HF portable June 2025

Last Tuesday I had the chance to spend a couple of hours outside in a location where I could do some portable QRP HF. The setup is my usual FT817, end-fed thrown over a tree branch, homemade tuner and CW paddle.

Many flies joined me on the table and many mosquitoes enjoyed my ankles. I had 3 QSOs on 20m, a local friend, a French station in CW and a Belgian in SSB.

I might want to change the capacitor in the EFHW tuner and use a more robust box since the antenna wire pulls quite hard. Weight is not an issue since this location is 50m from the parking lot.

 

 

DC plug for some Yaesu radios

I am not sure the Internet has already found out, but some Yaesu radios share the same DC plug size. In my case I discovered that I can power/recharge a VX-8E (VX-8R) handheld with the FT-817 DC cable. The polarity is also the same, with +/positive in the inner contact.

If I wanted to make a spare cable equivalent to Yaesu E-DC-6, the plug size is 4.0x1.7 mm and it is easily available from multiple sources.

I have also noticed that the universal laptop power supply I own, with exchangable heads and several output voltages, has a compatible plug. Althought it might not be an RF-friendly power source, it offers a way to recharge the radio battery. Make sure to set the voltage to 12V.

Edit.  You know what? Looks like Yaesu loved that DC barrel size, and it was used also on VXA-210 and VXA-220 aeronautical handhelds. Just look for E-DC-6 and see it yourself how many devices.

Not only that, even the Albrecht AE 2990 10/11/12m all-mode handheld uses the 4.0x1.7 mm barrel connector! Or something very similar not documented, but this one works.

Honey, I shrunk the loop

Like most amateur radio antennas, magnetic loop do not receive positive looks from relatives, neighbors and by-passers. My 20m magloop on the balcony could be seen by us and very few other people, but would still hurt the eye when looking out in that direction.

So, I shrunk the loop, from 2.3 m circumference to 1 m. Of course it now operates on a different frequency: 50 MHz. It has been chosen on purpose, since May and June are the Sporadic-E ("ES") season. Thanks to the lockdown and work-from-home situation I stand more chances to be in the shack when ES hits, unpredictable as usual.

I changed the tuning capacitor from an air variable to a RG-58 coax stub, meant to withstand higher voltage, thus input power. It did work on the 20 m loop, but it doesn't on 6 m.

This is what happens. On the VNA the antenna is perfectly matched. On the transceiver the SWR meter is happy.  Then, if you keep the key down, SWR increases to well over 10:1. On the 20m loop the stub tip would produce a bright white spark when I raised the RF power above 30-40W, which was solved by making a bit more space between the braid and the inner conductor. On 6m there was no spark: the RG58 stub would heat up and change the impedance.

IMPORTANT. How to check if it heats? Either use a thermal camera or touch the stub once that both these conditions are met: you have produced the SWR increase AND you have have switched off the transceiver completely (so that it doesn't transmit while you sense the temperature with your fingers).

This is a sign that the voltage at the open loop side is high, so the match is good. Also, being the circumference close to lambda/4, the efficiency is higher and the same holds true for the voltage.

The maximum power the loop can withstand depends on the environment temperature, but the heat produced with 5-10W is negligible and has no effect. At least at 20 °C!

Let it loop

Being in COVID-19 lockdown gives me the opportunity to be on the air during the day, once work time is over. I tried a magmount 20m Diamond mobile antenna on the East-facing balcony, but I managed one contact with my sloppy CW. Well, RBN receivers had me around Europe. But no contacts were possible in PSK31, neither a report on pskreporter service!

So I moved to something different: a magnetic loop. It had to be build with readily available materials: a hula-loop diameter 70 cm (then not needed to keep it in shape), 4 mm solid coax cable (it's too thin for a permanent loop!), a dual-gang air variable capacitor (two sections in series giving 10-130 pF) and FT817 to tune the antenna sur place.

The feeding loop is just a piece of coax "1/5th of the main loop" long. From the coaxial line, the center goes to braid of the small loop on one side, and the coax braid to the braid on the other side. In other words the feedline is terminated with a 44 cm long loop made of thick wire.

It took me a couple of hours to build. Most of the time was spent looking and implementing a solid mechanical solution for the variable capacitor.

The picture shows the resulting loop. It tunes 30 to 10m. On 20m it is about 20 kHz wide for 2 SWR bars on the FT817.

How to cut potentiometer shaft

I have always been very bad at finishing my projects with a proper enclosure. But something meant to stay like a CW keyer needs a good home. That's the case of my reproduction of the excellent K3NG Arduino keyer. The main challenge for me is drilling holes, and the keyer needs at least 6. I had an unused L-C tuner and its box was pre-drilled too!

