K6ARK Mini Microphones for KX3 and IC705

The MH3, the standard microphone for the Elecraft KX3 is rather big, and the Icom mic for the IC-705 is not much better. I was looking to replace those with something smaller.

There is a nice design for a 3D printed mini microphone by Adam, K6ARK. The 3D files are here:

https://www.printables.com/model/320559-mini-microphone-for-qmx-trusdx-usdx-kx2-and-kx3 

There are build instructions here: https://k6ark.com/mini-mic-build-instructions/

Now, I don't have a 3D printer, but a good friend was so nice to print me two of these mics, one in orange, one in white.

KX3

I built the KX3 model first, that was a piece of cake, just putting an electret element and a pushbutton inside, and connecting a 3.5mm TRRS cable ... ready !
I did not use the 3.5mm panel jack, but made a direct cable connection.
A long ferrite bead over the cable, near the connector, helps to keep RF out of the rig (see top picture).

This is the result after clicking both halves toghether.

IC-705

I studied the circuit of the HM-243 microphone, this looked a bit more complicated.

The shield is the main GND line. 

RING1 is a seperate line for the 8V DC supply, needed by the electret capsule.

TIP is the microphone signal, but also the PTT line. PTT is active when a 33k resistor is connected to ground.

Finally, RING2 is used for the four programmable buttons (A, B UP and DOWN), connecting four different resistors to that line.

While I was figuring out how to connect everything in such a small space, I got the crazy idea to add a second button to use as the 'A' button. It would enable me to send the first voice memory from the microphone, without even touching the rig.

I distilled my own circuit diagram from the original circuit.

I used a combination of SMD and normal components, and it looked like this:

Ferrite beads over the signal lines help to protect against RF ingress. Then, I covered everything with some heat shrink tubing.

The first test with the microphone was a bit of a disappointment. The microphone level was way too low, compared to the HM-243. 

I made a test setup, putting a speaker with a fixed 1 kHz tone, at 10 cm from the test capsule, and measured the output on my oscilloscope. I found output levels from 34 mV ptp to 84 mV ptp, quite a difference.
So I selected the one with the highest output, and that worked out OK. I got about the same modulation as with the original microphone.

I closed the box with some superglue, and this was the end result

Happy tinkering !

73,

Luc ON7DQ

Yet Another AtTiny85 Keyer

After a renewed discussion on the SOTA Reflector about using a Quansheng UV-K5 handheld for CW, I built yet another AtTiny85 keyer, by just using the chip, and not replicating the DigiSpark layout.
(see my Digispark keyer in a previous post here).

Leaving out all unneeded components made it a lot smaller and lighter, this is the (very) simple circuit.

I built this circuit on a piece of perfboard, it measures only 70 x 12 x 9 mm.

If built with SMD components, it would even be much smaller, maybe it can then be built inside a paddle ?

I found a small plastic box that used to contain some O-rings from the DIY shop, and it fits the keyer nicely, powering it from a 650 mAh Li-Ion cell from a cordless phone.

Total weight , including the cable, but not the paddle, is only 48 gram.

Now, instead of building a keyer into a paddle ... I had another idea : buid the paddle inside the keyer !

I found two very small pushbuttons from old 3.5" floppy disk drives (the write-protect switches).

I glued two of those in the corner of the plastic enclosure of my keyer, and connected them in parallel to the paddle input connector.

And while I was at it, I also added a 4-pin header to the battery, to connect a Chinese charging board. Inserting the pins the wrong way does no harm, nothing happens, since only two of the pins are connected.

For the Quansheng, I built two adapter cables, one with the cut-off 2.5mm connector, to listen to the receiver on speaker. The other cable has both the 3.5mm and the 2.5mm connector, and is meant to be used with headphones.

Both cables have a pushbutton that serves as a straight key. 

Total weight of the keyer with the small adapter cable is 59 gram, with the larger adapter it's 80 gram.

I posted a short video of the keyer on my YouTube channel.

If you have questions about this project, feel free to mail me at my QRZ.com address.

Happy tinkering !

73,

Luc ON7DQ

A small CW decoder

 Another Cassette Box project ...

I wanted a small portable CW decoder, and since I'm a big fan of using old cassette tape boxes, it had to fit in one of those.

