I’ve used this Gizmo infrequently over the years, it’s in a used condition but quite rare . This is the blurb from the website ( http://www.samsontech.com/samson/products/wireless-systems/airline/airline-ap1b/ )
The AirLine UHF Bass Guitar System eliminates body packs with a tiny micro transmitter that plugs right into your bass guitar. The AP1B, the system's receiver, is designed to easily integrate into an effect pedal setup and features a shape circuitry yielding a fat, full bottom end never before heard in a wireless system for bass.
The revolutionary AirLine "plug-in" AG1 transmitter is designed for traditional end-mount inputs. Less than half the size of conventional body packs, this miniaturized transmitter runs on a tiny triple-A battery with 14 hours of battery life. It features an array of on-board controls: A Power On/Off and Mute switch, red/green LED for Power On/Off, a Peak LED and an Input Level control for different pickups. And UHF (Ultra High Frequency) means clearer frequencies with less interference.
Designed for use with your compact effect pedals, the APB1 pedal receiver provides reception you can always depend on. It features a 1/4-inch output jack, Power switch, Peak LED and a Volume control. You can use a 9-volt battery or an AC adapter to power the receiver and when you unplug the unit, the battery is disabled to conserve power.
I use the small pouch for the transmitter, the main unit sat on the Pedaltrain nano plus.
Clips on the battery compartment are broken but never bothered me as it as powered by a Volto powerpack.
Thanks for looking