PoRG v2

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The PoRG v2, in a nice blue box, now including a built-in power supply.

A couple of years ago I built my first PoRG (abbreviation for “Power over RG-cable”), a simple phantom power supply to power some device over antenna cable (e.g. a preamp, active antenna, coax switch, etc). I recently built an active antenna for Adrian PA0RDA, and since his tests were very successful he wanted to have his own PoRG. For me this was a nice opportunity to reinvent this little thing:

  • I included a built-in power supply, so no external power supply is needed anymore.
  • The built-in power supply also prevents the PoRG from moving around your shack due to the forces of the connected cables.
  • It has different connectors for hooking up the transceiver/receiver and antenna, making it more difficult to accidentally swap the cables, insert DC power into your radio and see smoke appearing through the vents of your rig.

Circuit description

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Circuit of the renewed PoRG, see text below for remarks on the components tagged with a ‘*’ symbol.

 P1 is the mains connector, followed by the power switch SW1 and a 100mA fuse F1. The AC power is converted to 12V AC and rectified by a diode bridge. The DC signal is stabalized by the capacitor C1 and the LM7812 (U1). The LED (D1) indicates that the power is turned on, the LED current is limited by R1. The value of R1 depends on the selected LED, in this case a generic 5mm 20mA LED. Since Adrian is blind but can still see some light, I decided to apply a very bright LED, drawing a 30mA current with a 3V voltage drop, thus requiring a resistor R1 of (12V – 3V) / 30mA = 300 ohm (I used 330 ohm).

The RF part consists of the 2 connectors P2 (trx) and P3 (antenna). I used a TNC connector for P2 and a PL connector for P3, to ensure that the antenna and the receiver can’t be swapped. The TNC connector is not very common in hamradio applications, but sold by most shops thanks to its common use in wifi networks. Both connectors are internally connected by C4, and DC is inserted at P3 via L1. The values may vary, depending on your application. The values given here allow you to use this PoRG from 40kHz. If you want to receive lower signals (e.g. the SAQ station at Grimeton) you may increase the values to 1 uF (C4) and 1 mH (L1).

This PoRG easily provides 200mA to your outside device. This is normally enough to power an active antenna, mast preamp or antenna switch. If you need more power, increase the power of the transformer (more VA’s) and get the LM7812 cooled. Also be sure that the inductor L1 can handle the current.

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