March 2017 A little aside - back in May 2016 there was a technical article which I thought was rather poor with a 'construction' which I thought was a complete waste of time. So much so, that I wrote to the editor and told him so. The editor said they were always looking for technical / practical articles so I offered an article based on my UKAC exploits. I wrote the words, got up to speed with Express.sch for the circuit diagrams and took a few new pictures. I submitted in November and to avoid any copyright issues, I haven't put anything on this blog since.
Three email reminders sent later, nothing from RadCom. No acceptance, no decline, nothing.
So off we go again.
This is the normal operating set up for G4HGT/P with the KX3 sat on the control box, sat on the 144MHz transverter, all on the front seat of the car.
The transverter was built in the late 1980's with a BF981 front end. Inside the pretty case is a good old diecast box providing a solid screen. One day I really must take it into work and make some measurements, then decide if I need to bring it into the 21st century. For now, the covers are staying firmly in place.
Inside the control box are 5 functional blocks: 12V regulators, RF switch, 28V inverter, sequencer and audio amps
The KX3 is a pretty expensive box so getting the polarity of the DC feed wrong and when rushing to get the station on-air could be disastrous. So I've used a low-voltage dropout regulator to add a little protection. The second regulator feeds the audio amplifiers. This can also be switched off by the sequencer if I ever get RF breakthrough
RF switch - I need a sinple way to split the I/O of the KX3 into separate TX and RX lines. This box uses a G4JNT design pin-diode switch / attenuator from 1994. The RF output from the KX3 at 28MHz is turned down to the minimum setting, roughly 100mW, then the potentiometer in the switch box sets the drive level into my transverters at around -10dBm
28V inverter - I have a 28V RF relay so i needed an inverter. This little module was bought off eBay for less than a tenner - no point in trying to design my own.
Audio amps - probably a little overkill at the start, I could have just plugged my headphones into the KX3 but the audio out seemed a little low and with little LM380 amps available on eBay for pennies, I now have plenty of audio plus a combined audio if I ever need to peak the beam when outside the car
Sequencer - antenna relay switch, transverter switch, power amp switch and +12V feed for a preamp. A stripped down version of a W1GHZ design
22 June: So a week after writing my last entry, Giles Read, the
RadCom technical editor, got back in touch and the article started moving in
the right direction again. It is now in for final tidy up and should be
published in a couple of months.
