National RF Resonance Dip Meter is a test instrument used to determine the resonant frequency of a tuned circuit or resonant network, such as an antenna system. In addition, the unit may function as an RF detector, or a secondary frequency source. The instrument is analogous to the older vacuum tube “grid dip meter,” once popular in every electronic laboratory or radio station. Unique to this updated version is a buffered output that may drive a digital frequency counter for exact measurement of resonant frequency, or connected to an oscilloscope to be used as an RF detector and waveform/modulation monitor.
The unit is hand-held and powered by a single replaceable 9-volt battery. Battery lifetime is estimated to be over one year with average usage. Plug-in coil sets are provided to provide a useful frequency range from under 1 Mhz to over 70 Mhz. Each plug-in unit has its own separate analog scale which gives approximate RF frequency. Exact frequency is determined by the use of an external frequency counter, not provided with this system.
The NRM-2D is the deluxe instrument set, including a ruggedized carrying and storage case (manufactured by Pelican Products) and the standard three coil sets, covering the 3.5 MHz to above 40 MHz frequency range. Sells for $299.95 new. Buy my which has barely been used as shows no wear for $75 plus shipping. Check out their web site. This device is still being made today.