The decoder is based on the work of Budd, WB7FHC, which is also used in the OST Morse Box project. You can find the original here: https://wb7fhc.com/m2-cw-decoder.html 

His project uses a 20x4 LCD display which is too big for my project, and the OST Morse Box was rewritten for a small OLED display. So what I did is just program an Arduino Nano with the complete OST Morse Box firmware (largely overkill, I know), but only connecting an OLED display, and an LM576 tone decoder circuit.

The firmware can be found here: https://github.com/on7dq/OST-Morse-Box-V3
The easiest way is to use the HEX file with Xloader (first file in the list), no need to open the project in the Arduino IDE.

The decoder circuit was described in the user manual for V2, and can be found here: https://github.com/on7dq/OST-Morse-Box-DG

The output of the decoder (LM567, pin8) goes to pin D2 on the Arduino. It's also best to connect pins A6 and A7 to ground, since I don't use any potmeters. Some of the parameters can still be set via the Windows Control program. 

OLED connections are straightforward : GND and Vcc , SDA to A4 and SCL to A5.

The Arduino + OLED + decoder fitted nicely on a piece of perfboard, and I even could put a 1200 mAh Li-Po battery in the case. See picture at the top for the front view. 

And this the back. The battery has a 4 pin header (bottom right), but only pins 1 and 3 are used. It connects to a small charger board. When the pins are inserted the wrong way, nothing happens (I hope 😉).

Charger board connected:

Building and controlling the Pi Pico RX

Some time ago I was handed a free Pi Pico WH processor board.
To test what it could do, I made a simple webserver with it, and it worked ... but I got bored, what would I use it for ? I had no direct application for it.

Somewhat later, I found this online article : https://101-things.readthedocs.io/en/latest/radio_receiver.html  , by Jon Dawson.

Aha! This looked more interesting.
The article describes an HF receiver with minimal hardware and some nice features. Read the full article if you want to find out how it works.

The receiver needs no WiFi, so I ordered a couple of basic Pi Pico boards without WiFi.
The software for the Pi Pico can be found on Jasons' Github page and is very simple to program, just drag the correct file to the Pico like you would do to copy it on a flash drive.

There are versions on Github for the basic Pico (2040 CPU) and for the Pico2 (2350 CPU), see Releases

Still later, there was an article in the Belgian ham magazine CQ-QSO (January 2025, pages 11-13), by a French ham : Anthony, F4GOH. It described a ready made PCB to facilitate building this receiver.

All info is on his Github page , it contains two projects : a simple board for a QSD Detector (Tayloe detector), and the full Pi Pico board I am using.

My good friend Gil, ONL12523 (you may know him from our OST Morse Box and Forty-Niner PLL projects) was prepared to have the circuit boards made in China, and prepare them with the SMD components.

From there, it was only a little work to build a couple of these receivers. The first one was built for a friend, and looked like this:

It was built on a U-shaped chassis made from pieces of PCB. It includes a built-in Li-Ion cell (1800 mAh) with a charger board. There is no filtering at all at the receiver input, so for best results, external bandpass filters can be added.

When everything worked,  I bent a piece of metal (from an old instrument case) to close the box. It is attached with 4 Parker screws in the sides.

This receiver changed owner, so I had to build a second one for myself. 
This time I took  a slightly different approach.

I built a flat box out of PCB pieces, put the encoder on the side, and since everyone always asks "Can we see what's inside?" ... I made a clear cover out of an old CD jewel case.

The cover is press-fit between the left and right sides, so opening it is also very easy.

This also saved me the tedious work to drill and file a rectangular hole for the OLED display.

The two buttons for MENU and EXIT, which are on the PCB were extended with two plastic spacers, where I drilled a fitting hole in the bottom. This way I can reach the buttons through the plastic cover. The rotary encoder is soldered between two small pieces of PCB, which are in turn soldered to the chassis.

Here some pictures of the sides of the box.

Right side with encoder and antenna input (BNC).

Back side with ON/OFF switch and USB-C connector for charging the 1800 mAh Li-Ion cell.

Left side with USB-C connector of the Pi Pico, and the audio output for headphone or external amplified speaker.

