[Elecraft] Elecraft RFI Problems
Hi Guys and many thanks for all the responses both on and offline. I've some excellent advice and plenty of things to try. To recap, problems are on 20m with HI FI and AM radio and on 80m with PC modem. I did a bit fiddling around with the feeder on Sat with some surprising results. Firstly out of curiosity I wound about 8 turns of the coax feeder into a coil (about 6 inches diameter) not at the feed point (didn't fancy getting the ladders out on a wet day) but at ground level (about 30 feet from feed point). The breakthrough on the HI FI on 20m got much worse (seriously worse) but it did at least indicate that the feeder was a big factor. I then remembered that because there was a bit of slack in the feeder where it meets the ground (at the base of the old apple tree) I had taken to coiling up a few feet of it (say only 2 or 3 turns) and hanging it on a branch. So I straightened out the coax so that there were no coil turns at all. This produced a dramatic improvement on 20m, with 100W (CW BTW) the 50HZ hum on the HI FI was almost inaudible. The 80m breakthrough on the PC modem has been reduced by disconnecting a long length of elevated internal telephone line (all on the same circuit) which isn't used any more and by winding the line on a ferrite at the PC, don't know which measure did the trick but I can now use at least 50W on 80m without any probs. Have also re-routed the feeder to come away from the dipoles at 90 degrees for as far as poss before turning back towards the house. The AM radio is still a problem but will try a ferrite on the mains lead. So I have a temporary working solution whilst I try some of the ideas raised on this reflector. I will try coiling the coax at the feed point when I get the time and checking for RF on the rig (touching rig when looking at SWR). Thanks again for the wealth of advice. Martin M0KWV K1 #1534 feeding TS520 Tube PA to multi dipole. Why not take a look at our Web site? http://www.simoncarves.com * The information in this email and any attachments may contain privileged and/or confidential information intended solely for the use of the individual or entity to whom it is addressed. If the reader of this email is not the intended addressee, or the employee or agent responsible to deliver it to the addressee, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify me by telephone or email and delete all copies immediately. * ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re:[Elecraft] Elecraft: RFI Problems
Two approaches to dealing with transmission lines that have been of great help to me at various locations in substantially reducing or usually eliminating RFI when using power at HF or VHF are: Coax - Bury as much of the run as possible, as deeply as possible, although even a few inches down is better than not burying the line at all. Major problem is Work. Needs to be put in a protective pipe with holes at bottom, preferably on a bed of gravel. Buriable line likewise to keep rabbits etc from eating line. Open Wire Line - 4 wire cross-connected line radiates / receives much less than 2 wire line with similar wire spacing. Also low Zo lines can be made eg 200 ohms. Problems - heavier than 2 wire, should not change direction too quickly in theory but can within reason, and more tedious to build than 2 wire line. A little more difficult to handle physically than 2 wire line, but this problem is eliminated after practice. Have never had to use a RF Ground. 73, Geoff. GM4ESD ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
[Elecraft] Elecraft: RFI Problems
Regarding the RFI problem when running 100W. I also had a bad RFI problem when running 100W. It would get into the computer, TV and all the audio equipment in the house. What I finally did to cure the problem was I ran 3/4 inch flexible copper water pipe from the shack out 20 ft to the yard, where I laid down a 50 ft length of 3ft wide galvanized fence. The 3/4 inch soft copper flexible pipe provides a large surface area for the RF. Then every 10 ft along the length of the fence I drove in a 3 ft copper ground pipe and soldered it directly to the fence. So I have 5 ground rods at different points along the fence as it lays on the ground. Next spring the grass will grow over it and hide what I have done. Then in the basement ham shack I used a copper ground buss behind the equipment and ran 3/4 copper braid to all equipment including the computer. This took me about a weeks worth or hard work. Now I run 200 Watts without any RFI at all on any band. If I run a full legal limit 1.5kw there are a couple of bands where I get into the audio of the HiFI set. And that can be solved with some RFI filtering on audio amp and speakers when I get around to it.Its a real treat to run the ham rig without having anyone in the family getting upset :-) -- frank W7is - This mail sent through IMP: http://horde.org/imp/ ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Elecraft: RFI Problems
In a message dated 29/01/05 16:36:57 GMT Standard Time, [EMAIL PROTECTED] writes: If you have a balanced antenna system, or even an unbalanced system with RF properly choked off from the outside of your coax, there will be no RF on the chassis that 'as to go somewhere'. In addition, it is very difficult to provide an RF ground at HF. - With my shack in an upstairs spare bedroom it is difficult to provide an RF ground in any case, the only ground being the power ground. The house is built on rock so I doubt if a ground rod would go in very deep even if I tried. Opted like Vic for a balanced antenna with balanced feeder. Using 100W have not seen any problems unless I try to operate on a band that the antenna is not resonant on. Using 75 ohm balanced twin as the feeder as the use of 300 ohm ribbon or higher would be impractical from my shack. The 75 ohm twin seems quite docile in use and can be installed in close proximity to metallic objects which is not recommended for 300 ohm or