On 2/5/21 3:31 PM, Bill AA6BD wrote:
Manfred,
The OCF Dipole has a common mode choke at the feed point. I ran a coax to my shack and connected all three analyzers at the same end of the coax and at the same physical position. The only physical difference is that the MFJ analyzer has a PL259 connector on it, the NanoVNA has a PL259 to SMA adapter, and the K6BEZ analyzer has a PL259 to BNC adapter. I find it hard to believe that this much frequency difference is due to the adapters, and all three were measured at the same operating position. I have an older NanoVNA (V1?) and it gave almost the same measurement as the NanoVNA H4. Since three of four analyzers yield almost the same values, while the MFJ is off by itself, I suspect it is the inaccurate one but I will test some more.
The choke at the feedpoint doesn't mean that the coax is totally decoupled from the antenna - the fields from the antenna will couple to the shield of the coax.
A symmetric dipole, with the feedline coming away perpendicular, will be decoupled, but that's a special case.
If your OCF feedline has chokes every few meters, then it's not going to "participate"
But I'd check the frequency accuracy of the MFJ - There's a 4MHz crystal that sets the frequency of the PIC16C73.
