Is a Common Mode Choke Even Necessary at QRPp Power Levels?

[Jeff Weinmann]

Hello,

I'm using an SI5351a clock generator to generate a WSPR signal at 10-100 milliwatts.  An antenna design, the

  MicroVert
https://www.dc4fs.de/microvert.pdf

 suggests using a common mode choke to keep current off part of the coax used as a counterpoise.

Now I understand that common mode current may be troublesome in the shack, affecting the radio electronics and giving the operator a shock if the radio is touched in the wrong place,  but I will be operating only 10-100 milliwatts out in the field with an arduino and an Low pass filter connected to a Microvert.

Is there really a need for a CMF at such low power levels?

I realise that with this antenna design part of the coax is used as a counterpoise, but does it matter at 10mw?

73 Jeff

[T3sl4co1l]

As I said in the other thread, it's part of the antenna.  Omitting it will change the tuning, radiation pattern, sensitivity to nearby things, etc.  Doesn't depend on power, it's about the fields themselves.

Tim

[radiolistener]

I realise that with this antenna design part of the coax is used as a counterpoise, but does it matter at 10mw?

The power doesn't matters. The antenna geometry matters.
Common mode choke affects your antenna geometry, because it prevents to use feeder, equipment chassis, mains line and other things as a part of antenna.

So, it doesn't matter if it's TX with 1000000 W, 0.001 W or 0.0000000001 W, or if it's RX signal.
In any case you're needs RF choke to keep proper antenna geometry.