This article is an analysis of why my recently acquired MFJ-993B will not match my multiband antenna system on most bands above 20m. The MFJ-993B replaces an Ameritron ATR-30 which was capable of matching the antenna system on all HF amateur bands.
A detailed analysis is performed 18.15MHz on the first problem band.
Configuration
The antenna system uses a tune feeder configuration.
The alternative tuned feeder arrangement described at (Varney 1958).
In this case, the open wire line is 9m of home made 450Ω line (2mm copper wires spaced 50mm air insulated), a 1:1 current balun and 0.5m of RG400 tail to the ATU.
A 470K 1W metal film resistor and a 2095-100 gas discharge tube in parallel are connected in parallel with the ATU antenna terminals to reduced static build up and modest transient protection.
Impedance was measured looking with a Rigexpert AA-600 into the cable end that plugs onto the ATU, at 18.15MHz is is 4.7-j69.5Ω.
Continue reading MFJ-993B on my G5RV with tuned feeder