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Author Topic: Terrorizing family with RFI.  (Read 6085 times)

Posts: 7894

« Reply #15 on: September 19, 2009, 07:40:12 AM »

It is not that the feedline shield is radiating but that the feedline shield can provide a conductive path for RF current. The path for the current can be:

Radials to house wire via displacement current then house AC wiring to antenna feedpoint via feedline shield. The goal of the ferrites is to reduce the current through the house wiring. The ferrites must present an impedance substantially higher than the radial-to-wiring path. A back of the envelope calculation says the radial-to-wiring impedance at 7 MHz is 100 ohms. This is low enough for ferrites to be effective.

I had similar RFI issues and decided to go for broke and spent $200 on snap-on ferrites. That and an RFI filtered GFI outlet took care of things.

Posts: 0


« Reply #16 on: September 21, 2009, 12:03:10 PM »

I fixed my RFI problems by putting an RF 1:1 balun between my coax and antenna. Cheaper than buying snap on ferrite chokes.
Only problem I now have is the subwoofer but then again it has a built in amplifier and even with no audio cables connected to it, it still makes noise when I transmit. All of my ham friends have the same problem and we simply unplug them when not in use. I tried many chokes on the power cable without improvement. Since I only use my subwoofer while watching a DVD two hours a week at most, it is no problem to unplug it when not in use.

Posts: 0

« Reply #17 on: September 27, 2009, 08:53:15 AM »

I worked thru a similar set of problems with a home brew vertical on the roof of my house.  

First as a precaution I applied ferrites to the cables connecting the DVD to the TV, the cables for the PC speakers, the telephones, alarm system etc.  

Where possible I used both mix 43 and 75 ferrite cores on the cables.    Mix 31 might be a better choice but I haven't tried it.

I also kept the ground system I installed for lightning protection isolated from the HF radials and applied several mix 43 and 75 ferrites to the ground wire just prior to the point where it is bonded to the main electrical ground (at one of the electrical service ground rods.)   I suspect that the ground cables on the roof pick up a substantial amount of RF and don't want it getting into getting into the electrical ground system.   I still have some doubts about using ferrites on the ground wire, but lightning is very rare where I live, there are grounds that should absorb much of the energy of a lightning strike before it gets to the ferrites, still I suspect the ferrites would simply get vaporized in the event of a lightning strike.    Bonding the two ground systems together and using ferrites to supress any RFI seemed a better choice to me than not bonding them together, but I don't profess to be an expert in this area and this may or may not be the correct approach in all cases.

I still had a few nagging RFI issues especially at higher power levels.   (Smoke detectors and the carbon monoxide detector were troublesome at times.)

Over time I,

Added lots more radials (which both cut down on RFI and seemed to improve the performance of the antenna.)

Applied several large mix 43 ferrite chokes to the feed line of the antenna where it entered the house.

Applied several large mix 43 ferrite chokes to each of the pipes and cables that were routed thru the attic.    

Applied several mix 43 ferrite chokes to all the other antenna feed lines (VHF, UHF etc..) where they enter the house.

I suspect that other conductors (ie a copper natural gas line, BX electrical cable, other antenna feed lines etc..) on the roof and in the attic were picking up RF from the antenna and re radiating it throughout the house..  Putting several ferrite chokes onto each of these conductors where they leave the attic seems to have tamed the remaining RFI issues.

The only lingering problem is the carbon monoxide sensor sometimes goes off when I run high power on 80 Meters.  From what I can find on the internet certain carbon monoxide sensors are particularly prone to be being affected by RF.  I just turn it off when I plan on high power 80 meter operation.

Looking back I've probably spent more money on ferrite chokes and cores than on the rest of my antenna system but it's worth it to be able run 100 watts on 20 or 40 meter RTTY and not cause ANY RFI on the TV, phones etc..

I also would suggest not skimping on the number of ferrite chokes used.   Several may be needed on each conductor.

I believe some one else has already posted a link that explains a lot of the theory behind the use of ferrites.

Good luck and 73's
Mark VE7AFZ.

