Hi, I am having an issue with my omni connected to R52 wifi card, where if there is rain, wind or lightning in the general area, the card keeps blowing.
The omni is a 12db
Rb433
Lightning arestor in place, and grounded.
Wifi card Mikrotik R52
Very interesting.This is a continuing problem with omni antennas that are NOT DC grounded. Many are not. To test yours, take an OHM meter and measure from the center conductor of the antenna connector to the outer conductor. It should read almost 0 ohms. If it does NOT show any reading then it is NOT DC grounded and will build up a static charge and blow your radio's. NO amount of external grounding will fix this. There IS a fix however. See below
A DC Grounded antenna is NOT a short to the radio signal but is a short to DC (Direct Current). This short will bleed off any accumulated static charge. NO amount of grounding to the outer conductor will help if the active element of the antenna is NOT at a DC Ground potential.
For those who understand how RF (radio frequency) resonant lines work, a 1/4 wavelength from a short is an open and the reverse is true too. The grounded antenna uses a shorting stub internally. The stub is invisable to RF but is a direct short to ground at frequencys far away from the active frequency. DC is 0 (ZERO) megahertz.
I have salvaged PacWireless 2.4gig Omni's that have zapped several radio cards by adding a
"T" connector at the base of the antenna, then screwed a crimp connector to one leg of the "T" connector and soldered the center brass pin to the edge of the connector at the far end away from the center pin inserted into the "T" connector. It so happens that at 2.4 Gig 3/4" or so is approximately a 1/4 wavelength. I have 2 antennas in service right now that had zapped radio card before and have been running for over a year now with this fix.
To prove my point, I hooked up a test setup and measured my signal level without the modified "T" connector, then added the modified "T" with the shorted connector and saw NO change in signal strength. I then removed the short from the "T" connector and the signal level dropped signficantly because I changed it from a short to an open. A 1/4wave from a short is an open and the reverse is true too, a 1/4wave from an open is a short. When I removed the short, it became an open and the other end became an RF short thereby attenuating the signal.
I hope this is easy to understand. Take it from me, this DOES work. In the future, make sure any antenna you purchase to install, is DC shorted or do not install it.
Yes, you are correct. If there is NO continuity then the antenna is NOT DC grounded.
Hi, I would also appreciate a picture tutorial if you have time.Have you tried to check for continuity on the omni's from the center pin to the outer shell? I am willing to bet that your 12dB omni is an open instead of a DC grounded antenna.
I see someone is requesting a picture. I will try and get one of the modified T connector to make this clearer.
What is happening is: by putting a short to ground from the center conductor of the feed end of the antenna and by making this short to be 1/4 wavelength long you make a path for the static build up to bleed off and by using the 1/4 wavelength the short is invisable to 2.4 gig raido signal.
I will post a picture when I have time.
In answer to the sectorial antenna. I do not have information about these as I have not had any problems with them. I suggest you test the continuity of any antennas and see for yourself if they are a shorted type antenna.
Does this apply to 5.8Ghz?This is a continuing problem with omni antennas that are NOT DC grounded. Many are not. To test yours, take an OHM meter and measure from the center conductor of the antenna connector to the outer conductor. It should read almost 0 ohms. If it does NOT show any reading then it is NOT DC grounded and will build up a static charge and blow your radio's. NO amount of external grounding will fix this. There IS a fix however. See below
A DC Grounded antenna is NOT a short to the radio signal but is a short to DC (Direct Current). This short will bleed off any accumulated static charge. NO amount of grounding to the outer conductor will help if the active element of the antenna is NOT at a DC Ground potential.
For those who understand how RF (radio frequency) resonant lines work, a 1/4 wavelength from a short is an open and the reverse is true too. The grounded antenna uses a shorting stub internally. The stub is invisable to RF but is a direct short to ground at frequencys far away from the active frequency. DC is 0 (ZERO) megahertz.
I have salvaged PacWireless 2.4gig Omni's that have zapped several radio cards by adding a
"T" connector at the base of the antenna, then screwed a crimp connector to one leg of the "T" connector and soldered the center brass pin to the edge of the connector at the far end away from the center pin inserted into the "T" connector. It so happens that at 2.4 Gig 3/4" or so is approximately a 1/4 wavelength. I have 2 antennas in service right now that had zapped radio card before and have been running for over a year now with this fix.
To prove my point, I hooked up a test setup and measured my signal level without the modified "T" connector, then added the modified "T" with the shorted connector and saw NO change in signal strength. I then removed the short from the "T" connector and the signal level dropped signficantly because I changed it from a short to an open. A 1/4wave from a short is an open and the reverse is true too, a 1/4wave from an open is a short. When I removed the short, it became an open and the other end became an RF short thereby attenuating the signal.
I hope this is easy to understand. Take it from me, this DOES work. In the future, make sure any antenna you purchase to install, is DC shorted or do not install it.
Anybody got a picture of this at 5.8ghz and where to pick-up "t" n connectorThanks Normis, this is very helpful. It seems this topic keeps popping up. I will try and post pictures of my simple modified "T" connector to add a DC ground to any antenna.
Thank you Normis, this will be very helpful for many people.I have updated this page with information about DC grounded antennas: http://wiki.mikrotik.com/wiki/Wireless_card_diagnostics