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#1
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WiFi out to 800 feet
On 10/4/20 5:59 PM, Arlen Holder wrote:
You can look up the Fresnel zone stuff separately, which, in my experience, is more theoretical than practical since you just shove more directional beam power to overcome the losses due to lack of height. What the hell? Clearly you don't do this for a living. |
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#2
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WiFi out to 800 feet
On Wed, 14 Oct 2020 00:23:10 -0700, Johann Beretta wrote:
Clearly you don't do this for a living. That is an absolutely correct assessment. You can advise the OP better than I on potential Fresnel Zone issues, as he's apparently asking how best to paint a LOS location 800 feet away with the transceiver on a pole I believe. You can run the math to explain to him how high that pole may need to be. (We do that stuff by trial and error - but you may know the math better.) Please advise the OP on the math so he knows how high to mount the radio. |
#3
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WiFi out to 800 feet
On Wed, 14 Oct 2020 07:45:18 -0000 (UTC), Arlen Holder
wrote: On Wed, 14 Oct 2020 00:23:10 -0700, Johann Beretta wrote: Clearly you don't do this for a living. That is an absolutely correct assessment. You can advise the OP better than I on potential Fresnel Zone issues, as he's apparently asking how best to paint a LOS location 800 feet away with the transceiver on a pole I believe. You can run the math to explain to him how high that pole may need to be. (We do that stuff by trial and error - but you may know the math better.) Please advise the OP on the math so he knows how high to mount the radio. I am talking about a target I can hit, unobstructed with a laser. It really looks like the HOA has cooled on the idea ... again. There are some privacy folks who certainly do not want any cloud solution and they are talking about the disposition of the video we collect. OTOH the Ring fans say "let'r rip". I am at the point of saying, let Comcast do this and pay the damned bill. |
#4
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WiFi out to 800 feet
On Wed, 14 Oct 2020 07:45:18 -0000 (UTC), Arlen Holder
wrote: On Wed, 14 Oct 2020 00:23:10 -0700, Johann Beretta wrote: Clearly you don't do this for a living. That is an absolutely correct assessment. By the way, I officially retired on Sept 30, 2020. The office is closed, the bank accounts emptied, and much of the equipment donated or sold. You can advise the OP better than I on potential Fresnel Zone issues, as he's apparently asking how best to paint a LOS location 800 feet away with the transceiver on a pole I believe. You can run the math to explain to him how high that pole may need to be. (We do that stuff by trial and error - but you may know the math better.) Sigh. I've lost count how many times I've done that in this newsgroup. Start he https://www.proxim.com/en/products/knowledge-center/calculations/calculations-fresnel-clearance-zone 800 ft is not far enough apart to worry about the curvature of the earth. 800ft / 5280ft/mile = 0.152 miles At 2.4Ghz, the Fresnel Zone is 9 ft radius at the midpoint of the link. Therefore, the antenna at both ends of the link need to be at least 9 ft off the ground, or 9 ft above any major obstructions (fences, trees, buildings, cars, etc). Actually, it's somewhat more complicated if I throw in fade margin, frequency selective fading, and system availability, but we won't need to go there for this example. At 5 GHz, the Fresnel Zone radius is only 6.3 ft. Therefore, the antenna pole can be 2.7 feet shorter. Please advise the OP on the math so he knows how high to mount the radio. Methinks we've lost the OP long ago. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#5
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WiFi out to 800 feet
On 10/14/20 9:42 PM, Jeff Liebermann wrote:
By the way, I officially retired on Sept 30, 2020. The office is closed, the bank accounts emptied, and much of the equipment donated or sold. Well done sir. -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com |
#6
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WiFi out to 800 feet
On Wed, 14 Oct 2020 19:42:48 -0700, Jeff Liebermann
wrote: On Wed, 14 Oct 2020 07:45:18 -0000 (UTC), Arlen Holder wrote: On Wed, 14 Oct 2020 00:23:10 -0700, Johann Beretta wrote: Clearly you don't do this for a living. That is an absolutely correct assessment. By the way, I officially retired on Sept 30, 2020. The office is closed, the bank accounts emptied, and much of the equipment donated or sold. Congratulations. You'll now enjoyably find everything you knew disappainting or being replaced by new kids on the block. I don't see any of those filling your shoes here and I usually only bother to lurk to see what you are posting. You can advise the OP better than I on potential Fresnel Zone issues, as he's apparently asking how best to paint a LOS location 800 feet away with the transceiver on a pole I believe. You can run the math to explain to him how high that pole may need to be. (We do that stuff by trial and error - but you may know the math better.) I've run cantenna line-of-site over 400m reliably for years. I didn't measure the fresnel zone but a farmer's apple tree in his front must have encroached the signal line every few years and he would kindly lop a few branches, restoring normal service. I have a note of the speeds somewhere but the system gave me office access from home, home broadband via the office and all I remember is that the Wi-Fi speed was better than the rather poor broadband speed available at the end of a long exchange line. After moving several years ago from the little hamlet (60 properties) the pathetic broadband (I think I had one of the best connections at 2mbps) was replaced by FTTP. I don't think I could have got mi Wi-Fi signal to keep up with the resulting 80Mbps broadband. Those we now Zoom with in that hamlet are always very clear and no blurring motion issues - I'm somewhat jealous. (UK in case any folk are struggling to understand any terminology or words). -- AnthonyL Why ever wait to finish a job before starting the next? |
