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Author Topic: Grounding a Balanced Dipole to Reduce RFI/EMI  (Read 7032 times)
VE6ETP
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« on: December 29, 2013, 02:50:43 AM »

Sorry for the rather generic topic. Couldn't think what else to title it.

I've been doing a lot of further reading on proper grounding including dealing with common mode interference, differential mode interference, and of course ground loops.

I believe I have a terrible grounding setup so I'm looking to improve it. Let me describe my setup.

I have a metal pole (probably should change that to PVC?) mounted to the side of my brick chimney two stories up on top of my house. From that I have a center fed inverted V dipole hanging from it however it is not connected to the pole in anyway electrically as it's tied up with rope to the pole. The antenna itself is an inverted V in the vertical and horizontal (not the best I know but it's due to shape of my roof and where I could mount my mast, i.e. chimney).

I have a ground wire clamped to the base of the metal pole that runs down the two stories straight to a ground PLATE that's hammered into the ground right beside the chimney. So, the shortest ground line I could possible use.

The antenna is feed by RJ-11 (75ohm coax but very well shielded) that runs down the side of my house down to fairly near the ground plate location and then enters my house. From there it runs all the way across to the other side of the house (again just the way my house is setup). So this is a rather long feed line (at least 75 feet long if not 100).

At my transceiver I've clamped another ground wire to a cold water pipe just above in the roof (the radio is in the basement). This then runs to a metal rack which is where I've grounded all my gear to (at single point). Even though I've grounded everything to a single point I believe I may still have a ground loop here as the power cord itself for the power supply is grounded to the wall plug. However I'm not overly concerned here as from what I've read, it's probably not my biggest issue.

You may have noticed I didn't mention grounding the feed line as it enters the house. Therefore, the main question I wanted to ask is whether I should cut my feed line just before it enters my house, screw it onto a lightning protector and then ground the lightning protector at that point. One, this obviously will help protect my equipment and it's just generally safer I assume. But will it also help with interference?

On 80m I'm getting a noise floor around 90dBm and I'm getting some rather nasty interference lines right around the JT65 frequency I hang out on later at night. I'm hoping to improve on the noise floor and reduce some of that interference that's probably coming from both my house and the neighbours I've tried chokes, and AC filters etc with minimal success. To get any noticeable improvement I've had to use 10 ferrites with multiple wraps each and it only improves the interference mildly. I end up with an entire power core of ferrites wrapped around it. I'm thinking I need to hit the interference problem in a more vulnerable area first before going around, tweaking it with ferrites.

Finally, my second question is, whether I should ground the feed line as it goes into my antenna on the roof. Keep in mind that the nearest ground is 2 stories down (a good 25 feet) so I'm concerned that the impedance will be too high on the ground for it to be effective. Thoughts?

Also, I'm running a Flex 3000 so it's got a good noise floor that I've seen when the antenna is detached.

Sorry for the run on message. I appreciate any advice the community can give especially on those two questions.

Thank you!

Regards,

Peter
VE6ETP
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« Reply #1 on: December 29, 2013, 07:39:12 AM »

I have a center fed inverted V dipole
...
The antenna is feed by RJ-11

RG-11. 

You're feeding a balanced antenna with unbalanced line.  That means your well shielded line is serving as a "third wire" to your two wire antenna.  So effectively your antenna is the two wires of the vee, and also runs from the feedpoint of your vee on the outside of the shield to the back of your radio.  If there is a noise generator anywhere nearby, even a very weak one, you will very efficiently couple to it.  If there is noise/EMI on your electrical ground you are effectively connecting your antenna directly to the noise source via your chassis ground.  So first thing to consider is a balun at the feedpoint and even an unun or two in between for improved isolation.

Carrying that thought a bit further, a coax-fed dipole/vee will tend to have a lot of loss if used on multiple bands with a tuner.  You didn't mention if you were using it this way but if you are, you could consider switching out the coax with window line and putting a balun closer to the shack.


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At my transceiver I've clamped another ground wire to a cold water pipe

Water pipes are not recognized grounds.  Consider where these pipes go before they may, or may not, end up grounded.

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Even though I've grounded everything to a single point I believe I may still have a ground loop here

The minute you start adding grounds that aren't real grounds, you invite a host of problems.

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what I've read, it's probably not my biggest issue.

Several seemingly insignificant issues can add up to a significant problem.

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the main question I wanted to ask is whether I should cut my feed line just before it enters my house, screw it onto a lightning protector and then ground the lightning protector at that point.

