Arduschreiber HF-Beacon mkII

[greator]

After having test run the mkI version in my garden with good results I have done a new construction of the transmitter, the basic design is the same but the source of the schematics is different(came with Chinese QRP TX from Ebay), some of the values are a bit different, and the source of the 74HC240 is other. I 3d printed a holder for the Arduino Nano, witch turned out nicely.

Now im just waiting for a few more components for the lowpass filter, according to the designer, the PA-stage will put out about 10W at 13.8v. Im expecting more lika 2-3W.

[ChrisSmolinski]

Looks nice! I hope to hear it on the air!

[greator]

This circuit gives a bit more than i expected, driven with 13v i get 5W out, with 55% efficiency! It also works surprisingly low in voltage. In standby mode the TX only uses 4mA. The frequency can be adjusted with about 2kHz, using the 22pf variable capacitor on the oscillator.

[greator]

Testing "CQ TEST" at 7001,6kHz, fieldhell, at 5W once every second minute from southern part of scandinavia. I will have a look at the web-sdr to get a picture of the range. The antenna is a longwire with a reasonable ground plane.

[greator]

I havent seen my tx on any of the web-SDR, so i tried to switch over to slow-hell but discovered that the PA has a bit of an issue with frequency drift when transmitting longer than the short pulse of field-hell. The signal starts our at one frequency, but then drifts about 250Hz higher during that "dot".

This is a problem with fldigi, since the filter is very narrow. When using the shorter field-hell "dots" this isnt seen, but it wouldnt bee an issue either since the fldigi filter is a lot wider.

The TX didnt have any other issues, so i will take if off the air and start building its enclosure and work a bit more on the code.

[ChrisSmolinski]

I did try checking a number of KiwiSDR receivers when you first posted it was on the air being tested, but could not get any reception, either.

[greator]

I accidentally overheated the circuit when it got stuck in transmission for a longer period of time(a wire short probably) whilst enclosed in a small airtight box, i think a couple of the components overheated. Since i didnt get the stability i wanted to be able to run slow hell i have started looking around after a better design of the PA-stage.

[syfr]

That's a nice looking build BUT I think you'll find that getting enough frequency stability for good HELL images is going to be tricky .   

BTW, design might have worked fine with a resonant antenna rather than random/long wire.  Feed it into a dipole and I bet it's happy!

[Stretchyman]

Wondered what that HUGE heatsink was for!
You need to be running the PA in class E.
You won't need the H/S at all just use the PCB and an insulating pad. Efficiency is around high 80% min. Also using a single Xtal it will be nowhere near stable enuf and will pull noticibly under transmission, I can see you're already seeing this. There's no reason to use a Xtal as they're rather expensive! DDS's are under $2 and will generate any frequency upto 12 MHz (using the AD9833). Stability is improved massively.

Str.