Before ordering a GPS tracking radio it might be useful to test GPS satellite reception in the areas you are planning to use the tracking devices and which may seem problematic due to overhead coverage.
For GPS-log testing with your Android phone we recommend to download this free app.
It will provide details on the GPS satellites signals which can be received on the device at the specific location (see below).
Unfortunately there is no equivalent for iPhone users as the Core Location Framework of iOS does not pass on this level of detail. However, this iOS GPS app does a good job at least showing the accuracy of the GPS.