higher impedance twin feeder. To date the only interference problem have been with telephones whose drop wires are parallel to my antenna. The phone company fitted RF filters to the affected telephones at the point of entry into the house and one modern telephone had to be suppressed internally. Older telephones seem less affected. A problem that may be coming up is the use of ADSL broadband would probably prevent normal telephone RF suppressers being used at the point of entry to the house as this would also stop ADSL from working. A separate RF filter at each telephone would be the only answer in this case. As a parallel subject there was an interesting article in the February 2005 Radcom, EMC column advocating the use of ADSL telephone filters as being very suitable for use as RF filters on telephones for the lower bands and the performance figures for one type of ADSL filter were quoted. See them available at computer fairs at about £3 each ($5.70 US). Bob, G3VVT ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Elecraft: RFI Problems
Vic: Certainly it is the case that the remedy that solves one emi problem might make another one worse. That is what makes emi so difficult. 73, Steve AA4AK Brunswick ME At 04:33 PM 1/29/2005 -0800, you wrote: Stephen W. Kercel wrote: If radiation from the exterior surface of the antenna feedline were the only mechanism that causes emi, then you would be right, choking it off would solve the emi problem. The energy in the transmission line would be radiated by the antenna or turned into heat by either the line losses or by the losses in the materials used to make up the choke. However, emi can be caused by many other mechanisms, and as one other poster to the reflector has reported, improving his RF ground substantially mitigated his problem. I understand that there are other paths, such as pickup on the power/phone/speaker lines directly from the antenna, etc. This is why I suggested that the fellow use ferrites on the power leads to his stereo and modem. My point about choking off RF on the feedline was just that an RF-free feedline is easier to achieve (unless you are using a random wire antenna) than an RF ground. I have to say that the guy who reported an improvement may have gotten an improvement -- but not from the fact that his rig had a better ground, rather from the change in the RF environment that his ground system caused. In other words, it might make it better, but it also could make it worse. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Elecraft: RFI Problems
In a message dated 30/01/05 01:32:53 GMT Standard Time, [EMAIL PROTECTED] writes: All of the 75 ohm stuff that I've seen wasn't rated for high voltages anyway, so it's likely to melt at the voltage loop when hit with high power. AT the very least, it'll be rather lossy. --- There is more robust USA sourced 1kW rated 75 ohm twin available in the market though sadly not as easy to obtain now as in the past. Believe red/black power cable makes an effective 75 ohm twin feeder and this is available for quite high currents though not with high voltages. Am using commercial 75 ohm twin feeder cable rated at 300W at present which is very adequate for the 100W maximum I use. In any case we have in the UK a maximum license power of 400W pep which restricts our exposure to high power effects. Guess would be rather different in the USA with your maximum of 2kW pep. QRO can have it's downside! Not sure that the statement that it would be rather lossy is correct as I have been led to believe that twin feeder is less lossy than coax and particularly the 50 ohm version. Even the 75 ohm hard-line coax as used by cable TV companies was always better than the 50 ohm coax in the loss figures for a given diameter cable. I do use a resonant 1/2 wave trap dipole on 40/80m only at present with the feeder cut to the length recommended by the antenna designer of 70 ft (or multiples of this). Working towards adding a two extra pairs of traps for 80/20 to give added bands of 160m and 20m. With always using resonant antennas the problems that could arise on the twin feeder are minimised and hopefully any interference problems as a result. So far telephones seem the only problem area. The wider spaced twin feeder would be impossible in my case as the operating position is on the opposite side of the room from the window and built into a fitted wardrobe. At a previous house the shack was just that, a wood hut under the centre of the dipole and wide spaced twin feeder came direct to a balanced ATU. As always it is a matter of cutting the cloth to suit your circumstances. What will be suitable for one situation may be hostile in another. Bob, G3VVT ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Elecraft: RFI Problems
Bob, G3VVT wrote: Not sure that the statement that it would be rather lossy is correct as I have been led to believe that twin feeder is less lossy than coax and particularly the 50 ohm version. Even the 75 ohm hard-line coax as used by cable TV companies was always better than the 50 ohm coax in the loss figures for a given diameter cable. Quite true about the relative losses, Bob. We've kicked this subject around here in the past. It's been pointed out that, while it is true that there are dielectric losses in feedlines, feedlines operating at high SWR's are more prone to resistive losses in the conductors than dielectric losses. Several people have pointed to the fact that the losses are directly proportional to SWR as shown in all the transmission line loss charts, suggesting that what the loss charts are showing are the increased ohmic losses occurring at the current maxima points (current loops) along the transmission line as the SWR increases. Voltages and currents do depend upon power, but low power does not guarantee low currents or voltages on a feedline operating with a high SWR. I melted a nylon banana jack running 15 watts! The jack was in a grounded panel connecting my