Why wouldn't you want to do this?

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But will it also help with interference?

If your noise problem is tied to your third wire/common mode issue, then it could make it better, worse, or no change.  For safety purposes this ground point should be your single point ground, and it needs to be bonded to your service entrance ground.

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I'm getting a noise floor around 90dBm

Egads, that's a megawatt.  No worries about powering the rig then!  Let's see, if that was -90dBm that would be around S6 on a calibrated meter, right?

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I'm hoping to improve on the noise floor and reduce some of that interference that's probably coming from both my house and the neighbours I've tried chokes, and AC filters etc with minimal success.

With your antenna effectively coupling to wiring and a myriad of potential noise sources you would have to isolate, bypass and shield just about everything.

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I'm thinking I need to hit the interference problem in a more vulnerable area first before going around, tweaking it with ferrites.

OR, improve the isolation between your antenna and the noise sources by minimizing your common mode.

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Finally, my second question is, whether I should ground the feed line as it goes into my antenna on the roof.

Doing so would create a "fourth wire".

Mark K5LXP
Albuquerque, NM
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VE6ETP
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Posts: 19




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« Reply #2 on: December 29, 2013, 12:25:45 PM »

RG-11. 

You're feeding a balanced antenna with unbalanced line.  That means your well shielded line is serving as a "third wire" to your two wire antenna.  So effectively your antenna is the two wires of the vee, and also runs from the feedpoint of your vee on the outside of the shield to the back of your radio.  If there is a noise generator anywhere nearby, even a very weak one, you will very efficiently couple to it.  If there is noise/EMI on your electrical ground you are effectively connecting your antenna directly to the noise source via your chassis ground.  So first thing to consider is a balun at the feedpoint and even an unun or two in between for improved isolation.

Carrying that thought a bit further, a coax-fed dipole/vee will tend to have a lot of loss if used on multiple bands with a tuner.  You didn't mention if you were using it this way but if you are, you could consider switching out the coax with window line and putting a balun closer to the shack.

This makes sense. Before I built the antenna I read about using 75ohm wire. The consensus was that it shouldn't make much of a difference. I'm guessing because people were using baluns.

So I do have a balun up at the antenna. An ugly balun in fact (http://k8dns.com/balun.html). However it's not directly at the antenna. I have it anchored to the mast and then have a short piece of coax feeding the antenna. Short as in probably 3 feet. Has this essential negated the benefit of this balun? Is it the right kind of balun to use? I remember when I installed it, it did help the interference and swr a little.

Also, I should state that my antenna is a fan dipole with two sets of lines coming out of it for 20m and 40m. Both are resonant at the middle of the band ranges at about 1.1:1 SWR.

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Water pipes are not recognized grounds.  Consider where these pipes go before they may, or may not, end up grounded.

The minute you start adding grounds that aren't real grounds, you invite a host of problems.

Sounds like what I suspected and I should get rid of this half assed ground. When I connect or disconnect the ground it doesn't seem to make much of a difference at all anyway. Should I be running a long ground wire from the ground point just outside my house where the ground rod is installed all the way to my transceiver? Again I'm concerned that the length of the ground wire will negate any beneficial effect. Sounds like I should just stick with the grounding provided by my household wall plug?

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I'm getting a noise floor around 90dBm

Egads, that's a megawatt.  No worries about powering the rig then!  Let's see, if that was -90dBm that would be around S6 on a calibrated meter, right?

Isn't it 1 watt, 1000 milliwatts? But yes it's around S6 on my meter, thus what triggered me to start hunting to reduce the noise seen on my transceiver. I can still pull in signals but obviously the weak stuff is getting clouded in the noise.

Quote
With your antenna effectively coupling to wiring and a myriad of potential noise sources you would have to isolate, bypass and shield just about everything.

OR, improve the isolation between your antenna and the noise sources by minimizing your common mode.

With a ground at the entry point into my house and possibly another balun here (another 1:1 or should I be looking at a different type of balun?) will the RG-11 be suitable? Or should I really consider running new line?

Quote
Quote
Finally, my second question is, whether I should ground the feed line as it goes into my antenna on the roof.

Doing so would create a "fourth wire".

I figured this would be a pointless exercise. So the coax shielding at the antenna connection does NOT need to be grounded then? It is sufficient, or better, to ground at ground level where the ground wire is at it's shortest possible?

Also, will a single ground rod suffice? I've also heard about radials or possible using multiple ground rods. It is winter here so installing radials in the ground is not going to happen until June at the earliest. But I could hammer in a ground rod or two. Thoughts?

