On 2/2/23 12:10 PM, Benford inspain wrote:
Been using the nanovna for just about 2 years with no problems. Today I fried a few resistors on the tx port. The schematic values dont match up with what is used in my nanovna. Mine uses 68 ohms instead of 49r9 values in the shunt to ground positions for example. I have been looking for another version of the schematic that represents my vna, bit so far nothing. I want to order smd resistors and am thinking to order values as per the schematic. Is anyone aware of a different input pad schematic?
On my schematic (Nanovna-H, 3.4.2) the CH1 pad is 56 ohms shunt, 240 ohms series, 49.9 shunt
The bridge on CH0 is all 49.9 with 200 ohms across the middle. with the balanced input to the detector being 49.9 in series with 390 ohms.
I don't think it makes a huge difference. When you calibrate, it compensates for whatever the values actually are. There's some optimization possible, so that the "uncalibrated" data are closer to ideal, but that's of limited value.
If I were designing it, I'd be looking at reducing the number of parts on the BoM. with some tradeoffs along the lines of "do you use 2 10k resistors, or use a 20k resistor"
