Non-resonant dipole with two wire feed line and T match ATU discussed some of the issues with the common multi band configuration with emphasis on the lower bands where ATU losses can be sufficient to cause internal damage.
This article explores a scenario that came up in discussion with another ham.
His scenario is a moderately long dipole (just under λ/2) fed with a moderately long length of nominal 450Ω windowed ladder line… I am being obscure, but I don’t want to dwell on the details from that angle. This is not a case of someone loading up the roof rain gutters, or window frames, it is a serious antenna.
The chap is using a MFJ-941E ATU, which appears to use the same componentry as the MFJ-949E with which I am very familiar, the 941E appears to be a version of the 949E without internal dummy load.
So, he was able to get a good match easily using the internal balun (4:1 voltage balun), and from the settings we can estimate the matching and particularly the losses.
A model
I have separately come to a view that the Q of the 949E inductor at ‘A’ switch position is about 170 @ 1.8MHz. I also measured the magnetising impedance of the balun, it was 2.8+j350Ω @ 1.8MHz.
Above is a model capturing: Continue reading Analysis of a practical non resonant dipole scenario on 160m
Last update: 10th March, 2024, 10:46 AM