Copper pipe loop for 40m

Inspired by the work of Peter, VK3YE, I visited the local hardware store to get bits for a 40m loop antenna. Purchased a 3m length of copper pipe, some hose clamps, some copper saddles, a piece of dowel, and a plank of wood. Here's the result:

The variable capacitor is clearly not going to be able to stand much power but at 20W it doesn't appear to be arcing. This capacitor has a reduction drive and I'm using a switch to add a bank so that I can tune both 40m and 20m. Joining the tuning shaft to a dowel rod with a piece of plastic pipe and cable ties worked out quite well although there's a little slippage.

Matching stub:

Tuning is incredibly sharp but a very low SWR is achievable.

The offset of the tuning stub was a guess but seems to be reasonably close to 50 ohms. I had a pre-arranged contact with Stephen, VK2BLQ who could hear me reasonably well.

Reception seems excellent and of course the very narrow bandwidth leads to nice low noise.

Update

Had a visit from Bob Bray who liked both the shed and the loop antenna, although I suspect he wasn't impressed with my impression of a circle.

Robert John Bray is a prominent astronomer who has been honoured by having a main belt asteroid named after him.

Update - motor drive tuning

I've changed capacitors and added a 36RPM motor drive and a box to switch direction. The drive is still way to fast and now I'm looking for a reduction gear or multi-turn capacitor of some sort.

Built an Ultimate3 Beacon

This week an Ultimate3 QRSS/WSPR kit beacon kit I ordered arrived and this morning it was easily built.

The display is super crisp.

I ordered mine with the 30m low pass filter.

The whole thing runs on 5V so I chopped an old USB cable and have been running it from a USB charger or battery.

It's a great kit, with very clear instructions and it came together very smoothly. Mine was missing one small capacitor but it was no trouble finding one in the shack.

The software is very well done and everything is set up using two push buttons placed in just the right spot for your fingers while holding the board with the display facing you.

Amazingly this does WSPR as well as lots of modes:

- QRSS mode (plain on/off keyed slow CW)
- FSK/CW mode (frequency shift keyed slow CW)
- DFCW mode (dual frequency CW)
- WSPR mode (Weak Signal Propagation Reporter)
- WSPR-15 experimental WSPR mode with 15-minute frames
- Opera modes (8 speeds)
- PI4 beacon mode
- Slow-Hellschreiber (frequency shifted slow-Hell)
- Full-speed Hellshreiber
- Half-speed ("DX") Hellshreiber
- CW (plain CW)
- FSK (0-999Hz shift, fast-speed FSK CW)
- Customisable FSK patterns
- manually-keyed CW/FSK transmitter

I ran Hellshreiber for a while but it didn't look too good on fldigi in the house, now I'm running 20WPM morse but that's not decoding perfectly either - my guess is that the signal is so strong that AGC is messing with it but I'm still trying to figure this out.

Useful M8 transistor tester

I purchased a transistor tester kit from AliExpress a few weeks ago and it's a useful gadget for the workbench.

Often when home brew circuits haven't worked it has turned out to be because I didn't get the pinouts on transistors right and this device figures out the EBC pinouts of a given transistor. It also analyses other components although not small values.

Cost about $25 landed.

Digital voice ove HF radio talk

This week the ARNSW Home Brew Group was honoured with a visit from David Rowe, VK2DGR, who spoke about codec2, FreeDV, and the upcoming hardware implementation called the SM1000.

Install freedv on Ubuntu 14.10

Just a note for others who might run in to the same issue. Freedv depends on libtiff4 which is not available for Ubuntu 14.10. Here's how to install freedv and avoid that bump in the road.

# grab the library from an old version of ubuntu
wget http://mirrors.kernel.org/ubuntu/pool/universe/t/tiff3/libtiff4_3.9.7-2ubuntu1_amd64.deb
sudo dpkg -i libtiff4_3.9.7-2ubuntu1_amd64.deb

sudo nano /etc/apt/sources.list
# add these lines to /etc/apt/sources.list
deb http://files.freedv.org/debian/ stable main
deb-src http://files.freedv.org/debian/ stable main

sudo apt-get update

sudo apt-get upgrade

sudo apt-get install freedv

Now you'll find the app if you search from the dock.

New version of WSPR Watch for iOS is out

I've updated the iOS app WSPR Watch with support for iPad, iPhone 6 and 6+.

The program is simpler than before but I think more useful with a feature I've long wanted, a direct view of how long ago each of the spots were reported.

