Ultimately when you break things down a receiver is not all that complicated. Sure in its entirety it can range from ultra simple to overly complex, but fundamentally they all share the exact same building blocks, switches, attenuators, amplifiers, mixers, filters and oscillators.
Within each of these individual building blocks there are many different variations of circuit topology that can be used. For sometime I have been thinking of writing a series of posts looking at each of these fundamental building blocks in some detail and offer some typical circuit typologies that are often used in homebrew receivers.
The image above is a block diagram of the receiver that I have been building for what seems like forever. What I will probably do with each building block is take a look firstly at different typologies and then at the specific topology I used, why i used it and will more than likely add in LT Spice simulations as well just for good measure. Being able to test and compare different circuit typologies without murdering parts is certainly a good skill to have.
So I will approach things in this order, Filters, Mixers, Amplifiers, Oscillators and then a quick look at switches and attenuators.
Hi Rob,
Reading your older posts. I enjoy following your activities and subscribed a bit ago (maybe 6 months ago, might be less). I have an electronics background but not as extensive as yours. Interested to hear if you know if the use of one type of radio building block enables or precludes the use of other types of building blocks. Or are they in reality pretty exchangeable “black boxes”? I’d expect that a basic low tech block feeding another much more intricate/capable design in the next stage would result in a “what’s the point” type of assessment, but that’s not quite the same thing (performance vs functional) maybe. Thoughts? You have a wealth of knowledge and it would be interesting to talk to you sometime. I know there are others that have commented, might be interesting to do some kind of group call/chat if you and others were up for it. I’d say on the air but I’m in the US and not sure that would work well, at least for me. I only have an Ic-7300 and an inverted sloping G5RV. It does well enough for this side of the ocean(s) but I don’t make it to Australia or Europe very easily except maybe on wspr or another similar protocol.
Anyway, curious to hear your thoughts about the building blocks.
Best regards!
-Mark
Hey Mark, if you look at say a direct conversion receiver, you have a bandpass filter -> Mixer -> audio amp and a local oscillator. There are dozens of different bandpass filter typologies. What one you use can be determined by any number of metrics. But ultimately a BPF is a BPF and any one of them will work, some better than others. I think that approach can be taken with just about any of the basic building blocks. Build 10 filters, build 10 mixers, build 10 amps and then mix and match them to your hearts content like lego. Actually there is a lot to be learned by doing that and you end up with some goto circuits that you always use.
I use a double tuned circuit for bandpass filters as an example, in everything i build. Its easy to design and build, has acceptable performance, uses minimal parts and is easy to align. But, it took building many different other bandpass filter types to come to that conclusion, from elliptical, nodal shunt cap and many others to come to that conclusion.
Like you, I have a crap antenna situation and FT8 is really the only way currently that I can work any dx with any certainty and I no longer have any voip modes here either. Happy to chat here or via email or if you are on facebook I am a moderator on a group called Ham Radio Home Brew Corner :: https://www.facebook.com/groups/hamradioconstruction they are the best places to reliably catch me 🙂