From all this it seems that I should at the very least ground at the entry point into my house. I'm omw to home depot now to grab a ground rod as the ground plate is a good 15 feet away from where my feed line comes into the house. I figured the shorter the better. Also since that ground plate is only grounding the mast and not grounding the antenna in anyway I hope this will not cause any ill effects (i.e., ground loops). If so I could always pull this ground wire from the mast to the same ground rod.

Any further thoughts?

Thanks very kindly for your help!

Regards,

Pete
VE6ETP
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K5LXP
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« Reply #3 on: December 29, 2013, 09:44:40 PM »

Before I built the antenna I read about using 75ohm wire. The consensus was that it shouldn't make much of a difference. I'm guessing because people were using baluns.

When it comes to common mode/third wire it won't matter if your feedline is 50 or 75 ohms.

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I do have a balun up at the antenna.

A choke balun won't be as effective as a ferrite one but it's better than nothing.

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I remember when I installed it, it did help the interference and swr a little.

That might justify bolstering up that aspect of the system with a better balun, at the feedpoint and possibly one or two chokes along the feedline.

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my antenna is a fan dipole with two sets of lines coming out of it for 20m and 40m.

OK.  This could be in your favor as far as maximizing the effect of any balun you would use.

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Should I be running a long ground wire from the ground point just outside my house where the ground rod is installed all the way to my transceiver?

No.  You should be reading up on the three different ground types and understanding the application of each:

AC safety ground
Surge/lightning ground
RF ground


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I'm getting a noise floor around 90dBm

Isn't it 1 watt, 1000 milliwatts?

1 watt is +30dBm.

Quote
With a ground at the entry point into my house and possibly another balun here will the RG-11 be suitable?

Your feedline is fine. 

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So the coax shielding at the antenna connection does NOT need to be grounded then?

As you noted, the length of this ground would negate its effectiveness as a ground.  It would end up being a radiator/receptor.

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It is sufficient, or better, to ground at ground level where the ground wire is at it's shortest possible?

"Sufficient" for what?  (See "ground types", above.)  Depends on what you're trying to achieve - an AC safety ground, a surge ground, or an RF ground?  At ground level this would primarily be a surge ground.  A balanced antenna is ground independent, so no effect there.  The AC safety ground is the third prong on the AC outlet. 

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Also, will a single ground rod suffice?

Depends on your goal - AC ground, or surge ground?  If you're bound to putting in a ground rod be mindful there are codes to go with it.  Not sure about the specifics in Canada but here they need to be bonded to your AC service entrance ground with #6 copper.

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I've also heard about radials or possible using multiple ground rods.

Radials are for RF grounds.  Multiple ground rods make AC and surge grounds more effective if deployed correctly.  Ground rods can never serve as an RF ground no matter what you do.  Because we're talking a ground independent antenna, I'm not sure what your goal is with all this grounding.  "Ground" is not some magical termination point where all energy connected to it magically disappears.   Hence the different ground types and their specific implementation.

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From all this it seems that I should at the very least ground at the entry point into my house.

If you're suddenly concerned about lightning then I suppose.  If it's to cure your RFI, I think you're better off putting work into improving feedline isolation.

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that ground plate is only grounding the mast and not grounding the antenna in anyway

I think you're fine with that.

Given your observation that things improved with a choke balun you might see an incremental improvement with a better performing balun.  Once that's as good as it gets you can re-assess the noise and see about finding the source.  If it's still coming through once your antenna is better isolated that implies that it's a relatively strong source and when they're strong, they can be tracked down more easily.  That's the topic of a separate thread, but first get your isolation and grounding situation worked out. 

Mark K5LXP
Albuquerque, NM



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VE6ETP
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Posts: 19




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« Reply #4 on: December 30, 2013, 12:08:02 AM »

Mark,

Apologies, the whole reason why I got hung up on grounding was this article, http://www.iw5edi.com/ham-radio/5/grounding-is-key-to-good-reception. Maybe it led me astray or I just mis-interpreted the article. Or perhaps this guy is completely on the wrong track?

Sounds like the summary of all this is that I should focus at adding more balun's to my feed line?

What's your thoughts on the MFJ-915?

Also I've been doing some more reading on a common mode choke at the antenna, at the transceiver, and perhaps one somewhere in the middle is a good idea. I think this is what you've been trying to tell me all along. However, I've always struggled with finding the right ferrite cores. Seems there are a number of different kinds of material but I'm getting conflicting answers on which is the best as it's largely determined by frequency I'll be operating on. My best guess is that I should be using type 43 or the new 31 by the company fair-rite?