As always, it's free and all data is gratefully pulled from the legacy database page on wsprnet.org.

I'm happy to report that there are a couple of equivalents for Android, one from developer Derek G4SWY, who made WSPR World Watch, and another called WsprNetViewer by Joseph D. Glandorf with source code and it's in the Play store. Great work!

My own WSPR beacon station is on 20m running a vertical wire antenna on a 6m squid pole. It doesn't take much to reach around the globe.

wspr on Ubuntu 14.10

The easy solution

Thanks to this post, from Greg, K17MT, here's what you do.

sudo add-apt-repository ppa:ki7mt/wspr
# press enter when asked something
sudo apt-get update
sudo apt-get install wspr ntp

Now you can use the Ubuntu launcher to launch wspr, or as I did, drag the icon to the side dock and launch.

Note that I also recommend installing the ntp time sync service as I find my ubuntu laptop clock drifts off and by default Ubuntu only syncs the clock on each boot.

Watch out for me, vk2tpm, on 20m.

Thanks Greg!

Obsolete below here

Building WSPR on linux is often a bit of a puzzle. With the help of the clearly very clever George Smart M1GEO I got most of the way.

He didn't draw a lot of attention to it, but after running ./autogen.sh you do need to edit the Makefile and change /usr/bin/f2py to /usr/bin/f2py3.4

After successful make and make install, running wspr gave me a python exception ending in ImportError: cannot import name '_imagingtk'

The solution is:

sudo apt-get install tk8.5-dev tcl8.5-dev
sudo pip3 install -I pillow

It's now running although I now get a crash shortly after it starts decoding.

So audio in is working. My guess is something is wrong with the fortran to python interface. Any tips would be most welcome.

Another hobby - Quadcopters

Accidentally purchased a little quadcopter and then found that the expensive ones have come down in price since I last looked. These videos look much better on YouTube at 720p full screen.

You can see my 20m vertical on a squid pole on the balcony at the front. It's running my WSPR station.

I bought a Quattro-X which can easily lift a camera and has the advantage of GPS stabilisation so it's not too hard to control even when there's wind. A surplus of trees does lead to some messy landings however.

The quadcopter is getting pretty beaten up.

Back home, back on lower bands

For the past eight months we've been living in an apartment and while I enjoyed learning about antennas on a balcony, it's good to be back at the normal QTH. The neighbours behind us have a magnificent gum tree which supports my new 80 and 40m dipoles.

You can't see the thin wires so hopefully it won't annoy the neighbours too much. I don't really have enough space for the 80m dipole which runs along the side fences, but 40m works really well and tunes up beautifully.

It's good to be back and while I have lots of unpacking and re-organising to do my hope is that ham radio projects will again get some time.

iPad version of WSPR Watch coming

Here's a sneak peak:

It updates itself every few minutes but I am concerned about loading wsprnet.org too much.

New transceiver for the shack - with valves!

Great day at Dural today. Particularly impressed with the home brew moving coil compass built for a model boat. I didn't mean to but ended up walking away with a beautiful Yaesu FT-101E for $200.

Had a contact with Stephen, VK2BLQ, who reports that I sound normal so that's all good. Plate and Load knobs are new to me but fun to learn about.

For my younger readers, this is what a valve looks like:

The compass was fascinating, it uses a spinning coil with an amplifier in the centre. Power is fed in through the ball bearings and the output is sent by an LED light.

We turned it on and compared with a compass in a smartphone.

A wonderful device, but I think technology may have moved on.

Update

Here's a video of what it's like to tune across 20m on the FT-101E back in the flat with a dipole on the balcony.


We're moving out of the unit back to the normal QTH in a few weeks so I thought I'd capture this for future reference.

Appearance on RN's Download this Show

A busy week, media wise. I was on RN's Download this Show:


Also wrote an opinion piece about how the BitTorrent technology can be used for good as well as evil, published by the ABC.

What's cheaper than a Raspberry Pi and runs linux well?

I'm interested in playing with some of the new virtualisation technologies, such as docker. For this stuff my usual go to toy, the Raspberry Pi doesn't quite cut it. This morning I spotted a Dell Optiplex PC, Core 2 Duo 2.5GHz, 2G Ram, 250GB disk for $35 on eBay with no bids.

Ending an auction at 7:15am on Sunday morning may not be the best way to sell technology.

