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winagain
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Wifi cards keep blowing

Fri Dec 11, 2009 10:05 pm

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
 
RK
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Re: Wifi cards keep blowing

Sat Dec 12, 2009 11:03 am

is it the R52 or R52H?

Have you seen the other threads in this forum regarding the safe use of omnis?
 
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Re: Wifi cards keep blowing

Sat Dec 12, 2009 1:29 pm

Yeah I have,

But still getting blown cards,

Going to try the earth wire down the side of omni, but that apparently reduces perfomance, but will try anyway.
 
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Re: Wifi cards keep blowing

Mon Dec 14, 2009 4:35 am

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.
Steve Loomis
 
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winagain
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Re: Wifi cards keep blowing

Mon Dec 14, 2009 9:12 am

Hi, Have have just measured one that has never been in use, when connecting the leads, I get no diffirence in reading, display remains on 1, but if I connect to leads to each other, I get a variable of .xxOhms

Measuring continuity shows that there is no short, and if it were dc grounded like you explain, then it should show continuity is this correct?
 
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Re: Wifi cards keep blowing

Tue Dec 15, 2009 5:59 am

Yes, you are correct. If there is NO continuity then the antenna is NOT DC grounded.
Steve Loomis
 
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Re: Wifi cards keep blowing

Tue Dec 15, 2009 9:38 am

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.
Very interesting.

I have a little difficult whit inglish.. cna you post a image of misurement point and of shorted T connector?

This problem can affect sectiorial antennas?

tnx ;)
Best Regards...
 
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Re: Wifi cards keep blowing

Tue Dec 15, 2009 12:14 pm

Yes, you are correct. If there is NO continuity then the antenna is NOT DC grounded.

If I were then to open up the antenna on the top whip section I should then theoretically just short out the tip inner rod to outer metal.

I have seen this on how to make omni's tutorials on the net, as I have made an omni 9dbi and it works great, just time consuming for all the measurements, and then making a jig to solder everything straight, it is not as strong as the 12dbi that I have that is blowing cards, but am willing to loose some db's to make sure I can save money in the long run.

Do you think this may work?


magnavox: I don't think that Sectors, Grids or even flat panels have this issue, as their design is completly diffirent.
or at least I have never had issues with any of them even with a direct hit from lightning on tower.
 
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Re: Wifi cards keep blowing

Tue Dec 15, 2009 3:07 pm

I DID SOME TEST WITH OMINS AND FOUND THAT I BLOW RADIOS WITH THE 12DBI THEN I CHANED THE OMINS WITH A 9 DBI AAND PROBLEM SLOVERD


FOUND THAT SOME MAKES OF 12 DBI OMNIS HAVE STATICK PROBLEMS
If i dont No Ask someone That Does!
 
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Re: Wifi cards keep blowing

Thu Dec 17, 2009 4:59 am

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.
Steve Loomis
 
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Re: Wifi cards keep blowing

Thu Dec 17, 2009 9:48 am

tnx ;)
Best Regards...
 
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Re: Wifi cards keep blowing

Thu Dec 17, 2009 11:50 am

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.
Hi, I would also appreciate a picture tutorial if you have time.

I hacked my backup omni to pieces to see how it works, and where if possible I can put dc short in, managed to get one in place but when putting back into fiber sleeve I damaged it beyond repair :-(

I also noticed that if the short is longer than the 2.4Ghz 1/2 1/4 and full wave then it too is invisible to that frequency.
 
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Re: Wifi cards keep blowing

Thu Dec 17, 2009 12:09 pm

I have updated this page with information about DC grounded antennas: http://wiki.mikrotik.com/wiki/Wireless_card_diagnostics
No answer to your question? How to write posts
 
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Re: Wifi cards keep blowing

Thu Dec 17, 2009 3:03 pm

Thanks 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.
Steve Loomis
 
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Re: Wifi cards keep blowing

Sat May 21, 2011 6:37 pm

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.
Does this apply to 5.8Ghz?
N21roadie,
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Re: Wifi cards keep blowing

Sat May 21, 2011 6:41 pm

It would apply to any frequency where the antenna is not DC grounded.

Test using multimeter check continuity between the outer part of the connector with the inner part, and if you hear the continuous beep from multimeter, then you have DC grounded antenna.
 
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Re: Wifi cards keep blowing

Sun May 22, 2011 3:46 pm

Thanks 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.
Anybody got a picture of this at 5.8ghz and where to pick-up "t" n connector
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Re: Wifi cards keep blowing

Mon May 23, 2011 2:12 am

I have updated this page with information about DC grounded antennas: http://wiki.mikrotik.com/wiki/Wireless_card_diagnostics
Thank you Normis, this will be very helpful for many people. :)

In the last picture it says that the multimeter display indicates overload. I'm quite sure it means beyond the limits of the meter to register, or that there isn't continuity.

If the leads are not in contact with each other, or touching opposite ends of a broken wire, the meter will indicate infinite resistance (usually by displaying dashed lines or the abbreviation "O.L." which stands for "open loop").
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