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.
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.
One of the annoying things about the HackRF is that its only 1/2 duplex. It could be a receiver or a transmitter but never both at the same time as a transceiver. Not anymore. SDRangel now has a new feature, the PTT button that automatically switches from RX to TX and back again. To use it is very easy. Setup your source device, then setup your sink device, click the play button and then when you hit the PTT button you will switch from RX to TX like a pro,
I have been playing with this new feature this morning using a 2m handheld and the HackRF and having QSO’s with myself at the milliwatt level LOL. The received audio in SDRangel sounds rather rubbish, i am sure I have some setting wrong somewhere, but it sounds thin and at times distorted. The transmitted audio does sound a little better.
As far as software goes, its good to see the developers of this continue to improve and expand it. There are also a lot of new demodulation types as well since I last updated it.
Ok first off, there is no full schematic for this board, I have already moved on to adding new stuff to it and changing how some parts of it work so I can add in new features. So the best i can offer is this extract that shows where the pins on the micro go to.
Secondly, I wont be releasing my code, the reason is that I do not program using the Arduino IDE and teaching everyone how to program in GCC, to install all the tools required, and uploading the code using an external programmer is beyond my ability to teach anyone let alone everyone. There are just to many things that can and will go wrong and it will only make my life miserable trying to help everyone.
That said, the ESP32 can be programmed in Arduino and the actual basic code is not that hard to write yourself. Turn a encoder and it steps through the relay combinations.
With these relays, I would not put much more than 50w though them. Though the data sheet says they will take 1A but that makes them marginal at 100w. As it stands I think 50w is a very safe bet.
Relays: Omron G5V-1 5V subminiture.
Transistors: PDTC114ET pre-biased SOT23
Caps: 1206 or 1210 Ceramic Multi-layer 1Kv or higher rated, for tuner, 50V 100nF for bypassing. 1uF across the coils of the relays.
Voltage Regulators: 5V and 3.3V 1117 variants SOT223 package.
Toriods: T68-2 T50 would be suitable also, its just what I had, 2,4,8,12,20, 24 and lots of turns.
Top side of the board as 3d rendered.
Bottom side of the board, 3d rendered.
The board as built by me.
I was bored yesterday so i thought i would try building an amp from these transistors I have sitting in the box. Ummm yeah I smoked it pretty hard before I even got any significant power out. I think the main thing is that I could not drive it hard enough to get it into the linear region and I might have had a bit to much bias happening. I will try again, but from what I was reading online, these transistors have a habit of wanting to detonate.
This has been a fun little journey. What started out as look at me i can WSPR on one band, is not looking like, look at me I can WSPR on 5 bands. So what we have here is the 3 band WSPR TX that does 20, 15 and 10m and with an extra PA board and a little bit of code i can add 80 and 40m into the mix also, all this from just 2 antenna.
Here is the schematic for the PA board, less the power supplies. It requires 7V for the fets and 3.3V for the bias. The 10K pots and 3.3v bias supply allow for really fine changes in bias voltage. If memory serves me correct, 600mV was enough to run the fets at about 400mA draw each. The fets themselves are for VHF to GHZ range, so running them at HF is not ideal but its all about what you can find. These are 50 cent parts and what is used in many dual band HT’s as their 5w PA. The fact that I am getting 5w out at HF is rather nice.
Here is the PA board sitting in the box I made for the never ending story transceiver LOL. Note the 5A buck converter being used for the 7V power supply.
Here is a more broad view of how things are looking. 2w out using the old LPF board that was more loss than pass. Built new filters and things are now much better.
Fresh built LPF board without the losses of the old board means I am not wasting 1/2 the power in the filters. I was always going to be happy with a couple of watts, but the fact its making 5w, is nice. Note the heatsink stuck to the back of the PA board. A tone of vias are uses to wick the heat away from the fets and into the heatsink. Its been running for 24 hours straight and temps have remained steady around 50deg C.
Close enough to call that 5w. Its a little less on 20m, more like 4. But that is ok.
And finally, no spots on 15 or 10m, that is to be expected, but we have a number of spots on 20m. So i am calling this a success. Learned a bunch thought this project and the outcome was better than I expected.