My next problem is where to get them. I can't seem to find a good place to get them. I checked digikey as I've always been amazed at their speed of delivery. I assume I want some toroids that are 1-2 inches wide in order to get the wire through them. The best I could find were these suckers which are 1.4" internal diameter.

http://www.digikey.ca/product-search/en?pv1727=227&FV=fff40034%2Cfff802aa%2C2dc116d&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

The problem is they state the impedance is 135 ohms and the test freq is 100MHz. So I assume this is the wrong material.

They do have type 43 material ferrets but they would only be wide enough to pass the cable through once. Sounds similar to snap on chokes which I've found to be pretty much useless.

Any further thoughts?

Regards,

Pete
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W1VT
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« Reply #5 on: December 30, 2013, 07:41:22 AM »

I'd suggest turning off circuit breakers to help figure out the source of  "nasty interference lines."

In theory, a good radial system will provide a low impedance ground that will reduce conductive interference.  In practice, many hams can't do that.  Ground rods effectively have 50 ohms or so of series resistance, severely limiting their usefulness in interference reduction.

If you can't locate/turn off the interference, you might consider some sort of separate receive antenna.

Zack Lau W1VT
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« Reply #6 on: December 30, 2013, 03:08:49 PM »

I got hung up on grounding was this article,

He's making an argument that you can ground RFI away.  While a lot of what he says can be true in some circumstances it's not true in all of them.  Certainly in your case you can't ground both ends of the feedline and bury the line in between.  What then?  How do you ground an antenna in an airplane?  Grounding can be a solution to some noise problems but it isn't a cure-all.  When the EMI is in MHz, the idea that you're going to solve it with a wire connected to a rod in dirt seems a bit difficult to believe.

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perhaps this guy is completely on the wrong track?

I think he is just relaying what worked for him in his situation.

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I should focus at adding more balun's to my feed line?

That's part of it.  Good bet any solution you'd try would not be 100% effective.  You start with the known issues and keep chipping away until the interference is at a level you can tolerate.

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What's your thoughts on the MFJ-915?

No opinion, I've never owned one.  Would be useful if they told you what the mix of the ferrites were but at face value it should be better than the air core choke you're using now. 

Quote
I've been doing some more reading on a common mode choke at the antenna, at the transceiver, and perhaps one somewhere in the middle is a good idea. I think this is what you've been trying to tell me all along.

The more you have, the better your isolation. 

Quote
I've always struggled with finding the right ferrite cores.

Amidon, Fair-Rite.

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I'm getting conflicting answers on which is the best as it's largely determined by frequency I'll be operating on.

Also the desired degree of attenuation.  If you don't need the "max" but rather "enough", then whatever mix gets you there will work.

Here's a great comparison of different choke configurations:

http://www.karinya.net/g3txq/chokes/

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I should be using type 43 or the new 31 by the company fair-rite?

I would agree.

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I can't seem to find a good place to get them.

Amidon is a distributor for all the big magnetics outfits.  Just a $20 minimum.

http://www.amidoncorp.com

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Any further thoughts?

You could go with a packaged solution from like likes of Balun Designs, DXEngineering, et al, where you know what you're getting.  Not cheap but depending on how much time you want to mess with balun and choke construction there's some value there.

Just to set your expectation level- this is just one part of the solution.   I always zero in on common mode first because if you have that even small levels of local EMI can wipe you out.  Once you have your antenna to where only the antenna part may be picking up the interference, then you can be more confident the source is much stronger and usually more readily dealt with.

Have you done any steps to characterize or isolate the source?  Killing the house mains (not just individual breakers) is a good starting point.  Noting times of day, frequencies/bands, sound of it, etc are all clues.


Mark K5LXP
Albuquerque, NM
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VE6ETP
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« Reply #7 on: December 31, 2013, 01:23:22 PM »

After I wrote my last response I had found a good place for ferrites. Looks like Amidon would have been good too but I ordered from Mouser. I got 10 of the Type 31 2.4" toroids. Ordered them yesterday and they arrived today. Still amazed by those electronic online warehouses.

I have a MFJ-1026 Noise & Interference canceller hooked into my feed line that I've tried with some success in the past. Here I have the main feed line going into this device and then some regular RG58 cable going into the flex radio. I've tried directly connecting the feed line to the flex and in this configuration. With the MFJ off there is no difference in noise (nor my SWR).