So far I've installed the 64bit version of Ubuntu Server 14.04 and following the instructions from the excellent Ubuntu documentation created a virtual machine in which I've installed another copy of the Ubuntu Server.

This works magically, the qemu environment can be set up to share the virtual console via VNC and from my desktop machine I answer the install prompts as if sitting at an actual machine. Here's how it looks:

Now I can safely try all sorts of crazy things in this virtual server and just delete anything I'm not happy with.

Here's the giant new server (with a Raspberry Pi next to it for scale):

There are bargains out there, but I should say that this was a crazy price. You can pick up similar systems for under $200 pretty easily though.

Balun day at Amateur Radio NSW

Today was "balun day" which began with breakfast followed by a terrific talk from Mark, VK2XOF, about the theory and practice of building current baluns. The biggest mystery for me is what core to use.

After the theory, and lunch, we all received out balun kits from TET-Emtron. I went for the TB-11K 1:1 kit rated at 1kW peak. We then built our kits under the guidance of folks who had built them before.

Finally there was a spectrum analyser and antenna analyser on hand to measure the baluns. Some home constructed baluns were found to have high reflected power which was very interesting to see.

The method for assessing a balanced to unbalanced balun's operation is to attach a 50 ohm load on to the antenna terminals, feed it from an antenna analyser and connect one and then the other of the antenna terminals to the ground of the input and see if the impedance changes very much - if all is working well it should not change.

My sincere thanks to the ARNSW committee and all who clearly worked hard to make this day a great success. Thanks also to TET-Emtron for producing the fantastic kits and for their support.

Windy in Sydney this afternoon

Up here on the 28th floor it was pretty windy today. The doppler wind radar looked pretty interesting. RNDSUP seems like a fun technology.

ABC Download This Show appearance - Chromecast, Upworthy, Unicode

We're videoing radio again this week. Here we are in the Radio National studio talking about technology.




Exciting news for people who like watching radio programs on video - Download This Show is now available on ABC iview. (Search for it or look in the iview channel).

DDS VFO purchase

I recently purchased an old crystal controlled Codan lunchbox radio and want to put it on 40 and 80m so I've found a rather nice DDS VFO on ebay for AU$45. This one has two PIC CPUs on the board, a nice backlit display and comes with a tuning knob but no info on wiring it up.

The same unit is in other ebay auctions and one of them has this "schematic" which will be a help, if it's correct.

My board came with some cables with sockets to match the connectors on the board and the rotary encoder. Here's other info, for future reference. (It all seems a little mysterious to me but hopefully will be clear when I play around with it).

Note that the wiring of the rotary encoder in the sketch above (from an eBay ad) is shown from the rear of the encoder. I wired it up in reverse and it works but the tuning goes clockwise for up in frequency.

My thanks to Stephen VK2BLQ for access to his workshop, here's my VFO all boxed up.

One criticism of these boards is the lack of mounting holes. I've stuffed the box with cloth to press it against the front and that works fine but is not ideal.

I've now added a 9V three terminal regulator so that the unit can run from my 12V bench supply.

All up this is a terrific VFO, pushing while turning the knob changes the digit that will be adjusted so it's quick to get around. Thanks to commenter Yiannis, the documentation and software source has been traced to Ham Radio India.

The objective of this device for me was to use it as a VFO for my Codan 6924 radio. There's a handy page outlining how to do this. This weekend I ran a cable to an empty crystal spot.

This makes the old radio look very fancy.

As I tune around I notice carriers sweeping by at some frequency ranges but not others. I took the DDS over to VK2BLQ's lab and it seems that for many frequency ranges the output drops dramatically. I'm not sure what's going on here but my guess is that it's designed to cover only certain bands and not others.

Report from WWDC for Download This Show

Australian broadband needs upload speed too

I'm in San Francisco this week for the Apple WWDC. The flat I'm sharing has apparently typical broadband. It certainly seems very snappy for downloads but what absolutely kills me when I compare what we have in Australia is the upload speed.

This is over Wifi by the way. At home on Telstra I get 100Mbps down but around 2Mbps up. This makes sending files or backing up to the cloud very difficult. Will the NBN fix this?

I asked the other residents of the unit if their internet connection was typical, amusingly they took this as a complaint and apologised for the poor speeds and asked if I was having trouble. They expect to get 100 down and 50 up. There is no download limit. They pay $400 a year.

Update

I'm currently in San Francisco at the Apple developer's conference and here we have the fastest internet I've experienced so far.

