Codan made very heavy duty HF mobile antennas used by for example the Australian police. The antenna is a typical tuned whip design like the “screwdriver” designs pioneered by amateur radio designers long before the Codan antennas appeared on the market. They use a end fed method with autotransformers in a switched configuration. There are two combinations that switch in a step up, step down or a paralell combination of autotransformeres. There is also a nice motor break function that shorts one of the spetter motor windings to ground.It looks like there is a scan function where the antenna switches in a broadband amplifier. The antenna is very narrowband due to the tuning and high Q so a wideband amplifier may be needed so the radio can determine what HF channels are open without tuning mechanically.
The CG-3000 is a clone of a SCG tuner. It uses a PI network for tuning. There are many schematic diagrams on the Internet. However 95% of those have so low resolution that they are not readable when you zoom in. I finally found a schematic with enough resolution to show the component values. It is the output circuit that receives the highest voltages when matching a high impedance antenna and those are the most likely to be damaged. To be proactive I changed mine to 6KV types low loss Vishay Cera Mite and TDK CC45SL3 types. Below you can find the schematic, should you need to repair your tuner.
If you need to change components in the output circuit and want quick info, all the capacitors are either 100pF or 50pF ceramic. There are series and combinations of from right to left 4x100pF par, 2x100pF par, 2 x 50pF par, 2 x 100pF ser, 2 x 50pF ser. This gives the values 400pF, 200pF, 100pF, 50pF and 25pF. The relays can then switch in several combinations from 25pF to 775pF. Note that the schematic does not show that the 100pF cap is two 50pF in parallel, that the 50pF is two 100pF in series, that the 25pF is two 50pF in series. I may have an older or newer hw version than the schematic.
I found a schematic of the Turner +3 mic online. It is more advanced than you should think as Turner already implemented compression in the late seventies. They called the compression technique “modu-guard”. It is a rectifier circuit that rectifies the audio and sends a DC attenuation signal back to Q3 in the source of the FET amplifier.
To use the CG 3000 antenna tuner for remote operation there is a control box (CTU) that could be purchased from the manufacturer. Some people want to make such a control box themselves. Here is the schematic info.
Thanks to https://sp5kab.pl/pl/sterownik-cg-3000-cg-antenna-tuner-control-unit for doing the work with determining the schematic
SGC has made an automatic antenna tuner that has several smart ideas implemented. It uses a phase detector to be able to know if the load is capacitive or inductive. The design uses a RF mixer and several clever multifilar transformers. SGC also included several practical antenna antenna ideas in their manuals. I have uploaded the information here. Credit: SGC
Manual 1 PDF1
Manual 2 PDF2
Manual 3 PDF3
