Wednesday, October 16, 2013

Broad band 1:1 current/choke balun

In search of a no nonsence 1:1 balun i came up with this easy to build unit. It offeres a almost flat swr curve from 1 to 30 MHz  as you can see in the plot. Use 10 turns of side by side1 mm enamelled copper wire on a 4C65 or FT140-61 toroid . Teflon tape was used on the toroid but this is not essential.

SWR plot of the balun bridged with a 50 Ohm resistor.

Tuesday, September 24, 2013

End fed half wave high pass for 20m.

A common problem with qrp transceivers is a weak frontend . Most end fed antennas use low pass tuners causing high stress due  to strong signals coming from BC stations .
The High pas tuner used here helps to reduce these problems. Put 19 turns 1mm transformer wire on a T130-6 torroid to form a 4.8 uH coil. The trimmer used is a 60pF type set to about 25pF .  Put a 3.3K resistor between the antenna connector and the ground of the coax connector and tune the trimmer for resonance at 14.180 MHz.  Keep in mind that a thin antenna wire has a higher Z.
After tuning the unit connect the half Lambda wire ( 10.15m PVC covered stranded copper wire) and cut it for lowest swr. A  1:1.2 swr is easily obtained with this unit. The cabinet is a PVC type G302 made by Velleman. Every end fed / vertical needs some kind of counterpoise to push against and in this case that's the coax , so don't forget a line choke near to your transceiver.

Monday, June 03, 2013



My Iler 20 is finally oparational. The IF has changed to 4.000 MHz and the vxo has 10.250 MHz crystals.(Ebay)  The VXO coil now holds 64 turns no.26 (0.31mm) magnet wire and the tuning range with the polyvaricon is 14.129 - 14.246.4 MHz  with a stable signal .  C15-C18 in the 4 MHz cristal filter  are replaced by10 pF  to give a clear audio on rx and tx. As you can see, even the microphone was to bulky and was replaced by a home made model. Audio sounds verry good and the rf power is 6 Watts PEP at 13.8V. Also C28 was lowered to 33nF to get more high tones in the audio output, but that's a question of personal taste. I found a perfect little speaker named : Visaton K 50 WP , 3 Watt 8 Ohm that gives a real boost to the audio. In order to lift the microphone  input, R6 was changed to 470K. The mini counter comes from Hendricks QRP and was chosen for it's low power consumption and small size . Some humming interference can be caused by the display multiplexer of the counter but a small filter takes care of that:

The cabinet was ordered from Qrp Project in Berlin  It fits the board like a glove . For smooth tuning a 1:10 ball drive is added. Because of the 180 degree tuning range of the polyvaricon, only a 1:5 reduction remains. Ball drive reductors:

The BD135 driver heats up at long qso's . This heat can cause the standard vfo to drift ,especially in vertical use.  Connect the transistor to the cabinet  by means of a u-shape alluminium strip for better cooling.

The Iler kits  represent a modern and compact, easy to build alternative, to the Bitx and Taurus.
More info about this nice kit :

Update 25/11/2014
 Today i installed the Iler DDS generator. I expected some digital noise but surprisingly the audio stayed verry  clean after a small mod. almost without any spurs or birdies.
Tuning is verry smooth and accurate with the provided step levells.
Next mod wil be a simple NE 555 tone generator to generate a carrier for swr readings.
The final version with dds

Despite of a reasonably good working lf AGC, verry strong signals can produce a loud popping sound due to a massive overload of the LM-386 input. 2 Bat-85 Skottky diodes in anti-parallel over the 10K-B volume potentiometer and a 10K resistor between C32 and the potentiometer cure most of the problem.
The extra parts can be mounted directly on to the potentiometer.

The DDS adds some noise to the audio. A small 100uH choke and a capacitor to ground at the DDS power pin are the solution 

Iler base station 20m.  70 Watt

Disclaimer:I'm not responsable for any damage due to improper reproduction of my projects.