This is not some science fiction future world, this is today.

Noise in flats

This appeared in the lift last week.

Most interesting. I'll have to avoid raucous laughter and talking over other people.

Apple ARM laptops - not what you think

There have been rumours for years that Apple is working on ARM based computers with keyboards, after all the phones and tablets are already ARM processors. Recent rumours, talk about MacOS X, but Google's success with Chromebooks for education suggests another alternative.

I think Apple might make a low cost laptop running a version of iOS that would be perfect for users who want the simplicity and security of iOS, combined with lower cost and long battery life from an ARM processor. It would be popular with eduction but also the huge audience of users who find full operating systems confusing.

This laptop would have a keyboard and a large trackpad. My guess is that they would not do a touch screen as poking the screen on a laptop is not a good experience.

The whole idea is a reprise of a past product, the eMate, which was a laptop version of the ill fated but much loved Newton. The App eco-system would provide a rich set of applications that would need a little tweaking but port over quickly. Many apps already work well with external keyboards. Without touch presumably a "mouse" cursor would be needed but not much else.

First look at the Intel Galileo embedded linux board

I've just received an Intel Galileo board and am starting getting to know it. In the past I've used Arduinos for low level hardware "bit bang" style projects, and Raspberry Pi or Beagleboards where a little embedded Linux is needed - both are great for their purpose.

The Intel Galileo is kind of a mash up between the two worlds, underneath it runs Linux and it has software that emulates the Arduino's hardware enough for many sketches to run as they are.

You can see that it includes the standard, weirdly offset, Arduino sockets for taking "shield" boards.

The board is just 7x10cm and pretty capable:

• USB 2 client and USB 2 host ports.
• Serial port (wired to a convenient 3.5mm stereo socket)
• Ethernet socket
• Standard 5V 2.1mm power socket
• Mini PCI Express slot with USB 2.0 Host support - this is probably most useful for adding a Wifi card.
• All of the Arduino's analog and digital I/O ports.
• It has the normal pin 13 LED that you get on an Arduino.
• The CPU is an Intel Quark SoC X1000, which is a 32 bit Pentium class processor running at 400Mhz. (Single core).
• 256MB of RAM
• 8GB onboard flash which contains the linux boot
• uSD card slot that can take up to 32GB cards and will boot from this if present.

As an Arduino

First up I wanted to try it as an Arduino emulator. I connected a microUSB cable from my Mac to the USB client port on the board.

The version of the Arduino development tool which has been modified for the Galileo can be downloaded from Intel's download centre. Annoyingly it's also called Arduino, so will collide with the normal Arduino app unless you rename one of them. (I read that spaces in the name are a bad thing by the way).

Choose the virtual serial port and choose "Firmware update" from the Help menu.

The update was faster than the 5 minutes they warned about. After the update I had to quit and re-launch the Arduino environment.

I selected the Blink example from the sample sketches bundled with the environment, clicked compile and then run. 

Now we see a little blinking green LED on the board, just like a real Arduino.

But this seems a waste of a Pentium CPU with a quarter of a Gig of RAM!

Talking to Linux

Sketches can fire off linux commands using a system() function.

I plugged a short ethernet cable from the port on the back of my Mac directly in to the ethernet port on the board. (Macs don't need crossover cables). To bring up the interface on linux you need to write a sketch to configure the interface and start the telnet server.

system("telnetd -l /bin/sh");

system("ifconfig eth0 169.254.1.1 netmask 255.255.0.0 up”);

With ifconfig on my Mac I can see that en0 gave it self 169.254.248.1

I ran the sketch.

And I can telnet to the board:

$ telnet 169.254.1.1

Trying 169.254.1.1...

Connected to 169.254.1.1.

Escape character is '^]'.

Poky 9.0.2 (Yocto Project 1.4 Reference Distro) 1.4.2 clanton

/ # top

Mem: 22704K used, 215448K free, 0K shrd, 0K buff, 12972K cached

CPU:  99% usr   0% sys   0% nic   0% idle   0% io   0% irq   0% sirq

Load average: 0.98 0.56 0.26 2/36 3476

  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND

 3468   875 root     R    10100   4%  99% /sketch/sketch.elf /dev/pts/1 /dev/ttyS0

 3476  3475 root     R     1268   1%   1% top

  951     1 root     S     1268   1%   0% telnetd -l /bin/sh

  197     2 root     SW       0   0%   0% [kworker/0:1]

