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Author Topic: Station Grounding Question  (Read 3746 times)
K0WA
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Posts: 95




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« on: November 26, 2012, 06:57:12 AM »


I am running an AL82/K3 with a Force 12 C3E at 60 feet.  When I am on 15 meters, the N1EL WinKeyer locks up if I run more than 500 watts output.  N1MM locks up and will not working until I kill it all off and start the program again.  Or, at times, I have to reboot the computer.  I have choke the USB line to the keyer and grounded the case of the computer. (Also, the mouse point gets a little crazy too)  With all the USB cables coming out of the back of the Computer case I am not surprised something like this happens, but I am at a loss as to how to stop it.

I am grounding to a 8 foot rod right below the desk....which is connected to a copper pipe attached to the back of the operating table...where all the equipment is tied to.

Anyone have any ideas or have dealt with this issue?

Lee K0WA
 
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KE3WD
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Posts: 5689




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« Reply #1 on: November 26, 2012, 07:16:21 AM »

Does your Force 12 install include a balun at feedpoint to decouple the RF from the coax shield? 


73
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K0WA
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Posts: 95




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« Reply #2 on: November 26, 2012, 07:31:39 AM »

Yes, I do have the balun on the Force 12 antenna.

Lee  Smiley
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WX7G
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Posts: 6198




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« Reply #3 on: November 26, 2012, 07:53:58 AM »

ALL PC cables to the radio should run together though a single ferrite core(s). The Winkeyer cable can run though another ferrite core(s). The PC power cable should run though another core(s). Be generous with the cores. Type 31 or 43 mix is good and DX Engineering stocks clamp-on cores. 
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W5LZ
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Posts: 477




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« Reply #4 on: November 26, 2012, 11:36:51 AM »

The simple fact is that computers and radios just don't like each other.  I'm surprised you haven't had problems at a lower power level.  As '7G' said, ALL the cables into or out of the computer can benefit from those torroids.  It can also help if you increase the distance between the computer and radio/amplifier.  While you're torroid'ing those computer cables you might as well do the ones in/out of the radio and amplifier too.  Computers were never designed to work in an RF environment, consider your self lucky.
 - 'Doc
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WX7G
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« Reply #5 on: November 26, 2012, 12:25:49 PM »

The reason to route all cables through a single ferrite or ferrites is to maximize the CM (Common-Mode) impedance. If each cable has its own ferrite the CM impedances parallel.

PCs are designed and tested to perform with no evidence of malfunction in a 3 V/m field. Any amateur station greatly exceeds this.
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AA4HA
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Posts: 1581




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« Reply #6 on: November 26, 2012, 02:39:38 PM »

The reason to route all cables through a single ferrite or ferrites is to maximize the CM (Common-Mode) impedance. If each cable has its own ferrite the CM impedances parallel.

PCs are designed and tested to perform with no evidence of malfunction in a 3 V/m field. Any amateur station greatly exceeds this.

Correct, most computing devices are Part 15 class B rated devices. Even if they were Part 15 class A rated the E field would only be tested up to 7 V/m. "General Population/Uncontrolled" exposure is limited to less than 27.5 V/m from 30-300 MHz, well in excess of what could cause disruption to a computer. Manufacturers only need to test a device when attached to a standard set of accessories (keyboard, mouse).

To give you an idea of what that corresponds to a 0 dBm signal would be around 6.7 V/m. I have seen some antenna sites that had signal levels as high as +20 dBm (67 V/m). Needless to say I spent very little time on that rooftop, you get to the point that you are afraid to expose a spectrum analyzer input to signals like that.

If you see signal levels in excess of -7 dBm then you are crossing the 3 V/m threshold, all bets are off with your computer.

Using unbalanced feedline of poor quality (regular 'ol RG-8) it has poor shielding (loose copper braid and not the tight braid overlaid on foil like LMR-400) and acts like a significant radiator of RF energy. If you have SWR mismatches then you get standing waves on the feedline that starts right at the back of your radio. It as if you brought the antenna into the room with you.