Using the Pi Pico Receiver

Even without any filtering , it's amazing what you can do with this receiver. See the user manual and check all the possibilities here

Using my long wire antenna, I get good results on longwave, medium wave and shortwave. 
The only strange effect I noticed, is a kind of "motorboating" noise when no signal is present.
But once a station is tuned in, the noise disappears, so it's not a big problem. 
The results still exceed my expectations, for a receiver that costs less than 20€.

Control Software - Work in progress ... 

Remembering all the combinations of buttons to control this receiver is rather cumbersome, so again we got the help of goood friend Gil ... He has made a basic CAT control program.
It's still in its' beta version, but it's already looking good !

At the moment, it contains a few favourite fixed frequencies, and it can set any frequency via the input box. The small rectangle at the right shows the CAT commands being sent.
Next to the frequency display, the MODE can be set.

At the bottom, the COM port can be selected and the connection can be opened or closed.

You'll have to come back later if you want this program, I'll publish it on my Github page when it's ready.

73,

Luc ON7DQ

ON7DQ Teeth Key for SKCC Weekend Sprint

As a member of the SKCC, I try to be active each month for the "WES", the SKCC Weekend Sprint.
Weekends are often busy with other activities or family visits, but I always try to get at least a few contacts in the log.

What is the Weekend Sprint ? From the SKCC website:

The SKCC WES aims to bring together operators with different skill levels in a regularly scheduled, informal operating event lasting 36 hours. The event starts at 1200 UTC on the 2nd Saturday of each month and ends at 2359 UTC on Sunday. Participants can operate for the full 36 hours.

Of course, all contacts are made with a mechanical key, be it a Straight Key, Bug or Sideswiper (Cootie).

The August edition favours the use of a home built key, giving 5 bonus points for each QSO made with that key. So I had to think of a new key ...

After building a few Cootie designs in the past, I decided to build a new straight key, using my own teeth !

My own teeth, huh ?
Well ,not my actual teeth, but a 3D printed replica I got from my dentist. It was made at the occasion of a dental implant a few years ago.

I did have a varnished plank, that was a first test object when I aquired a router some time ago.

[ Sidenote: I used the router to make a Christmas decoration with 3 LED candles that used 3 AAA batteries EACH. I got rid of all the batteries by connecting all three candles to a 5V adapter, or it can also work on a powerbank. This was the result: ]

Now, how to make a straight key with that set of teeth. I took a few pieces of wood in my garage and started tinkering ... this is the result:

Two bolts (through top and bottom) touching each other do the keying. The spacing is adjustable with the top bolt. Keying force can be adjusted by removing some wood from the top plank, but I think it's just right as it is now. 

The teeth were simply glued to top and bottom with hot melt glue.

No springs attached !

A groove in the bottom houses the wires,  and the wire is fixed with two rubber pads, pressed into the groove.

ON7DQ Friedrichshafen 2025 - Day 11

From Yutz (FR) to Ostend (B), 374 km

To split the ride in two and have some rest, I chose a POTA Park near Brussels

POTA BE-0508 Laarbeekbos

I parked here , pos 50.884172, 4.302819
First I had my lunch, and to quickly set up, I put up my 5.6m Chinese vertical on the fence, the top of the antenna resting between the leaves of the trees. The 4m counterpoise was weaved along the fence.

After 10 QSO's and 1 P2P, it was time to get on the road again ... 

I arrived home at 16:00 local time, and that was the end of a wonderful 11-day SOTA/POTA trip.

I hope you enjoyed the report, and found the information useful.
See you on another trip soon!

73 de Luc, ON7DQ

Go back to overview HERE

 

ON7DQ Friedrichshafen 2025 - Day 10

 From Karlsruhe to Yutz (Thionville), 225 km

DM/RP-411, Hohe Derst - 561m, 4 points

I got some good info from Ingo, DH5ST, about how to get to a nice operating spot for this summit.

Parking is here 49.087561, 7.925953, it is shown on the maps as Wanderparkplatz "Drei Eichen", and can be reached via a narrow forest road, drive carefully and hope that nobody comes from the other direction, hi.

The forest road starts here 49.097757, 7.941459, along the L492 in Böllenborn.

From the parking, follow the paved road upward, but after a big bend in the road it gets a bit tricky : you come at  a point where you can choose from 7 different tracks ! See map below.

The paved road (white line) will take you to the real sumit, near a transmitting tower. But Ingo advised me to take the narrow track just left of this road, it is steep and overgrown in some places, but it takes you via the "Ritterstein" , and finally to a nice  spot in the activation zone, where you will see two benches.

