Dipmeter
A dipmeter , also known as a grid dipper , is a device for measuring the resonance frequency of electrical oscillating circuits or antennas. It consists of a tunable oscillator with a coil that is accessible from the outside. The measuring range is typically between 0.1 MHz and 500 MHz and can be selected in rough steps by exchanging the coil (plug-in coil).
The measuring objects of a dipmeter are often oscillating circuits, such as those used for IF, oscillator and tuning circuits in HF receivers, transmitters, measuring and testing devices. They consist of a coil and a low-loss capacitor . The dipmeter can often also be used as a selective measuring receiver.
The term was coined because the active element of the oscillator used to be a electron tube was whose grid current ( English grid was measured). At the resonant frequency of the measuring instrument shows a characteristic decrease ( English dip ) to the grid current.
Working principle
If two resonant circuits are (weakly) coupled, for example because the magnetic fields of their coils penetrate each other, they exchange energy with each other. The active circuit (i.e. the oscillator) loses energy, which the passive oscillating circuit either converts into heat or radiates. This power loss is at resonance of the two circles is greatest and can at the "tuning" as waste the grid current ( English grid dip oscillator are measured) and the base or gate current. The stronger the coupling between the oscillator and the absorber circuit, the more pronounced, but also "wider" the dip. In the case of resonance, the damping of the oscillator circuit by the measurement object is greatest and its detuning is least. Since the tuning is done by hand, the accuracy of the frequency measurement is limited to a few percent. An additionally connected frequency counter can therefore only increase the reading accuracy of the dipmeter compared to an analog frequency scale.
construction
The picture shows the typical main components of a dipmeter. The air core coil, plugged into the device at the bottom left, consists of only one turn in this (uppermost) range around 200 MHz. The variable capacitor adjusts the oscillator frequency of the dipmeter. It can be seen on the right edge of the picture in its light, transparent plastic coating. The disk for adjusting the capacitor on the underside also serves as a scale for reading the measuring frequency. The deflection of the small moving coil instrument in the upper area of the picture changes with the transmission power.
Operating modes
- Active : As a measuring transmitter , the measuring arrangement is e.g. B. a passive resonant circuit or an antenna is excited by the built-in oscillator, and the "loss" at resonance at the frequency set on the dipmeter is qualitatively determined. A frequency meter could also measure the transmission frequency of the dipmeter directly. This is the "normal" operating mode of the dipmeter.
- Passive : The resonant circuit to be measured must radiate power itself. For this purpose, the dipmeter's oscillating circuit is not operated in an oscillator circuit, but rather serves as an input filter in the measuring receiver ( single-circuit receiver ). After this input filter has been manually tuned to the reception maximum (dip), the deflection of the pointer instrument shows the relative strength of the transmitted signal and the tuning scale shows its frequency ( absorption frequency meter ). With some devices, headphones can also be connected to monitor the modulation.
literature
- Author collective: amateur radio . German military publisher, Berlin 1963.
