#beach 40

[typefaster]

Beach 40 - Part 3, RF Amplifier

Another wet weekend so made some more progress on the Beach 40. Built RF amplifier stage and learnt a few things, or more correctly was reminded of a few things, along the way.

Lesson 1: Amplifier stages need to be connected to the power rail.

The PA power is switched by the transmit relay. The layout of which isn't that clear on the schematic I'm using, especially on the printed version where the line runs off the side of the page.  Doh!

Lesson 2: The Emitter and Collector leads are not interchangeable.

I installed the 2N2222 round the wrong way, which unsurprisingly didn't work, and  fried the transistor.  Doh!

Lesson 3: To test the stage it needs to be complete. 

I tried to test the stage once the coil was installed, with no luck. Once I added the 100n decoupling capacitor and the 470 ohm load resistor it worked as expected.  More Doh!

I also added another PCB as I was going to run out of PCB real estate. The final product wont fit into the nice little box Peter had, but I don't think that's an issue. While I was replacing the fried transistor I changed the layout so that the RF stages run from front to back of the PCB. I had originally placed them all on the front PCB. I think that will work much better.

I've realised I don't have any BD139's, which is annoying as I thought I had everything and could easily have bought a couple over the last few weeks. So the bench has been cleaned up and building has stopped for this week. 

[typefaster]

Beach 40 - 40m DSB Transceiver - Part 2, Mixer.

A wet weekend meant a few productive project building hours. The mixer and the microphone amplifier are the next stages. 

Peter recommended listing to the radio at this point to adjust the trimmers to knock out the carrier. I didn't want to get set up for that, so just used the scope.

Before and after adjusting the trimmers. (Same voltage but different time base on the scope)

I've got an old  dynamic mic to use with this, where the circuit is really for an electret. It took a bit of fiddling about to work out the pin out and the PTT switch was a bit rough But it seems to be working now. I tested it out by playing a tone on the PC and holding the mic to the speaker. I'm not sure I if it's getting the amplitude it should from the mic. I might still have to try a higher value coupling cap. 

Here's the board. I can see I'm going to run out of PCB real estate, so I'll have to put in a vertical board for the final stages and AF amp. The microphone amplifier is hard wired on here as I hadn't put the relay in yet. 

[typefaster]

Beach 40 - 40m DSB Transceiver - Part 1

I've decided to have a go at building a little QRP transceiver designed by Peter Parker, VK3YE. He's posted a collection of videos describing the design on YouTube. It's been around for a couple of years, so there's a bunch of other builders with notes and some schematics. I thought this one was easiest to read.

I started off collecting all the bits. Mostly the parts are generic and readily available, so a bulk order with Futurlec was in order. These guys are cheap, and I've never had any issue with the product. Though they are slow, and have zero proactive communication skills. So if a parts on back order you won't know unless you ask. (If you shoot a note to them a couple of days after placing the order they're quite happy to tell you if there are issues, and if needed make changes)

Saddly there were a few parts they didn't have, in particular the 7.2 MHz ceramic resonator. In fact they have stopped making the 2 leg version and it was only after a LOT of Googling I managed to finally obtain the last 2 that a supplier less than 100km away had.

Once I had the bulk of the parts I needed to make up a base to mount it in. As I haven't tried a project like this I've opted to build it on a bread board. Once working I'll move it into a more practical container.

Here's the blank PCB with a front face plate that has the tuning cap, power switch, etc, mounted and ready to go. I really don't know how much room I'll need. If I have too I can mount a second PCB behind this one. Hopefully I won't need it.

First stage is the oscillator and buffer. I think they call this the Ugly build style. I hope I don't have to rework to much as it won't be the easiest to follow later.

I've read others notes where getting the oscillator running has been a trick, but mine ran first time. Here's highest frequency. The wave form is starting to collapse.

 Lowest frequency.

Wave form with the tuning around the mid point:

I'd read that the peak to peak voltage of the wave with no load should be more than 6 volts, but mine was showing on the scope as less than a volt. I was starting to wonder how I might address that when I realised that the scope probe was set to x10, so the real voltage was more like 8.8v.

Next is the Balanced Modulator and Product Detector. I need a 200 Ohm pot and a 4-40 uF trimmer cap, neither of which I have. Not sure how that happened.