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  • RobertS203 commented on Biotele's instructable Easy to Build WIFI 2.4GHz Yagi Antenna4 months ago
    Easy to Build WIFI 2.4GHz Yagi Antenna

    50 meters? That is 6 MHz. Wifi he is describing is 2400 MHz. Take a look at a stepper ir. They tune thru that band and are around $6000. It is a huge antenna but very good. It is a loop like the formed paperclip. In case you are confused, the term meters is the actual physical wavelength in meters of the transmitted signal. The lower the frequency the bigger the antenna has to be. It is factored on 1c, which is the speed if light, 299792458 meters per second. Rounded to 300,000,000 you divide this by the frequency in cycles to get the full wave length. Shorten it by using 300 for length of light / speed and 6 for the MHz instead of cycles and you get 50 meters. A balanced antenna such as a dipole is a 1/2 wavelength, so divide that by 2 for the physical length of a 50 meter d...

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    50 meters? That is 6 MHz. Wifi he is describing is 2400 MHz. Take a look at a stepper ir. They tune thru that band and are around $6000. It is a huge antenna but very good. It is a loop like the formed paperclip. In case you are confused, the term meters is the actual physical wavelength in meters of the transmitted signal. The lower the frequency the bigger the antenna has to be. It is factored on 1c, which is the speed if light, 299792458 meters per second. Rounded to 300,000,000 you divide this by the frequency in cycles to get the full wave length. Shorten it by using 300 for length of light / speed and 6 for the MHz instead of cycles and you get 50 meters. A balanced antenna such as a dipole is a 1/2 wavelength, so divide that by 2 for the physical length of a 50 meter dipole, so 25 meter length is correct. For 50 meters you are talking about a huge antenna. You can build an active antenna for just a receiver or use an LC network to tune a shorter wire but it will be compromised in ability. Hint: the antenna is a network, compromising of everything from the board connection point, all the way to the tip of the antenna. Using coax, you will also need a balun. I'm an extra class ham radio operator and an electrical engineer. Look online for antenna calculators will be your best bet. Beverage antennas are great, especially for summer time noise from lightning static crashes but they are even bigger. Sorry for the delay on the post but I just saw this.

    One more thing. If you are mounting this any distance from the wifi, db loss is extreme on higher frequencies like wifi 2400 MHz. Keep the coax short as possible and use cat5e to get to your laptop. LMR400 is a good all around coax but is is nearly 1/2" diameter. The higher the frequency the larger the center conductor has to be because of "skin affect". You can use a short piece of smaller coax and then adapt it to a larger coax. LMR has superior shielding also. Every 3db loss is half of the signal strength. 6db is 75% loss. 9db is 87.5% loss. Every 3db cuts it in half each time in the math. Antenna gain and loss are added to get the ERP...effective radiated power. 5db loss of coax with 8 db gain on the antenna will give you 3db gain so you can double you wif...

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    One more thing. If you are mounting this any distance from the wifi, db loss is extreme on higher frequencies like wifi 2400 MHz. Keep the coax short as possible and use cat5e to get to your laptop. LMR400 is a good all around coax but is is nearly 1/2" diameter. The higher the frequency the larger the center conductor has to be because of "skin affect". You can use a short piece of smaller coax and then adapt it to a larger coax. LMR has superior shielding also. Every 3db loss is half of the signal strength. 6db is 75% loss. 9db is 87.5% loss. Every 3db cuts it in half each time in the math. Antenna gain and loss are added to get the ERP...effective radiated power. 5db loss of coax with 8 db gain on the antenna will give you 3db gain so you can double you wifi output power to get the ERP. Just look into a Ubiquity wifi and their antennas. They are nearly 30dbm...1 watt with some very high gain antennas. That can get you 60 km distance if applied correctly...line of sight.

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