When everything was almost inside I noticed something I had forgot: the long pot shaft! The knob on the very top doesn't look too nice, does it?!

No way I would take everything apart, and a quick web search revealed few methods to cut it out. The simplest solution was to use a pipe cutter: no electric tool! I passed over the requirement for a vice, crossed my fingers and started turning around:

At this point I held the lower part with pliers and snapped away the top length of plastic:

The final result is nice and I have a CW speed potentiometer, that is much more practical and immediate than "tap here n'there" methods.

Then another problem arose: the 3.5mm panel plug is too short for the box thickness and I cannot put the nut on!

Like a child on 70 MHz

The day after Italian HAMs were allowed to use 70 MHz band again for a few months in 2014, I reconnected my transverter and erected the dipole on the balcony. I tuned the band checking the local beacon with my ears and looking at the DX cluter with my eyes: the band was open.
All of a sudden I heard someone distant having a QSO. Disappeared. QSB was very fast. Then another voice, very strong, GM4JTJ, that came back to my 5W SSB balcony signal! Hooray!

I felt like 25 years ago, when as a child I worked my first DX'es on CB channels. I kept tuning, calling CQ, tuning, trying to ignore the female voice(s) calling me for dinner. But this time it wasn't my mother's voice, it was my youngest daughter's reminder that dinner was on the table.

I walked to the kitchen, explained that a unique event was going on, an event that happens 4-5 times a year and doesn't last long. When returning to the shack I got the familiar "don't complain if there won't be food left for ya", this time thrown at me by the older daughter.

It was a funny parent-child-parent role inversion.

In the following days I came up with a quick way to explain propagation. You must have seen Stargate movie to understand it: sporadic-E looks like a wormhole opening to some random part of the world.

Now waiting for another randomic wormhole...

Newly built memory keyer (based on K3NG work)

This is the 400th post on this blog!

One year and half after discovering my old memory keyer had been dipped in battery chemicals, I finally managed to assemble a replacement. This time I reproduced K3NG's excellent work based on Arduino. I did my little code adjustments to get it working with an Arduino Leonardo clone (ATmega32U4), and now it works the way I need it to.

The circuit pictured still misses the internal buzzer for audible feedback, otherwise it is 100% operational.

Now it requires proper housing and power supply. I do want to check its current consumption, just to know how long a battery will last.

Even though the box will need to be "large" to house all those controls, this keyer is a perfect companion for FT817, which lacks memories in its internal keyer.

First time in Japan

This morning on 12 m I got my first reply from JA. OM JF2IWW was 539 with deep QSB, but he copied my 5 W and gave me a 439. Then fading took him away and I missed most of his message, but I heard his final greetings.

I would like to know more about his power and antenna, but there is nothing online.

Musings about going Bluetooth

I occasionally receive a question about transporting bidirectional audio over Bluetooth and not only CAT controls. The answer is "technically possible", but there are two possible scenarios.

Voice

This is the case for handsfree operation, be it in on the move or just around the house. Using the VOX this is possible, but on the RTX side we need a Bluetooth "master" device. In order to establish a Bluetooth link there must be a master initiating the connection towards a slave. Since all in-ear handsfree earphones are "slaves", there is need for a master device connected to the transceiver: I have not found yet a master bidirectional audio Bluetooth module (maybe the one mentioned in an earlier post?!).
The discontinued Jabra A210 seems to be the only device with such characteristics, and it must be modified in order to work with a transceiver.

Digimodes

Since digimodes are generated in the computer/tablet/smartphone, we already have a master Bluetooth device. So theoretically any handsfree BT earphone would work. Besides difficulties in modifying such tiny electronics, I have been told that the audio encoding and compression operated by BT audio devices introduces unacceptable noise and phase distortion. The former affects the ability to copy weak signals at our antenna, the latter makes it impossible to work phase-based digital modes (PSK31, for example, while RTTY would probably work).

First 23 cm QSO

The first 23 cm monthly activity contest date came too soon. It was my first opportunity to test on the air a 20W transverter and 23 element beam. The antenna went up easily and I used the TV coax already installed plus two BNC-N adapters: losses everywhere!

The 23 cm antenna on the balcony, beaming 60°

Apart being away for a long time from an SSB contest, I immediately felt restricted to the 3000 Hz bandwidth of the FT817, while for the last 12+ months I was able to see 2 MHz of RF spectrum.

The RTLSDR does offer an advantage. Even though I have probably not missed a QSO, I was thrown back to the good old days of search and pounce with the VFO.

I was able to speak with all the people I have heard last year. All signals were very strong, with the ODX being S9+60. Curious band!

Next month I will try to arrange more room in the shack/lab desk so that I can switch the antenna to the SDR when done with QSOs: at last I will be able to compare the two RX solutions.

