This is a updated collection of easy to build projects for radio amateurs and swl's. See all my projects in the OLDER POSTS down this blog.
Have fun.
73' John

Wednesday, February 11, 2015

1:4 Voltage balun 3.5 - 30 MHz

Flat SWR  from 3.5 to 30 MHz with 8 double turns on a 4C65 or FT140-61 toroid.
SWR  1: 1.1 in the centre.
The 4C65 was used  because it was in stock . A FT240-43 with 12 turns wil provide a almost flat range from 160 - 10m.

Sunday, January 25, 2015

ZS6BKW galvanic feedline isolation

Connecting a balanced antenna like a ZS6BKW to a coax feedline can cause serious problems be means of a high noise levell,  for the cabinet of the transceiver is connected to the antenna. This means that all nearby QRM is transported to the trx by the coax schield. A galvanic isolator helps reducing this noise. 11 turns  of side by side 1.2 mm magnet wire on a FT140-61 or 4C65 toroid  formes the coupler. The coupler is placed at the low-Z feedpoint in the balanced feedline of the antenna. SWR is 1:1.3 at 3 MHz and 1:2 at 30 MHz.  A additional line choke is a good option.
I used the 4C65 toroid for it was in stock but a FT140-43 with aprox. 8-10 turns  might even be a better choise.

Friday, August 22, 2014

Single knob Travelloop 6.5 - 31 MHz

This small loop can handle 20 Watts from 45-10m . Loop circumference is 2.5 m with a Faraday coupling loop of 50 cm . Sticks are 6 mm glass fibre ( kiteshop).The 2 vertical sticks are 41cm and the suports are 34cm long.  A 2 x 500 Pf tuning capacitor with the sections put in series is used for tuning. Because of the high Q , a 1:3 reduction is convenient but not mandatory . The loop is made of RG-213 with the shield and centre soldered together. Highest SWR is 1:1.5 .  Despite of bad conditions, contacts were made troughout Europ with 10 Watts SSB. The Faraday coupling loop is made of RG-58 and is bend to a slightly horizontal oval. Reducing the space between the loops leads to a drastic improvement of the swr / return loss.
40m PLOT

Plot 14.200MHz after coupling loop modification.

Improved coupling by reducing the space between the loops . I used a piece of U-shaped plastic for the looprest.
Although fast tuning is a big plus with this loop, the overall efficiency is less than the twin capacitor Travelloop further down on this blog. The broadband coupling loop makes a perfect match impossible. A perfect match can only be made with a 2 capacitor coupling . The efficiency on 40m. is only about 5% but enough for cw. The fun realy starts at 30m. and up. On 20m.the performance is verry acceptable . On 10m.efficiency equals a full size 10m. band dipole and amazing contacts can be made with a verry low noiselevel.

Saturday, August 02, 2014

Cheap 5A power supply for the FT-817

The Toshiba PA3083U-1ACA laptop powersupply deliveres 15V at 5A.without any noise.
It has been my travell supply for more than 3 years now without any problem. They can be found on Ebay for fair prices and need oly a new Molex plug to match the set.

Tuesday, February 04, 2014

Mini Travelloop for receivers

Portable shortwave receivers are normally equiped with short telescopic whip antennas producing  a poor  reception. This option has more selectivity and a better impedance (low Z) over the 5-21 MHz range. A 2-section capacitor can be used wit a larger loop aswell. Construction is easy and a plastic enclosure should be used. If you switch a 1200 pF capacitor over the loop base you can tune 80m. aswell  (-:  The loop is made of 1m. 3mm brass or copper wire.
Even a preamp with a low Z imput could be an option.
22 pF to the frame and 100+22pF in parallel to the coax
 Compact design

Thursday, November 21, 2013

Traveltuner 3.5-30 MHz

There is no known qrp tuner for both small magnetic loops and longwire antennas for sale so here is an idea for your next holiday .  A 2.5 m circumflex loop wil cover 6.5 - 30 MHz  ,  a 5m loop wil cover  3.4 - 8 MHz. To tune a loop tune C1 for resonance and C2 for low swr . To tune a longwire switch to the coil for the desired band and tune C1B for best swr. The coil can be replaced by a T130-2 toroid with 50 turns 0.8mm enamelled wire on a 12 positions rotary switch. Use a plastic cabinet for this tuner.
Tuning capacitors :

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:
 A series 3000 Multiplex RC transmitter was the donor for the tilt stand, but US builders can find one here :
Here is a tuning range video :


The latest boards have a litle bug causing a shortcut to ground of C37 and R22 .This prevents the noisefilter from doing his job.  Before installing C37, take a  4mm drill and make a smal cone in the board surface to remove the ground connection .

