[VHFcontesting] HamIM/APRS and Non-ham observers [was: Captive Roving...]

[Ev Tupis]

----- Original Message ----
From: Nate Duehr <nate at natetech.com>

I interpreted the rules restricting no more than one transmitter active per band to mean that if the APRS is on VHF, the VHF SSB must be off, or vice-versa.

Wouldn't you agree?
---------------------------

Ah yes!  You're right, of course.  Here's how that is addressed...

TNC's use an anti-collision method called CSMA.  Carrier Sense Multiple Access.  They use their RXing to assure that there is no signal on the channel prior to TXing.

Even at 147.585 MHz, there is significant QRM from SSB operation on 144.2 MHz.  As a result is (often, but not always) that the packet HamIM system will not TX until your SSB station stops TXing.

Even if the TNC doesn't act this way at first, there are often CSMA settings that can be played with until the TNC operates in this way (though those setting vary from one TNC manufacturer to another -- and I'd refer you to the manual).

Lastly, if it no combination of settings works, use a contacts on the 2m SSB station to activate a relay that makes/breaks the TNC's PTT control.

The advantage of HamIM is significant where home-based stations know to employ the strategy.  Even Rover-to-Rover communications is enhanced since they often operate from hilltops (LOS) and get noticed more easily.  I've completed QSO's with HamIM equipped rovers because of HamIM that I would have missed otherwise.

By the way, the term HamIM was coined because it allows keyboard-to-keyboard "IM-like" communication using Ham bands.

Regards,
Ev, W2EV