Testing a filter with noise

 I built a noise generation circuit out of EMRFD ages ago, but I don't think I ever did much with it.  I was looking at my crystal filter today, and thinking how the TinySA is limited in its minimal bandwidth.  Then I remembered I had an SDR and could look at it with that.

I was using CubicSDR, and the display isn't as clear as I'd like.  Would like if I had some averaging to give me a nice picture, may look into that.

Beautiful sounds from my ssb receiver

 
I started building an SSB rig ages ago.  Or at least the parts of it.

I build the crystal filter and the various amplifiers over three years ago.  And I had the mixers (ADE-1), audio amp (one of these left over from a defunct synth project), and the VFO/BFO (an SI5351 board/Arduino) ready to go.  I got it partially wired up and then... stopped.  My interests are a fickle thing.

Anyway, I wired it up, tweaked a lot, and can sort of, kind of hear stuff!  

I haven't been able to make out any people yet, but have heard some code, and I managed to decode FT8 using the iFTx app on my iPhone!

You'll notice in the top picture, I am using my signal generator.  I had mis-remembered some things about the SI5351, so I had a pad in front of it, which was not getting the mixer to the +7dbm it needed for LO.  So in debugging I used my signal generator and just stuck with it.

I may want to try some other configurations (like actually make a BPF for the front, and maybe a LNA in front of that) and might try some more gain in the middle (between the filter and the product detector).  But pretty pleased it is working at all.  Also need to have a bit more of a think around where exactly I want the VFO/BFO.  Lots more to do, but pleased where it is.

Quick and dirty L match tuner

After having good success with the little wspr thing I put together, I decided to put up my old end-fed half-wavelength qrp antenna outside.  I still have a under-window coax connector, so strung it up between my workshop window and the garage across the driveway.  Got much nicer results.

I did notice though that it was resonating low - it was more like 13.5 rather than 14MHz.  I need to adjust it, but it was already dark.  So I decided to have a play with throwing together an antenna tuner real quick.

I took the 3D printed variable capacitor I made a while back, wrapped some wire around an inductor (making taps every once in a while, and threw it together on a little board I made the other day to hold my low-pass-filter.  I'm using an alligator clip to adjust the inductance (choosing different taps on the inductor).

I managed to tune it for 7MHz ok. 

Was having trouble dialing in 14MHz - I think I needed more inductor value choices, and maybe the ability to go lower on the capacitance.  I could have a play with some switches to switch caps in, but this was more just an excuse to put one together, as I've not built one before.  Probably won't use it, but was fun.

Long time, no ham

 I haven't done anything radio related in quite a while.  The past few weeks though I have started poking at stuff again.

I started off building a QRP Labs QDX.  Build went ok, but I keep having an issue where it restarts when I transmit.  I need to debug it more.  But I didn't feel like debugging it, so instead I thought it would be fun to just build the transmit chain.  

Not working great, either.  Probably the stray wires are a bad idea.  Should have built it ugly/Manhattan.

But I got enamored with the drive chip.  I had some 74AC240's sitting around, so built one like was done here.  

I figured while I was at it I should try it out by itself, so put together a 20M lpf, and built up a little board with an SI5351, and made a little wspr transmitter using the gist here.  Pretty sure I used the same one years ago.  

Didn't expect much since I just threw an old efhw antenna around my office.  Checked with my vna and saw it was resonating low (more like 13.5MHz), and was like 2.5:1 at the wspr frequency, but tried anyway.

When I going into a dummy load, it was doing around 1.4V rms, so I think it was only doing 40mw, and with the mismatch less than that.  Still, got picked up.  WSPR is pretty much magic.

I might try to put a transformer after the `240 to lower the impedance it is seeing to get more power out, but ran out of time.  

Also somewhere in the past few weeks, I got a neat BM83 dev board.  I wanted to see if I could use iFTx working via a bluetooth connection.  Unfortunately, I didn't really fully understand the various BT profiles.  The only bidirectional one (before the latest BLE "gamer" profile) is the headset profile (HSP), which is pretty low quality.  I think it would have been enough, but the iPhone won't use that except when answering a call.  (You could access it via your own program, but that isn't what I wanted.)  I found a program that lets you route audio to it, but it doesn't use the microphone.  The only other option would be to use two bluetooth devices in A2DP mode (one source and one sink), but the iPhone apparently won't act as a A2DP sink for some reason.  ::sigh::  Wish I would have understood all of this before buying the dev board, but going through the exercises of trying to get this to work made me understand all of this a lot more than reading would have I think.