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:

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 detour 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

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Go back to overview HERE

ON7DQ Friedrichshafen 2025 - Day 8

The one with the flat tyre and  ... a second Mountain Goat !

It was Sunday morning, and I had planned a day trip to Bavaria, to activate two summits that I needed for complete : DL/AL-273, Laubenberg (1 point) and DL/AL-148, Riedholzer Kugel (2 points).
With 3 points, these two summits would have brought my activator score at 1999 points, just one point short of another Mountain Goat.

But my car decided otherwise. 
The evening before I got this warning about a tyre with low pressure, so I first went to check my car.
When I looked around the tyre, I found a screw, which must have caused the drop in pressure, but it was not completely flat.

Since my car no longer has a spare tyre, I phoned the Toyota Assistance number in Belgium, and must admit they provide an excellent service. Around 10:30, a man from German ADAC came by to repair the tyre ... for free ... and on a Sunday morning, GREAT!

OK, I could drive again, but by then, it was too late to start my planned trip, and I decided to go to the nearest summit, trying to keep cool ... it was already 30°C in the shade.

DM/BW-348, Gehrenberg - 754m, 8 Points

I drove to my regular parking spot near the summit at position  47.742628, 9.423206.
I verified again : there is no forbidding sign if you follow the Hinterharresheim farm road, which starts at pos 47.747471, 9.403920 along the Gehrenbergstrasse. The small road becomes a gravel road, called Turmweg.

NOTE : I heard a few activators call CQ SOTA on 2m, telling they were on a lookout tower ...

There is no lookout tower on the summit of Gehrenberg, the tower "Gehrenbergturm" is not in the activation zone. Also the place called Gehrenberg on the maps, at pos 47.7371,9.39977 is NOT the summit. All very confusing, I know.

I found a spot to setup a bit away from the real summit, where often walkers and mountainbikers come by, it can get busy at the top !

Even being hidden somewhat, I got several visitors, hams and non-hams alike, who were interested in my setup. One of those was a mountainbiker AND a HAM, it was Yannick DO9YAN. He was recently licensed, and came to activate the summit on 2m, using an FT70 and a 4-element Anjo logperiodic antenna (the same antenna that I sometimes use).

I made 30 QSO's with an incredible 15 Summit-toSummit contacts, WOW !
That made my day , but wait ...

I hadn't been paying attention to my score, so with the 8 points of this summit, I made it to second Mountain Goat a bit unexpectedly.
The honour should go to Harald, DG1YBN, who was my fourth contact. He called me from his mobile on 2m FM.

Not knowing at the time that I was already there, I didn't make any special pictures, also no champagne ... hi.

After being on the summit for 3 hours, I decided to go to my apartment and take some rest.
It was 32°C when I arrived there. Also, I had some preparation to do for the next day : a trip from Friedrichshafen to Karlsruhe, with more summits of course!

Continue reading on DAY 9

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Go back to overview HERE