Once again ive had the lid of the ATU. I did so a couple of days ago when my curiosity got the better of me and i decided to take a look inside, and im glad i did. The connection from the capacitors to the inductor was dry joint and loose, and the inductor itself was slightly deformed. I resoldered the joint and repositioned and straightened the inductor.
Today, whilst messing trying to calibrate the antenna, i decided to switch to the dummy load and check the rig in straight through 50 ohm unbalanced load. Hmmm, SWR 1.1:1? should be perfect? wait a minute! 30W? im running 10W?!
so, out came the bird meter and the 25W load. Ive only got a 25-1000MHz element for the bird, so set the alinco on 24.990 and low power - perfect 10W, so, the old MFJ is out of cal.
Ive now calibrated the low power (30W range) of the ATU both forward and reversed in bypass mode to the dummy load at 10W. Ive also calibrated the high power (300W) forward reading, this being done on 3.8MHz at 100W to aerial, as ive no suitable load for this power, and the antenna can tune a 1:1 SWR on 80m.
It just shows, its worth taking the time to check 2nd hand gear carefully! The antenna is still no better, but at least any readings i take from the MFJs SWR bridge are meaningfull now.