It’s the “no probes” part that’s the killer here. The probes are what gives the meter its bandwidth. Probes are usually bad because users like to measure the signal. Schematic of Boonton Model 92 A RF Millivoltmeter; Boonton Electronics Corp. . In the Ballantine Model A RF millivoltmeter, which is. The old Boonton RF Millivoltmeter or Boonton RF Microwattmeter or . Ballantine Labs A Standard RF Probe – 10KHz to GHz with pf.
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Successive approximation techniques are employed in commercial radio frequency millivoltmeters such as the Boonton Electronics Corp.
Relative gain or loss measurements are simplified by a 0 dB reference adjustment. There are three display ways including voltage, dB and dBm, supplying a clear and intuitive display.
3440A RF Millivoltmeter | Ballantine
Front panel meter zeroing is accomplished by adjustment of a ten-turn potentiometer R81 which provides an output reference for amplifier U4. My Boonton’s use special diodes in the probe for full-wave rectification, which is then converted back to AC in the instrument via a mechanical chopper. In the Ballantine Model A RF millivoltmeter, which is constructed generally in accordance with the embodiment described here, the probe housing is heavy brass with a double wall, to prevent localized external temperature variations from changing short term calibration by providing a long thermal time constant.
Measuring RF at microvolt levels presents a whole bunch of challenges. Resistor R72 adjusts full scale calibration of the indicating meter. In the embodiments of FIGS. The apparatus of claim 5 wherein the diode detector is 34440a germanium point contact diode. In the Ballantine Model A RF millivoltmeter, which is constructed generally in accordance with the embodiment described here, the following semiconductor device types have been used:. You can ignore that, but I suspect the calibration won’t meet exact specs unless it’s reset.
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A RF Millivoltmeter | Ballantine – TechRecovery, LLC
By amplifying the signal before detection, the entire detector output can be placed in the linear response region ballantien no further compensation is required. The precision resistor network comprising resistors R52, RR63, plus the feedback network of meter amplifier U9, performs the required scale linearization. The apparatus of any of claims 1 through 4 wherein the diode detector is a germanium point contact diode.
Resistors RR63 are selected to provide a constant output impedance. The probes are usually much more complicated than that. Aug Thu 25, Lead is connected to the main ground of the millivoltmeter. TLC’s which are connected in an instrumentation amplifier configuration with very high common mode rejection. Some of the old Millivac RF voltmeters MV series, for examplecould get down to the single millivolt range with nothing more than crystal detector probes.
These characteristics cause the probe to have high input impedance over the very wide frequency range from 10 kHz to beyond 1. The square root converter circuit requires only three adjustments: Aug Sat 27, In the 10 mV range, a further reduction is provided by substituting resistors R85 and R87 for resistors R84 and R86 in the voltage divider.
Dec Mon 31, 2: Range switching in this embodiment of my invention is accomplished electronically by use of field effect transistor FET switches. Resistor R74 and relative reference potentiometer R75 shunt the meter and can be used to provide a different calibration to facilitate dB ratio measurements.
Aug Thu 25, 3: For a typical RF diode detector of the type used in RF millivoltmeters, a square law response or transfer function is obtained for signals below approximately 30 millivolts mVa linear response or transfer function is obtained above approximately mV, and the response between approximately 30 and mV is in transition between square law and linear.
The probes are what gives the meter its bandwidth.
I googled RF probe and found lots of information about making a probe for use with a vom or dmm using the 1n34 diode. If it isn’t practical to work with everything shielded, the project has to be moved into a shielded room.
In the 3 mV range, the reference is reduced by a voltage divider comprising resistors R82, R83, R84 and R86, to correspond to the reduction in gain of the preamplifier Where I am convinced milllivoltmeter they were supplied to people who didn’t have the slightest clue how to use them.