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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A SumoBrain Solutions Company. As the input signal exceeds 30 mV rms the response gradually approaches peak-to-peak at mV and above. Measuring RF at millivoltmetdr levels presents a whole bunch of challenges. The connections made by switch U14 are given in Table 1 above. Where I am convinced that they were supplied to people who didn’t have the slightest clue how to use them.

A — Ballantine Laboratories, Inc.

The apparatus of claim 6 wherein the diode detector is a germanium point contact diode. This portion of the circuit is shown in FIG. Potentiometer R68 can be used to adjust the recorder output for one volt full scale open circuit or to normalize the output to the recorder being driven.

It’s the “no probes” part that’s the killer here. Resistor R45 is the zero adjust for offset compensation on the 3 Volt range, where amplifier U4 has the least gain. You might also consider that if these meters had their probes and accessories, and were in good working order, they’d be worth a considerable amount of money.

I have invented an improved meter circuit which is particularly ballamtine for measuring radio frequency signals over a broad bandwidth in the millivolt ranges.

Preamplification at first appears to be the ideal solution. First, everything has to be well sheilded, since even an exposed probe tip can pick up enough RF “noise” to throw off your mullivoltmeter. Where k is the mixing factor determined by a given position of the range select switch SW, EQU4 As a result, the output voltage V o of the meter drive amplifier can be defined as follows: Therefore, it may well be worth the time and expense to track down some probes.

Front panel meter 344a0 is accomplished by adjustment of a ten-turn potentiometer R81 which provides an output reference for amplifier U4.

Resistors R10 and R81 in the buffer amplifier circuit are used for meter zero adjustment.

Table 1 above includes a truth table for FET switch U8. DC output proportional to the ac input is provided for analog recorders and to allow operation as an ac-dc converter. 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.


The probes are usually much more complicated than that. A monolithic square root converter U6 typically a Analog Devices type No. And its detachable design reduces your work in servicing. Ballantine A RF millivoltmeter. The voltmeter matches the characteristics of the probe by processing the signal on leadwhich is representative of the probe output, in 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 Housed in superior grade of ABS body, unique design, very strong in construction, unbreakable and very high insulation.

The identification of specific components, component values and circuit details in this specification are for illustrative purposes only. There was a QEX magazine article a while back about building a compensated RF voltmeter using a pair of matched diodes and some high-impedance opamps, if you want to homebrew something.

Ballantine RF Millivoltmeter 3440A With Accessory Kit

If you can find a diagram for the probe, you might be able to make something up using low-barrier diodes, but you’d have to verify the calibration and you would probably lose performance at the higher frequencies. Showing results 1 – 9 of 9 products found.

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. The detector operates in the square law region below 30 mV rms input and the instrument provides rms response in this region.

Relative gain or loss measurements are simplified by a 0 dB reference adjustment. 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.

Since this transition region is often an important region for voltage measurement, as are the regions above and below, it is necessary to avoid or compensate for the transition response characteristic as well as to provide the appropriate response in the square law and linear regions.

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. Dec Mon 31, 2: Millivoltmeer [Bot]Prutser and 7 millivoltmete. Secondarily, it is very difficult to rectify such low signal levels with any hopes of linearity or repeatability, so the usual practice would be to amplify them directly, or heterodyne them to frequencies that can be amplified, which is the job of a spectrum analyzer.


The apparatus of any of claims 1 through 4 wherein the diode detector is a germanium point millivoltmerer diode. The resistor network R e determines the proportions of Vs and V a as components of V 4.

Resistors RR63 are selected to provide a constant output impedance.

Antique Radio Forums • View topic – Ballantine A RF millivoltmeter

I googled RF probe and found lots of information about making a probe for use with a vom or dmm using mlilivoltmeter 1n34 diode. A voltmeter ballantinne a diode detector, a square root converter and a linear amplifier each connected to receive the diode detector output signal, a resistance network connected to receive the outputs of the square root converter and the millivoltmteer amplifier, means for selectively switching the resistances of the resistance network to change the proportion at the resistance network output between the signal from the square root converter and the signal from the linear amplifier to inversely match the response curve of the diode detector, and means for displaying the amplitude value of the resistance network output signal.

All switches are touch switches with high quality, providing good hand feeling and ballantien reliability. Range switching in this embodiment of my invention is accomplished electronically by use of field effect transistor FET switches.

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.

Since the approximations in each range except the 3 V range include from two to five steps, this type of instrument provides only a rough approximation of the response required to match the diode detector.

Is the probe proprietory or can I make a probe?

Although some of the figures include typical component values, this disclosure is not limited to the values shown.

For example, the shaping amplifier in the Boonton Model No.

Common calibration errors are eliminated through temperature compensation of the probe detector diodes; double shielding protects the interchangeable probes from rough handling and pickup.

Last modified: April 21, 2020