So I tried out one of the toroids on this RG-58 and gave it 4 wraps on one side of the toroid and 4 wraps on the other side as I've seen many times online, ensuring the ends are coming out at opposite ends of the toroid.

Now granted this is just the first attempt and it is right at the radio side of things, but I didn't see any difference in my noise level. Which was quite disheartening. I thought I would at least see some difference.

I've done some further looking and it looks like some people use other kinds of wire around the ferrite and then connect these to PL-259 female connectors and put them in boxes. I saw one that use magnet wire as seen here http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&ved=0CGAQtwIwAg&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3Dv0lhNQumkmA&ei=hTPDUuaMLpTioASZgIKAAw&usg=AFQjCNFRuKqZgaRm6vuQqojceCn3mTNLHg&sig2=uph2K2CfgqjrD6VGmGTBYg&bvm=bv.58187178,d.cGU

Is this a good approach?

Thanks for the great link to the different kinds of chokes. That chart will be very helpful in future.

Finally, I have turned off all the breakers and ran my radio (and my laptop) off of battery. I've identified two areas of bad interference. One is an LCD TV and satellite receiver which I just unplug (its a second tv) but would like to improve this in future.

The other area is where I have computers. I have two rooms, one in my shack in the basement and one 2 floors up in my office. Again I can just turn these off. However I've found they don't always pose that much of a problem. Depends on time of day of course and which band.

One particularly bad bit of interference is on 80m and comes from my PC video card. Took me awhile to find that one. But it's the PC I use to control my flex. So I'm not sure what to do about that one. It hits right at the JT65 freq I use there on 80m. I've tried the MFJ with limited success. It just seems to bring up the noise floor to hide the interference.

Should I be sticking all these ferrites on the power cords of all these troublesome devices or should I be putting them on my feed line?

I'm going to run up to a local electronics store in town right now and pick up some of that magnetic wire and try to reproduce what was built in that video. It seemed close to what a lot of others had built in other videos I've seen on this topic. Hopefully I have more success with that.

Regards,

Pete
VE6ETP

« Last Edit: December 31, 2013, 01:40:45 PM by VE6ETP » Logged
K5LXP
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« Reply #8 on: January 01, 2014, 10:46:29 AM »

I tried out one of the toroids on this RG-58... I didn't see any difference in my noise level.

I would reserve judgement until you can get the feedpoint isolated.

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some people use other kinds of wire around the ferrite and then connect these to PL-259 female connectors and put them in boxes. 
...
Is this a good approach?

If you're going to maintain 50 ohms it needs to be wound like a balun (parallel windings, proper spacing).  Common mode chokes like the one in the video are OK for AC and DC.

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I've identified two areas of bad interference.

Excellent.  Like solving antenna common mode, there are basic mitigation techniques for devices.  Could be as simple as ferrites on the cords, reorienting cables, adding bypass caps, to ditching them for different devices.  Just unplugging them while you operate is just a valid cure as any.  My worst offender ever was a cordless drill charger in the garage.  Rather than fix it, I just plugged it into a switched outlet strip.

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One particularly bad bit of interference is on 80m and comes from my PC video card.

Having a "local" device like a PC next to the rig cause interference does imply that your feedline is "leaking" via common mode.  I doubt that video card is "spraying" enough EMI to go 50+ feet or whatever up to your antenna.  Does it go away when you unplug the monitor cable?  Maybe a ferrite on that cable could help if it doesn't have one already  If it's a desktop PC, swapping it for a different card might be an option.  May seem extreme to replace devices because of EMI but some devices just aren't conducive to simple cures like cable ferrites.  You could spend a lot of time digging into a device to byplass all the I/O and construct shields. 

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Should I be sticking all these ferrites on the power cords of all these troublesome devices or should I be putting them on my feed line?

Whatever works.  The typical process is to note the baseline level of the interference you're getting, make a change and observe the effect.  If it's an improvement, you know you're on the right track.

Mark K5LXP
Albuquerque, NM
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VE6ETP
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« Reply #9 on: January 03, 2014, 01:37:34 AM »

Thanks again Mark. I'm waiting on the RF isolators form MFJ to arrive. Should be here next week. See how they go.

I'll also be trying out the ferrites I have on the monitor cords etc. It is odd that the video card is causing the issue. I'll try disconnecting the cable as you suggested to see where that gets me.

I'll keep you posted on progress.

Regards,

Pete
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