features but now I think it's looking better than ever, particularly for stations that band hop.


There is a catalyst version of the app for macOS but it's not a great macOS app at this point. Thanks to everyone who has sent encouraging emails (you can do this through the app) and if you like it, please consider leaving a review. Latest version as I write is 3.29.

Friday, August 20, 2021

Digital modes with a Xiegu-G1M and DigiRig

Prompted by carrying too much equipment on a SOTA outing, I purchased a new low cost QRP transceiver from China. The Xiegu-G1M is very small and was dwarfed by the SignaLink USB I normally use for digital interfaces so I sent off for the new Digirig interface and have been working to get it going.


As there's no VOX I need to control PTT via CAT. The G1M manual is rather vague about CAT control and the radio doesn't appear in the Hamlib options yet. The user guide suggests using IC-7000 but that didn't work for me. IC-7300 worked to some extent but was very slow, including PTT on and off.

Examining the event log in Fldigi, I could seen loads of errors and timeouts which would explain the slow operation.

I took the RigCat IC-7300.xml and stripped out everything except frequency and PTT. Later I found the xml for the Xiegu-G90 and took the mode setting from that. Rig control works enough now for digital modes. I've put Xiegu-G1M.xml up on GitHub. (Download the raw file and configure Flgidi rigcat to use it). 

The serial connection on the DigiRig is 3V and this talks nicely to the G1M with a straight through 3.5mm stereo cable. Next step is to make up a cable for audio in and out.

One note on the Digirig... one of the 3.5mm sockets broke off after light usage. It looks like the connectors are surface mounted and there's not much solder there so I re-soldered them and hope they'll hold up to normal use now.

The Digirig interface is a very neat device containing a USB hub and both serial and audio interfaces working through a single USB-C cable. I feel the 3.5mm sockets are a weak point though.

I've made up an audio cable with a 100uF cap to block the DC bias on the mic. All seems to work fine with fldigi.


Listening off air, the transmit audio sounds a bit over-driven - I may need to add some gain reduction on both transmit and receive. A bit more feedback to the fine Digirig makers - the 3.5mm sockets are very close together and I hunt around to find plugs that were narrow enough to fit.

Sunday, August 08, 2021

New SDR++ software works well on Linux

I've been playing with SDR++ by Alexandre Rouma is available for macOS, Windows and Linux. Others, such as SDR#,  work well on Windows but mostly I run Linux for ham radio and it's great to find one that works as well on Linux as on Windows. Here it is on Windows:


Even on a low end laptop, the spectrum display updates fast and the receiver works well. (My reception here is terrible though). Here it is on Ubuntu 21.04:


I did run in to a common issue on Ubuntu 21.04. The app crashes on startup. If you run it in a terminal you see this alarming log message: 

"Hash collision!!! Fatal error!!"

Apparently it's due to multiple drivers in the soapysdr system. A workaround is to remove them all by running:

sudo apt remove soapysdr-module-*

It's mentioned in the troubleshooting section but I searched for the message with exclamation marks and so didn't find it.

Fantastic to see a high quality, high performance SDR client. I've used it with an Airspy HF+ and an SDRPlay. Others are using it with audio re-direction to receive digital modes.

Friday, July 23, 2021

The best digital mode for weak signal keyboard to keyboard QSOs?

Since moving from Sydney to Melbourne I've wanted to be able to chat with my Sydney friends but have wondered about the best mode to use for this from the huge list in fldigi.

Stephen, VK2BLQ, and I have been running WSPR and watching the signal to noise ratio for band openings on 40m. Today looked like this:

When WSPR shows an SNR of better than -10db we try for a contact. Until today I had thought that the best mode would be one of the wide modes such as Olivia 16/500 and we tried that for a while. We could hear each other but could not decode.

On a whim I suggested switching to good old BPSK31 and suddenly we were talking!

I find this rather puzzling and would welcome an explanation. Some commentators compare digital modes and rate BPSK31 very poorly compared to other modes. Local hero David Rowe has been doing some work on data modes for HF radio and I intend to try out what he's been working on.

