Inductors are everywhere


Last update: 30-4-2017


Manual antenna tuner

29-4-2017: The antenna tuner is something you can do yourself, variable capacitors, roller inductor and knobs are all used components and they come from the Rosmalen radiomarket. The case is from CONRAD. Unfortunately there is no step counter with the inductor, but it has a stop which you can feel, so just count the left hand turns.

The antenna tuner (also called matchbox or antenna coupler) is a T-shaped network, the inductor does something like 35 microhenry (and probably more), and the capacitors are 30 to 300 pf. I mounted the components on wood because they need to be isolated from the metal case. Straps keep them on the board, and rubber thules are used to isolate the components from the metal case.

Performance-wise this tuner is able to adapt a 200 dummy load to 50 Ohms between 1.8 MHz and 30 MHz, I checked this with my antenna analyzer, it works. There is still space to store a 1:1 or 1:4 balun if needed (see entry on 7-5-2017 how I solved this). I’m not sure how much power the tuner can dissipate, the heat could go in the inductor, or, the capacitors could spark, etc. These capacitors are rated for 1200 Volt, so maybe we can go up to a kilowatt. (hi) (see the entry on 4-5-2017 that discusses where the dissipation could occur in the tuner)


Added on 4-5-2017, a note:



7-5-2017: Added a 1:1 balun to be able to handle twin-lead lines. Glue, polycarbonate, green tape, some banana jacks and an extra SO-239 case part do the job. The balun is separate from the tuner, you need a patch cable to connect the output of the tuner that goes to the right most SO-239 connector to the left most connector which is the input of the balun. The input of the tuner goes via the middle antenna connector. The balun is nothing more than a common mode filter. The magnetic field lines will stay inside the ferrite core, and any forward magnetic field leaving the tuner will cancel against a returning current that has an opposite magnetic field. This will work fine up to 30 MHz which is the design area for ferrite (it is a 4c65 material), beyond this point you need another trick to design your balun. I added some green tape around the 4c65 core although it is not strictly necessary, on both sides you glue two pieces of polycarbonate and with two parker screws you attach the balun to the aluminum back plate. Check the end result with an antenna analyzer and a multimeter.


Bill of materials:

  • three SO239 connectors, (relatively easy to get via stores in Rotterdam or Delft)
  • a 300 by 200 by 100 mm aluminum case (difficult to get, consider CONRAD)
  • two banana jacks and the matching case parts (a store in Delft had them)
  • a 4C65 ferrite core, you need it for HF and it shouldn’t saturate below 1 kW (got it from dx-wire in Germany, see also my article on the 1:4 guanella balun)
  • two 30-300pf variable capacitors (got it from a hamradio market)
  • roller inductor (got it from a radio market)
  • wooden ground plate, cut it as required
  • three tules, three knobs (hamradio markets have them)
  • 0.8mm or thicker copper wire (again, the ham radiomarket)
  • 30 cm of 50 Ohm patch cable with two SO239 connectors (I found a store in Rotterdam that I refuse to reveal, it is the only one in town, otherwise, CONRAD or radiomarkets)
  • various M4 nuts and bolts and straps (via any hardware store)

Options to consider: possibly an integrated SWR power meter, this is what I currently solve with a separate AV-CN600 cross-needle meter. The schematics is well known, however, I could not find a cross-needle microamp meter, the electronics is not very difficult, perhaps the calibration is.  Also, many transceivers already have a SWR/Power meter, so perhaps you can skip this step as well.

