FET DIP Oscillator G3WPO Mk1 (Ambit)

Cirkit dist.Ltd. (Ambit); Broxbourne

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  • Year
  • 1981–1987
  • Category
  • Service- or Lab Equipment
  • Radiomuseum.org ID
  • 211591

Click on the schematic thumbnail to request the schematic as a free document.

 Technical Specifications

  • Number of Transistors
  • 5
  • Semiconductors
  • Main principle
  • TRF with diode detector
  • Tuned circuits
  • 1 AM circuit(s)
  • Wave bands
  • Wave Bands given in the notes.
  • Power type and voltage
  • Dry Batteries / 9 Volt
  • Loudspeaker
  • Electrostatic Loudspeaker (high bias DC voltage) / Ø 1 inch = 2.5 cm
  • Power out
  • 0.01 W (unknown quality)
  • Material
  • Metal case
  • from Radiomuseum.org
  • Model: FET DIP Oscillator G3WPO Mk1 - Cirkit dist.Ltd. Ambit;
  • Shape
  • Portable set > 8 inch (also usable without mains)
  • Dimensions (WHD)
  • 58 x 92 x 125 mm / 2.3 x 3.6 x 4.9 inch
  • Notes
  • DIP oscillator and Wave meter

    5 Wavebands from 1.8MHz to 215MHz
    A: 1.6 ... 4.2
    B: 3.5 ... 10.0
    C: 9 ... 26
    D: 25 ... 90
    E: 80 ... 210
    Progressivly poorer "dip" at lower bands in Oscillator "GDO" mode
    Sensitivity control varies drive from peak rectifier diodes to meter rather than oscillator level
    Audible tone volume controlled by detected level (piezo-ceramic beeper)
    You can add your own coils. A common modificaton is an FET buffer (2N3819 or similar) to drive a frequency counter.
    Labelled "Made in England by Ambit International", the MkII in 1987 is "Cirkit" branded and adds a resistor on the plug in coils to set Oscillator level, so coils are not exchangeable. See Articles for operation and use.
  • Net weight (2.2 lb = 1 kg)
  • 0.320 kg / 0 lb 11.3 oz (0.705 lb)
  • Author
  • Model page created by Michael Watterson. See "Data change" for further contributors.

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The model FET DIP Oscillator is part of the collections of the following members.

 Forum

Forum contributions about this model: Cirkit dist.Ltd.: FET DIP Oscillator G3WPO Mk1

Threads: 1 | Posts: 2

If you search on "Dip Meter" on RMorg you may find 60 pages of results. My first meter was something like  this Leader (link) in about 1981. Joe Sousa suggested I write something as the "Dip meter use" is almost like a lost art today. I left the Leader Transistor Dip Meter behind when I moved in 1983.

Originally called a Grid Dip Meter or GDO (Grid Dip Oscillator) when they used a valve (tube), the name has stuck and often bipolar or Transistor or FET  Dip Meters are also called "GDO".

The principle is simply to have an oscillator where the tuning coil is external and easily influenced by coupling to another tuned circuit. A diode detector feeds a meter so the oscillator level is visible. If an external tuned circuit is at the same frequency then some of the oscillator power will couple to it and the meter needle will dip as you move the tuning capcitor past the resonance. The meter can thus be used to tune aerial "traps", IF filters and loop aerials. If the oscillator is too powerful or stable then the dip will be too small. This is why the main tuned circuit is usually on the grid, base or gate of the amplifier.

Band switching is just manually using a different plug in coil.

Today with cheap 0.01% or better frequency meters that work 100kHz to 2GHz a good option is an FET buffer on the oscillator to drive a counter for accurate frequency display. This output can also be used as a "cheap" RF signal gernerator.

Most meters have a mode where the oscillation is disabled. This is traditionally called a "wavemeter". It's nothing more than a single tuned "crystal radio" or TRF with a meter replacing the headphones!

One problem is that without a band dependent oscillator gain control the oscillator can be too strong on the lower bands and thus little or no "dip". The G2WPO mk1 suffers badly from this which is largely mitigated on the mk2 by using dual gate FETs and a gain set resistor on each plug in coil.

Michael Watterson, 31.Jan.12

Weitere Posts (2) zu diesem Thema.