They say one of the juggling things one does when building their first transmitter or receiver is between two key things:
1) Simplicity – to ensure success;
2) Usability – to ensure it's worthwhile and doesn't end up on the shelf collecting dust.
To address item 1 I want to build a crystal locked SSB transmitter for 40m (I would have gone CW for greater simplicity, but I'm only just learning CW – slowly). However, there is a risk building a transmitter which is not frequency agile when you live in Australia – vs. Americas/Europe – with a lower AR population. That is, you may find no one is ever on the frequency your rig is built for and you can't just simply tune to another frequency when you find someone and jump in and have a chat. Thereby, you sacrifice the usability element and potentially end up just placing the resulting item on the shelf.
However, what about WSPR! It's only on one frequency per band, and there's always someone listening – more or less!
So, my plan has evolved into a crystal locked WSPR transmitter for 40m. This is also nice and simple on the audio input as well as it can just take the audio from a computer output. I was even contemplating building a simple VOX circuit into the audio line to do the PTT – but maybe that's over complicating things and I should just add a simple switch that can be controlled from a computer via serial port – such as with my current digital interface. Maybe, I might even add a simple mini-din socket like used on the Yaesu radios so that my interface can just plug straight into that for starters.
Really then, it looks like I can come up with a simple transmitter through just having a locked oscillator and relying on audio from a computer – as opposed to a mic requiring amplification etc. Ideally, I'd love to do a direct conversion crystal locked transmitter (for minimum stages), but I'm currently struggling to find a suitable crystal so I may have to look at a single conversion transmitter in the end – but we'll see.
So currently it's looking like my transmitter would be looking like:
* Direct Conversion
* Crystal locked
* Balanced Modulator using an NE602 – or maybe I could make it simpler by just using a two diode balanced modulator
* Audio in from computer
* Simple transmit switch – possibly controllable externally
* Oh, and some kind of filter to convert the DSBSC to USB, and then possibly a pi-coupler to the antenna connection
* And power wise, I'm happy with 1W as I know that'll yield results with WSPR – as will 500mW like I've been using recently
But in the mean time for a bit more reading, one of VK3YE's video about his DSB 30m WSPR transceiver has pointed me to here:
Have a good week-end all – maybe I can get some photos taken of my FSM and digital interface (but no promises – we know how long it's taken me already).