MHZ100Q Documentation

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Wideband preamp

Board layout, front view

This is a simple preamp using the Analog Devices AD8067 IC, which is an opamp-like device with a rated bandwidth of 54 MHz at a gain of 10. It has a high-impedance FET input and the output can drive a 50-ohm load. I'm experimenting with it as a high-impedance range-switched front-end amplifier for the MHZ100Q boards. This is the first try at a pcb, so it's a work in progress.

For compactness and cost, it uses 0.1 inch jumpers instead of switches. The R3,R4,R5,R8 resistor ladder forms an input attenuator with 10x steps and 1 Meg input resistance. A jumper from tie point P7 to one of P3-P6 selects the desired input attenuation.

Jumper P2 is equivalent to the AC/DC/Gnd input switch on many scopes. With no jumper, the input is AC-coupled. With a jumper on pins 2 and 3, it's DC-coupled. With a jumper on pins 1 and 2, the input to the divider chain is grounded.

Pot RV1 and resistors R9 or R10 are for experimenting with adding a DC-offset to the signal. All 3 are being left off until I get a chance to see how well they work.

Inputs and outputs are designed for an SMA connector to be mounted sideways on the pcb. Room for two-pin header for input and output are also provided if one can get by without coax interconnecting cables.

Input power is +5 and -5 volts, connected to the K1 connector.

Blank PCB's are available from Oshpark. See the link on the widgets page.

Comments and questions can be posted to my blog at

I'll update this page when I get boards assembled and working.

$Date: 2014/02/28 19:34:06 $