I had 3 broken units a few months ago (the first version of the SAA). Replaced the switches and they were back to life. On one unit I installed esd protection diodes. But since I have my V2plus4, I don't use the old analyzers anymore. I still have to modify all the other analyzers. TVS diode part number: ESD101B102ELE6327XTMA1, a 5.5V TVS bi-directional diode from Infineon, 0.1 pF capacitance. Diodes are cheap. Switches are also cheap at Aliexpress. Replacing the switch is not for the faint hearted. It is a tiny package with a ground pad under the device. Hot air soldering is your only option. A good stereo microscope helps.
Reinier
Op 4-2-2021 om 14:26 schreef schweppe:
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When looking at the front end of the nanovna you see a 10?F capacitor in series with the MXD8641¨CSP4T Switch. This switch can resist 100V in electrostatic discharge sensitivity testing (Machine Model). This test is done with a loaded 200pF capacitor and a 0.5 ?H inductor in series.
A typical koaxcable (RG213 od RG58) with 100pF/m and 20m length will have 20nF of capacitance. If this koax is loaded to 200V by electrostatic, it will damage the MXD8641. Also if you measure an outdoor antenna and there is electrostatic in the air, you may damage your measuring equipment also.
It may be a good thing to protect your nanovna with ESD-diodes when measuring long koaxcables and/or outdoor antennas.
73, DK5DN
Am 04.02.2021 um 10:30 schrieb Stephen Laurence:
Does this mean that a long length of coax can store/return dangerous (to the vna) voltages, for example like a Tesla coil, or was the coax connected to something at the other end?
Should we all be installing esd diodes to the port 1 input? Port 2 already has a 14db attenuator.? Is there a limit to the length we can measure?
Steve L
