Long-distance wireless sound pick-up/Wireless sound pick-up

The 980 professional wireless audio frequency transport of GM series
is a wireless hearing-aid tool that can help you to hear distant sounds.
 It has characteristics as clear sound, far distance, small size and perfect
functions, which using sophisticated high-tech devices, innovative
circuit design, US ASIC and STD installation process. It is applicable to
scene monitor and wireless audio transmission, such as security monitoring
system, hidden interview, audio-visual education, tourism, amusement,
filed expedition, the industrial and mining enterprises, and so on.

Technique parameter

1.Frequency band: ISM/UHF band. GM980 use fixed frequency point
  and GM980DJ use broadband to transmit signal.
2.Transmission distance:2800(max 7km) in widen area,
  which is according to its using conditions
3.Power supply: the monitor head uses a high energy lithium battery
  which can be used for 16hours in total. The receiver uses two 7th
  batteries of 1.5v which can be used for 24 hours in total.
4.Sensitivity: (all directions) of sound picking up is better than 12Db,
  differentiate rate is high within 200 square meters.
  Impedance of audio input circuitry is low.

Use instructions:

1.Swith ON the monitor head JT980 to enter work state and place it
  at the position away from the main sound source of 1-5 m with the
  antenna extended previously. Plug earphone into the hole marked with
  EAR of the receiver, and turn on the power switch(V0L/OFF) to fit
  volume for hearing the scene sounds.
2.A compatible cable can be used to connect the sound pickup with the
  secondary equipments such as recorders, amplifiers, stealth headphones,
  wire or wireless relays, etc. through inserting one end of the cable to
  the hole (3.5mm) marked with A-our of audio output regulating V0L can control
  the electrical level output. It can realize the second relay transmission
  to use withGM910B.
3.The jack (3.5mm) of the monitor head can be input all kinds of audio signals
  wireless, which can be regulated for a loud and distortion less sound.
4.The monitor head will be auto power off when the electric energy has been
  used up. Please charge in time with the charger of 5V DC and 300MA. When charging,
  the power switch should be turned off. The charger can be used as an external
  power under the state that the electric energy has been charged enough
  ( the green light die out). There may be light AC noise that would be reduced
  or disappear when expanding the receiving distance.
5.When the monitoring distance is longer, please carefully adjust the direction
  and position of the receiver to keep its best receiving state. There will be
  blind spots(some closer points have weaker signals) in dense buildings area
  because of signal have been greatly changed by being obstructed and multiple
  reflections. It is particularly important how to choose a suitable receiving
  point and position for the monitor-head, and the receiver should be as high
  as possible or in an open space. The monitor-head should be near the window
  when used in a room. The fewer the building obstructs are between the receiver
  and the monitor-head, the farther the transmission distance is.
6.Transmission distance is deeply affected by use environment and climatic
  conditions, such as ,the higher place is better than the lower place,
  the widen area is better than the building dense area, the suburb is
  better than urban area, the evening is better than daytime, and signal
  is stronger in the direction parallel to the antenna. Users can use the
  sound pickup and the receiver according to foresaid points.