  870     1 root     S     1272   1%   0% {launcher.sh} /bin/sh /opt/cln/galileo/launcher.sh

 3475   951 root     S     1268   1%   0% /bin/sh

  720     1 root     S     1264   1%   0% /sbin/syslogd -n -O /var/log/messages

  884     1 root     S     1264   1%   0% /sbin/getty 38400 tty1

  883     1 root     S     1264   1%   0% /sbin/getty 115200 ttyS1

  724     1 root     S     1260   1%   0% /sbin/klogd -n

  875   870 root     S      876   0%   0% /opt/cln/galileo/clloader --escape --binary --zmodem -

    1     0 root     S      796   0%   0% init [5]

  873     1 root     S      768   0%   0% /opt/cln/galileo/galileo_sketch_reset

    3     2 root     SW       0   0%   0% [ksoftirqd/0]

Interesting, I guess the Arduino software loader uses zmodem, that takes me back to the old dial up BBS days!

There’s a /sketch directory containing sketch.elf which is the binary of the sketch I’m running.

The little Yocto Linux distribution in the 8GB of onboard flash is pretty basic and doesn't have ssh for example so it's time to upgrade.

Boot Linux from uSD Card

There's a larger Linux distribution from the Intel download centre. 

I found a spare uSD card, stuck it in an SD adapter and stuck it in to my Mac, a USB reader would do.

Using Disk Utility, partition the uSD card as MSDOS FAT single partition. I called mine BOOT.

The Linux image is compressed with 7zip. I think I have that from Homebrew so you might need to find something else to uncompress the file if you don't have that.

I extracted directly to the root of the uSD card like this:

$ 7z x LINUX_IMAGE_FOR_SD_Intel_Galileo_v1.0.0.7z -o/Volumes/BOOT

Unmount the uSD card. Power off the Galileo board, insert the uSD card and power up. Lights flash enthusiastically for a little while.

To find the IP address the board has taken I use arp on the Mac:

$ arp -i en0 -a

? (169.254.165.5) at 98:4f:ee:1:45:c0 on en0 [ethernet]

? (169.254.255.255) at ff:ff:ff:ff:ff:ff on en0 [ethernet]

So we can see it’s on 169.254.165.5.

$ ssh root@169.254.165.5

The authenticity of host '169.254.165.5 (169.254.165.5)' can't be established.

RSA key fingerprint is 09:ff:22:6c:5b:1f:7b:39:53:a2:a7:6d:d4:d7:fe:54.

Are you sure you want to continue connecting (yes/no)? yes

Warning: Permanently added '169.254.165.5' (RSA) to the list of known hosts.

root@clanton:~# 

And we’re in. (No root password). I’m using an old 8GB uSD card and that leaves me with 140MB free. You can use up to 32GB cards.

I can see the on board 8GB there so presumably that could be wiped and used as a drive if you’re booting from the uSD card.

# df -h

Filesystem                Size      Used Available Use% Mounted on

rootfs                  295.1M    139.5M    140.6M  50% /

none                    115.3M      4.0K    115.3M   0% /dev

/dev/mmcblk0p1            7.2G    306.4M      6.9G   4% /media/realroot

/dev/loop0              295.1M    139.5M    140.6M  50% /

/dev/mmcblk0p1            7.2G    306.4M      6.9G   4% /media/mmcblk0p1

tmpfs                   116.3M    116.0K    116.1M   0% /var/volatile

tmpfs                   116.3M         0    116.3M   0% /media/ram

There's lots of standard utilities, sshd, python and node are there so it’s a very familiar environment. Plus there’s the Arduino emulation software as well.

Conclusion

At around $110 plus shipping the Intel Galileo makes an expensive Arduino, but as an x86 Linux board it seems like a bargain. (It comes with a beefy 3A 5V power supply which explains part of the price).

I'm keen to see the things that this extra processing power can handle that a Raspberry Pi would not be able to cope with, things like FFT processing for real time signal processing. (I'm looking at you FreeDV...).

I realise the on board space is short but it might be nice if the network port was able to join a network and at least listen for telnet without the need for a sketch or uSD card boot to get to Linux. Presumably they want users to at least try the Arduino emulation side of the product.

My sincere thanks to Intel Australia for early access to the board.

Great videos from Dave, VK3ASE

Dave, VK3ASE, is a prolific video maker. Recently the quality of his work is extremely good. For a taste, check out this story about a Gibson Girl SCR 578 life boat radio he found washed ashore in Melbourne.


