This is a follow up to Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites.
Steve saw the above article and revisited the FT240-52 measurements which he apparently did, and found them wanting:
I see that in a more recent blog Owen has commented that some of my measured values of Rs for 2 turns on an FT240-52 toroid look low compared to those you would predict from the FairRite u’ and u” data. I agree with him, and I’ve spent this morning trying to find the problem!
I have several sets of data for 2 turns on an FT240-52 toroid, and all of them have significantly higher values for Rs than the set I used for that chart. I thought at first I may have had one “rogue” toroid, or one that had been mislabelled by the supplier, so this morning I re-ran measurements on all 5 of the FT240-52 toroids that I have; they all produced similar, significantly higher, values of Rs!
I was puzzled until I realised that the unique feature of the data-set used for the chart was, unusually, it had been produced using my AIM4170 running v882 software. I say “unusually” because for the past couple of years all my choke measurements have been made using a VNA2180, but I had recently unpacked my AIM4170 to check some of the problems claimed for its 882 software, and must have run the FT240-52 measurement using it. So it looks like the AIM882 bug “bit me”, although I haven’t yet unravelled why it would have affected values of Rs quite so dramatically.
His revised measurements, whilst not exactly in line with prediction are closer and more believable given the wide tolerance of ferrites.
I understand the associated FT240-K measurements which seem to have been made by Cecil (W5DXP) seem to be from an AIM measurement system. Sadly, I have very little confidence in AIM based on my experience over a few years. (W5DXP later advised his measurements were flawed.)