Date
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Locked Interesting double-decode
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Noise blanker IMD can cause multiple decodes based on the frequency of repetition rate of your impulse noise.
73 -Jim NU0C On Sat, 22 Feb 2020 12:15:41 -0800 "Martin G0HDB" <marting0hdb@...> wrote: On Sat, Feb 22, 2020 at 07:57 PM, Philip Rose wrote:The spacing of a Doppler-shifted signal on 20m is, in my opinion, extremely unlikely to ever reach several 100Hz; the plane causing the Doppler would probably need to be moving at hypersonic speeds! I have to confess I've never seen multiples of the same signal (other than those using FT8 Fox & Hounds mode or the MSHV software) with spacings of the several 100Hz you mention. |
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Jim Brown
On 2/22/2020 11:42 AM, Bill Lederer wrote:
So i am under the impression that switching mode power supplies don't operate at mains frequency, or at least their switching will spit off an array of frequencies due to the switching. AC Mains I can understand, but I think a switching mode power supply will emit some range of frequencies that may not be related to the mains frequency.Right. SMPS start by rectifying AC, there's a minimal capacitor filter, then a square wave generator running typically running in the range of 10-40kHz chops the DC, which is then rectified and filtered by a much smaller capacitor. RF noise results from the harmonics of the square wave, and often extend to 10M. A very high fraction of the RF noise we hear is generated by SMPS. I estimate that the average home has several dozen, and wiring connected to them, both on the AC side and the DC side, radiates the noise as the result of common mode current. Lots of detail in this tutorial. http://k9yc.com/KillingReceiveNoise.pdf BTW -- Bill, you and I met around 2003-4 sitting next to each other on NSRC Field Day. Your BIC time was an inspiration to me! 73, Jim K9YC |
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Jim Brown
On 2/22/2020 11:48 AM, Bill Lederer wrote:
So that would be multipath then likely?Yes. There can also be multi-path on the HF bands -- it's the fundamental cause of both "selective fading," and "picket-fencing," the difference being the period of the fading directly related to wavelength. It's the addition of two copies of the same signal that have taken different paths, and are thus shifted in time from each other. That time variation results in a phase difference that is proportional to frequency. 73, Jim K9YC |
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Jim Brown
On 2/22/2020 12:58 PM, Jim Shorney wrote:
Noise blanker IMD can cause multiple decodes based on the frequency of repetition rate of your impulse noise.YES! 73, Jim K9YC |
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Denny - K0TT
I see this occasionally on HF, usually when the geomagnetic field is disturbed. I assume it's caused by multipath or doppler distortion.
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Paul <w8aef@...>
I see that effect quite often on 6m from a station that is on
the other side of the Phoenix airport.
Paul, W8AEF From: WSJTX@groups.io [mailto:WSJTX@groups.io] On Behalf Of Martin G0HDB Sent: Saturday, February 22, 2020 1:16 PM To: WSJTX@groups.io Subject: Re: [WSJTX] Interesting double-decode The spacing of a Doppler-shifted signal on 20m is, in my opinion, extremely unlikely to ever reach several 100Hz; the plane causing the Doppler would probably need to be moving at hypersonic speeds! I have to confess I've never seen multiples of the same signal (other than those using FT8 Fox & Hounds mode or the MSHV software) with spacings of the several 100Hz you mention. In my experience, over-driving a transmitter's audio input usually results in harmonics of the eight FT8 tones that appear as one or more 'bar-code' signals elsewhere across the audio spectrum. Sadly this is very common. As for ALC, I believe FT8 uses a constant-amplitude waveform so I'm not sure what effect ALC might have on that; I wouldn't expect running with a degree of ALC to have any adverse effect on the purity of the transmitted signal. However, I recall there have been many previous discussions on this so I probably need to refresh my understanding of this aspect! Does ALC have any adverse effect on the quality of an RTTY signal, which is in effect a 2-tone FSK signal rather than the 8-tone (G)FSK signal used by FT8? -- Martin G0HDB |
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parker@masterdigital.com <parker@...>
20200207_121045 -10 0.3 2741 ~ TI9A W5CIA EM40
20200207_121045 -4 0.3 3221 ~ TI9A W5CIA EM40 20200207_121045 2 0.3 2141 ~ TI9A W5CIA EM40 20200207_121045 3 0.3 1301 ~ TI9A W5CIA EM40 20200207_121045 5 0.3 1541 ~ TI9A W5CIA EM40 20200207_121045 6 0.3 1781 ~ TI9A W5CIA EM40 20200207_121045 7 0.3 1421 ~ TI9A W5CIA EM40 20200207_121045 6 0.4 1950 ~ TI9A N0FW -07 <---- clean signal This is not caused 1) on the receive end, 2) by plane scatter, nor 3) by any other reflections in the near or far field. I am using a Flex 6700 connected to the computer over LAN only, and the station is apparently using a 160m horse fence antenna 3,800 ft from me. I know the cause, but the problem persists. Parker W5ADD Parker W5ADD |
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Bill Lederer
Jim: Dude, you were going neck-and-neck with me on 80 and 20! Miss those days. w8lvn On Sat, Feb 22, 2020 at 3:15 PM Jim Brown <k9yc@...> wrote: On 2/22/2020 11:42 AM, Bill Lederer wrote: -- --w8lvn-- |
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