K3 Dual Receive Surprise
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I was working on 160m CW during the contest and noticed an interesting
phenom when hearing static crashes. The subRX (vertical polarized antenna) received the noise later than the receiver on the long wire (horz pol). The K3 was set in diversity receive mode. Being new to receiver diversity, I'd never thought through all of the implications. Is it possible that two wavefronts arrive at times different enough that this can actually be detected audibly? Anyone else ever noticed this or have any kind of explanation? I don't know if it's a DSP audio delay thing, or something physical Out There. 73 and :) matt zilmer K3 #24 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Ordinary and extraordinary? I.e. different polarisations being refracted at different heights.
I am surprised it is that much delay though. If it was the other way around then Ground wave vs Sky wave would be a reasonable explanation but this is ruled out if the vertical was receiving the crashes later and in any case the extra delay would be very short. Alternative explanations: One antenna was favoring the short path and the other the long path. The vertical radiation pattern could cause this. The Vertical would ideally have a low radiation angle and may then favour long path, so local storms might travel around the world to reach the vertical but also arrive at a high angle on the horizontal via a shorter hop. You were hearing different crashes or an echo that was vertically polarised. There is a known DSP delay on the K3 that depends on the filter bandwidth, but that would only be a few 10s of ms at the most. So if you have the 150Hz filter set the audio may be 10ms behind that of a wide open filter. You have programmed the K3 to have a longer delay than I thought plausible (AFX?). I don't think the K3 delay is more than a few ms. You have a longer delay from one ear than the other or a problem in your wetware. I hope it is not this. It would imply you have become unbalanced, but you might expect this would happen all the time even on a single receiver, so it is not likely. Mike |
Re: K3 Dual Receive Surprise
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In reply to this post by Matt Zilmer
Matt:
At an unconscious level of cognitive processing if you were listening to two replicas of the same signal, with one slightly delayed, if the delay were on the order of 1/100 second and if your ear were very highly trained, you might be able to tell that something is different about the two signals, but you would not be able to describe what. The delay would need to be on the order of 1/10 second or more before you would consciously recognize that one signal is delayed compared to the other. Recall that radio waves move at 3 x 10^8 meters per second. If you look at multi path propagation at HF radio waves over intercontinental distances, and suppose that your two receivers were responding to two different signals taking two different paths, the differences in time of arrival of the different signals would be 1/10000 second or less. Also supposing that you were listening to the same wave on two antennas 3 meters apart, the delay would be 10^-8 second. Thus, by either (or both combined) delay mechanism, the delay is many orders of magnitude too short for your internal cognitive processes to detect the difference in arrival time of RF wave fronts. On the other hand, DSP delays can be very long by comparison, and if you are using two receivers with non identical DSP parameters, you might very well be able directly to hear the delay (a difference in latency in the jargon of the trade) audibly. One curious phenomenon I've noticed is comparing digital versus analog TV signals. My cable service uses the same channel on cable as the "over the air" VHF channel for the local broadcast TV stations. At the present time the local stations are still simulcasting an analog signal on their VHF channels that I can pick up with an antenna and receive on the TV, and a digital signal on UHF. The cable company captures the digital signal, converts it to analog and retransmits it over the cable circuit on the analog VHF channel. I have an RF switch that lets me switch between the antenna and the cable service. If I'm listening to the VHF analog "over the air" signal and quickly switch to cable, I can hear the last syllable or so of the transmitted dialog repeated quite distinctly. This suggests a delay for the digital modulation and conversion back to analog on the order of 1/10 to 1/2 second. Thus, I'm more inclined to believe that what you're hearing is an artifact of the DSP in your receiver rather than an effect occurring Out There. 73, Steve Kercel AA4AK Matt Zilmer wrote: > I was working on 160m CW during the contest and noticed an interesting > phenom when hearing static crashes. The subRX (vertical polarized > antenna) received the noise later than the receiver on the long wire > (horz pol). The K3 was set in diversity receive mode. > > Being new to receiver diversity, I'd never thought through all of the > implications. Is it possible that two wavefronts arrive at times > different enough that this can actually be detected audibly? > > Anyone else ever noticed this or have any kind of explanation? I > don't know if it's a DSP audio delay thing, or something physical Out > There. > > 73 and :) > matt zilmer > K3 #24 > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by AD6XY
On Sat, 24 Jan 2009 10:06:22 -0800 (PST), you wrote:
> >Ordinary and extraordinary? I.e. different polarisations being refracted at >different heights. > Pretty sure it's The Weird Stuff Out There. What occurred to me after reading your reply is that it seems possible that the e-m fields' components have different characteristics due to polarization, and are arriving at the two antennas simultaneously. They just sound different, maybe have different durations and strengths. As I said, this is my first time using a diversity-capable receiver, and it looks like there is a lot to learn... Um, I don't *think* it's my hearing. But, well.... you never know. 73 and Thanks, matt _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Stephen W. Kercel
