Storms Passing By

Last week's storms were a good test of my sky hook, even though no aerial wire is yet attached. It was bending quite a lot, but the guy ropes held it in place, and It seems to me that bending is better than breaking.  I believe we had wind gusts forecasted at 50 - 70 kph. I don't know if this is what we actually got, but it felt like a sample of the worst we normally get around here.

This weekend the weather was clearing, but I thought I'd like to get further with the Softrock before trying any new aerial ideas.

In the end I decided just to press on and get the main board assembly finished. I decided not to stop for all the tests at each stage as it really breaks the flow of the soldering, so to speak. Just stopping at each stage to test the power rails to make sure of no shorts seemed enough for now. I can run through a full signal test when it is all assembled.

Some observations:

The build instructions advise fixing the PCB when working on it. I don't find this necessary. In fact being able to spin the board around quickly to get to it from all angles seems a great benefit. The board is heavy enough to sit well on the surface. The four corner screws no doubt helped here.

Winding the coils: I found it useful to start the single windings from the middle. It is easy to estimate the middle of the recommended length of wire, then doing half the turns in one direction then the other half from the middle going round the other way seemed to quite convenient. It also means half the length of wire to pull through each time. 

I noticed that the bandpass filters have an undocumented phase reverse in the way the PCB is laid out. The circuit diagram shows the top of the T100 secondary winding connected to pin 3, but it actually goes to pin 2, and conversely the bottom goes to pin 3 instead of pin2. However the circuit does not show any phase "dots" identifying the matching ends of primary and secondary, so I assume it is not important. Apart that is from the secondary pair needing to be correctly connected to get the centre tap, I assume that phase reverse between primary and secondary is not a problem.

Power testing: For some reason the current scale on my multimeter seems to have stopped working. It is probably the built-in fuse but I don't have a replacement. In the end I skipped the first test of each stage with the 100 ohm series resistor, and settled for a 10 ohm in series. This seemed to me to represent a safety measure for any shorted power rails. A quick test for voltage drop would show up a short quickly enough to remove power. It also meant I could measure current consumption by the voltage drop of about 1 volt across this, and I could leave it in circuit for the actual rail tests and other voltage test points as it did not drop enough to interfere with normal operation. This sped up the power test before moving on at each stage.

The story so far:

The underneath:

Anyway, this weekend I got the main board assembly finished, a couple of bandpass filters done, and started on the 80/40m PA stage. I'm hoping next weekend to finish the PA and to get the PC connected up and Rocky software installed  for some signal tests.

Soldering the Chips

Last weekend I got as far as getting the clock chip soldered on and working, which felt like a bit of an achievement...

Soldering on the small chips is definitely not easy. In the end I was thankful that I have a microscope, and I did the soldering under it. You get used to zeroing in with the soldering iron and tweezers into the field without melting anything on the way, and it geat to see exactly how the solder is flowing. Maybe my multicore is too big, but I found it very difficult to get anything less than a lot of solder onto the joint. Still, in the end it seemed to flow okay, I got almost no spills, and tests so far seem to indicate that it works, so I think it will do. The picture attempts to show how the solder steeps up against the edge of the pins on the clock chip. I can only guess whether it runs underneath ok.

To check this, I got out my very old and cranky oscilloscope, and got this picture of the quadrature signals at 7MHz, so it looks like the oscillator is okay, and the PIC is programming it okay.

I had one doubt here, as I want to control the oscillator from the add-on USB module when it arrives, and the connection pins seem to be underneath the 8-pin switch module, obviously designed as an alternative to the 8-pin PIC. In the end I mounted the switch above the board, as high as its pins would allow. This will make it easy to cut off if I need to remove it later. On the other hand, the I2C programming pics can be soldered onto underneath the board, so simply removing the PIC should be enough to free up the oscillator chip programing pins later. 

That was all I had time for last weekend, but it felt like I was getting somewhere.

Softrock Arrived

The Softrock xtall-v6.3 transceiver kit arrived last week, though I am still waiting for the 10m PA kit and the USB interface kit. Still, now the main board is here I can get started assembling, as neither of those is essential.

Fortunately I have had to work on surface mount boards before, though only to change odd components when problems with prototypes have been found during software development. I've never had to build one from scratch though. 

Managing the components is a challenge. It was good advice in wb5rvz's build notes (http://wb5rvz.com/sdr/RXTX_V6_3) to check all the components against the inventory before starting. This helps identify and distinguish similar parts. I have quite a good collection of small antistatic plastic bags into which I put the separated parts to keep them organised. 

Since the pictures were taken I've got to the end of step 1 and I'm about to test the power regulators before moving on. Since I'm nervous about my soldering I've been testing for shorts after every component.

I was confused for a few minutes when it came to placing the first tiny 5-pin 3.3v regulator IC as the pads were hiding between a couple of capacitors. The lack of silk screen component ref on this side of the board made it difficult to identify which caps were which. I finally found the site though, as in this picture:

The size of the pads was challenging. Luckily I have the luxury of a microscope so I could check that my "first tack" had managed to get it well within its pads, so I completed soldering it under the microscope. I hope I did not overheat it as one pad was slow to flow.

Now on to the first test then the next assembly step...