From: liz@poppyrecords.invalid.invalid   
      
   john larkin  wrote:   
      
   > On Mon, 5 Jan 2026 08:56:35 +0000, liz@poppyrecords.invalid.invalid   
   > (Liz Tuddenham) wrote:   
   >   
   > >I am looking for a device that can be placed across the centre of a   
   > >dipole aerial tuned to 150 Mc/s, so as to short-circuit it at about 200   
   > >c/s.  The impedance at that point is around 75 ohms, so 5 ohms would be   
   > >as good as a short and 500 ohms would be as good as O/C; therefore the   
   > >maximum capacitance of the O/C device would have to be around 2pf.  The   
   > >power level is negligible - probably microwatts.   
   > >   
   > >The control signals could be any convenient voltage but they would have   
   > >to be isolated from the RF, either by a choke or by some other form of   
   > >galvanic isolation.  As the switching frequency is so low, I had even   
   > >wondered about a cheap photovoltaic panel illuminated by a few LEDs.   
   > >   
   > >Does anyone know of a suitable device, especially one with built-in   
   > >isolation such as a high-side driver for power control?   
   >   
   > Why not use a relay?   
      
   The high on/off ratio of a realy isn't needed and the 200 c/s switching   
   will wear it out.  Also, I need to synchronously detect the signal and   
   any delay in switching will upset the null point.   
      
      
   --   
   ~ Liz Tuddenham ~   
   (Remove the ".invalid"s and add ".co.uk" to reply)   
   www.poppyrecords.co.uk   
      
   --- SoupGate-DOS v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)