On Tue, Sep 24, 2019 at 11:45 AM, vbifyz wrote:
I have a suspicion that they are not the right material for the low
frequencies involved (3.5-14 MHz).
For these frequencies, the key is the number of turns. You need a ring (not a
snap-on cylinder), and thread the coax as many times as you can through it. If
your application is QRP or RX only, use thin coax (like RG-174).
A single snap-on only helps on VHF. You need a dozen of them to see a
difference.
73, Mike AF7KR
Mike,
Thanks for the comment - I think you are absolutely right about that for HF. In my case, the ferrite chokes were mainly tried with the wall wart power cord going into a Tivo DVR, and I tried to loop the line a few times around the ferrite. So for nanoVNA measurements I am thinking of sacrificing a dead wall wart to harvest the DC line cord and using that as a test line to try different amounts of looping and different ferrite cores to see if I can tamp down the RF ingress into the Tivo box with the HF frequencies of interest. Going from memory the reboot was triggered even when the TV line coax was disconnected...so the DC power line is the main suspect...unless the chassis itself is picking up the RF.
Bruce KX4AZ
