2018-09-18, 05:03
(2018-09-17, 23:10)allsorts Wrote: michidragon (station 2284) yes horrible noise band centered about 60 kHz. Watching for a while it's a curious interference, it's always there at a low level but occasionally builds up over 100 uS to something quite large that remains for several seconds.
You're 77 miles (bearing 13 deg) from WWVB at Fort Colllins. WWVB is a frequency and time standard transmiter on 60 kHz with a 70 kW EIRP. The carrier from WWVB is reduced in level for 0.2, 0.5 or 0.8 of a second every second to indicate the second start and encode the actual (UTC) date/time. I have MSF, another frequency and time transmitter also on 60 kHz 30 odd miles away. That shows as a single spike not a broad noise band. MSF similary drops in level once per second but I don't see that all.
When I first saw your signal plots I thought "noisey PSU" but they are normally around 30 to 40 kHz and don't vary as much as is indicated by the plots. As WWVB is only 70 miles away that could be the source but it doesn't match what I see from MSF, ie a single spike and no big level variation.
PSU is fairly easy to check, go to the Signals page, scroll down and set the Sampling: Channel: to V_in and click start. The signal plot will now show you what V-in looks like. It might bounce about a bit but it should be a well defined line with little or no noise.
I wonder if there is some resonance sort of thing going on between the ferrite antennas and WWVB? It doesn't take much stray capacitance to bring a ferrites resoanant frequency down to 60 kHz. Resonance being set off by WWVB would explain the slow rise over 100 uS, I'm pretty sure that the WWVB carrier actually rises and falls within a cycle.
The H field amp needs to as close to the ferrites as possible, no extending the wires. And the wires should be spaced apart, not all neat and tidy together. Try playing with the orientation of one ferrite to minimise any pickup of WWVB, there should be a well defined and deep null. With the null carefully pointed at WWVB it's signal should all but disappear.
Does doing any or all these things have any affect this 60 kHz ish noise band?
Wow, ok, let me look into that.. Yes, I am not that far from WWVB; I checked around it with SDR @ 60kHz with an old Palomar Engineers LF Probe, so I can't really see any **other** source of 60khz around.
So let me look at the power supply, first, then for anything else at 60khz or -near it-, and then i'll check my H-field config.
The wires aren't together, and I haven't extended them... they're at the length they came, but I'm wondering if after the above if maybe I should shorten them.
Will report back... Thanks for taking a look at those signals for me...