I noticed that the noise filter even causes the noise levell to rise , so i desided to remove C37 and R22 permanently.
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. without any spurs or birdies. I kept the old counter for this made the DDS unit smaller and easyer to mount. At trials the new counter was only atached for the DDS setup in the generator mode , from 10.000 - 10.350 MHz without IF ofset . The IF ofset is already programmed in the Hendricks counter. Once the DDS was programmed the bleu Iler counter was removed.
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.

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 at the DDS power pin is the solution 

Friday, December 21, 2012

Adjustable bandwidth

A  MAX7400 is an 8th order elliptical filter giving a 100 Hz to aprox. 3000 Hz tuning rate. It  means much more selectivity in many homebrew receivers.
The output can drive a LM386 . This filter is a must have for cw operators with simple ssb receivers.

Thursday, April 19, 2012

Multiband end fed antennas 3.5 - 30mHz

The picture shows 1 turn to much in the secondary winding (red)

This is a 200 Watt PEP step up transformer for end fed full and half wave antennas without radials, designed as a 200 Watt PEP upgrade by PA0EJH for the originaly Par Electronics designed 25 Watt HF endfedz multiband end fed antenna.
The original design has a 27/3 turn ratio ( 1: 81 ) on a small 43 material toroid, but the larger toroid has more wire so the nr of turns had to be reduced for max.efficiency on 10m. The coil now has a 16/2 ratio  ( 1: 64 )  For max. performance the 2 turns to ground must be twisted . The 100-150pF capacitor gives a better match on 10m.and both windings start at the ground side of the coil .Don't try to stack toroids for more power for this will increase  overall inductance . This makes it impossible to tune the high bands. The best results are obtained with a small toroid.....The 3 band  antenna has a length of aprox. 10.1m. followed by a coil of about 34 uH  ( 90 turns 1mm enamel wire on a 19mm pvc tube ) and a endpiece of about 1.85m , offering you a perfect vertical or horizontal antenna for fieldwork at 40 -20 and 10m. There is also a 5 band version with aprox. 20.35m wire followed by a 110 - 120uH coil ( about 260 turns 1 mm cul on a 19mm pvc tube ) and a aprox. 2.39m. endpiece. Use a longer wire for testing for surrounding object can interact .
*** Start tuning the antenna by tuning the long wire at the high bands  with the coil and the endpiece attached, for the coil interacts. Many people do this the wrong way ! Don't use an other type of toroid like the nr 2 or 6 mix for the AL value of these toroids is far to low and will result in heavy losses.  ***
 This antenna works on 80 - 40 - 20 -15 and 10m.without radials and has a verry low swr combined with a low noise level. Keep in mind that 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.

Tranformer with 150pF and 3K3 resistor to ground

Transformer on a smaller FT140-43 toroid for max. 100 Watt pep

Update 2014-03-21
I live in a apartment on the first floor so you can imagine my antenna problems....
My balcony however is 10m. long ,so i mounted a horizontal endfed antenna without the coil, for 20-10m on the wooden windowframe . Because of the capacity of the wood and the paint overall length was reduced to aprox. 9m.. but provided a near 1:1 swr on 20 and 10m.
First contact on 10m. was with 5B4AHL (5-9) on cyprus folowed by 9K2QA (5-9) in Kuwait  and 4S7VG (5-8) in SRI Lanka despite of a huge pile-up. This antenna is going to stay HI.

Sunday, July 24, 2011

No ground antenna for backpackers, balconies or plastic car bodies

A common problem with backpacker or balcony antennas is finding a good counterpoise. Also cars and caravans with a plasic body are a problem. Althow nothing beats a set of resonant radials, the shown solution offers a 1/4 wave stub that wil create an artificial counterpoise. The mobile antenna mount must be isolated from any metal by a epoxy or plastic sheet and a normal T-Connector is used at the antenna feedpoint.  Be shure to shortcut the end of the stub. The length of the stub in meters equals  1/4 Lambda x 0.66 (this is the velocity factor of 50 Ohm RG-58 ) or can be calculated by deviding 50 by the frequency .So  if  you need a stub for  14 MHz the outcome is 3.57 m. but this length is not critical. The setup can be easily mounted on top of a rucksack. On a balcony the stub can be layd on the floor.

