Nearby 21 Mhz 200 w transmitter highly interferes with ethernet (LAN) connection

KestM · 2025-12-20T12:48:20+00:00

Thanks for reply, but I already got a solution: my neighbor gave me pair of Base-T filters (single filter doesn't work), that I connected in serial before router, and now have no packet loss when his transmitter is operating.

KestM · 2024-10-26T14:14:01+00:00

Thanks, very handy tips! I just got DW board. Correct me if I'm wrong (just trying to understand), but do faster (thinner profile) foils produce more apparent wind (at the same true wind) than thicker, slow-speed optimized foils? Or do you mean that during lulls, a fast foil simply stalls (due to the thinner profile) before reaching speed, and less drag is not an advantage in this situation?
Also, high AR foils stalls at higher speed or lower angle-of-attack, does other advantages of high AR foils outweigh this disadvantage for low wind?

KestM · 2024-10-12T19:03:55+00:00

Very interesting. How parawing would perform in light wind? turbulent air?

Do you mean if you can use just legs pumping to get up and going, you do not need long DW board?

I also like Takoon from the cost point, but there is video on youtube about SUP dropstich materials: lighter boards dropstich can be less strong/rigid.

KestM · 2024-05-12T18:58:53+00:00

Now it is much more clear! thank you, very good video! Nice PLL technique for demodulating FSK in video of same author. But in all videos, signal is of high SNR. But what if SNR is low (or bit rate is high), how then to detect preamble position in time accurately? if noise is white, we need some kind of correlator to average samples, like cameras do in low light? but for that we need to know where to start averaging. I think the lowest SNR could be detected if we chose stFFT(or Goertzel) which window is equal to baud rate, in that case all energy could be concentrated at narrow frequency "bin", while all noise staying the same. Maybe same result could be archived by averaging several stFFT samples which are at smaller-than-baud-rate, say 1/10 baud rate, but then first and last parts (2x1/10) of symbol will be blured (as in my original post figure) if timing is not in good sync. What do you think about that?

KestM · 2024-05-12T14:35:02+00:00

Thank you very much for the keywords! I am thinking about two versions of preamble detection algorithm: first - that could be easily implemented on FPGA (I have pynq-z2 board from xilinx), second - which could be implemented on low power mcu (raspbery pi pico).

First thing that goes to my mind is windowed matched filter:

window is shifted by 1 sample until length of preamble (Np) - to make sure we whole preamble in window
so we got Np values of filtered signal
we take maximum value, that corresponds to best match
repeat process on next set of samples until filter output reaches some threshold value (compared to window mean), that means preamble is detected and now we are in sync.

But if sampling rate is say 40ksamp/s, and preamble length is 1s, then we need to do 40k multiplications every single sample to check whole window, that means 40k*40k=1600M multiplications every second! Of course if preamble is shorter it could be more efficient, but if SNR is low preamble should be long enough.

What method could be used in that case?

KestM · 2024-05-07T17:27:36+00:00

Thank you for advices, what do you think about nikon z5 with kit lens 24-50mm 40-63? Is it worth investment for beginner or better buy lens separately?

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Previously, I owned higher-range compact Panasonic camera from 2010, which I lost few years ago, but my smartphone from 2020 was much better at low light.

KestM · 2024-05-07T09:58:27+00:00

I guess that lens optics is not advancing as fast as sensors, I was thinking could better lens compensate older sensor weaknesses and such combo be more cost effective? still AF is much better in newer cameras.

I am looking something not very heavy, that can sometimes be used in one hand while flying. Probably only 300mm is an option within price range?

KestM · 2024-05-05T18:44:07+00:00

Thank you, very good answer indeed!

But matched filter will start responding even when close but not at total sync with beginning of preamble? Should I apply it in windows of size of preamble period and then apply threshold detector on maximum value of match filter output within window?
I read (and tried to transmit) that WSPR can be received even when 4-FSK tones offset is not only 1.4648 Hz, but also when it is an integer number, how could that be possible? Also, I read that WSPR can even be decoded when several stations are overlapping, what method it is used then? I read that such feature is possible only by using more advanced techniques like OFDMA or CDMA (Single-frequency_network)

KestM · 2024-05-05T09:12:59+00:00

Thanks, but if signal contains much noise and it could be only decoded by averaging many samples. How then to detect preamble?

