An available aluminium baking tray, though a bit oversize, came in handy as an enclosure. A piece of aluminium sheet was used to coarsely fabricate a recessed cover.
|Homebrew RF Ammeter|
|Homebrew 1:1CT RF Ammeter - Schematic|
In the final assembly, the primary was a piece of 18SWG solid bare copper wire soldered to the BNC sockets and the secondary a length of flexible insulated copper wire. A rubber grommet ensured positioning of the toroid. Wiring was on a piece of perfboard, supported directly on the meter terminals.
Calibration was done using a homebrew CW rig and a Weston 1.5A RF Ammeter, after which the variable resistor was replaced by 3 series-wired 10KΩ resistors.
|Homebrew 1:1CT RF Ammeter - Inside view|
However, the 1:1 transformer could cause the secondary load to be directly reflected as a series load in the feeder. Also, the higher secondary current could result in overheating of the toroid and the 82 Ω resistor.
Hence it was decided to have 20 turns on the secondary side, thereby dropping the load ratio to 400 :1.
|Homebrew 1:20 CT RF Ammeter - Schematic|
The series load imposed on the feeder would now be in the region of only 0.1Ω.
The secondary was wound using solid hookup wire and the RF Ammeter rewired.
|Homebrew 1:20 CT RF Ammeter - Inside view|