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).

[N8YX]

What I would suggest is this:

Make the rig a single-conversion superhet, and choose an IF frequency that allows you to use a readily available crystal filter (e.g., 455khz, 500khz, 9.000mhz, etc). For a reference oscillator I would use a DDS and either a PIC or BASIC Stamp to provide the control words.

Amplified vs passive-mixer front end...how many sources of high-power RF are in your immediate vicinity?

If you go with the IF frequencies I mentioned above, you can easily obtain the required BFO crystals from a number of places. For that matter, you could even construct your own crystal filters and incorporate "variable bandwidth tuning" via varactor diodes in the interelement coupling stages. I would also look at implementing BFO frequency adjustment (with varactors) and an AGC-derived hysteresis-style squelch.

[KC2UGV]

What I would suggest is this:

Make the rig a single-conversion superhet, and choose an IF frequency that allows you to use a readily available crystal filter (e.g., 455khz, 500khz, 9.000mhz, etc). For a reference oscillator I would use a DDS and either a PIC or BASIC Stamp to provide the control words.

Amplified vs passive-mixer front end...how many sources of high-power RF are in your immediate vicinity?

If you go with the IF frequencies I mentioned above, you can easily obtain the required BFO crystals from a number of places. For that matter, you could even construct your own crystal filters and incorporate "variable bandwidth tuning" via varactor diodes in the interelement coupling stages. I would also look at implementing BFO frequency adjustment (with varactors) and an AGC-derived hysteresis-style squelch.

I think I've gotten where to start at (I found a block diagram, and a really nice explanation of the module's functions). Now, I know I'm getting ahead of myself, but in the spirit of prototyping it, when I get to transmitter stages, where would this tie into?

[N8YX]

I think I've gotten where to start at (I found a block diagram, and a really nice explanation of the module's functions). Now, I know I'm getting ahead of myself, but in the spirit of prototyping it, when I get to transmitter stages, where would this tie into?
Input RF - RefOsc - BFO = AF

Conversely:

Modulating frequency (AF) + BFO + RefOsc = output RF.

BFO frequency stays constant; reference oscillator does the tuning. Signal path is through the first mixer and product detector on receive; balanced modulator and first mixer on transmit...with the receiver circuits muted and switched out of the circuit via reed relay or PIN diode arrangement. (The RF PA stages and associated bandpass filters are always connected to the antenna, by the way.)

The first mixer is bi-directional and a number of the older Handbooks offer examples of this type of circuit, along with its associated T/R control.

[KC2UGV]

Ok, so designing and building a transceiver is still in my sights, however, I think I might need to cut my teeth first with a complete unit. Instead of the PSK20 unit from SWL, has anyone had experience building this:
http://www.qrpkits.com/bitx20a.html

I (http://www.qrpkits.com/bitx20a.html)t fits with what I'm aiming for (A QRP PSK rig), and am about read to pull the trigger on it. For a first time "big" project, is this doable, or am I still biting off more than I can chew here?

[NQ6U]

While I haven't built a kit since the Heathkit SW radio I put together when I was a teenager, the Bitx 20 looks doable as a first project to me. You'll have to wind a few toroid coils but it's all through-hole components (no SMDs) and comes with step-by-step instructions. I say "go for it!"