This is a updated collection of easy to build projects for radio amateurs and swl's.
Have fun.
73 John

Thursday, April 17, 2014

Helical Loop Antenna for 20m. Window/Balconey use.

Always in surge for a better Window/Balconey antenna i found this nice Russian design by UA9JKW.
My copy is a little smaller with a 70cm loop made from 19mm.PVC. It has 650 turns 1.5mm PVC isolated electrical wire .Coil value is 134.6 uH. There is no need for a tuning capacitor and the feedpoint has a low Z . Power handling is  easy 100 Watts and the recieved signals have a verry low noise levell. This antenna radiates like a dipole , that makes it perfect for window use. I could make clean and loud contacts throughout Europe on my first attempt having bad conditions. At the feedpoint is a line choke made of a ferrite rod with 15 turns RG-58 , giving about 1000 Ohms at 20m.  SWR is 1.7 ( 83 Ohm X=0 ) at 14.200MHz with a sharp second resonance at 37.485MHz .( 50 Ohm X=3 )This little Russian is a big performer an will stay at my apartment window for shure HI

The effective line choke
First results with bad conditions

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 :

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.

Tuesday, December 11, 2012

LM386 on steroids

A problem with DC receivers is getting enough audio output. With a simple mod you can lift the gain of the LM386 to 34-74 dB .This is the ultimate mod for Pixie type transceivers. My Pixie needed a volume control after this mod  (-:

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 10.1m. followed by a coil of about 34 uH  ( 90 turns 1mm enamel wire on a 19mm pvc tube ) and a endpiece of 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 20.35m wire followed by a 110 - 120uH coil ( about 260 turns 1 mm cul on a 19mm pvc tube ) and a 2.39m. endpiece. 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 made by Tony PA3GWO 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, February 26, 2012

Coaxial half wave antenna


For those who don't like to wind transformers there is handy solution for making a have wave antenna for fieldwork on a 12m.fisching pole. Althow a coax stub is a little lossy , this antenna is easy to build and effective . My first contacts with VK and JA on 20m. were made with this antenna . The other half wave antenna further down on my page has more gain.
Other bands ( center freq. )
28.3 MHz : A 1.51m. B 25cm.
21.2 MHz : A 2.02m. B 33cm.

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 plate and a normal T-Connector is used at the antenna feedpoint.  Be shore 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 gives me sufficient tuning range. Being a high-pass type it contributes to less receiver noise.  The capacitors are radio types and can be used up to 150 Watts. I used a plastic cabinet but a metal type would provide better HF isolation. 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 :


 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 .

Saturday, June 25, 2011

Simple antenna analyzer 0.1 - 30 MHz

This is a verry simple but good working swr analyzer based on the LTC 1799 smd generator . Tuning is easy: Connect your antenna to the analyser with the meter at full scale and look with the 100K potentiometer for a dip on the meter.
Disconnect the antenna and push the set switch.  Now adjust the power for a 1:3 reading on the VSWR meter.Releasing  the switch will make the meter jump in to the right corner, but that's normal due to the simple bridgeform . Connect the antenna and read the axact VSWR. The first model had a 6.5 V power suply but this caused the LTC 1799 to warm up and drift. At 5V the current is low and the IC is stable.
Most components are mounted on the back of a little pcb , the rest is soldered directly on to the meter and " point to point ". To expand the range downwards to about 0.1 MHz , just put a switch between pin 4 of the generator and the ground. If you want to use a counter , put a 1K resistor in series with the connector. Those who want to build in a counter can replace the 100 K potmeter by a 10 turns type and omit the presets.A verry small counter is available by Hendricks QRP Kits  If you are not using a counter , a tuning scale can be made with the help of digital receiver. By lowering the value of C1 the amplitude can be reduced so a more equal power setting can be obtained over all the bands. The meter should have a 100-200 uA reading. PE1IWT did an interesting mod on this analyzer project , you can find it here .It's in Dutch but the pictures explain it all. This versatile instument offers the novice radio amateur a lot of help with his antenna and balun projects .

1:1 PCB
Not to scale alternative pcb suggesture made by carving with a steel scribe
Wil need 2 jumpers to complete  


Wednesday, June 01, 2011

20m. 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, over the north and south pole, 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 reproduction of my projects.


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