A bare Bluetooth module for audio transceive

While shopping for serial (CAT) Bluetooth modules, I came across a not-so-documented not-so-popular circuit sold as "XS3868 Bluetooth Stereo Audio Module".

The heart of the circuit is the OVC3860 chip, whose datasheet is hard to find, but specs look promising.

As I understand it, the XS3868 module is somehow what you would find inside a large Bluetooth headset for a cellphone, featuring playback buttons, volume control and a Li-xx battery charger. It runs off a 3.7 V Lithium cell and it can be controlled with AT commands via an embedded serial port.

Theoretically, if the resulting audio signal is not too distorted, this circuit can be used to build a wireless audio interface between a computer (Bluetooth master) and an RTX. This is most interesting for digital modes.

First tests may complete in late February 2014.

At about 7 USD, this is a worthwhile experiment for the future of HAM radio, HI.

Monitoring transverter output

Without a correspondant to try a QSO on the air, I had to test my 70 MHz transverter output with my own equipment.

First of all I used the RTLSDR dongle to record my output, so that I could easily play it back afterwards for a self-audio-quality check. Easily done, with the transverter transmitting into a dummy load in the shack.

Then I wanted to check for harmonics at 2x, 3x and so on: the RTLSDR tunes much higher than that. So I moved the output to the 70 MHz dipole and started calling CQ, while RTLSDR receiver was running on the computer screen. Look at what appeared:

That's the fundamental and two noticeable splatters about +/- 200 kHz away, about 30 dB below the center frequency. What the ...?!??

Checking at 140 MHz and 210 MHz the remaining signal was not too strong, spurs obviously following. If I transmitted in FM there was no splatter whatsoever, nowhere.

That's when I remembered an article by SM5BSZ about the (mis)use of ALC in the FT817 (search for "The abominable ALC"), which creates heavy splatters, especially at lowest power settings. While they are barely noticeable in the HF noise, they pop up in VHF and do annoy neighbouring stations!

So I checked the FT817 output at 144 MHz USB, 0.5 W output, and spurs were there. No surprise. My RTLSDR does not tune down to 29 MHz, my 4 m transverter IF output, but I bet the situation is not different.

Since you always have to doubt the bounty of your test equipment, and a 15 USD TV dongle should not be over estimated, I cross-checked with a true receiver: splatters are generated for real.

A quick check at 5 W output has shown that the FT817 doesn't behave acceptably better. One solution, that would improve my '817 in any case, is to change the ALC timing with a hardware mod. Otherwise I will have to drive the transverter with the IC706MKiiG, but SM5BSZ pages contain a warning about a full-power spike when PTT is pressed...

Transverter 29/70 TX'es fine

In a careful hurry I checked the 4 m transverter if it is suitable for SSB traffic.

Since it must be driven with 100 mW, a 7 dB attenuator was built so that FT817 500 mW would not fry the mixer stage. A "real-world" 7 dB Pi-attenuator consists of a 2W 120 ohm resistor across, 47 ohm straight, 120 ohm across. I used standard carbon resistors and a quick check with MFJ-259 reported a 1.2:1 SWR max up to 170 MHz.

With full manual switching I listened to my whisper transverted to 70 MHz on a different receiver and it sounded good.

This was the "GO" signal to start planning for a sequencer (probably embedded into one of my I-F-R-K accessories) and a suitable box: this time I will have to do the mechanical work!!

Transverter 29/70 arrived and switched on

The "ten to four metres" transverter has arrived from Ukraine. The very first impression is that it is indeed SMALL! A picture-to-real comparison with the original 10-to-2 m transverter shows that coils are different, so it has somehow been retuned to 70 MHz. Look at it on a 5€ note:

First on-air test was the reception of the local beacon. I started closing the output on a 50 ohm load "just in case" (yes, I know the load shown is not able to handle more than 0.5W). Then about 4 m of RG58 going to the FT817 tuned on 29 MHz: the local beacon was coming through S7, with the dummy load as antenna! Actually, dummy load or not, it made no difference.

The transverter circuit is very very very simple (and I have spotted one error on the included diagram), but the RX chain is hot. Using the same coax length on the IC706 tuned to the beacon frequency resulted in the same signal strength. So, apart from RF leakage, it is a (good?) sign of life.

Transverter 29/70

While searching online for parts for a 70>23 cm tripler I came across an auction for a 10m to 4m transverter board. Just the fully assembled board and an A4 sheet with instructions.

It is supposed to output 5W on 70 Megs with 150mW drive on 29 MHz. It should be all-mode. It needs a heatsink, housing, wiring, IF attenuator and RX/TX sequencer.

Looks like a good companion for the FT817. Time will tell, since I bough one of those.

