A Better Diagram for the 74HC240 QRPp TX

Another example (with clearer diagram) of the 74HC240 digital IC based QRP transmitter that  I posted about previously.

CW tx based on 74HC240
74HC240 IC CW Transmitter Puts Out 500 mW
 This one also has values for the VXO capacitors. I now have the parts for this, so perhaps it will show up on the work bench soon. I've added a link to this example on the Kits and Homebrew page.

By the way, there are some great on-line circuit simulators out there, such as CircuitLab, that are a great help for hands-on homebrewers, such as me, who are still learning about electronics.  For learn-by-example hams, these simulators reduce the amount of smoke on your work bench.
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  1. What is the max frequency the 74HC240 can be used at ? How stable is the frequency ? Looks like an awesomely simple toy transmitter.

  2. Honestly, I don't know the max freq. At 10M and above, though, you'll probably have stability problems.

  3. Prior to use it in a Radio Beacon for an high altittude experiimenf with Argentine AMSAT, I try in 28 Mhz and work OK. You can see my work in the website, with an IRF 640 providing 8 watts with 2 LiPo Cells. No CW clicks and a nice derivated LO output for the DBM mixer, in case you want a CW transceiver. Key off is only 25 mA.
    Have a nice 2014: Edgardo Maffia LU1AR


Thanks very much for your comment! 73, Casey


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