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Explains how the dip meter works using inductive coupling by placing the coil near the circuit.
Details the dip meter's capacitive coupling method for measurements without coil contact.
Provides instructions for installing the battery and loading oscillation coils into the unit.
Offers guidance on adjusting the dip meter's proximity for accurate resonant frequency detection.
Advises on measuring resonant circuits in transistorized transmitters and receivers.
Step-by-step guide on selecting coils, connecting, and operating the DM-801 as a dip meter.
Covers measuring resonant circuit frequencies and antenna resonance using the dip meter.
Instructions for using the DM-801 to align receivers by acting as a signal generator.
Details using the DM-801 for checking crystals and acting as a marker generator for calibration.
Guide on using the DM-801 to measure oscillator and transmission frequencies by absorption.
Explains how to use the DM-801 to measure the field strength of transmit antennas.
Methods for calculating unknown capacitance and inductance values using resonant frequencies.
Explains how the dip meter works using inductive coupling by placing the coil near the circuit.
Details the dip meter's capacitive coupling method for measurements without coil contact.
Provides instructions for installing the battery and loading oscillation coils into the unit.
Offers guidance on adjusting the dip meter's proximity for accurate resonant frequency detection.
Advises on measuring resonant circuits in transistorized transmitters and receivers.
Step-by-step guide on selecting coils, connecting, and operating the DM-801 as a dip meter.
Covers measuring resonant circuit frequencies and antenna resonance using the dip meter.
Instructions for using the DM-801 to align receivers by acting as a signal generator.
Details using the DM-801 for checking crystals and acting as a marker generator for calibration.
Guide on using the DM-801 to measure oscillator and transmission frequencies by absorption.
Explains how to use the DM-801 to measure the field strength of transmit antennas.
Methods for calculating unknown capacitance and inductance values using resonant frequencies.
The TRIO DM-801 is a versatile DIP METER designed for the adjustment of radio equipment and antennas. This self-excited oscillator offers both inductive and capacitive coupling, a notable advancement over conventional testing instruments, particularly for measuring enclosed and toroidal coils.
The primary function of the DM-801 is to act as a dip meter, which involves measuring the resonant frequency of a circuit. In inductive coupling (Fig. 1A), the coil unit of the DM-801 is placed near the circuit under test. As the DM-801's oscillation frequency matches the circuit's resonant frequency, energy is absorbed, causing a momentary "dip" in the meter's pointer. This dip indicates the resonant point, hence the name "dip meter." For accurate readings, it's advised to initially couple the coil tightly to find the dip, then slowly move it away to narrow the dip and precisely read the frequency. The A band, however, may exhibit a broader dip due to a larger pull-in effect.
A unique feature of the DM-801 is its capacitive coupling capability (Fig. 1B). This allows for resonant frequency checks by simply touching the capacitance probe to the "hot" side of the resonant circuit. This method is particularly useful for coils enclosed in metal shields or toroidal coils, which are difficult to measure with conventional inductive coupling. For frequencies around 50MHz or lower, both the ground clip and probe are used, while for 50MHz and higher, only the probe is needed. The probe must be connected to the hot side of the circuit, not the ground side.
Beyond its core dip meter function, the DM-801 serves as a signal generator. By coupling it to the antenna circuit of a receiver, its output carrier can be used for alignment. For AM receivers, setting the FUNCTION switch to "MOD" generates a 1kHz tone, aiding in alignment. For SSB and CW receivers, the "OSC" setting provides an unmodulated signal. Adjustments to capacitor trimmers and inductor cores can then be made for maximum "S" meter reading or speaker output. If the output is too strong, the oscillation level can be lowered, the DM-801 moved further away, or a shorter receiver antenna used.
The DM-801 can also be modified to function as a crystal checker and marker generator. By installing a crystal (HC-25U, FT-243, or HC-6U) in place of the oscillation coil, it can check crystal quality and generate marker signals at specific frequencies (e.g., 1MHz, 3.5MHz). This is useful for calibrating receiver dials.
Furthermore, the DM-801 operates as an absorption frequency meter. With an oscillation coil installed and the SENSITIVITY control adjusted to minimum deflection (just before OFF), and the FUNCTION switch set to OSC, it can receive external energy and indicate its frequency. This is valuable for measuring oscillator frequencies by coupling the absorption frequency meter coil to the oscillator coil, or for checking transmission frequencies by coupling it to a transmitter tank coil.