Edit: (At the time writing there is one board left in Ukraine)

IFR, Knob evolution

2012 Xmas season has taken me back to the IFRK code, so that transverter functions would be finally included, paving the way to a long-awaited public release. Curiously, after almost 3 months without looking at the source code, I was able to identify a simple way to support the transverter math.

The current IFRK state-of-the-art is:

• frequency computed down to 10 Hz resolution, like the FT8x7 display
• transverter LO 10 Hz precision
• maximum shown output frequency is above 21.4 GHz
• tuning knob supported!
• tuning knob has 11 steps and "fast" 10x mode
• direct dial; in transverter mode, only kHz digits can be inserted (1296.xyz.000)
• LO value <> memory location mapping
• FT817 proprietary functions for power level control and A/B/C repeat on IFRK display

In order to summarize current key mappings I have compiled a table with key functions (opens in new window).

Besides some cosmetics on the display and a thorough testing, I am planning to output in binary form the LO position and/or the band selected (2 bits each). These last features would control unused pins on the ATmega168 chip, so there will be no impact on existing IFR(K) circuits.

HNY 2013!

R1235 bypassed

After much thinking and no time to test the polyfuse solution, I opted to bypass the burned R1235 resistor in my FT817 with ... another resistor.

I picked an axial 16 ohm 1/4W which was at hand and soldered it in parallel to the original resistor. One lead goes directly to the MiniDin8 socket (PCB solderside). The other lead is held with an ugly blob of solder at the junction of R1235 with the bypass capacitor. I used heatshrink pipe to insulate resistor leads.

One remark about re-assembling the FT817. If you need to move/remove the bottom side PCB, the job is much easier if you remove also the top cover. That's because the mask around the microphone socket is then free to move.

No pictures taken this time.

I might get back inside the 817 and do a proper replacement, but now I am able again to continue the development of my Interactive Frequency Reader with Knob (that's display, keypad and knob all in one!).

Yaesu FT-8x7 CAT-to-Bluetooth dongle, a user's manual

I have composed, in the form of an online slideshow, a user's manual for my CAT-to-Bluetooth dongle (no download, no registration required). It shows technical specifications, words of caution wisdom and screenshots from the WinXP Bluetooth pairing process.

Use your keyboard left and right arrow to move between slides.

Locating R1235 on FT-817

Two weeks ago I proposed a "play safe" procedure for testing the health FT-817's ACC port (Vcc line only). If R1235 is blown, what can be done? First let us find out where it is.

Remove all power sources to the FT-817, including the internal battery.

Unscrew the top cover (note, this procedure is the same of the "optional filter installation") and gently unplug the speaker cable: a shiny PCB full of SMD components is exposed. Well, that's not the correct side for R1235.

FT817ND without top cover.

Remove the five screws that hold the board (red circles in the picture above), the flat cable near the DATA connector (yellow rectangle) and the two coax connectors (yellow circles). Now the PCB can be lifted and rotated 180° above the front panel.

Check out the video to understand where you have to look for R1235 on the bottom side of the top board.

 

And here is an annotated picture of the area of interest:

Area of interest to locate R1235

It is tiny, isn't it?

A Vcc line shorted to ground though this 10 ohm resistor for a couple of seconds increased the resistance to about 7000 ohm. Voltage without load is the same of the supply, but as soon as some current is drawn the voltage reading drops.

Fix? Stay tuned.

Checking FT-817 ACC port health

Probably not many FT-817 owners know that the rear ACC port is not much tolerant to misuse. This is particularly the case of the +V line protected only with a tiny 10 ohm 1/8W 1/16W resistor (R1235): if this line is shorted to ground the resistor blows and goes open circuit (I've already heard of two blown resistors).

So, even testing the health of the ACC port +V line can be dangerous. But since that line is always connected to +V of the power supply or internal battery, you may use the following safe trick.

Power off the FT817. Unplug the internal battery. Remove any external power supply but leave the power cord connected to the radio. Get hold of a 1.5V cell and find out how to use it to power the FT817 (button cells can be held in place with a clothes peg).

The RTX will obviously not power up, but an accidental short circuit on the ACC line will not damage immediately the internal 10 ohm resistor (P = V^2/R = (1.5)^2/10 = 0,225W, about 1/4W instead of 14W at 12V!).

Extract +V and GND lines from the ACC socket with two insulated wires and measure voltage across them with a voltmeter. If you read your battery's voltage out of the ACC port, then everything should be fine.

You may also try to guess the internal resistor value, in case you have doubts it was damaged before. How? Connect a 10 ohm resistor across your loose wires and measure the voltage: it should be half of the battery reading. Or use Ohm's law to do the reverse engineering.


This procedure only tests the health of the +V ACC port line, not the whole ACC socket health.