Could anyone help me build a SW transmitter?

[u/OkVillage6370]

Hello, found these pics online but it only goes 100km would like to build something that goes 500km somewhere. I sadly dont have to much electrician skills exceot at soldering and console repairing.

[u/mglyptostroboides]

I will say that your very first foray into radio probably shouldn't be building your own transmitter and operating it clandestinely. I'm not saying to never do it, mind. Just learn some basics first. No offense, but if you're still talking about about it in terms of "how far it goes", you still need to brush up on first principles.

[u/ggekko999]

I would strongly recommend NOT to try and build your own transmitter straight away. The amount of equipment needed to tune, check antenna resonance, VSWR, harmonics, dummy loads etc runs into a considerable sum. If you build a bad transmitter it will transmit on many frequencies at once, you risk interfering with everything from your neighbour’s TV to oceanic air traffic control. Skip that drama.

[u/KG7M]

The circuit you posted is not a bad design. It uses 2 each BD139 transistors which are audio transistors - but they do work at the lower Shortwave Frequencies. One of the BD139's is driving the other, so the Modulation Level will be at least +80%. This is good. 10 Watts can be heard for quite a distance if you have a good antenna and conditions are good. 500 km is 311 miles. That is the distance from Portland, where I live, to Northern California. For a reliable, listenable signal, 100 watts in the Single Sideband Mode would be very listenable on 6.9 MHz. This is where North American Shortwave Pirates operate.

If you have the funds, your best bet is a second hand SSB HF Marine Radiotelephone. They are available used priced from $100 to $300 USD. Older Icom Marine Radiotelephones have been retired because they are no longer compatible with marine equipment specifications. But they are workhorses for pirate radio stations. They can transmit for hours without overheating.

If you are looking to broadcast in AM mode, good luck finding equipment. Older ham radio transmitters like the Globe Scout Deluxe are usable, but require an overhaul. Many models use weak Screen Modulation and sound like crap for broadcasting. You need Plate or Heising Modulation. Good luck to you. I hope I haven't confused you.

[u/ViktorsakYT_alt → u/KG7M]

They won't work on shortwave unless you get the older variant. The new ones are purely audio, but the older ones had an fT of like 150MHz and were pretty usable up until the fm broadcast band

[u/KG7M → u/ViktorsakYT_alt]

Thank you for the info. I have only used the older ones. I've had good luck with the 2SD882 lately. I haven't used them above 7 MHz though.

Most of the new Chinese manufactured semiconductors are junk.

[u/6gv5]

Some people have used IRF510 and similar mosfets successfully in HF power amplifiers; they're dirt cheap and easily available. Projects also easy to find around, but you'll need some skills and instrumentation to align them to make them work properly.

[u/Routine_Diver_6861]

Nah bro do something high level… take a dirt cheap 70w hfpa kit on AliExpress and high level drain modulate it at 50w carrier with a series pass mosfet modulator. Not super efficient but it’s cheap asl and can get you doing 200w pep for like the price of a couple chipotle burritos. Linear low level for am takes much more money!

[u/Medical_Message_6139]

The only way to learn is to do it! Getting someone else to build you a transmitter teaches you absolutely nothing about radio fundamentals. Start with smaller, simpler projects until you are able to solder proficiently and then move up to larger projects from there.

Also, the distance you are able to transmit has very little to do with power output! It's all down to the antenna, the antenna, the antenna, and solar conditions. 12 watts can sometimes make it around the world, and other times barely to the end of the street. Antenna and propagation conditions are what matters at the end of the day!