On 11/3/20 10:22 AM, ERNEST AEC-RADIO wrote:
Bruce:
You might have caused the AD602 devices to open, as they have almost zero
protection, aside from a capacitive input.
The level of R.F probably killed them.
The devices are readily available, and not costly,
There should be 3 devices, all identical.
SA602AD, 8 pin D.I.P packaging
There's 20dB of attenuation between the external port and the mixer. More likely a overpower situation would blow up the resistors in the attenuator before it cooked the mixer. The series resistance might also limit the current through the mixer inputs.
Sure, putting 100W into it probably would blow it up - The 50 ohm load resistor would cook first from the 70Vrms, then the 250 and 50 ohm resistors in the attenuator. And if the 250 ohm survived, then the mixer sees it.
It's a Gilbert cell mixer which is basically a differential amplifier pair, and the RF inputs go to the bases of the transistors (see Fig 3 in the datasheet) with a 1.5k resistor to ground. A negative voltage will reverse bias the BE junction, but that's probably "volts" max Vbe-rev. Too much positive voltage reverse biases the mixer transistors.
On Mon, Nov 2, 2020 at 6:43 AM BruceN <k4tql@...> wrote:
Did a stupid. I was measuring an antenna and left the VNA connected to
the feed line while I went off and did something else for a bit. My
automatic message system kicked off and transmitted from a different
antenna pouring 100 watts into the aether. The antennas were close,
parallel in fact.
When I came back to the VNA, I found that I couldn't calibrate it. The
display showed traces all over the place instead of the nice straight lines
you get after calibration. I guess I may have bricked it but would
re-loading the firmware correct the issue? I hate to dig into it because
it is a "real" nanoVNA-H with the nice plastic case and kinda tough to
break into. I suspect that repairing it wouldn't be worth the trouble
since a new one is so inexpensive.
Moral of the story: turn off all RF sources while using the VNA and
disconnect it if you walk off to do something else.
--
*"To invent, you need a good imagination and a pile of junk"* -- Thomas
Alva Edison (1847-1931)
