Avoid uncontrolled transmissions with this simple modification on your radio interface

Ham radio operators interested digital modes will often use these computer interfaces to automate CW contacts (send morse code from the PC), use the PC soundcard for RTTY and control push-to-talk functions among other things.
Many of the PTT interface drawings  found on the net suffer the same problem. Well it is not really a problem.


Let’s have a look at a typical interface :interface_before.jpg
You have the RTS and DTR line tied together with diode, then comes a transistor that operates as a switch. And finally the ptt line from you transceiver. So when the RTS or DTR signal goes high, you are on the air. So what is the catch ? Ever booted your computer or used other software besides your regular hamradio soft ? Of course you did 🙂 and what happened ? My transceiver went in to TX on the wrong antenna / receive converter / mistuned antenna. Luckely the radio was set in SSB and no harm done without modulation. But it could be worse.

interface_after.jpgSo what have I done ?
A simple modification that costs almost nothing : add a simple switch in the PTT line. See the red switch in the interface drawing.

That’s it. When the computer has booted and ready to use, I toggle the switch and can operate the digital modes.

20m band report in WSPR

A friend of me asked if I could detect some WSPR signals on 20m. He has been monitoring it a while without any activity.
I also read the comments of G4ILO on the WSPRnet.org site : http://wsprnet.org/drupal/node/384
I must admit that I was also stuck on 30m.
He made a statement and yesterday I had a day off. A whole day of listening later this is what passed my screen :

Timestamp        Call   MHz       SNR Drift Grid   Pwr Reporter RGrid  km    az
2009-01-21 10:48 EA1FAQ 14.097137 -24  0    IN71op 0.5 ON3JT    JO21fe 1274   30
2009-01-21 09:58 VK6BN  14.097091 -23 -1    OF88ac 10  ON3JT    JO21fe 14167 313

Not much.

Hey guys, if you want that propagation monitoring works, we need to activite all bands.