#7
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WiFi out to 800 feet
On 10/14/20 12:45 AM, Arlen Holder wrote:
On Wed, 14 Oct 2020 00:23:10 -0700, Johann Beretta wrote: Clearly you don't do this for a living. That is an absolutely correct assessment. You can advise the OP better than I on potential Fresnel Zone issues, as he's apparently asking how best to paint a LOS location 800 feet away with the transceiver on a pole I believe. You can run the math to explain to him how high that pole may need to be. (We do that stuff by trial and error - but you may know the math better.) Please advise the OP on the math so he knows how high to mount the radio. All he has to do is search google for "fresnel zone calculator" At 1,056 feet (0.2 miles) the Fresnel for 5.1 GHz is 7.1 feet. (for 5.8 Ghz it would be 6.7 feet). The higher the freq, the smaller the zone. You can intrude the fresnel by 40% (max), but I try to avoid even that. |
#8
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WiFi out to 800 feet
On Sun, 18 Oct 2020 12:12:01 -0700, Johann Beretta
wrote: All he has to do is search google for "fresnel zone calculator" At 1,056 feet (0.2 miles) the Fresnel for 5.1 GHz is 7.1 feet. (for 5.8 Ghz it would be 6.7 feet). The higher the freq, the smaller the zone. The question was for an 800ft link. 800ft / 5280ft/mile = 0.152 miles Please adjust your computation accordingly. You can intrude the fresnel by 40% (max), but I try to avoid even that. That depends on whether the intruding material is absorptive or reflective. You can get a way with much less clearance if the signal is absorbed. Yes, the signal level goes down, but it also stays down and does not vary. However, if it's reflective, then it will refract (bend) part of the signal, creating the opportunity for fades, nulls, cancellation, etc. It can also create reinforcement and stronger signal levels, but those tend to change radically if anything moves. 40% intrusion is a usable number for real links, but only works if you have a sufficiently large fade margin, also known as SOM (system operating margin). 20 dB would be a good minimum. I carry 20dB and 30dB attenuators in my toolbox. If the system still works reasonably well with 20dB loss inserted at one antenna, it will probably be reliable. If it dies completely, you need a bigger antenna or more transmit power. While I'm ranting on the topic, fade margin (or SOM) is related to reliability (or downtime): SOM dB Reliability % Downtime per year 8 90 876 hrs 18 99 88 hrs 28 99.9 8.8 hrs 38 99.99 53 minutes 48 99.999 5.3 minutes 58 99.9999 32 seconds 99% reliability might sound great, but that means your link will be useless for 1% of the year, or 3.6 days per year. Don't go below 20 dB fade margin, which is 70 hours of downtime per year. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#9
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WiFi out to 800 feet
On 10/18/20 1:45 PM, Jeff Liebermann wrote:
The question was for an 800ft link. 800ft / 5280ft/mile = 0.152 miles Please adjust your computation accordingly. Yep. And the calculator I used could handle tenths. That's why I calculated for .2 miles. I couldn't do 0.152 miles. |
#10
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WiFi out to 800 feet
On Sun, 18 Oct 2020 19:26:40 -0700, Johann Beretta
wrote: On 10/18/20 1:45 PM, Jeff Liebermann wrote: The question was for an 800ft link. 800ft / 5280ft/mile = 0.152 miles Please adjust your computation accordingly. Yep. And the calculator I used could handle tenths. That's why I calculated for .2 miles. I couldn't do 0.152 miles. That's an input error of (0.2 - 0.152) / 0.2 = 24% Perhaps using the online calculator which I provided might have been a better idea? Or maybe a different Fresnel Zone calculator? https://www.google.com/search?q=rf+fresnel+zone+calculator This is interesting and might explain a few things: http://radiomobile.pe1mew.nl/?Calculations:Propagation_calculation:Fresnel_zone s Since the F2 zone is detrimental to receive signal level, antenna heights are often selected so that F1 is an unobstructed path and F2 is obstructed by a hill or the earth bulge along the path. In other words, the area around the F1 line is where you get your usable signal, while the area around the F2 line is where you get your problems. The reason you can get away with 40% incursion into the F1 zone is that reflecting objects on or near the F1 line will add, not cancel. I guess it really should be something like: 0.0 to 0.6 F1 = OK. Direct path. 0.6 F1 to 1.4 F1 = problems due to destructive cancellation. 1.4 F1 to 0.6 F2 = OK 1.4 F2 to 0.6 F3 = problems due to destructive cancellation. I'm not too sure the exact coefficients are correct. I'll check (later). In other words, there is a "band" straddling the various odd numbered Fresnel Zone lines which define areas that should not contain reflective objects. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#11
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WiFi out to 800 feet
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