Friday, August 25, 2017

QRP labs QCX 5 Watt cw trx kit


Here is my new winter project:  http://qrp-labs.com/qcx.html 
I couldn't resist buying this little 10 x 8 cm gem with a lot of features for just 49 $ 

The two SMD ICs are already factory pre-soldered.
Compleet unit size incl. spacers : 101.6mm x 81.3mm x 34mm.

A nice 110x88x38mm enclosure for this transceiver can be found on eBay : Link
The grooves for the pcb are not used and have to be reduced about 2mm near the volume potentiometer and the pcb pylons. Also the groove at the LCD side may touch the soldering pads of the LCD . The PCB is mounted on the original 12mm pylons. These pylons are held by countersunk headed bolts to the lower cover. So to open the enclosure, remove the two knobs and the upper 4 screws of the side panels. To prevent stress to the PCB , the huge plastic BNC connector is replaced by a metall chassis-mounted type. This will automatically ground the enclosure.πŸ˜‰
By means of a shaft extender the difference in height of the controls is matched.
Don't use the standard BNC connector from the kit.  The PCB will be off centre.

 



Making markings for 3mm holes.



Making space for the potentiometer and pylons
Pylons fitted
 Removing the groove in the cover is verry easy. By carving into the alloy as the picture shows the material weakens and can be removed with a small srewdriver .

Perfect fit😎




At last the controls of the QRX are fixed. I had 2 extended push buttons in stock as wel as some cheap plastic potentiometers.  The shafts were cut of and appeared to be hollow. A 1/8( 3mm) drill was used to enlarge the shaft inside for aprx. 2mm.
Next the shaft was pushed over the button’s shaft and fixed with superglue.

The original potentiometer was replaced by a longer one . A simple pice of modified shaft and a small pice of plastic tube were used to extend the encoder shaft.









There was a power-on and LCD fluctuation on TX problem with the kit caused by the tiny inductors L5 and L6 . These had to much internal resistance and were replaced by bigger types with 47uH.
In the 20 and 17m kits C33 ( 1nF) is reduced to 150 pF for a better drive of the PA.

Monday, July 17, 2017

IC-7300 preselector idea.

The IC-7300 has a signal overload problem. A preselector can be an option.
L1 - T80-2 .  L2 - T68-6 .  L3 - T50-6 .  T1 - T2 are 1:9 transformers. By adding a 470pF capacitor to ground between T2 and the polyvaricon the overall swr drops to a verry acceptable levell.


Sunday, April 02, 2017

Voice keyer ( CQ parrot )

Calling cq in ssb with only 5 Watt can cause a sore throat....
Although in production for severall yaers this exellent kit BX-184 from Box 73 is still a must have for the QRP operator. Link
Easy to build high quality kit that provides 60 seconds voice recording and a strong punch to the modulation . I had to reduce the mic. gain to 25% on ssb and 15 % on fm/am at the FT-817.
This kit is also available with a extra MH-31 type mic. enabeling the use at other transceivers with 5V or more at the mic. cable. The red dot marks the fst button that controlles the functions,

The modified MH-31 mic.with pcb




Friday, January 20, 2017

EFHW antenna for 40-10m qrp

I had a BN43-202 core in stock and attempted to try to create a small QRP EFHW transformer from 7 - 29 MHz. As you can see in the plot the swr is verry flat from 40-10m so a capacitor at the input is not needed. A 3300 Ohm resister to ground was used for the plot but at 1700 Ohm the transformation is near perfect. Don't use thin antennawire for this rises the impedance of the antenna. 1.5mm is a minimum . With just 20.3m wire this makes a nice 40-10m antenna. You can also use the 34uH coil of the endfed down this blog to create a compact 3 band atenna of just 12m long. 10 Watts PEP is the max. power here. Be carefull, each pass is 1 turn here. A test with 2 transformers back to back showed a power loss of about 18% on 20m. I used 0.7mm transformer wire .




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. 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 W3NQN 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. I replaced the FETs by a pair of IOR IRF530N resulting in more stabillety en less input SWR however the input swr is highly effected by the drive power . At 5 Watt the swr mounts to over 1:3... . Best results with this PA are obtained on CW and FM .
The test was in the original configuration at 13.8V and 5Watt FM input from my FT-817. Max. power was 80 Watt . At  3 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 acceptable but far from perfect.  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 12V 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 .
A  You Tube impression by KC2IRV : Overall impression of the amplifier
                                                               Testing the PA 
Visit the blog of John DK9JC for a nice test : Link

Conclusion :  This is a nice kit with acceptable results  for a low price. For best results reduce the drive power to 2.5 Watt.
swr at 5 Watt input : 1:3+.   swr  at 2.5 Watt input 1:1.8 with more than 50 Watt output. This is more than enough for fieldwork.




A second amplifier was build without cooling fan . You can clearly see the 7 element filter for 20m
.The enclosure comes  from eBay :  Link
The heatsink also comes from eBay: Link


 Assembled lowpass filter is also available on eBay :



Sunday, February 14, 2016

Wall Loop 20m.

A stealth solution for apartments .
This max. size open 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 QRZ.com :https://forums.qrz.com/index.php?threads/wall-loop-20m.511714/
See de Walloop at DK9JC : https://www.dk9jc.de/blog/equipment/128-20m-indoor-loop-nach-pd7maa 

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.
READY TO TRAVEL
HOLIDAY SHACK
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 QRZ.com to get more info:
HB9AYR Travelloop Mono
 
Disclaimer:I'm not responsable for any damage due to improper reproduction of my projects.

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