Using FT8 to demonstrate Antenna Orientations

Discussion in 'Amateur Radio News' started by KM9G, Oct 6, 2021.

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  1. KL7AJ

    KL7AJ Ham Member QRZ Page

    If it's done in a relatively short period of time, you can make some approximate measurements. Ideally one would transmit a CPOL signal so as to be able to distinguish between X and O mode propagation. I go into this in some detail in my December 2010 QST article, "Gimme and X, Gimme an O; What's that spell? Radio!"
    Eric
     
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  2. DO1FER

    DO1FER Ham Member QRZ Page

    I didnt talk about cow ways, you should know. But think about the difference of a linear optimization and an asset utilisation. What is the result? At next think about the probability calculus and when the data is getting unsharp that they are not reliable anymore to get an answer. When you find the answer to this topics, then you are a step further.

    73,

    Cornelius DO1FER
     
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  3. W1YW

    W1YW Ham Member QRZ Page

    Hi Eric,.

    Relatively short is very short. As in essentially real time.

    Had a nice discussion with WA3FET about this very topic yesterday. He independently agreed with my assessment. The QSB and the roundoffs kill you on this approach with FT8.

    It turns out that real time propagation analysis is becoming a hot topic for some outside of ham radio; FT8 is considered and rejected as a mechanism for same.

    Even the flavors of the month (Big Data and AI) can't remove selection effects, and digital roundoff at low SINR.

    73
    Chip W1YW
     
    Last edited: Oct 11, 2021
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  4. K2ENF

    K2ENF XML Subscriber QRZ Page

    It occurs to me that I haven't commented directly to the video but more to the ancillary stuff. So, I'll do that here.

    Since the antenna that I'm using for this purpose is an omnidirectional vertical, trying to figure out the radiation pattern at least in terms of front end gain is useless. The radiation pattern is assumed to be omnidirectional.

    I know very well that immediate spot checks on a single antenna are pretty much impossible, given changing conditions. And frankly, I never figured on having any more than a rough guide from and from the signal reports from my local net. And understand, the design consideration was a balance between the two. Add to that the physical considerations of wind loading and whatnot when you start getting the antenna extremely high.

    I found over a period of months how about 6 months then once I started getting beyond about 35 ft the signal report increases reached diminishing returns as you went further up. I decided that as far as I was concerned the additional physical problems with installing the antenna at a greater height probably wasn't worth it.

    As far as DX is concerned I made observations over a period of a month or two for each height that I tried at each step using psk reporter to tell me what the average distance was for each antenna height that I tried. I found that once I got beyond about 35 ft the average distance readings started getting a little fuzzy, and I attribute that to varying conditions. But interestingly I found that once I started getting below 35 ft, my distance readings on DX tended to drop off rather dramatically regardless of conditions and I attribute that to not so much the radiation pattern of the antenna in a horizontal plane but how much of the signal was going straight up because of the proximity to the ground in other words, nvis more or less.

    So I settled on a 35 ft height at the antenna tip as the best all-around setup for the purpose.

    So, yes, you can in fact use FTA or if you like wspr has a tool for antenna performance. Just don't expect that you're going to have a decent comparison in an afternoon or even tremendously conclusive results numerically. That said, when used as I described here, it can be a great help
     
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  5. W1YW

    W1YW Ham Member QRZ Page

    Eric,

    A vertical monopole has a null at the zenith and is poor at high angles.

    What you are probably seeing is the launch angle of the vertical monopole is decreasing as you raise it and about that height you are getting asymptotic decreases in the launch angle, which is then fairly close to the horizon. IOW the antenna pattern of the vertical monopole is getting close to what one sees in free space. Low launch angles favor DX.

    The differences you are seeing with the launch angle change (from the height differences) are fairly large towards the horizon--many dB-- and thus not as sensitive to fairly rapid QSB. In those cases there is no reason to use FT8 at all and analog modes have enough SINR to make the measurements useful. Just as with the 10M beacon network from decades back.

    Notice the only variable you changed was height, for the antenna.

    73
    Chip W1YW
     
    Last edited: Oct 11, 2021
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  6. KF0DHQ

    KF0DHQ Ham Member QRZ Page

    I know this is probably not the greatest question to ask on this forum because its about antenna angles or something but WHY THE HECK IS FT8 SO IMPORTANT? As far as I know (Which is not to much) FT8 is another digital mode that uses packets I think. So can someone tell me why its so important or why it's better than any other digital modes?
     
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  7. W1YW

    W1YW Ham Member QRZ Page

    FT8 is a version of earlier digital modes invented by Joe Taylor, K1JT, and then enhanced in collaboration with others. By using a sync-clock at a fixed sub band , the mode allows a matched filter that has a lower detection threshold than many other digital modes, and certainly far lower than legacy analog modes, while also allowing a small QSO exchange. This is done in a fairly short period of time.

    The release of this free digital mode coincided with the bottom of the sunspot cycle, with pea-poor propagation on the HF bands. People quickly discovered that low power, even with really poor propagation and modest antennas , allowed transcontinental contacts on otherwise dead HF(for example) bands, when using FT8.

    FT8 just requires a rig and a clock/laptop. These are things already in peoples' shacks.

    Essentiallly it was the right 'product', at the right time, at the right price. At this point the 'install' base is a large fraction of the worldwide ham population.

    IOW FT8 wins because it is 'good enough', free, easy, and universal.

    73
    Chip W1YW
     
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  8. KF0DHQ

    KF0DHQ Ham Member QRZ Page

    Okay. I don't really dabble in digital modes that much but I've herd so much about FT8 I just wanted to see what all the fuss was about. Thanks for Explaining!

    73's KF0DHQ Jack A. Weigel
     
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  9. W1YW

    W1YW Ham Member QRZ Page

    I suspect others may have additional thoughts. Jack. I am not a big user of FT8 or other digital modes. My perspective is coming from looking at FT8 as a disruptive innovation, and telecom mode, topics of personal interest to me.

    I like to be more physically engaged in my contacts. That is a bit old school, but works for me. Others have different opinions.

    73
    Chip W1YW
     
    Last edited: Oct 11, 2021
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  10. KF0DHQ

    KF0DHQ Ham Member QRZ Page

    I'm pretty new into the hobby ,going on the sixth month I believe, but I never been a fan of the digital modes and internet modes. I like the old school style, it's the only thing I understand.;)

    KF0DHQ Jack A. Weigel
     
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