H field big difference in gain
#10
(2016-10-13, 09:23)DrRobin Wrote: 1) My minimum H field noise is on bearing 85/265 degrees, by rotating my ferrite rod antennas around.  If I measure on GE, Anthorn is 265 degrees from me at a range of 97km.  I have attached the line of sight profile.

2) Skelton is 245 degrees and 79km.  There is a lot more hill in the way from Skelton, see attachment.

3) Looking at my H field spectrum (Blitzotung recent signals) I can nearly always see a signal just below 20kHz, so it looks like Anthorn might be my main source of noise.

I like those terrain plots, I'm glad you posted Alston > Anthorn/Skelton as well or I'd been asking. Smile

See my thread New Station Aerials and Noise Chasing it runs through the setup of the station here and has just been updated as I installed it into a loft yesterday. Doing anything about Anthorn/Skelton depends on how strong it is. How does it compare to my 300+ mV peak to peak (gain 4000, no LP filter). See my thoughts towards the end of today's post in the above thread, excessive filtering may be detrimental. And TBH your station currently does pretty well in the UK Efficiency-L rating.

(2016-10-13, 09:23)DrRobin Wrote: 4) Looking at my E field spectrum there is a spike at 38kHz and again 76kHz (smaller), I suspect these are coming from a switch mode PSU, 38kHz fundamental and the first harmonic.

That 38 kHz is near enough to the frequency that generally occurs when the controller board and "bad" PSU don't get on. If you have 4 NiCd or NiMH *1.2 V*  batteries try running from them and unplugging the PSU from the mains.  *DO NOT* use other types of dry batteries as they have too high a voltage for the regulators on the controller board.

Solution, better PSU or a filter. See RichoAnd's Noisy PS or the PoE recommendations for System Blue threads.

(2016-10-13, 09:23)DrRobin Wrote: So if I arrange my N/S antenna to have the null at 265 degrees it is working quite well.  I just need to sort out my E/W antenna, not sure if it possible to make a loop with a null to one side and the main lobe to the other?

Alternatively, I will have to look at filtering, either the filter IC or possible a notch filter for 19.6kHz in the antenna connections?

Yep, null out Anthorn/Skelton on one antenna and live with it or LP Filter it on the other but that really depends on how strong it is. Reading around these forums a notch filter in the antenna is generally considered a bad thing as it inevitably mucks up the timing, especially one with a high enough Q not to attenuate everything.

Now I like that idea of a directional loop, I *think* something might be possible. A loop has a figure of eight polar pattern combine that with an omni-directional polar pattern and you get a cardioid polar pattern, when the signal levels are equal. Now the figure of eight is the pattern on the front/back - left/right axis but if you look from the up/down axis it is omni but with variable level depending on the angle from the null.

My third, horizontal, loop certainly behaves as an omni but has far less signal than the vertical loop receiving the full benefit of Anthorn. Now if I reduce the number of turns on that loop it will have less output. Play time ...

Some one must have tried this surely?
Cheers
Dave.

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Messages In This Thread
H field big difference in gain - by DrRobin - 2016-10-09, 19:02
RE: H field big difference in gain - by cutty - 2016-10-09, 19:27
RE: H field big difference in gain - by allsorts - 2016-10-13, 14:54

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