K8JTK has quite a nice writeup of different modes here and we plan to test QPSK31 over BPSK31 soon.

The noise level here is distressingly high. A solid S9 of broadband noise. I've tried a loop antenna but it's similar.

Update: Good contact on Saturday

I received VK2BLQ at -10 on WSPR so we had a good contact using BPSK31 just now (local time 10:30).


For a while we had perfect copy (some errors are Stephen's typing) but then signals faded and I have a storm coming in.

We experimented with sending PSK carrier and measuring S/N and IMD. Stephen receives me with S/N 25db and IMD of -22dB which seems pretty good. I don't get him as well but we did determine that him reducing power a bit gave rise to a better IMD.

Noise levels for both of us are down today so that might be the explanation rather than just improved conditions on 40m.

Wednesday, July 21, 2021

Awesome Amateur Radio link list

Mirko Caserta has started a useful list of Amateur radio links. There's loads of these around the web but this one is on GitHub which means that contributors can fork and send pull requests to edit or add content. 

Mirko clearly favours alphabetical order.

The topic areas at the time of this blog post are:

  • Antenna
    • Analyzer
    • Balun
    • Tuner
  • Band Plan
    • CW
    • Digital Modes
    • Interface
    • Misc
    • Italy
  • Organizations
    • Global
    • by country
      • Australia
      • Canada
      • Germany
      • Italy
      • Japan
      • New Zealand
      • UK
      • USA
  • Propagation
  • Rig
  • Satellite
  • SDR
  • Shopping
So clearly there's lots more to add. I've contributed some Australian content and Mirko has granted me edit access so I'll keep going.

Sunday, July 11, 2021

Røde Wireless GO II microphone for iPhone review

Good audio with bad video is generally acceptable. Good video with bad audio is never OK.

In the past I’ve used the excellent Sennheiser radio mics but I’ve been tempted away by the prospect of digital output. My daughter uses the Røde Wireless Go kit and recently I purchased the Go II.

A third of the price of the Sennheiser but with superior features. Note that with the GO II you get two transmitters.

The GO II claims a range of 200m line of sight. I don't doubt this. Transmission is digital at 2.4GHz and seems highly resistant to interference. Compared to the analog Sennheiser system which needed an RF scan to avoid interference from other mics.

The GO transmitter and receiver are in a small 45.3mm square box with a clip that also conveniently slides in to a camera hot shoe.

The transmitter has a decent mic built in and comes with a fur wind shield. A lavaliere mic can also be used but is a separate product.

You can use just one transmitter and have it appear on both channels. Two transmitters can be used with one on left and the other on right (for later mixing). Transmitters can be muted.

Transmitters and receiver come paired although the instructions are rather brief.

Features I didn’t expect:

  • The two channels can be kept separate or mixed down to mono
  • The transmitters can record 40 hours of backup audio locally
  • You can record a second track at -20dB in case the level is so high that the main channel clips
  • The receiver has a USB-C port that, if plugged in to a computer, comes up as a sound card
  • Analog output from the receiver can be attenuated in three big steps or much smaller steps if desired.
  • There is an app, Rode Central, for iOS, macOS, Windows, & Android
  • When using digital output you can use a headphone to monitor reception

Connecting to an iPad pro is easy - a standard USB-C cable does the job and audio apps including Voice Memos and the Rode Reporter app switch input to use the device. Connecting to an iPhone does not work with standard USB-C to Lightning cables that you normally use to charge or sync. A special cable known as a Lightning Accessory cable is required and as far as I can find so far only Røde makes one called an SC15 cable.


Here's a little test recorded with an iPhone.


iOS is not great at showing use of external USB audio inputs. Generally, just plugging in an external audio device sets recording apps to use it but I read that in some cases you must launch the app first and then plug in the external audio input to get it to be used. I wish we could see all audio inputs and switch between them. In any case, test carefully before an important recording.