Finally, the DM-801 can be used as a field-strength meter. By setting it up as an absorption frequency meter and coupling it to an antenna, it can measure the field strength of a transmit antenna, assisting in transmit antenna matching and radiation pattern adjustments. It also facilitates capacitance and inductance measurements by combining an unknown inductor with a known capacitor to determine resonant frequency, or vice versa, using specific formulas provided in the manual.
The DM-801 offers a wide measurable frequency range from 700kHz to 250MHz across seven bands, making it suitable for various applications. All necessary accessories, including seven dip meter coils, a capacitive probe, earphone, and ground clip lead, can be conveniently stored within the unit, enhancing portability and ease of use. Its solid-state design and built-in battery make it suitable for both indoor and outdoor measurements.
The device incorporates HC-25U and FT-243 sockets, allowing for its use as a crystal checker and marker generator, adding to its versatility. Amplitude modulation is a convenient feature for aligning receivers when the DM-801 is used as a signal generator, and it aids in precisely calibrating the dial scale for receivers without a BFO when used as a marker generator.
The meter circuit utilizes an FET and transistor, providing extremely good sensitivity for accurate readings. An earphone plug is included, enabling users to monitor transmit signals. The capacitive probe is a significant advantage, allowing measurements without the need to remove coil shields, simplifying the testing process. The ability to measure resonant circuit frequencies of toroidal coils, which is not possible with conventional dip meters, further highlights its advanced capabilities.
When measuring resonant circuits, the proximity of the dip meter to the circuit affects the dip's depth and breadth. A closer coupling results in a deeper but broader dip, making it harder to find the exact resonant frequency. Therefore, it's recommended to move the dip meter slightly away from the circuit for a sharper, more accurate dip.
For measuring transistor resonant circuits, which may not always show a dip by dipping load, the manual suggests temporarily disconnecting the transistor or operating the circuit with power on and measuring by absorption.
When measuring transmitters, caution is advised. The DM-801 should be brought near the tank coil slowly to avoid damaging its transistors and other components with excess RF energy. The earphone can be used to monitor modulation. Users are warned about high RF and DC potentials in tube-type power amplifiers and high RF levels in transistorized power amps, emphasizing the importance of normal safety procedures.
The DM-801 is designed with user-friendly maintenance in mind, primarily focusing on battery management. To load the battery, the coil compartment is removed to access the battery snap connector. The battery take-out ribbon should be laid into the battery holder before installing the battery. The supplied oscillation coils are then placed into the coil compartment, and the compartment is reinstalled.
Before operation, it's crucial to verify the battery's serviceability. This is done by turning the POWER switch on and setting the FUNCTION switch to "BATT CHECK." The battery is considered usable as long as the meter pointer remains within the "B.C" zone. A weak battery can lead to unstable or no oscillation, or frequency errors, necessitating replacement.
After use, the POWER switch must be turned off to conserve battery life. If the DM-801 will not be used for an extended period, the battery should be removed. The take-out ribbon facilitates easy battery removal without the need to remove case screws.
The manual also provides adjustment instructions for various internal components. VR1 (Q1 Bias adj.) is adjusted using the G band to achieve maximum meter pointer deflection at 83MHz. VR2 (Meter zero adj.) is set so that the meter deflection is zero when the sensitivity control/power switch is just before the OFF position. VR3 (Sensitivity adj.) is adjusted to its optimum position. VR4 (Battery voltage check adj.) is set so that the meter deflection reaches the left edge of the "B,C" zone at 7V when the FUNCTION switch is set to "BATT CHECK." These adjustments ensure the device operates accurately and reliably.
General| Type | Digital Multimeter |
|---|---|
| DC Voltage Ranges | 200mV, 2V, 20V, 200V, 1000V |
| AC Voltage Ranges | 200V, 750V |
| Accuracy | ±(0.5% + 2 digits) |
| Operating Temperature | 0°C to 40°C |
| Power Supply | 9V battery |
| DC Current Ranges | 200μA, 2mA, 20mA, 200mA, 10A |
| Resistance Ranges | 200Ω, 2kΩ, 20kΩ, 200kΩ, 2MΩ |
| Input Impedance | 10MΩ |
| Measurement Range | See DC Voltage Ranges, AC Voltage Ranges, DC Current Ranges, Resistance Ranges |
| Operating Humidity | 80% RH max |
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