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Saturday, April 30, 2011

Working on T/R circuit for HB WSPR rig --need help!

I'm finally working on the PTT T/R circuit for my homebrew DSB /Direct conversion 30 meter transceiver. I hope to use the simple one transistor circuit from W3PM's FB HB WSPR rig.

But I need info on the PTT signal that will come from the computer serial port. Which pins on the 9 pin serial port connector? What kind of signal comes out? Is it 5 volts on transmit? What settings should I use in WSPR? RTS? Any other setting changes needed?

I hope to be transmitting AND receiving soon.


  1. If you don't get a more direct answer, go to www.smallwonderlabs.com, follow the documentation links, and get the PDF manual for the "initial release" of the PSK-20. It was keyed by the serial line, and the manual has a full schematic.

    Paul - K0EET

  2. Not sure about WSPR, but most programs use either RTS (pin 7) or DTS (pin 4) vs GND (pin 5). Negative 10v on receive, positive 10v on send.

    The PSK 20 looks at both RTS and DTS simultaneously by connecting each to the anode of a diode (1n4148), hooking the cathodes together, looking for +10 at that point to signal transmit.

    Paul - K0EET

  3. should have said DTR, not DTS. WSPR manual says you can set the software to use either one. So take your pick, or do the diode thing above

  4. Bill,

    Here's a couple of example schematics that I've used for PSK31, but should work fine for your application. These are on a "Basics of PSK31" page that I put together for a on-air Tech-Net many years ago. The schematics show the RTS line, but would work fine for DTR if needed.

    73 de Alan W2AEW

  5. ...Oh - see section 3 of the webpage listed above..


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