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

Saturday, November 12, 2016

DIY kits 70W SSB linear HF Power Amplifier For YAESU FT-817 KX3

It's time for a new project.   eBay link to the seller                   

My first impression : High quality PCB ( 100 x 50mm ) , all parts in the kit including 2 power FETs type IRF530N. Capacitors are 10nF instead of 100nF as shown in the schematic but that's not a problem.
However i had doubts about the claimed 70 Watts output at 13.8V  for these fets are normally fed with 24 - 36V to get a good modulation. The 0.5 turns windings are on the PCB by means of the tubes inside the toroids. Construction is easy but a lowpass filter for each band is mandatory. I used the low pass data from W3NON for a 7 element Chebyshev with standard value silver mica capacitors and T68-6 toroids. The provided wire for the power chocke ( 2 turns ) has a weak coating . It's better to replace it to avoid shortcuts .Start soldering the small parts and end with the transformers. Turn the potentiometer anti clockwise and slowly adjust the bias to aprox. 3.7V.
The test was in the original configuration at 13.8V and 5Watt FM input from my FT-817. Max. power was 80 Watt . At  2.5 Watt input the output was about 50 Watt at 20m.but the modulation was as expected distorded in ssb mode at the recommended 2.7V  bias voltage.
At 3.7V ( gate ) bias the modulation is verry acceptable. For the best modulation the FETs can be powered with 24-28V by means of a Step-up converter and a small mod of the PCB. Turn the potentiometer fully anti clockwise and set the bias carefully at 300mA through the FETs at 28V. The 150 Ohm resistors over the FETs heat up strongly at full power FM. It's better to reduce the drive power to 2 Watt when working FM/AM . Don't reduce the drive by reducing the Bias voltage for this results in a distorted modulation in SSB mode. Better use a power attenuator : Power att. calculator PA1B
Unfortionally the seller often forgets to add the documentation. I made a copy of the pdf file . Click on the  schematic to enlarge.
A  You Tube impression by KC2IRV : Overall impression of the amplifier
                                                               Testing the PA

Conclusion :  This is a nice kit with acceptable results  for a low price.

click to enlarge

 150 Watt 12 to 28V step up converter for $ 2.50 on eBay

Sunday, February 14, 2016

Wall Loop 20m.

A stealth solution for apartments .
This max. size magnetic loop antenna for 14 MHz with a totall circumference of 6m. ( 19.68 feet )  is designed to attach to a wall . Not sutable for reenforced concrete walls . It has a no tune bandwidth of more than 300 KHz with a centre swr of 1 : 1.1.  A capacitor was put over the feedpoint to shunt up the feedpoint impedance. The 150 pF parallel capacitor was the best value in my situation ( brick wall ) but can be replaced by a 500 pF tuning capacitor in order to find the lowest SWR at resonance in any setup. First contacts gave good reports in Europe. Although a lot of the hf power is absorbed by the wall, the results are surprisingly good. A test was made with 100 Watts without arcing however 5 Watts are more than enough for indoor use...
The top capacitor is made of twisted pvc coated antenna wire or a piece of 25cm RG-213 coax and is cut for tuning to the frequency . This antenna can also be build on a fibreglass or wooden frame in a diamond shape for field or attic use. Loop circumference for other bands:
30m  : 7m
20m. : 6m
17m. : 4.8m
15m. : 4.2m
12m. : 3.5m
10m. : 3m
Tuning steps :  Change the length or the turns of the top capacitor to tune the loop to the desired frequency then put a 500 pF tuning capacitor over the feedpoint and look for the lowest swr.
You can replace this capacitor by a fixed type.
Follow the thread on :

The capacitor . A piece of RG-213 coax can also be used
Verry good SWR
Feedpoint with 100pF and 47pF in parallel. Notice the line choke.
The loop made by  SP3BGD

SP3BGD feedpoint capacitor for wide range use
The loop at DB9MAT

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.

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, first contacts were made troughout Europ with 10 Watts SSB. Meanwhile contacts were made with 5 Watts SSB over the Atlantic including the Caribic , Brasil , USA ands. See the list below.  The Faraday coupling loop is made of RG-58 and is bend to a slightly horizontal oval, reducing the space between the loops that 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.
Some september 2014 holiday QSO's made with my FT-817 and 5 Watts PEP ssb mainly on the 10m band :

HB9AYR made a verry nice copy of the Travelloop Mono . Enter his call at to get more info:
HB9AYR Travelloop Mono

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 6.8-31 MHz range.
The design uses a single 15-520 pF type combined with a FT37-43 toroid having 7 turns  on the coax side. The loop is made of 3mm brass wire 1m long. Use only plastic enclosures.  Tuning range is 6.8 - 31 MHz with oustanding performance. This is also a verry good direction finding antenna. A RG-213 loop gives a higher Q with much stronger signals.

The coupling by a FT37-43 with 7 turns

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 :

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 and a capacitor to ground at the DDS power pin are the solution 

Iler base station 20m.  70 Watt

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

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 objects 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.
A small QRP version is also possible using a BN43-2402 balun core from 7 - 29 MHz


If a high efficiency antenna is needed here are the data.  Use thin 50 Ohm Teflon coax wire  for the capacitor ( one side open ) . 1 cm coax is aprox. 1 pF.

Tuning without the antenna : connect a 3300 Ohm resistor fom the  coil end to the ground of the coax connector. cut the coax-capacitor carefully for lowest SWR . Connect the antenne and cut the antenna wire for best SWR .
Calculate L and C for your own matching unit:
Reactance L and C :
Disclaimer:I'm not responsable for any damage due to improper reproduction of my projects.