I love the music.

ARM Chromebook for Amateur Radio

A while back I bought a Samsung Chromebook, the one that runs a non-Intel ARM processor. I see they are AU$320 and work nicely as a low cost web browsing laptop. Just the thing to take away if there's a risk of it getting lost or stolen.

It turns out they can be encouraged to run Linux along side the normal operating system and it seems it's quite practical to run software like Fldigi.

The trick is to put the Chromebook into developer mode and install the crouton chroot software. There's plenty of instructions around the web so I won't repeat here except to say that I first tried the xfce target but fldigi crashed on startup. Installing unity did the trick.

Fldigi finds the Signalink USB adapter just fine and all seems to work nicely.

There is a bug where the linux environment doesn't do tap to click or right mouse button, but if you switch to Chromebook and back again all is well (there's a whacky key command for this). It seems like this bug was fixed a year ago but has returned.

These laptops are very light and have a keyboard better than most of the old "netbook" class machines. Very low power consumption too.

Meccano exhibition 2014

Mal, VK2BMS, and I enjoyed the Meccano exhibition held in Forestville today. It was well attended and the organisers had put a lot of work in to the display.

Meccano can be used to build gearboxes and differential transmission.

This guy had made a knitting machine.

Electronics is creeping in, this machine had an Arduino at the core of it with a fantastic relay board running everything.

I remember using one of these Philips electronics kits as a child.

Circuits were built to a template with components joined with little spring things.

This electronically controlled car had everything including electric windows.

A two story elevator with doors and interlocks was built by a retired lift mechanic!

Here's Mal learning about steam engine control from a fellow amateur.

Slinky dipole for 40m on balcony

My 10m wide balcony works fairly well for 20m but I wanted to try 40m. Good news, Australian Geographic stores carry very nice metal slinky's for $10 each so today I made up a balun and strung up two slinky's as a dipole.

A question: should the turns go the same way on both sides or should they be opposite? I have them in the same direction but it's not working very well.

With the slinky's extended to fill the available space I get a very good match but a little high in frequency for 40m.

This is an astonishingly good SWR and impedance for any antenna in my all-metal balcony, much better than what I get with the simple 20m dipole.

I can tune up on reasonable 40m frequencies, such as 7.146, with the Emtronic EAT-300 tuner but presumably co-ax losses are quite high.

As usual, I'm using about 10m of RG-174 thin coax to get from the balun, in through a window, to the transmitting position.

The windows here have soft rubber like seals and the thin coax will happily go through a closed window without much damaging compression.

Signal reception on 40m is disappointing, I've heard a few nets this afternoon but my CQ calls on 7.2 have gone unanswered so far.

It's a fine looking antenna but I don't think I should leave it out over night for fear of it blowing overboard and clobbering someone - leading to the breaking of another by-law no doubt.

This morning I had a pre-arranged contact with Stephen, VK2BLQ, who could certainly hear me OK, although no where near as strongly as you'd expect given our close proximity.

Using a PC headset mic with a KX3

The KX3 is a radio with convenient standard looking connectors, either 2.5mm or 3.5mm sockets. Elecraft mentioned that many low cost PC headset mics can be used in the four conductor mic socket but I found for my Logitech unit a small adapter cable had to be constructed.

The wiring is as follows:

I used a standard 3.5mm, three conductor inline socket and a 4.5mm four conductor plug which Jaycar carries in store. Doing it this way means I could leave the Mic PTT switching turned on, but I use the transmit switch (XMIT) on the lower front of the rig for control. Here's how it looks:

When I first tried this, mic gain was way too low, but I noticed that Elecraft had a firmware update I hadn't applied that offered increased microphone gain.  "SUPPORT FOR HEIL HC-6 MIC ELEMENTS: Mic gain can now be set as much as 20 dB higher to support these low-sensitivity elements."

On air reports from Mal, VK2BMS and Stephen, VK2BLQ suggest that the audio from the $15 headset is a little lacking in bass compared to the normal microphone but this can be adjusted if required. The headset is very light and comfortable but probably not robust enough for field use.

Incidentally, I accidentally interrupted the firmware update process and this left the KX4 in a mode where it displayed "MCU LD" on the display with the red TX light flashing. I wrote to Elecraft customer support and Howard replied within minutes with the procedure to get past this. (I won't reproduce it here as I guess it might change over time).