Timeline for What would be the typical received power of an "S9" signal?
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| Apr 14, 2017 at 6:28 | comment | added | SDsolar | Thank you for this answer. Always thought it was fairly arbitrary. Certainly the sigreps you hear on the air are subjective, but I had no idea there was a specific standard like this. Good show, OM. | |
| Mar 21, 2017 at 22:38 | comment | added | Phil Frost - W8II | Playing with VOACAP you can get more realistic estimates of path loss. You'll also see that as a general rule, the received power is higher at lower frequencies, but so is the noise floor. | |
| Mar 21, 2017 at 20:15 | history | edited | natevw - AF7TB | CC BY-SA 3.0 |
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| Dec 17, 2016 at 21:16 | comment | added | AndrejaKo | Also, on VHF/UHF, the "radio horizon" will make big impact. You can work tropospheric scattering, but I myself don't really understand the actual numbers, so I can't comment. | |
| Dec 17, 2016 at 21:14 | comment | added | AndrejaKo | In fact, the only thing I can thing of right now, where the Friis equation is useful would be with satellite communications on high VHF or low UHF. | |
| Dec 17, 2016 at 21:13 | comment | added | AndrejaKo | In case of mountain tops, tall buildings and similar situations, you have the issues with Fresnel zones. Read up a bit about them. As a rule of thumb, on 2 m, first Fresnel zone is around 230 m and on 430, it's around 130 m at the widest point. Therefore, you'd need to be very high above local terrain for them to be insignificant. Things do change at microwave frequencies though, so if you have links on 1.2 GHz, 2.3 GHz or up, influence is not so high, but they still need to be taken into account in say WiFi planning or similar. | |
| Dec 17, 2016 at 21:08 | comment | added | AndrejaKo | @natevw - AF7TB Well, sort of, but no. Basically, you can use it to prove that communication is impossible, but not that communication is possible. In real life, for short-range, local reflections are going to be the biggest issues to propagation. Things are so complicated that EM-propagation modelling is mostly abandoned. Instead, statistical models have been made based on measurements. This is especially true for rooms and similar. | |
| Dec 16, 2016 at 17:27 | comment | added | natevw - AF7TB | @AndrejaKo Thanks, good to know. Is it at least somewhat valid in "open air" though, like across a room or with mountaintop-to-mountaintop type stuff? | |
| Dec 16, 2016 at 9:29 | comment | added | AndrejaKo | Friis equation really doesn't work at all outside of free space and shouldn't be used for range estimations on Earth at all. | |
| Dec 16, 2016 at 3:52 | comment | added | Phil Frost - W8II | On HF, the noise floor is already high, and if you are on SSB the power is spread over a relatively large bandwidth compared to CW. I'd suppose in practice it requires quite a lot more power than a strictly defined S9 to achieve a subjective S9 in these conditions. | |
| Dec 16, 2016 at 3:50 | history | edited | Phil Frost - W8II | CC BY-SA 3.0 |
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| Dec 15, 2016 at 23:38 | history | edited | natevw - AF7TB | CC BY-SA 3.0 |
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| Dec 15, 2016 at 23:33 | comment | added | natevw - AF7TB | Hmm, good point. Apparently, the original definition historically was in terms of voltages even when impedance varied. But I'll try edit my answer to bury this a bit. | |
| Dec 15, 2016 at 22:53 | comment | added | Kevin Reid AG6YO♦ | If it were me, I'd avoid putting the voltage figures up front, since voltage can always be transformed so it doesn't represent something inherent to the signal like power does. | |
| Dec 15, 2016 at 22:45 | history | edited | natevw - AF7TB | CC BY-SA 3.0 |
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| Dec 15, 2016 at 22:37 | history | answered | natevw - AF7TB | CC BY-SA 3.0 |