Where to start?

[KC2UGV]

I'm looking to actually homebrew my first rig, which is a low power PSK transciever.

My goals for it are, in order:

* Low power consumption
* SSB, for a very narrow slice of spectrum (5KHz, only)
* Audio in, and Audio Out (No in-built speaker).
* 20W out MAX, and can throttle down to 1W.
* No tuning: Will be tuned to only 3 frequencies (14.070MHz, 10.140MHz, and 28.120MHz). Ok, there will be tuning, a three way switch will work. 10.140 being my primary goal.

So, where in the hell do I start? I'm looking to do this with no SMT components. Has this already been done?

I was hoping to find a PSK-20, but those things are like hen's teeth to get.

I was thinking, "Well, the power supply is the easiest to do" (I can build a regulated PS no problem). But then I thought, "Well, hell! How much power will this think need?"

So, where does one start on a project like this?

[KG4CGC]

Before we get too deep into this, did you do that crystal radio project? Pics?

[KC2UGV]

Before we get too deep into this, did you do that crystal radio project? Pics?

I built the crystal radio. Didn't add the audio amplifier to it :)

[N8YX]

Start with the audio and AGC section first. Then get the oscillators constructed and working. I would look at doing this in a modular fashion so you can try new designs or modifications with a given circuit, thus permitting one to swap assemblies at will for testing purposes. That, and a lot of rework tends to make a single-board unit into a mess over time.

[mw0uzo]

Start with the audio and AGC section first. Then get the oscillators constructed and working. I would look at doing this in a modular fashion so you can try new designs or modifications with a given circuit, thus permitting one to swap assemblies at will for testing purposes. That, and a lot of rework tends to make a single-board unit into a mess over time.

Totally agree.

Do the initial prototyping of each module on breadboard, then transfer to copper clad when the design is near finalised. Use plenty of decoupling and a liberal sprinkling of inductors in the psu lines of each module. Stray RF getting into the wrong places can make all sorts of havoc. Include trimpots for easily adjusting the level out of modules. Use a PIC or similar for control purposes and allow yourself room for expansion from initial plans. Once you have a working controller and program with screen for feedback its easy to control and switch your modules to make the project 'sick'. Its so tempting to prototype straight onto copper clad, but its very easy to make a mess once you try a few designs and have a few failures. Keep that mess confined to the prototyping breadboard.

Use varicaps for adjusting things, PWM for generating tuning voltages, interrupts for servicing important control signals and high priority user input (like tuning).

[N1LAF]

PSK interface with this: http://www.nue-psk.com/

[KC2UGV]

Start with the audio and AGC section first. Then get the oscillators constructed and working. I would look at doing this in a modular fashion so you can try new designs or modifications with a given circuit, thus permitting one to swap assemblies at will for testing purposes. That, and a lot of rework tends to make a single-board unit into a mess over time.

Thanks! That's really what I'm wanting to do (Modular), so I can swap out "bad" sections, to improve upon. So, I guess Charles' question was pointing me the right way :)

PSK interface with this: http://www.nue-psk.com/

I looked at that, it's actually the "wrong half" of what I'm trying to do. I'm looking more at a design like the PSK line from SWL (PSK20,40,etc). Doing a PSK modem would actually be a snap for me, since software design I can do. I'm looking to "broaden my horizons" and start working on a RF project.

This might be the "off the shelf" half I get to work with it. I'm envisioning something rather small, since I really want single-band, single-frequency. If I do multiple bands, it would be one frequency per band.

[N8YX]

Million-dollar question:

Have you decided on an IF and conversion scheme?

That is going to play a huge part in the design of the oscillator, filtering and mixer stages.

Direct conversion? Single/double-conversion superhet?

Need some details...

[KC2UGV]

Million-dollar question:

Have you decided on an IF and conversion scheme?

That is going to play a huge part in the design of the oscillator, filtering and mixer stages.

Direct conversion? Single/double-conversion superhet?

Need some details...

Basically: I don't know. Hence, "Where do I start?" This would be my first ever RF design project :)

[KC2UGV]

As an aside, I'm not really averse to using someone else's work here. Are there any schematics out there that would meet the requirements I'm looking for? It's definitely something I want to actually build (Which is one reason I really was looking for the PSK20/40 kits).