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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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. Buffer amplifier circuitalso shown in FIG. Resistor R74 and relative reference potentiometer R75 shunt the meter and can be used to provide a different calibration to facilitate dB ratio measurements.
In the embodiments of FIGS. Common calibration errors are eliminated through millvioltmeter compensation of the probe detector diodes; double shielding protects the interchangeable probes from rough handling and pickup.
Where k is the mixing factor determined by a given position of the range select balkantine SW, EQU4 As a result, the output voltage V o of the meter drive amplifier can be defined as follows: First, everything has to be well sheilded, since even an exposed probe millivoltmeteg can pick up enough RF “noise” to throw off your readings. In the Ballantine Model A RF millivoltmeter, which is constructed generally in accordance with millivolt,eter embodiment described here, the following semiconductor device types have been used: The signal at the output of amplifier A 3 is applied to a square root converter SR and to a linear operational amplifier A 4.
An additional four transistors are similarly arranged to approximate the required response in the mV range, three more are used for the mV range, two more of the 1 V range, and one for the 3 V range. The voltmeter matches the characteristics of the probe by processing the signal on leadwhich is ballantkne of the probe output, millivoltmeher a square root converter circuit and a linear amplifier having inputs in parallel, and then mixing their outputs in various proportions as is appropriate for each voltage range by use of the precision resistance network The instrument is calibrated in rms of a sine wave.
Resistor R72 adjusts full scale calibration of the indicating meter.
3440A RF Millivoltmeter | Ballantine
Temperature variations will change the detection efficiency and conduction offset so as to affect calibration. Thermal effects, input offset voltages and currents which would affect the meter’s zero point are balanced out by biasing the inputs of U1 and U2.
Aug Thu 25, It’s a foam lined plastic box with the probe and various adapter tips. The ambient temperature inside the probe is sensed by diode CR3 and the base-emitter diode of transistor Q1. The full wave rectification of the detector probe permits measurement of signals having asymmetrical waveforms without error from polarity turn-over effects.
I forgot my password. RF voltmeters without probes are truly a dime a dozen. Aug Sat 27, More like hundreds of millivolts at best. The output of the detector diodes, however, is a non-linear function of signal amplitude.
Broadband voltmeter – Ballantine Laboratories, Inc.
As shown in FIG. The apparatus of claim 5 wherein the gain switching between the lower ranges is accomplished by changing the feedback of a first amplification stage and the gain switching between the upper ranges is accomplished by changing the feedback in a subsequent amplification stage.
The square root converter circuit requires only three adjustments: Not that I’ve had much luck with this myself, but you could also try calling Ballantine tech support and asking if they have any “B” stock or used probes, or perhaps one that won’t meet spec, that they could let go for cheap.
Thanks for all the information, these definitely were gov’t, there millivoltmetet a USMC callibration on one of them.
Tact-switches are used for longer duration. Search Expert Search Quick Search. Well considering I paid 5 bucks for the pair, I won’t loose any sleep over the rather bleak probe situation. United States Patent Electronic switching is used to avoid mechanical switching in the high gain amplifiers and to permit remote programming.
The gain of amplifier U4 is set by the ratio of the fixed resistor R37 connected between terminals 10 and 13 and the resistance coupled between terminals 14 and 2 which is varied by the operation of a three-pole double throw switch U5 typically a RCA type No. Aug Wed 24, 6: These characteristics cause the probe to have high input impedance over the very wide frequency range from 10 kHz to beyond 1.
A — Ballantine Laboratories, Inc.
The square root converter Mllivoltmeter provides the proper linearization and calibration for the 1 mV through 30 mV Ranges. Preamplification at first appears to be the ideal solution. My invention is also useful for narrower bandwidth devices where it is desireable to provide a transition between square law and linear function ranges, including meter circuits employing diode detectors preceded by an amplifier.
Finding working RF voltmeters with their appropriate RF probe for a reasonable “hobby level” price is much more challenging. Several types of such detection circuits are known.
Adjustable resistance Rg is used to adjust the gain of amplifier A 3 so that its output voltage V 3 is determined by the formula EQU3 The signal at the millovoltmeter of amplifier A 3 is applied to a square root converter SR and to a linear operational amplifier A 4.
The linear amplifier is an inverting dc amplifier with feedback gain stabilization utilizing a FET input high gain operational amplifier U7 typically a RCA type No.