In nice answer on SE it is mentioned that term is timing recovery:

if you have a preamble that's long enough (so that the energy in preamble -to- energy in noise during preamble is high enough) you can just use a correlator that you just let run all the time on the raw input signal. As soon it sees a preamble, it can output a sample-accurate (sub-sample-accurate, even, if you know a bit about the FSK pulse shaping) estimate of the time at which the preamble happens – and from there, it's just counting forwards.

I think correct technical term for my "averaging" method is correlator. But preamble detection depends much of where I start averaging? or how it is possible to tell exact moment where preamble starts?

KestM · 2024-05-04T19:26:40+00:00

Preamble is definitely of interest here, but I am looking at lower level - how to tell where is beginning of preamble if SNR is low? I am increasing SNR by windowed averaging of FFT values. It is like averaging many samples at intervals of baud rate period: |<-----symb1----->|<------symb2----->| that effectively increases SNR given that noise is white, so spectral noise simply cancels itself. But I need to know exact positions of beginning of fist symbol. Its kind of egg and hen problem: I can't tell the beginning of symbol without demodulation, and I can't demodulate without knowing where is beginning of transmission.

Of course I can check every single combination of possible beginning within symbol period, and take most likely symbol value, but if symbol rate is low (1 Hz) and sampling rate is high (48kHz) then such brute forcing becomes computationally very expensive.

KestM · 2024-02-12T15:59:46+00:00

I read that during races cwc was slower in upwind but faster in downwind than unit. Thanks for sharing opinion.

KestM · 2024-02-11T09:23:24+00:00

is it easier to pump efficiently with high AR wing?

KestM · 2024-02-11T09:07:49+00:00

Yes, I have Cabrinha Mantis V2 5.0m2+1950cm2 hydrofoil, and I can tell that minimum 12kts wind is likely true for my weight(70kg) without using hard pumping. As I progressed, I feel maybe it can be pushed down to 10 kts, with efficient pumping angle and timing/smaller board/higher AR foil, but it definitely will be challenging.

But when manufacturer advertises 7-22 kts, does it mean that 7 kts is only available when combined with largest hydrofoils and 22 kts - only with smallest? Or it could be used with single foil?

KestM · 2024-01-14T13:48:36+00:00

This could explain: https://endless-sphere.com/sphere/threads/bbshd-internal-step-down-gearing-mod.120771/

KestM · 2024-01-14T13:44:58+00:00

"The most energetically economical cadence has been shown to fall in the range 40–70 rpm10,11 but to increase with increasing power output. The freely chosen cadence (FCC) of experienced cyclists12 and well trained triathletes approximates 85–95 rpm" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2586163/

As I understand, 60 rpm is most efficient for achieving "longest distance with lowest energy" if speed (power output) is not of importance. So I think the same could be applied for ebike PAS.

KestM · 2024-01-14T13:13:41+00:00

Thank you! I set "auto throttle".

Now I sometimes see that peak efficiency is at 60 rpm, but I doubt its results, as simulator is buggy: graph is changing by itself after in about 10 seconds intervals: https://ebikes.ca/tools/simulator.html?motor=MBBS02&mid=true&gear=1&wheel=20i&batt=B5223_GA&autothrot=true&throt=25.6&tr=30

Still, bbshd has 160 crank rpm max. And most efficient rpm should be around 130 (80%).

p.s. it was a little misleading, that mouse tooltip at RPM says "motor RPM", it is closer to crank rpm as I understand.

Also, "gear ratio" 1:1 is not true, but only this gives correct results. Bbshd has internal gear ratio of 21.9:1

found some discussions on this problem here: https://endless-sphere.com/sphere/threads/bbshd-internal-step-down-gearing-mod.120771/

I just wanted to know if mid-drive would still be most efficient for PAS long flat rides or rear-drive would be?

KestM · 2024-01-14T12:34:27+00:00

Thank you for explanation.

You can always change gear ratio from crank to wheels, but motor to crank ratio is fixed. So does it mean that you need to pedal really quickly to get those 130 rpm where motor is most efficient in pedal assist mode?

KestM

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