I worked a new country today on 15m. Mongolia.
I have the Pi all setup now and its making RF. Next i need to see what I have around here in the way of amplification to get a bit more chooch for my chaach.
The signal is actually pretty clean, the noise you see is from the scope, not the Pi. Crap scope and overly sensitive to noise when its down on the lower power settings.
As you can see by the WSJT waterfall, 15m was going bonkers. Its great to see so much action on there.
The band was open all day and in the evening time, opened into the EU. Cant say I did all that well but I managed to make one contact into the EU and it is my first contact for the new solar cycle, it was with a station in Poland. You can see on the map i was not really being heard all that much in the EU. Probably not quite the sunspot numbers I need for my simple vertical antenna to be reliable enough. But seeing its still only early doors on the new cycle, things are looking promising. I did also spend 15m calling cq on CW, self spotted on the cluster and all and nothing. It was worth a shot.
5pm local time and Japan is running hot on 15m. I have not seen this many signals on 15m in god knows how long. I am even working some of them. My plan was to come in here and solder up a filter for the Pi board and here I am making contacts. Japan might be easy DX from Australia, but they are plentiful and that makes it fun.
I needed an AM modulated signal for something I am dicking about with. Selecting the AM wave type with a 7Mhz carrier produced a 50Mhz singal. I am not sure what is going on there, but I think it might be the DAC aliasing. So after RTFM and coming to the conclusion it was as good as toilet paper, IE something to wipe your arse with, I did the old Jazz hands routine and searched on google for the answer.
The answer was actually quite simple, set channel 2 to the modulation width you would like, in this case i think I went 20Khz, set channel one to the carrier frequency and the hit the modulation button, select the modulation type and Bob is your uncle.
This is the 20Khz signal 100% modulated.
And this is the view on the spectrum analyzer, it kind of sorta looks like an AM signal yeah? I probably should have reduced the carrier power level and increased the modulated signal level to make it look more legit, but hey, i was excited enough to get this far and was over the whole fix it till its broken work cycle that I employ. Anyway, I now know what I am doing, and probably need another signal source to try demodulating AM signals, something to use as the LO as I am tying up both outputs on the function gen.
Onwards and upwards.
What can I say, I like to trawl through parts catalogues and find somewhat obscure parts or ultra cheep parts to play with. So, when i found the MC3361, which is an FM Cordless phone IC, I thought why not. It costs 25 cents in one offs, and has some conversion gain and I assume its a gilbert cell in there, so its way cheaper than an SA612 and others.
LO in is on pin one, you can also add an xtal here for the LO. RF in is on pin 16 and the IF out is on pin 3. Now i did not try and match the impedance’s which are around 1800 ohms, i just fed in 50 ohms from my function generator into the LO and RF ports and then attached the spectrum analyzer to the IF port.
Other than some DC blocking caps and a 50 ohm termination resistor on the input there is not much to add to this. And as you can see from the plot below from the spectrum analyzer its working doubley balanced. RF in is suppressed and the sum and difference are the dominate signals. RF in was 7Mhz and the LO was 1Mhz for the sum and difference of 6 and 8mhz IF frequencies.
Is it as good as other mixers? I don’t know, but it works and its cheap, so i think its worth a go. Oh and it also has an FM de-modulator, AF amp and a op-amp for filtering in there also. I am yet to play with the other bits, i just setup the board for mixing only and well, mixing works.
I have had this intermittent problem with RF in the shack. Mainly this was on 20m where when transmitting some digital mode like FT8, the software would crash and the computer would send random serial commands to the radio and just mess things up. Mostly this was on 20m, but also on 15m the wireless mouse would stop working while in transmit. So i had some RF issue happening and by chance I worked out what it was.
Now, for work i spend a good part of my time on a motorcycle out delivering and I like to listen to the radio, podcasts and even ebooks using software that reads the text to me, while i work. I use these cheep arse bluetooth headsets to pipe the audio into my ears from my phone.
It turns out, when i have these plugged in and charging, they are acting as antenna and RF is then being fed into the mouse and keyboard dongle and computer VIA USB and then out the USB to serial cable for the radio’s cat control. Who would have thought that something as simple as USB charging would be the cause of all my problems.
Solution was simple, unplug the bluetooth headsets and everything is tickety boo. Oh and the reason why I have 2 of these, the battery only last 4 hours and 2 means I can work all day and keep the sounds coming. 🙂