Of course the industry has made a big joke of Part 15 testing and by far in most cases very few companies actually test their motherboards any more. They can reference a reference to a test they did ten years ago and say that the new design is "similar" to what they did before. When I was still assembling my own computers I added ferrites into the case since I expected them to be exposed to RF.
« Last Edit: November 26, 2012, 02:42:06 PM by AA4HA » Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
K6AER
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Posts: 3528




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« Reply #7 on: November 27, 2012, 09:16:30 PM »

The shielding of RG-8 (-70 dB) or LMR-400 (-95 dB) in not your problem. The radiation from the antenna is directly radiating into you control cables. Toriods on the cable will help but the best solution is to move the antenna further away or go higher with the beam.
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KC8OJU
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Posts: 31




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« Reply #8 on: January 07, 2013, 09:10:54 PM »


I am running an AL82/K3 with a Force 12 C3E at 60 feet.  When I am on 15 meters, the N1EL WinKeyer locks up if I run more than 500 watts output.  N1MM locks up and will not working until I kill it all off and start the program again.  Or, at times, I have to reboot the computer.  I have choke the USB line to the keyer and grounded the case of the computer. (Also, the mouse point gets a little crazy too)  With all the USB cables coming out of the back of the Computer case I am not surprised something like this happens, but I am at a loss as to how to stop it.

I am grounding to a 8 foot rod right below the desk....which is connected to a copper pipe attached to the back of the operating table...where all the equipment is tied to.

Anyone have any ideas or have dealt with this issue?

Lee K0WA
 

Hey OT

I might point out the national electrical code, you need to have a common ground point where everything is grounded at, every thing should have a ground wire going to that ground point. Ground wire from the antenna, whole house to that one point. I don't think your whole house electrical box goes to that ground rod.
73 OM
de N8ZU
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KC4MOP
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Posts: 753




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« Reply #9 on: January 08, 2013, 03:30:47 AM »

You must have a lot of RF in she shack...RFI
It takes a lot to lock up a computer from my experiences...
Is your shack directly under the antenna? 60 feet high is a good place for 15M. The antenna should be further away from the shack.....distance.
How is your SWR?? Good match? Good connectors?
The other responses are very good to stop the RF from entering the computer and locking it up.
Your network cables (Ethernet) Internet from the router can bring RF into the computer also.

Fred
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K1DA
Member

Posts: 525




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« Reply #10 on: January 08, 2013, 08:31:41 AM »

You might try another current balun in series with the antenna feedline.  Check the DX eEgineering catalog.  Good ones are not cheap. 
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K6AER
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Posts: 3528




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« Reply #11 on: January 08, 2013, 11:02:03 AM »

The elephant in the room is: How far is the antenna from the operating position?
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KE6EE
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Posts: 447




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« Reply #12 on: January 08, 2013, 11:27:26 AM »

You might try another current balun in series with the antenna feedline.  Check the DX eEgineering catalog.  Good ones are not cheap. 

I agree. A really effective choke unun in the feed coax just before it enters the shack. Something like three big clip-on ferrites with three turns of coax through each ferrite. The ferrites are about $15 each from Mouser so you can do it for about $50 or you can buy a more expensive DX Engineering or Balun Designs choke unun.
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M1BJR
Member

Posts: 13




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« Reply #13 on: January 13, 2013, 02:58:54 PM »

The USB leads on the plastic mouse are not normally choked, many USB or PS2 keyboards are.
The mouse lead is a great antenna.

I run flex gear so have a PC running here doing everything so have some experience....

Swap the keyboard and mouse for a wireless pair - I use the Logitech K520 and M310 mouse combo.
Should run you to about $50.
All my software glitches and wandering pointer issues vanished immediately - the wandering mouse pointer is a great indicator Smiley

KC4MOP is also on the money.
I had no more issues until running higher power, then the LAN cable was hot  - feeds RF right into the PC (I have Cat5 STP).
I can get a burn from the screen on the LAN cable - guess the shield is a resonant length.... another little job to fix.

My doublet is right over my head about 4m from the radio bench and we can use 400w RF max here.

So - go wireless, then pull the lan cable, and see how that works for you.

Steve M1BJR
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WA7PRC
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Posts: 265


WWW

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« Reply #14 on: January 15, 2013, 03:12:11 AM »

I didn't read anything that mentioned grounding of feedline shields at the point of entry into the shack.  As far as I know, Nat'l Electrical Code requires this (as well as bonding of all grounds to the electrical service entrance ground).  As it happens, doing so will also greatly reduce common mode current from getting into the shack.

I recently installed a 72' tower (photos + text) only a few feet away from my shack, and upgraded my ground system to comply with NEC.  This upgrade included installation of a feedline ground buss at the point of entry.  Even when running a kilowatt, I now have ZERO issues with RF causing problems in the shack. Previously, there were some pieces of gear that were affected no matter what I did (bypassing, isolating, shielding, grounding).

vy 73,
Bryan WA7PRC
« Last Edit: January 15, 2013, 03:14:28 AM by WA7PRC » Logged
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