EA8/LA3ZA April 2023

This was a fun holiday operation from the island of Tenerife with 2.5 - 4 Watts running digital modes, mostly FT8 and some FT4 using a low-band and a high-band QDX.

The best bands were 30 m (29%) and in particular 10 m (65%) with a lot of contacts across the Atlantic ocean as the picture shows. In total 62 different entities/countries were contacted. 

QSL via Logbook of the World.

3 tips for not blowing the finals of the QDX transceiver

I have now used both the low- and the high-band QDXes daily as EA8/LA3ZA for a period of two weeks without destroying the four BS170 final transistors. Here are some procedures and tips.

But first, I do actually have experience in blowing the finals. That happended under testing prior to leaving, and all it took was 9.5 Volts for my 9 V build and what I thought was a dummy load, but which might have been an open circuit load. One BS170 developed a short between drain and gate with the result that 9.5 Volts was passed directly into the outputs of the driver IC5, 74ACT08, so IC5 blew as well.

My three tips for avoiding such failures are:

QDX Twins 80-10 m

My QDX twins from QRPLabs: 

1. On top, the high-band version, 20-10 m, with a revision 4 PCB
2. In the bottom, the original 80-20 m version with a revision 3a PCB

Both have been assembled for 9 Volts operation nominally.

My wife and I have identical twins in real life and at times one of the ways to distinguish between them was by different colors. Here it is the same, so the high-band QDX has a yellow LED and the low-band one has a green LED.

QDX with voltage regulator

Here's my low-band (80m - 20 m) 9 Volt QDX with a voltage regulator. Its only modification is a green rather than a red LED, as I don't like red LEDs to indicate anything but error conditions. 

The power amplifier of the QDX has hardly any built-in protection and can be ruined if run at full power into a poorly matched antenna. It will also easily be ruined if run at a higher voltage than the 9 or 12 Volts one may choose for at build-time.

QDX on 17 and 15 m: Receiver

I got myself one of the marvellous digital transceivers from QRPLabs recently: The QDX - QRPLabs Digital Transceiver. It is set up with receiver bandpass filters and transmitter lowpass filters for 80, 40, 30, and 20 m. It has also been found that the 40 m filters work well for 60 m. 

The latest firmware, version 1_04, has a new "Band Configuration" screen where one may configure the list of supported bands. It is the intention that higher bands will eventually be supported.

I am not so interested in 80 m, so I wanted to see if I already now could get the receiver to work on 17 m and 15 m. With reference to the schematics, I modified the input filter's inductor, L12.