So, now that I have a working transmitter that I am happy with (See Here) and wish to actually use it, because it is not just popcorn fun, but actually very usable and of good quality, it is time to move on to the next issue and that is having a receiver to go with it. With that in mind, I have thought about what exactly I would like and came up with a small list of needs, modular was top of the list, so that I can modify and expand it over time as i develop greater understanding and skills.
So, as I have been listening a lot of late to the Solder Smoke pod cast, I became aware of a project by Pete Juliano that was created from the ground up with modularity and expandability in mind called the Simple-Ceiver, Here is a link to the actual project http://n6qw.blogspot.com.au/2015/09/moving-on-to-simple-ceiver-project.html, there are 20 odd blog entries to read chock full of information, the design decisions and the criterion used in the development of the board. I would recommend reading them all, Pete is not only a good home brewer but also a very good writer.
So in keeping with the idea of modularity, I have laid out my boards which I will route on the CNC Router with one stage per board. I have a pile of 100x65mm boards I bought off ebay for this very type of project, so they will be getting a workout now.
Now, something i also learned from reading the blog entries is that I would seem to be a really good idea to build your projects in reverse order, starting with the AF Amp and working towards the antenna. i can see the benefit in doing things this way, rather than my usual gun ho method of get out the flame thrower and start weldering up everything in sight 🙂 So in following Pete’s advice i will start with the AF Board and work my way forward. I will not be departing much from the published design, other than using a bandpass filter I have used before with success and to bring the only part missing from the original project and that is the Local Oscillator. I will upload the gerbers for each board as i build them to ensure they are working etc.
Here are by board layouts:
The AF Amp Board: nothing extraordinary here, 2n3904 preamp into an LM386, yes they sound like farts, but they do the job. I will likely use much less gain in the 386 than in the original schematic.
Dual Gate Mosfet Mixer: Now i actually like the simplicity of this circuit, yes I could use a NE602 but where is the fun in that. The 2 Jfets are J310’s which are cheap enough to get, though now they are not being manufactured anymore so they will soon become extinct, so stock up on them now while you can.
The bandpass filter is one i have used in a number of projects and performs well. Losses are low, out of band attenuation is good. I have modified it here for 50 ohms in and out.
Something I have not typically added in on any other DC receiver i have made is an RF Pre-Amp, the few times i have tried and built and added them into my designs have ended in dismal failure. Such is life when you are trying to shoe horn other peoples designs into things they are not really meant for. This design uses J310’s again to give 15db of gain before the bandpas filter. I am not sure why it is before the filter and not after, but this is something I will email Pete and find out the reasoning behind it.
This board is 150×100, and other than having the Arduino and SI5351 synth on it, it also has the TX and RX switching on it, and yes, if you look you will see a mistake on the layout, that I have just now fixed. HIHI. Anyway that is all from me for now, tomorrow I will start on making the boards and slowly building up this receiver project.
