Sunday, February 2, 2020

Old amp with new source

Getting back on the bench a bit after a while.  After tidying up, thought I would try fishing out the "Mighty Mike" amp I build a few years back out of the box and try it with the Si5351.  After putting on a new heat sink and soldering back on a cap that had come off, I hooked it up.  Wasn't getting anything at first and not sure why.  Went through hunting for shorts/opens and didn't find any.  But after doing that, tried again and it worked.  I'm getting 1w with 12v supply and 2w with 15v supply. 

Wednesday, January 8, 2020

On the workbench - 8Jan20

I haven't been taking many notes here, but have had the iron out.

First, I've been trying a Class E amplifier with an IRF510 being driven from a IXDD614CI Mosfet driver.   Since the Si5351 doesn't have enough oomph to drive that driver, I had a little amplifier in front of it.  Actually, at first I had a 2n2222 there, but it didn't seem to be operating quite like it did in simulation.  I managed to get about a watt out, which was about 7 watts less that I was aiming for.  It looked like the peak of the amp wasn't as high as I thought, so I don't think I was getting a 50% duty cycle to the IRF510.  So I tried a different tack with two 2n7000 acting as a level shifter instead of the amp.

Not sure what I did in all this, but I suspect I blew the driver.  Need to play more, but the last I left it, if I had the driver enabled, the constant current mode in my power supply would kick in.  So that's not good.  (Though the fact I have that is *awesome* - I love having a proper supply.)

I need to pull more parts off the board and test one by one.  I should have built it more incrementally, but I was told I shouldn't run the driver without a load, so didn't know what I could leave off.  In retrospect, I should have had it just feed into a 180pF cap (ie, the input capacitance of the IRF510) and make sure that was working first.

I wanted a bit of a break from that, so I tried out a TC4420 that I had (driving a cap).  That looks ok... except it doesn't look to be able to handle doing more than 4Mhz.  So, might work for 80/160M, but doesn't look like it is going to work for me right now.

Wednesday, January 1, 2020

New Year, New Band Pass Filter

I wanted to use my new rtl-sdr I got for Christmas on the 40m band (using my dipole).  But I was worried about what noise I might get in there, so I decided I'd make a band pass filter.  I used this design from ARRL.  I put it in a little hexagon box some sort of soap came in.  Possibly not the best idea - it was kind of hard to get the BNC connections is, but it worked out.  I measured it with the nanoVNA, and it looked like a band pass filter, so that is good.  I'm not sure I've calibrated anything else, as it looks like there is a lot of insertion loss that I don't really think is there.  Will need to look into that.

Sunday, December 29, 2019


I've been trying to figure out what transmitter I want to build next - spending a lot of time modeling it in LTSpice and trying to figure out how it will work.

But I wanted to actually get on the air.  I've been practicing my Morse a bit lately, so thought I should just see what I could throw together.

The things I had that were is somewhat working state (or could be made to be...) were my direct conversion receiver and a NS-40 CW transmitter.  First thing was I needed a way to connect them.  I wanted to make something with a relay and have the Arduino I was using for VFO switch it.  But I didn't have any lying around I could find.  But I did find a DPDT switch, so I made a little thing in a nuts tin

When the switch is in the transmit position, the transmitter is routed into the dummy load (I didn't want risk accidentally powering it with no load).  It doesn't give good isolation - the receiver screams when I key - but seems to somewhat do the trick.  Here it is spread over the table:

I tried to send with my homemade key but wasn't getting any responses.  I wasn't sure if it was my antenna setup, the low power, or my bad sending.  So I thought I should try using a keyer.  I found the k3ng Arduino keyer which looked like it would do the trick.

It went together pretty quickly.  The ns-40 had some interface circuits on the site that worked well.  Only thing is the circuit works on active being low, so I had to switch high and low in the software.

It was getting late, so I wanted to just do a quick test.  The keyer has a CW keyboard mode, so I sent CQ from there.  I didn't get anyone coming back.  But I did get spots on the reverse beacon network!

Very exciting!

Knock-off Nano Note

Quick note about how I got the random Nano I found in my junk box working.

  1. It wasn't showing up in list when I plugged it in.  Found answer here to install new drivers for OSX so it could see the board (links to this github repo).
  2. The upload wasn't working.  Kept getting a "not in sync" error.  Found answer here.  Turns out I needed to use the "old" bootloader under the "processor" section in the Arduino IDE.

Saturday, December 14, 2019

Decoding CW from WebSDR with Fldigi on OSX

I got the urge to play around with WebSDR this morning.  After a bit, I got the further urge to try to use Fldigi with it.  I figured I already had Loopback from some music things I do, so I'd have a go.

Worked really well.  I just have a simple setup where I have the output of Safari into an output channel, and then am monitoring that.  Then in Fldigi, under "PortAudio" I have it use "Loopback Audio" for capture.  

Couple of notes:
  • It didn't show up as a soundcard at first - probably want to setup Loopback before opening Fldigi
  • It was initially doing some mode *not* cw.  It looked like I was supposed to change that in the lower left (where it said the mode), but you actually go up in the menu under "Op Mode"

Sunday, December 8, 2019

Activities - 8dec19

Have been trying out WSPR with the Si5351 this morning.  I am using the sketch here.

Couple of learnings:

  • Can list serial ports on a mac with `ls /dev/tty.*`
  • The "serial" library it is talking about is pyserial (not serial).  I used pip to install the first and was confused why it wasn't working (the gist wasn't returning the error)
  • You can't program the arduino while the script is running (as they both use the serial port)
  • This script is set to run every 10 minutes.  Confused me why it wasn't working, but then it suddenly did.

No luck so far, though it isn't helping that the WSPRnet website doesn't seem to load very well.

So then I changed tact and decided to get my DC receiver back up and running.  Before even turning the VFO, I was getting in some local religious broadcast as strong and clear as could be.  Possibly need a stronger band pass filter...  Turning on the VFO, it was working, though I couldn't really hear anyone (some digital modes and someone speaking maybe spanish).  But it was 11am, so probably not the best time for 40m.  May try again tonight.

One thing I noticed this morning: powering my Arduino from my Mac works great.  Powering it from any power plug I can find is very noisy on the Si5351 output (either the 12v or usb).  Strange.