One small usability irritation is that the power on button, obtusely marked with a “Ø” symbol, is on the opposite side to the other two buttons on the receiver which makes it a bit difficult to press without pressing other buttons. The square form factor is a bit strange, particularly for the transmitter which clips on to a shirt with the mic pointing sideways. 

I can see the digital transmission at 2.4GHz:

I haven't pulled mine apart but the FCC listing shows a nicely made board:

Since Apple has started seriously messing with ad tracking I notice this rather weird targeted ad for dog food as a result of buying the Lightning accessory cable.


LOL. I really like this wireless kit and if you get the lightning accessory cable it makes a very compact video recording setup with excellent audio. The kit comes with a nice cloth pouch, two USB-C to USB-A cables, and three wind socks. There's not much documentation with the product but the online learning hub is pretty good.

Røde is an Australian company and from what I can see they've done fantastically well around the world. 

Friday, July 02, 2021

XIEGU G1M portable SDR HF Radio review and notes

After my recent SOTA experience I've become interested in more compact and portable QRP gear. A radio that's getting good reviews is the Xiegu G1M

As you can see it's almost dwarfed by the SignaLink adapter.

I bought via eBay and paid AU$354 plus shipping. (Prices vary a bit I notice).

The radio comes with a rather muffled microphone, a power cable (to open wire), a serial USB cable (for CAT and software updates).

A printed manual was included but it's not as up to date as the one available from the manufacturer.

The G1M puts out 5W sideband or CW and can also receive AM. It's general coverage receive and transmits on 4 bands: 80m, 40m, 20m and 15m.

It runs on 12-15V and works fine on a 3S LiPo battery from my drone days. Running on 13V it draws 400mA on receive with no audio and peaks at 2A on transmit.

Here's a backyard SOTA practice with a simple vertical on a squid pole matched with a Z-Match.


There is an active community discussing the radio on groups.io.

Mine came with firmware V1.06 but there is a new version 1.07 available. (For some reason it isn't yet on the Xiegu site here). Firmware is uploaded over a serial port using XModem. I used the go language uploader from Dale Farnsworth on macOS to upload the new firmware. 

You need to un-rar the file to get a .xgf file to upload.

The first two attempts stopped uploading before completion and I thought I might have bricked the radio but a third attempt worked.


As others have noted, the version still displays V1.06 Oct 22, 2019 but it's clear that the CW bandwidth is now narrower so it has changed.

There are several stickers to discourage disassembly but I couldn't resist. You need to take off the volume knob and remove the nut.


On the back, remove the nut from the BNC socket.



There are two thin co-ax links that need to be unplugged and two flat cables that can be released by flipping up the little plastic clip on the board end.



Interesting that there's space for another low pass filter on the board.



I've used the radio for WSPR reception and there is no reported drift. 


I'm quite impressed with this radio. It is an SDR and has a tiny little spectrum display that is actually handy for seeing signals. Reviews on eHam are generally good. There are a couple of reports of DOA units but mine works well and construction is of excellent quality.

To use CAT control with programs like fldigi, I have created a rigcat XML file for the G1M.

Saturday, June 19, 2021

ATS-20 Si4732 receiver firmware update

I recently purchased a nifty shortwave and FM receiver from AliExpress built around an Arduino Nano and Si4732.

I pulled mine apart to try to see if there was a label that would provide a clue about which version to write it it - there isn't. A tip: you can just undo the top screws front and back to get the lid off. Watch the speaker connected by short wires

On power on, it displayed V1.1.5 of the library by PU2CLR. After upgrade it now shows 3.04.

I followed the instructions on swling.com but used Arduino 1.8.13 on macOS just fine.

Basically the steps are:

  • Select Arduino Nano
  • Select ATMega 328P (Old boot loader)
  • Install libraries:
    • SI4735
    • Tiny4kOLED
    • TinyOLED-Fonts (it's a dependent)
As well as plugging in to the Nano I had to power on the radio to program it.

The source code is available here. For my hardware, I found the version titled "SI473X_ALL_IN_ONE_OLED_RDS_CHINESE_V3" was the one that matched the buttons on my front panel.