Posts: 213

« Reply #18 on: October 02, 2009, 05:59:59 PM »

I have had the same problem with a cut-to-frequency 40 meter dipole that ran directly over my house. I think it's just a matter of a strong enough RF field too close to susceptable appliances. I have had my wife yell at me about the computer speakers blaring at her every time I used that dipole. A similar antenna at the end of my lot did not cause any problems until I used my linear amp at 500 watts. There again, I think it's was just a matter of such a strong RF field so near susceptable appliances in the house. I really don't think it's that complicated.That much RF in the vicinity can do some strange things. I don't blame it on coax, SWR, baluns, bad grounds, or anything else except the presence of a strong RF field. Sounds to me like you are experiencing the same problem. The cure? Get rid of the things being affected if you can't do it with with filters or other means. Or do like I did...operate when my wife was a work and my daughter at school, or get the antenna away from the house. I don't think it's as complicated as some people might think.

Posts: 47

« Reply #19 on: October 03, 2009, 03:29:53 AM »

Drop everything and call GHOSTBUSTERS!!!!
RFI...?  Forget it!!!  Think: Demons at play!!!
Just kidding of course, good luck!!

Posts: 7

« Reply #20 on: October 15, 2009, 12:29:47 AM »

...just reporting back in case anyone can benefit from this info.

I have taken care of most of my RFI issues.  Here are the steps I've taken thus far:

I checked and re-checked the antenna and found that it was properly installed (as far as I can tell) and properly tuned according to my MFJ 259B.

I bought a bunch of big, type 31 toroids ( &SEARCHAGAIN=Y#select:onepart) from Mouser because I figured, heck, you can never have too many of these things, right?

I assumed at least some of my problem were just due to the proximity of my antenna (which is on the roof and just a few feet from some of the house wiring).  Otoh, I thought some might be due to the feedline radiating, so I decided to add a coax choke.  Since I was going up on the roof anyway, I also decided to add a remote tuner at the feedpoint of the antenna.  So I added the tuner at the antenna feedpoint, I added a choke (5 turns of my RG213 feedline through 5 of my trusty cores) at the point where the feedline enters the tuner.  I also added another choke about 30 feet down the feedline.  This improved things noticably, but didn't completely eliminate any of the problems.

So I decided to see if I could attack each of the specific problems, one at a time.

- The subwoofer has a long input cable so I wrapped about 10 turns of that around one of the cores.  That took care of MOST of the subwoofer noise.  I then wrapped its power cord around another core and that took care of the rest of the noise.  

- The Mac was the only problem computer in the house (we have several other computers, including two in my shack, that showed no RFI problems) so I wrapped the Mac's power cord around one of the cores, and that completely eliminated the problems.  

- I tried modifying the CO detector, but I couldn't get it to stop triggering its alarm whenever I transmitted on 40m.  So I bought a new one by a different manufacturer.  The old one that reacted badly to RFI was a Kidde brand.  The new one is a First Alert brand.  Before I even bothered trying the new CO detector, I made one modification to it.  These things all seem to include a transformer as part of the unit but with about a six foot cable running from the transformer to the circuit board.  The extra cable is just wrapped/waddded up in the back or inside the plastic case.  I shortened this cable to a few inches and wrapped it a few times around a little ferrite core.  This core is just a random one from radio shack, so I'm not certain of its type/mix.  Anyway, I haven't had any problems with this modified First Alert CO detector.

- My daughter has a little karaoke machine that started making noise when I transmitted full power on 20m.  This noise was coming from the long mic cable attached to the device.  So, of course, I wrapped a few turns of it around one of my trusty toroids and, voila, problem solved.

In the end, I haven't found a silver bullet, but I have taken care of all of my major problems.  I'm getting good performance from my antenna on all the bands I've tried (80-17), so I'm relatively happy with the situation.  Otoh, I'm eagerly looking for another antenna option -- one that will perform generally better (and especially with less receive noise than my HF6V), that will fit on my small lot, that will produce fewer RFI problems, and that will not offend my wife or our neighbors.  I think I'll try to put up a big inverted L soon and see how that works for me.  Wish me luck.