You are right it can't be simple multipath but it could be two entirely different paths. Or to put it more simply, a 1000km path difference equates to a delay of 3.3mS. If the long path is 30000km and the short path 10000 km the difference is 20000km and the delay 67mS which is probably detectable. Mike |
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In reply to this post by Stephen W. Kercel
On Jan 24, 2009, at 10:59 AM, Stephen W. Kercel wrote: > If you look > at multi path propagation at HF radio waves over intercontinental > distances, and suppose that your two receivers were responding to two > different signals taking two different paths, the differences in > time of > arrival of the different signals would be 1/10000 second or less. Sounds right. The ITU-R 1487 Recommendation for HF channel simulators has some numbers on path differences, and none showed more than 7 milliseconds. For low latitude quiet conditions, the ITU recommendation uses two paths, with a mean delay of 0.5 milliseconds. For disturbed conditions, the mean delay is 6 milliseconds. For mid-latitude quiet conditions (same as the CCIR 520 "Good" conditions), the mean delay is 0.5 ms. For disturbed conditions, it is 2 ms. For mid-latitude NVIS disturbed conditions, the relative path delay is 7 ms, the same as the mean path delay for a high latitude disturbed conditions. I went back and checked Watterson's 1970 IEEE paper (the grandpappy paper that all HF channel simulators are based on) which has some real measurements. For 9.25 MHz, they had measured relative path delays of the order of 1.1 ms for 2 hops off the F layer, 0.3 ms for 1 hop off the F layer and 0.04 ms for one hop off E layer. 73 Chen, W7AY _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Matt Zilmer
It is not unusual for me to hear some sort of multipath propagation on 20m late in the afternoon here in Arizona when beaming to Japan (single receiver and 4 element yagi with a good F/B ratio). The disparity in arrival time is often enough to make signals totally unreadable at CW speeds of roughly 25 WPM. The middle of a character or even a word sometimes just sounds like a continuous carrier. This might go on for an hour or more until one of the paths disappears. I have on two occasions this winter even heard three different arrival times for the same signal, which was very weird and I wish I had recorded it. Given the differences in path length necessary to generate that kind of delay I make no claim regarding the cause ... only that I have clearly heard it several times. In any case, if such delays are enough to blur 25 WPM CW, they would be enough to be easily noticed in static crashes. Of course, that still requires some sort of polarity disparity to create the effect observed by Mr. Zilmer. 73, Dave AB7E Stephen W. Kercel wrote: Recall that radio waves move at 3 x 10^8 meters per second. If you look at multi path propagation at HF radio waves over intercontinental distances, and suppose that your two receivers were responding to two different signals taking two different paths, the differences in time of arrival of the different signals would be 1/10000 second or less. ... the delay is many orders of magnitude too short for your internal cognitive processes to detect the difference in arrival time of RF wave fronts. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K3 Dual Receive Surprise
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Dave:
I had not thought of that. but you make a good point. It is kind of like optical interferometry, where the receiving electronics is inherently too slow to capture the instantaneous vibrations of either light wave, but can easily detect an interference pattern resulting from the interaction of the two light waves. 73, Steve AA4AK Dave Gilbert wrote: > > > It is not unusual for me to hear some sort of multipath propagation on > 20m late in the afternoon here in Arizona when beaming to Japan > (single receiver and 4 element yagi with a good F/B ratio). The > disparity in arrival time is often enough to make signals totally > unreadable at CW speeds of roughly 25 WPM. The middle of a character > or even a word sometimes just sounds like a continuous carrier. This > might go on for an hour or more until one of the paths disappears. I > have on two occasions this winter even heard three different arrival > times for the same signal, which was very weird and I wish I had > recorded it. Given the differences in path length necessary to > generate that kind of delay I make no claim regarding the cause ... > only that I have clearly heard it several times. > > In any case, if such delays are enough to blur 25 WPM CW, they would > be enough to be easily noticed in static crashes. Of course, that > still requires some sort of polarity disparity to create the effect > observed by Mr. Zilmer. > > 73, > Dave AB7E > > > > Stephen W. Kercel wrote: > > Recall that radio waves move at 3 x 10^8 meters per second. If you look > at multi path propagation at HF radio waves over intercontinental > distances, and suppose that your two receivers were responding to two > different signals taking two different paths, the differences in time of > arrival of the different signals would be 1/10000 second or less. > > ... the delay is many orders of magnitude too short for your internal > cognitive processes to > detect the difference in arrival time of RF wave fronts. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Stephen W. Kercel
> One curious phenomenon I've noticed is comparing digital versus analog
> TV signals. My cable service uses the same channel on cable as the "over > the air" VHF channel for the local broadcast TV stations. All signal en-, trans- and decoding will require at least one to two frames. At work the "broadcast" signals of the same program which leave our company will often have a delta of a second or so depending on what kind of processing was necessary (i.e. satellite broadcast, terrestrial broadcast, internet stream, etc.). Also any resynchronizing which may occur in the various system the signal is passed through also costs time. This is most likely what you are noticing. vy 73 de toby _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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