I am working this project and would like to get some feedback on interests about it.
I am make a high impedance amplifier that can enable you to use a 10X oscilloscope probe on spectrum analyzer.
The bandwidth is about 400 MHz, considering the target use case is power supply noise diagnostic. There is no plan to go higher bandwidth.
A 400 MHz+ 10X 10 MOhm probe will be required.
The amplifier comes with two boards. One for the amplifier itself, the other one is the supporting powering and control circuitry.
The support board has USB as power input, it will pull 100 mA from the power source, so you can take power directly from you spectrum analyzer, if it has an USB port.
It also come with a 300 mAh Lithium ion battery and lower noise isolated DC DC converter to get +/-5V the amplifier required.
There is a SP3T switch that you can set to put the amplifier into Power OFF, Power ON, and Battery Only mode. The Battery Only mode will power off all digital circuitry on the amplifier assembly to give you the best noise floor.
The amplifier support simultaneous battery charging and operation, so that you can continue to work, if you forget to charge it.
The +/-5V power is generated by an isolated DC DC converter. The USB power has no direct ground connection to the amplifier.
A RF signal relay is provided such that both AC and DC coupling can be supported.
A trimmer is also present to correct the DC offset, if you want to use it non-spectrum analyzer cases.
The first prototype shows noise floor at <500uVpp at 100 MHz bandwidth (the 100 MHz bandwidth limit come from Tektronix 7A13, which is the most quiet test equipment I have at the moment, a full 400 MHz bandwidth noise floor will be provided eventually)
The dimension of the amplifier is about 2.5" x 2" x 1.2", excluding connectors. Case has not been made yet, but of course there will be a metal case to cover the whole amplifier for shielding.