SWR strange problem

[Ve6mik]

I have an issue i can’t figure out

I have a new induction coil antenna. With my vna I can tune it anywhere between 80 and 10m. 3 separate radios agree that it is tuned and that the SWR is good

But 2 antenna analyzers will not show an accurate result. Both show an infinite SWR, resistance about 2 and reactance in the hundreds

All test correctly with a dummy load. I have tested the cables and connectors

A test at the antenna itself gives the same results, nanovna is accurate, both analyzers (comet and mfj) inaccurate across the range

Continuity test of antenna shows open, as it should

Choke inline tested

I can’t think of anything that I have missed

I tuned to 10m this morning and had good contacts on varahf. Everything was working well

And I am stuck on how to explain this and whether there is a problem

Any ideas?

Thanks, Mike

 

[RFI-EMI-GUY]

Is it possible that they are being overloaded from strong broadcast signals within their passband?

 

[Ve6mik]

Is it possible that they are being overloaded from strong broadcast signals within their passband?

I don’t know but the two analyzers are each incorrect on all bands

I have wondered if the analyzers use less power for a SWR test than down the nanovna. Certainly a radio uses more power to make the test

I don’t know what power these devices use

 

[RFI-EMI-GUY]

I don’t know but the two analyzers are each incorrect on all bands

I have wondered if the analyzers use less power for a SWR test than down the nanovna. Certainly a radio uses more power to make the test

I don’t know what power these devices use

I have always been suspicious of VNA plots on VHF/UHF antennas on congested repeater sites. HF antennas can accumulate a lot of uncorrelated RF energy just by their size and gross bandwidth. There was a navy study that I think demonstrated -30 dBm in many cases.

 

[Ve6mik]

Everything indicates that the vna is accurate. The analyzers are so far off that they simply aren’t working on this antenna

If it was one analyzer I would suspect the device. But the odds of 2 independent failures is astronomical and each works when tested on another antenna

So it’s not the connector or cable. It’s not the antenna itself. It’s not the analyzers. So it’s the environment in some fashion. From there I am stuck for an answer