Wednesday, June 29, 2011

Z-Match 100 and mini Z-Match


This is a one for all antenna tuner with wide range tuning on all the HF bands. The tuner is based on a G3WQW  design. A T200-6 should give a better Q but the T200-2 was in stock and gave me sufficient tuning range.The final version has the T200-6 toroid and a metal cabinet to provide a better HF isolation. Being a high-pass type it contributes to less receiver noise.  The capacitors are radio types and can be used up to 150 Watts. Using a metal cabinet needs a "floating"mount of the input capacitor. More info about the Z-match design can be found here
Tuning capacitors :

The QRP 160-6 m. mini Z-Match with a T130-2 toroid in a matal cabinet. Polyvaricons are used for tuning within qrp limits. By switching a  270-500 pF capacitor over the left side of C2 (2x 500pF)  the tuning range can be extended. It's possible to tune a doublet antenna on all HF bands. Together with the FT-817 it makes a great qrp combo.
 The mircro Z-Match with 12x5x3 cm ultra portable for 80-6 m. In this tuner a nr. 6 material toroid was used. There is still some room left for a tuning indicator....

QRP tuning indicator . A perfect match is indicated by a bright shining LED , suitible for QRP only. Can be mounted in any QRP tuner at the antenna output. Gives a better reading than the FT-817 internal swr meter.
Another mini Zmatch i made for the field.

Travel loop antenna type 40-10 and 80-10

Haunted  as many  others by radio interference and  noise I started looking for a wideband portable antenna . Soon I became focused on a magnetic loop antenna. The only catch was the method of feeding by a Faraday loop , it made the project hand sensitive …. In the Rothammel Antennabook I found a complete different way of feeding made by capacitors .
This was a big  improvement and made a perfect match possible between 6.5 and 30 MHz.
Both tuning capacitors come from old AM radios and because their  sections are switched  in series , they can be used up to 30 Watts without arcing. They interact so it’s wise to make some markings on the front for fast tuning.
The loop is made of RG-213 coax and rests on a cross made of 6 mm. fibreglass rods( kite shop )
Inside the tuner is a shortcut between the centre and the braid of the coax loop to form a solid ring .  By simply adding a second loop with a 5 cm.spacing and a switch to put the loop's in parallel or in series, the antenna becomes a 80-10 m. portable low power loop for travelling. The travelloop was born HI. It has been my travel companion for many years with many qso’s even far over the Atlantic.
Tuning capacitors :
GG8ODE added a smart tuning indicator , ideal for home made rigs without swr meter : 


 6.5- 30MHz tuner


Magnetic loop antennas can produce a high voltage that may be harmfull to your health.
Tune your antenna at low power and take a safe distance while operating .

Wednesday, June 01, 2011

20/11/10m.monoband end fed halfwave antenna

Working portable demands an easy setup of your antenna. The antenna also has to give enough punch at a low radiation angle without the need of radials.
The vertical end fed half wave antenna is my choice for it’s easy to employ and it's a perfect DX antenna . This antenna is grounded thus giving les static noise to your receiver.
A 20m. version is about 10 m. long and has aprox. 3000 Ohms at the feedpoint. So we need a simple tuner to reduce this to 50 Ohm .
Put 20 turns ( covers half of the toroid ) of 1 - 1.2 mm enamel wire on a T130-2 toroid with a tap at 3 turns from the ground .The first picture shows the first test setup with a 2.5 turn tap. You also need about 25 cm of thin Teflon coax (RG 178 b/u) that will act after tuning as a high voltage capacitor of about 22 pF.
The pictures explain the simple construction. The cabinet is a PVC type G302 made by Velleman.




Tuning : The trick to tune this transformer is to find the working frequency first by tuning the capacitor. Then we look for the the 50 Ohm point on the coil .  Connect a 3300 Ohm resistor from the top of the coil to the ground of the antenna plug.
Adjust the length of the open coax line until you reach the lowest VSWR in the centre of the band with an analyser. The coax will be about 23 cm in total resulting in  22pF .
Now remove the resistor and connect the antenna wire of aprox. 10 m. PVC coated copper wire. Tune the antenna for best VSWR by reducing it's length carefully. My antenna is 9.9m. long and is mounted on a 12.5 m. fishing pole. A near 1:1 VSWR  on 14.200 MHz can always be achieved ! Before tuning , fix the toroid with some hot glue and wait fore it to cool off. Beware of the high voltage at the antenna feedpoint , this can rise up to almost 500V at 100 Watts.

10/11m version
For 10/11m band  use 16 turns 1-1.2mm enamelled wire on a T130-6 toroid with a tap at 2-3turns.
A 15 cm piece of coax forms the capacitor. Antennawire length is aprox. 5.5m .

My first DX contact with a vertical half wave end fed antenna was with VK6MV in SSB using the long path,  with a 5-5 report.
 I was also able to work  Japan,Taiwan, Thailand, India, Indonesia, South-Africa, The Falklands ands. in SSB with good reports. 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. 
Good DX !

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

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