In the source code of the sketch there are some settings to adjust if you like such as default volume.

Before upgrade here's the splash screen:


After the update it looks like this:


The display in operation is a bit different too.


It's quite a sensitive receiver and sideband works pretty well. Here's an example.



There is no bandpass filtering on the input so it would probably be overloaded if connected to a broadband antenna. It's wonderful to have the source code to play with - all credit to PU2CLR.

Thursday, June 17, 2021

My first SOTA - cold and wet but not disappointing

Paul, VK3HN, kindly invited me along to a Summits On The Air (SOTA) activation today at Mount Disappointment close to Melbourne.  

The weather did not look promising but we decided to risk it and while it was rather damp and cool, it could have been worse. 

David, VK3KR, generously drove and Owen, VK3EAR cleverly opted not to come and stayed at home to monitor.

I took a loop antenna and an IC-705 with external battery. Paul had two home brew rigs and used an end fed antenna. David was on 2m with a home built beam.

Paul has created a video that captures the day very well:


Here is Paul's latest home brew rig. It is a crystal locked CW transceiver. I really admire his construction and recommend his video about how he hand makes printed circuit boards.


The mountain was beautiful but there was intermittent rain and the temperature fell to about 7C. We were all soaked through by the end of the outing.


SOTA is a great idea in that it encourages bush walks to mountain peaks with a bit of ham radio activity. David was the most successful and even had a contact with Peter, VK3YE on 2m.

Things I learned:
  • Use pencil for the log - my ink ran in the rain
  • Less weight is good - even though the loop was pretty light an end fed wire would be better
  • Don't take a chair - I thought I was being clever by bringing a folding chair but it turned out that there was a picnic table there anyway so that was unwanted extra weight to carry.
I'm looking forward to trying this again in better conditions.

Monday, June 14, 2021

Games on Netflix? My comments on ABC Download this show

Topics on ABC Marc Fennell's Download This Show were the Apple Developer Conference announcements, Facebook's ban on Trump, paying for extra Twitter features and the prospect of renting games on Netflix. Here's a video segment:


The full radio version of the show is available here. I enjoyed meeting Dr Emily van der Nagel who has done some very interesting research into social media platforms.

A book I mentioned in the radio show is Influence by Robert Cialdini.

Saturday, May 29, 2021

Wonderful new SDR design described by Ashhar Farhan

A video of a presentation by Ashhar Farhan, VU2ESE, has been posted and I can't recommend it highly enough. He describes a new design for what looks to be an easy to build SDR based around a Raspberry Pi. Along the way, Ashhar also clearly explains many of the key parts of how a Software Defined Radio works.


The paper that goes with it can be viewed here. Thanks to Stephen, VK2BLQ, for drawing my attention to this and for Bill at Soldersmoke for the link.

Today is a bit sad for me as I'd hoped to be going to MayHam at Wyong but due to a pandemic lockdown in Melbourne I'm unable to leave my home.

Thursday, May 20, 2021

A visit to Paul Taylor, VK3HN.

I have been a fan of Melbourne ham radio home brewer Paul, VK3HN's blog and YouTube channel for some time. We met a few years ago at Peter, VK3YE's QRP by the Bay but I discovered that he lives not too far from my new home in Thornbury so I invited myself over for a visit.

Paul's blog is of a very high standard, well written, with extensive technical information about his projects. In recent years, projects have been demonstrated and explained with well made videos as well.

Projects cover the spectrum from small portable CW rigs all the way to a high power AM transmitter using the efficient Class E mode.

There's a few things that stand out to my eye - Paul tackles complex projects with a logical modular approach, often building on tried and tested standard designs but without fear of trying more challenging designs. 

Circuit boards are manually etched using the resist pen method.


Most striking of all are the cases which are custom fabricated from aluminium angle stock and sized to snugly fit the enclosed circuitry.

Thanks Paul for an entertaining and educational evening tour of the shack.

Incidentally, you can hear more from Paul at HRDX via SolderSmoke and a terrific interview on QSO Today episode 298.