Posts: 185

« Reply #21 on: October 15, 2009, 06:52:22 AM »

Chad, thanks for the report.  I painted my hf6v black and use black rope from STI.  I have painted my rohn
25 tower black, my insulators are black, guy ropes are black.  against the trees the antenna system blends in very well.  it is great.  my next project is to take the mosley ta33jr down and paint it black.  


Posts: 1316

« Reply #22 on: October 15, 2009, 01:20:28 PM »

Chadd, I just read this thread for the first time today.

I can't see it from here, but I would suspect the radials need improvement.

I have the same antenna as you, the HF6V, and I made the 'recipe' multiband tuned radials from the balanced line per the instruction. By chance I spoke with another ham this week who has the same antenna and tried the same multiband radials.

The multiband radials work 'OK' but not particularly well. Given the proximity to your living space, you may consider cutting tuned radials for all the bands you plan to work.

Whether laying them on the roof is detuning them anyway I couldn't say.

The suggestions on checking the coax are right on. The outside of the coax is not s'posed to carry RF current. RF current should all be contained on the inner skin of the coax braid.

Nonetheless, the layout on the roof may cause the coax exterior to behave a bit like a radial, so the choke methods you used are appropriate.

Now as far as installing chokes on everything in the house, there is nothing wrong with that. But my real concern is whether this is regarded as the solution. If choking all the affected house wiring is the "cure," the problem still exists.

Finally, there is always the possibility something is not right with the radio equipment or things attached to it, such as SWR meters, matching boxes (I refuse to call them "tuners") and so on. A missing cover or other situations can be part of the problem.

A year or so ago someone gave me a bar room neon light that needed a new power supply. I jokingly suggested I would forgo the power supply and just use the neon light as a "rf-in-the-shack" detector. I tossed the neon light, but my point is there are some simple and inexpensive ways to detect RF in the house. That subwoofer is one method.

My feeling is the best thing to do is eliminate the RF inside the house BEFORE adding all the chokes to household appliances. THEN, add the chokes when you are confident the RFI has been minimized sufficiently.

Posts: 7

« Reply #23 on: October 15, 2009, 09:08:19 PM »

I tend to agree with you.  I was planning to seriously upgrade my radials -- going with 4 tuned radials for each band I work -- but I really don't have the space for it on the roof.  For instance, 40 meter radials will only fit in one direction.  The other 3 directions are too short (since this is on the topmost and relatively small section of the roof).  

Also, right now (and until I set up another reasonable antenna) this is the only antenna I'm using, and I've been active on 40, 30, 20 and 17 with a few forays on 80.  Given band conditions, I can't be too picky.  So without the resonant radials, I think I'd need at least 16+ tuned radials on the roof and I'm pretty sure that would severely test my wife's (and my neighbors') patience.  

I'm now thinking that I'll set up a new, decent antenna for 80 & 40 and then use the HF6V for the higher bands.  I already have tuned radials for 30m up there, so I could easily see taking down the multi-band radials and instead putting up 4 tuned radials for 20 and 4 for 17.

My next big problem:  our main TV is one of the early Pioneer Plasma sets.  The RFI that thing puts out completely shuts me down on 40m and 30m.  So I need to buy a new flatscreen TV.  The fun never ends here...

Posts: 9

« Reply #24 on: December 28, 2009, 09:24:52 AM »

I read with interest your elimination of RFI problems.  I have a Kidde Model KN-COPP-3 carbon monoxide detector that also triggered on 40 meters.  I minimized the problem by winding the 110V supply line around two small ferite cores and adding two RF chokes in series with the 110v supply.  The ferites and RF chokes were added at the circuit board end of the 110V supply.  Even with this approach, I would occasionaly set off the detector.   (I run maximum legal power to a dipole that is overhead my shack.)

I found by moving the detector to another 110v outlet just 10 feet away from it's original position, the problem was eliminated.

Just a few days ago, the detector went belly up, and you can be sure I will not replace it with the same make and model.  I see theat Kidde now makes one that runs strictly on battery power (KN-COPP-B, or 900-0146.)  I wonder if anyone has had success with either of those models or can suggest any other make and model that has proven to be immune to RFI.

Paul, W3GQ
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