I realise there have been many great posts on hunting RFI, i've got pretty close to tracking mine down, but would appreciate some insights from the ham.se experts :)
I've done quite a lot of work to hunt this down. The background - using a FlexRadio 6000 series inside a computer rack, radio is grounded to the rack via a short ground wire #6 awg (~40cm), rack is grounded currently to AC ground (work to be done in this area..)
Antenna is a K4KIO Hexbeam relatively low, around 20-feet above a flat metal roof on an insulated tripod, fed with RG8 around 25M, with the supplied Fairrite clamps on the RG8 at the antenna feedpoint. Ferrites (clamps) are on all cables, with the dc power-cable wrapped around a ferrite-ring around 4 or 5 turns at the radio end. An ethernet-switch (Ubiquiti) is outside the rack, and connected via a CAT8 cable (0.5M) to the FlexRadio via a narrow opening in the rack.
Using a switch-mode 40A psu (Manson) that has pretty good filtering within, and disconnecting the antenna, the RFI completely disappears, so i'm fairly sure everything around the radio itself is RF quiet.
Every 61khz precisely i have solid bars on 20M and 15M (40M is clear), that look like this:
I've used a vertical in the past and the bars were less obvious, so i'd assume this RFI is horizontally polarised. There is an Ethernet cable running under the antenna with PoE (indoors), but i've disconnected the cable and the bars are still there. There are ferrite clamps on each endpoint of that particular cable.
I've gone RFI hunting with a laptop and SDRPlay RSP1 and a random 800mhz yagi (i happened to have) and tried both orientations horizontal/vertical but the SDRPlay waterfall was fairly clear.
My belief is Ethernet interference, not from my equipment, but a neighbour. Wether it's home-internet, or perhaps a solar-inverter's IP interface, but that's just a guess.
Having 61khz bars around 14-21mhz is the signature of this particular RFI.
Apart from this issue, it's pretty RFI clean. Was wondering if anyone has any advice given the findings to date?