N2CX Accuprobe Plus
The N2CX Accuprobe Plus is a descendant of the common diode RF detector.
It uses a special operational amplifier with a compensation diode to cancel
out non-linear diode characteristics at low RF input levels. This allows
accurate measurements down to about 50 mV rms as compared to several volts
for ordinary detectors. This translates to a very low QRpp level of about
50 microwatts. The upper end of the range is 5 V rms or 1/2 watt.
A second uncompensated range is provided to allow measurements up to
35V rms or 24-1/2 watts. Compensation is not needed for the higher voltage
range since the detector is linear for high input levels.
The Accuprobe is used as an accessory to a reasonable quality digital
multimeter. It provides a DC output voltage that gives a DMM reading
calibrated to the RMS value of the Accuprobe RF input. On the LOW range
the DC is read directly while the DMM reading is 1/10 the RF input of the
The Accuprobe is AC coupled so it can be connected directly to biased circuits
with voltages up to 50V without upsetting circuit bias or inaccurate readings
due to presence of DC. Its high input impedance and low capacitance allow it
to be used with minimum loading on high impedance low-level circuits.
|Printed circuit board dimensions:||1.8 x 1.9 inches|
|Power:|| 12 VDC at approx. 1 ma using a standard 12-volt battery|
|Input levels:|| LOW range - 50 mV rms to 5V rms (usable to 20 mV)|
HIGH range - 5 V rms to 35 V rms
|Frequency range:|| 100 kHz to 30 MHz (upper end not tested but should extend to VHF)|
|Outputs:|| DC - compensated to rms input|
LOW range - 50 mV DC to 5 VDC (Uncalibrated readings to 20 mV)
HIGH range - 5 VDC to 35 VDC (1/10 RMS input)
|Output accuracy:|| approx. 10% of reading decreasing to 25% at 50 mv|
Supporting Files and Documents
Accuprobe Assembly Manual (3/17/13 update)
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