Ritterstein

The choice was not difficult, one bench was in plain sunshine, the other was partly in the shade.

From there, you also have a nice view of the area.

I stayed QRV for 45 minutes, and made 31 QSO's, with 5 S2S.

On the way to the next summit, I stopped for some shopping at the Zweibrücken Fashion Outlet. Parking position is 49.232226, 7.402977 if you're interested.

FL/VO-166, Stromberg - 314m, 1 point

This is an easy drive-up summit. Set your GPS to this position first:  49.454426, 6.347420, and take the Rue Saint Vincent, going in the North-Eastern direction. It becomes a narrow forest road, but continue on until you reach the summit at pos 49.449709, 6.355749.

I arrived there at 15:55 local time, and it was hot hot hot ... 35°C!
Lucky for me, there is a solar installation on the summit, where I could park in the shade, and setup my station a bit further under the shelter. The large grass field is ideal to put up big antennas if you wish.

From the summit you have a wonderful view over the area and the Moselle river. You will also see the nuclear plant of Cattenom to the South-West.

In half an hour, I had 10 QSO's in the log, no S2S but 2 P2P, since this summit is also valid for 2 POTA references. Working EA8ADS was one of the few DX contacts on this trip.

I really wanted to stay the night somewhere in Luxemburg, but couldn't find anything suitable. So I had to make a small detout to Yutz near Thionville, in France.

Tomorrow I'm going home, no more summits but just one POTA activation halfway the road.

Continue reading ... go to DAY 11

or

Go back to overview HERE

ON7DQ Friedrichshafen 2025 - Day 9

Trip from Friedrichshafen to Karlsruhe, 297 km

Another hot day was promised!

After I loaded all my stuff from the apartment into my car, I was already sweating like hell, despite it was "only" 24 °C. I left at 09:10 for my first summit.

DM/BW-064, Heersberg - 964m, 10 points

After a 110 km ride through heavy traffic, I arrived at the parking spot at 10:55.
The parking spot is at pos 48.237385, 8.932003, in the village of Burgfelden.

Lots of space, and some trees to let you park in the shade, the temperature was already 27°C.

The walk to a spot in the AZ takes only 15 minutes. I used the same location as suggested by Phil, G4OBK. Only difference ... I couldn't use the nice table to operate, it was simply too hot.

So I found some shade at the small building nearby.

17 QSO's in the log with 5 S2S.

Mystery object

Near the benches and table, I found this strange object. Anyone know what it is ?
Drone launcher, UFO landing platform, SOTA antenna mount ... ?

After the activation, I had a quick picnic near my car, then it was time to start driving to ...

DM/BW-147, Gespaltener Fels - 1000m, 10 points 

This summit is just 20 km to the West from Heersberg.
Being there on a Monday, I could drive up to the parking spot at pos 48.218898, 8.844863, marked on the maps as "Grillplatz".
I'm sure the good shepard would watch over my car ... so I started walking.

The first part is in the woods, but the last part goes over an open grass field, so take sun protection and enough water.
After 30 minutes I reached the summit, and found an old bench to use as an operating spot.

Again , I made 17 QSO's here, with 3 S2S.this time.

After this, it was a 100 km ride to the next one, and then another 66 to my AirBnb in Hagenbach near Karlsruhe. So I better got going ...

DM/BW-054, Hohloh - 984m, 10 points

This is an easy, almost drive up summit.
Best parking is Parking C , at pos 48.707374, 8.427898, I arrived there at 16:40.
Again, being late on a Monday afternoon, the parking was almost deserted, it may be different in a weekend. From there it's only a straight 800m walk with 45m ascent.

At the summit is a hut, which I used to set up my station, the antenna was outside the hut of course.

Several people came by to climb the tower, but nobody paid attention to my operation. 

Here my cosy indoor shack ...

I had to hurry a little, so made it a short activation. In just 15 minutes I had 13 QSO' s in the log, and just 1 S2S, still a good result.

 I left the parking at 17:30 local time, got me some food in a supermarket, and arrived at my AirBnb at  19:00. Temperature had risen to 35°C ... good that I still had that fan 😄

Continue reading on DAY 10

or

Go back to overview HERE