Problem recording with a lavalier wireless mic

I bought a Shure lavalier wireless mic but can't get it working with my Mac--or a friends Mac for that matter. The problem is I can't get an adequate input line level. I've tried using an iMic into the USB port and I've tried plugging into the input jack directly--no success. I bought a M-Audio Mobilepre USB preamp--no help. I then got an M-Audio DMP3 mic preamp which has more power (67dB of gain). When I hook up a Shure SM57 it works fine. The problem isn't lack of phantom power--the wireless system supplies it. Any suggestions?

 

Thanks to those who have offered suggestions. The mic itself works fine. I get a good response on the preamp meter. The battery is fine.

 

It's a Shure PGX4 mic. There is no output gain on the receiver or switch.

 

A little progress!

I picked up a different cable with a 1/8" stereo TRS plug. This makes a difference. Before I had a mono cable. Yet, still the line level is poor. It's worse with the iMic and the sound quality is terrible. It's better plugging straight into my Mac's input jack--but still not a great level.

Does anybody know of a good consultant I might call?

 

Thanks

Thanks to one and all for your suggestions. It turned out the problem was the cable connecting the preamp to my Mac. I had a 1/4" stereo to 1/8"mono cable. I got a stereo-stereo cable and the system now works fine!