There seems to be an endemic number of failing external antenna cables for these devices. You will know that you have a bad cable because the antenna will be detected, then not detected, then detected, then not detected. Shaking the cable results in more intermittent connections.
In many cases, the issue is pretty simple to fix. It turns out that it is not the cable, but the ground connection on the TNC connector is not making contact on the antenna side. (I know this is hard to believe, but I have seen a lot of this lately and I believe it to be endemic.)
Here is what you need to do:
Take a pen knife (or toad stabber as we call them here in Utah) and bend out the six ground connectors on the inside of the TNC connector, just a little (perhaps 2 mm). Of course, you should be careful to not stick your self with the toad stabber, because you are not a toad.
That is it. I have found that this fixes at least half of the errant cables. And the fix seems to last forever.
If you really do have a bad cable, you can purchase a new factory cable [ 702058 ] but this cable [ IG702058 ] (that we build here at iGage) seems to last longer and not pull out of the receiver when it rotates around the receiver body.
Stay grounded my friends! Mark