Friday, August 25, 2017

QRP labs QCX 5 Watt cw trx kit

Here is my new winter project:   
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 little gem needs a nice encclosure.
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.

QCX mods :

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 .

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