Last update: 7-May-2017

Chriet Titulaer 1943 – 2017

Op 23-April is Chriet Titulaer overleden. Hij was bekend van televisie uit de jaren 70 en 80 waar hij programma’s zoals de Wonder Wereld presenteerde.  Chriet had een Limburgs accent, en presenteerde het programma geheel in eigen stijl. Ik zat vaak ademloos te luisteren.  Het mooiste aan Chriet Titulaer is dat hij weigerde zijn Limburgse accent aan te passen, ze nemen me maar hoe ik ben, en anders zoeken ze maar een ander. En die vinden ze niet. Inderdaad, die hebben ze nooit gevonden. Chriet was een icoon uit de jaren 80, de Wondere Wereld werd veel bekeken en verschillende voorspellingen zijn uitgekomen. Op een gegeven moment liet zijn gezondheid het niet meer toe op televisie te verschijnen. De laatste paar jaren van zijn leven werd hij verpleegd in een instelling. Chriet, bedankt voor alles wat je achtergelaten hebt.

Last update: 24-April-2017

Easter Sunday fieldday

20m groundplane with low feed point, 10 minutes of work to get ready
40m ground plane with elevated feed point, this takes roughly 30 minutes depending on the weather, still have to figure out a better way of mounting the radials.
Fully deployed 40m ground plane, with PA2QXT Michael at the controls of the FT-857D

Last update: 17-4-2017

Field day with FT-857D

Got a second hand FT-857 last week, you can’t tell from the printed label whether it is a FT-857 or the D or the ND version, and also there are options like a TCXO and various filters. This one seems to be the D version because it has 60m and it has DSP filtering, and the CW filter is clearly there although I probably won’t use it. The receiver performs like a charm, maybe it seems somewhat noisier than the FT-991 but, if you play around with the RF gain and the filters, and if you listen on the headset then it is a very acceptable transceiver. No ATU, so your antenna SWR needs to be under 3 (probably), but to be honest, it is not very difficult to tune the antenna with a separate analyzer. Already did this for the vertical whip for 20m so I took the FT-857 in the field and made some QSOs.

FT-857 on the dashboard, it ran for 1,5 hour on a 3S lipo and I made a couple of QSOs. When the 3S lipo goes below 11.4 Volt I normally stop.
The whip got some tie wraps to prevent collapse, as you can see the weather was somewhat chilly, as was the 20m propagation on the 14th of April.
I modified the magnetic suction clamp from MFJ and added three radials, and a choke balun. For 20 m my car roof is not large enough to form a decent counterpoise, with the radials it works fine. The farmer did not care whether I was there with the car, we had a chat about his smart dog and antennas.

I like this set-up for in the car, it is easy to do, easier compared to getting the FT-991 in the field. The 857 fits on your dashboard, everything (cables headset, mike, ropes) fits in one suitcase, with the 991 I end up carrying at least a bag next to the suitcase. Getting my tuner to work with this set still needs some work, the LDG YT-1200 is designed for the CAT interface, and not a CAT-IV interface, so I need a conversion cable and some conversion electronics.

Last update: 15-4-2017

Westerbork, Dwingeloo and field day

Some photos made last week.

Close to one of the antenna’s in the Westerbork radio telescope array
Before Westerbork we had Dwingeloo, currently this dish is used by PI9CAM, see also
Fieldday 8-apr-2017
40m elevated ground plane
This is the antenna I tested on the 8th of April and I call it an elevated ground plane for 40m. The essential part is the 9 meter of wire that you loosely wind around the mast. Use an antenna analyzer to tune it. The simplicity is that it works on a glass fiber mast without any guy wires, the tripod at the base is sufficient to keep it upright, secure the tripod with three tent pins. At 9 meter with 5 turns the antenna is resonant in the high part of the 40 meter band. The length of the radials is not critical, the box is a straight through, it has a SO-239 connector, center pin goes to the vertical and there are several bolts with butterfly nuts on which you attach as many radials as you carry, I always carry four of them. At the end of the radials I fix them with a tent pin. The transceiver is kept 20m away with a RG-58u 50 Ohm coax cable which is light and flexible which is ideal for field activities, the transmission line loss at 7100 kHz is negligible, we only run at most 80W on the transceiver and we avoid any tuner. The transceiver was a FT-991 running on a 3S lipo battery 5000 mAh. I got the mast at dx-wire and the batteries at CONRAD.

Last update: 9-April-2017