I found this fascinating. I need to make an attenuator for my FT817 on
transmit as a 432 MHz
microwave IF radio. I have the appropriate carbon-film resistors. I
measured them on my NanoVNA to see what they measure at 432 MHz. This is
something I never could do before I had a NanoVNA. Two 200 ohm 1 watt
resistors measure 198 ohms on my DVM. The NanoVNA measures 198 ohms up to
about 500 kHz, and then the resistance starts to climb. At 432
MHz they both measure 225 ohms with a small amount of inductance (12 nH). I
measured a 68 ohm carbon-film resistor with similar results - it measures
67.5 ohms with the DVM and the NanoVNA up to about 500 kHz. At 432 MHz it
measures 86 ohms and a small inductance. I measured a 100 ohm carbon
composition resistor. It measured 102 ohms on the DVM and with the NanoVNA
up to about 1 MHz. The resistance barely changed on the NanoVNA above that.
At 432 MHz it measured 106 ohms.
I kind of figured the carbon film resistors weren't as accurate at VHF/UHF
frequencies compared to carbon composition resistors. This verified it.
Probably a skin effect problem.
73, Zack W9SZ
