The DC injectors
I made a pair of these some years back and they worked well enough but the SWR was around 1.5 on some frequencies.
You might ask why bother when I could buy MFJ injectors. There are two reasons: 1) cost, the MFJs would be around £100 inc VAT and postage. The parts cost me just over £40 inc postage from Mouser in the US. 2) For me amateur radio has always been about making stuff. When I first got on 2m as G8FRA in 1972 I made everything except the antenna. That is what we did then as there was little commercial equipment around.
I have a lot of time now and enjoy ‘making’. It also means I am not afraid of taking the lid off and fixing stuff. Most of all it is the shear enjoyment of making contacts on something home made.
The design I am using is from AD5X and a PDF can be found here.
This is the schematic of the two units, please see the PDF for more details.
The parts from Mouser included two small aluminium boxes which makes life easy. I built the first unit exactly as shown in the article by AD5X.
A test of the first unit showed an SWR of no higher than 1.06:1 from 2Mhz to 170Mhz. I was pleased with that result so made the second unit which will be placed inside the tuner box.
There was no need for connectors on the aluminium case. The cable is attached to the input PL259 socket that came with the box. The RF input and DC output will be wired to the tuner modules.