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.

Monday, July 12, 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

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.