A HAM radio preamplifier can be used to enhance the received signal at the cost of amplifying the received noise as well. Typically preamplifiers are bundled with HAM radio amplifiers but it is also possible to find self-standing preamplifiers that will work without needing an amplifier.

For this project a J310 Push-Pull Low-noise HF pre-Amplifier has been used that was created by SV1AFN and advertised to work between and (and above) which seems great for HAM radio usage. The pre-amplifier will be wrapped in a metal case and a remote relay toggle will be used in order to switch the antenna signal between connecting directly to the antenna or connecting through the the pre-amplifier.

We have been having lots of luck with a remote double relay, that seems to provide the extra benefit of having a remote in order to toggle and operate devices remotely, in order to deliver selective signals to an Arduino ESP. However, for this project it seems that the schematic is rather straightforward and would not require the usage of an ESP.

The electronic schematic is based on a dual coil latching-relay that is activated by a dual relay remote module (in total, three relays). This format was chosen because we did not want to take apart the remote module given that it a very neatly executed piece and chose to rather add pins to the remote control relay and slot it onto the PCB. Without modifying the remote relay, a latching relay is needed in order to switch between either a direct connection or a connection through the preamplifier. When dealing with high power RF signals a latching relay is almost a must given that there is no induced current that would make a non-latching relay jitter.

Here is the schematic of how the antenna is connected through the dual coil latching relay with the serial number starting with G6SK:

v RTX                                      ^ ANT
|                  G6SK                    |
|                  +---+                   |
|                 o|   |o                  | 
+------------------+   +-------------------+
                   \    \
         +---------+   +---------+
      in |                       |  out        
    +----|-----------------------|----+    
    |    *                       *    |
    +---------------------------------+
 J310 Push-Pull Low-noise HF pre-Amplifier

the main highlights here is that the RTX and ANT connections are both soldered to the common pin of either side of the dual coil relay, with one straight-through connection between the two switches of the relay made by connecting the top-most pins of the relay together. In doing so, the relay now switches between a signal connection that goes through the pre-amplifier though the lower part of the circuit or a direct connection between RTX and the antenna by going through the upper part of the circuit.

Switching the dual coil latching relay is relatively easy and convenient given that the two coils will both trigger either a "set" or "reset" depending on which coil is set under electric potential. Hence, wiring in the dual remote relay is a breeze with connected to one side of the relay and then common ground mapped to either of the two relays such that either the "set" or "reset" coil can be triggered.

        +----------------------+
        | DOUBLE COIL RELAY    |
        | REMOTE MODULE        |
        |                      |
        |    C G   C   G       |
        |    O N   O   N       |
        |    M D   M   D  12V  |
        |  +-+-+-+-+-+-+-+     |
        |    | |   | | | |     |
        |    +-|---+-|-+ |     |
        |      |     | | |     |
        +----------------------+
               |     | | |            
          +----------+ | |
          |    |       | |          
        +-|----+    +----+
        | |         |  | |                      Vcc
        | |         |  | +-----------------------+
        | |         |  | 
        | | +----+  |  | 
        | +--o  o---+  |                        GND
        |   |o  o|  |  +-------------------------+
        |   |o  o|  |                            |
        |   |o  o|  |                           ---
        +----o  o---+                           ///
            +----+
             G6SK 

As established, the traces on the bottom part of the PCB are built using copper wire.

Placing components on the PCB is relatively easy, with the double coil latching relay being mounted perpendicularly with the remote dual coil relay. Otherwise is pulled via a jack and luckily both the dual coil remote relay and the preamplifier by "SV1AFN" accept voltages that high. If the components were not rated for , then a buck converter would have to be used which would mean implicitly introducing a small oscillator very close to the RF circuit that might induce and perturb the RF signals.

The rest of the components are now added and the project is finalized. A switch is added just in case as a last resort to shut down the device, even though in the current format no switch would be needed given that the build is all controlled by the remote.

Here we go, the last vanity shot, with labels and indicators added and the remote within the same frame.

One thing to observe here is that the RF connections are all made out of pure copper without messing around with solder, tin, aluminum or other materials, which is identical in methodology to the ATAS antenna controller created previously by Wizardry and Steamworks.