This page claims the DTR thing is Delorme only.

Not really, because the streetfinder connects directly to the palm and doesn need a palm->DB9 serial adapter. And it claims that only delorme needs to have the dtr connected in that adapter. It doesn't know what the streetfinder uses because it doesn't have to.

But If you open the receiver you can check whether the pin that should be DTR is connected to anything or if it's pad is completely isolated. If it is connected it must be used for something...