ATU to a voltage-fed antenna. On the other hand, very high currents can occur at the current loop in a feedline operating at high SWR even at very low power levels. That's why flat feedlines having little or no standing waves are less lossy. The current and voltage are directly proportional to the power applied and do not swing through large extremes along the length of the feedline. Feedlines with larger conductors fare better in general. As you pointed out, hard line and other heavy duty transmission lines have excellent insulation. They also tend to have larger conductors with more surface area to reduce the resistance to the RF flowing along the surface. I count myself lucky to be able to use open wire line with #12 conductors. We all have to deal with compromises. But that's half the challenge of the hobby - finding the compromise that produces the best results! In my case it's no high supports nor length enough! (Great feedline, marginal antenna!) A lot of modern telephones are incredibly RF-sensitive, having amplifiers and other circuits that have absolutely no RF protection. Your residual problem may be simply direct pickup by the phone wires of the RF signal acting as an antenna. Ron AC7AC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Elecraft: RFI Problems
Ron, Bob and all, It is quite true that losses increase as the SWR increases - the ohmic losses are the contributing factor with increased current, but the dielectric losses will be important as the voltage increases - so both are a contributing factor. How much contribution is due to the ohmic loss or the dielectric loss is dependent on the feedline construction and frequency. With smaller feedlines and lower frequencies, the ohmic losses are likely to predominate, but as the physical size of the feedline increases, the dielectric losses may become the greater factor. The crossover point depends on frequency - and at HF, the ohmic loss usually predominates. Perhaps I am being overly technical here - and it really may not be important - if you have losses, you simply generate heat instead of RF - these subtle points are only appropriate if you want to persure the proper path to reduce the loss. If you have already made the compromise choices that are right for your station, there is not much that can be done in the way of improvement - just understand your choices (decisions). If you want to adopt a 'rule of thumb', a feedline with a higher characteristic impedance will have lower loss when comparing feedlines of similar size. Even though the center conductor of 75 ohm (RG-11) has a smaller diameter that 50 ohm (RG-8) coax - compare Belden 8237 with #13 center conductor with Belden 8213 with a smaller (#14) center conductor and you will see that the 75 ohm Belden 8213 has lower loss at higher frequencies even though the ohmic loss through the #13 center conductor will be smaller - the higher impedance cable wins in the loss game. Several other comparisons will reveal similar results. 73, Don W3FPR - Original Message - From: Ron D'Eau Claire [EMAIL PROTECTED] Quite true about the relative losses, Bob. We've kicked this subject around here in the past. It's been pointed out that, while it is true that there are dielectric losses in feedlines, feedlines operating at high SWR's are more prone to resistive losses in the conductors than dielectric losses. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
[Elecraft] Elecraft: RFI Problems
Sorry this is off topic but there is so much experience here. I've been licensed for only 2 years, my only rig is K1 so I've been QRP CW only (and enjoyed it immensely). I've recently started using a PA to get up to 100W on 3.5 to 21MHz, but RFI problems have started to appear. Here are the symptoms: 50Hz hum on key down on hi fi Similar problem on mains MW radio. Freezing of PC modem on key down. These are all in different rooms of the house and all at least 15 feet away from the rig. The rig is on the ground floor right next to the outside wall where the coax feeder runs out at ground level. Feeder is about 70 feet long and all at ground level until it rises to a multi dipole at 30 feet up, cut for 80/40/20m. Feed point is at least 50 feet from house. The feeder shield is connected directly to the PA ground point and therefore to the mains ground wire. I have no Balun and no RF ground so I guess I've broken all the rules. I suspect RF is on the mains 240V house wiring and can see it on my scope (about 5mV P-P superimposed on the mains). I have a number of things to try but not sure in what order of priority, maybe someone could help, I want to tackle the source of the RFI first, rather than the affected domestic equipment. Here's the list: Make a coax choke balun in the feeder to reduce out of balance currents (quick and cheap) Fit a commercial balun (heavy and pricey) Construct an RF ground in the garden and connect to feeder sheath at entry into the house. (time consuming) Fit a ferrite ring choke to the PA mains lead Build an inductively coupled ATU to avoid connection of feeder sheath to the mains ground. Fit ferrite ring chokes to the affected equipment Fit a proprietary RFI filter to the telephone line (to cure the modem problem) Or maybe I should just go back to QRP hi. Any advice would be greatly appreciated as I don't want to run the risk of causing RFI to the neighbours. Why not take a look at our Web site? http://www.simoncarves.com * The information in this email and any attachments may contain privileged and/or confidential information intended solely for the use of the individual or entity to whom it is addressed. If the reader of this email is not the intended addressee, or the employee or agent responsible to deliver it to the addressee, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify me by telephone or email and delete all copies immediately. * ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Elecraft: RFI Problems
On Fri, 28 Jan 2005 09:59:35 +, [EMAIL PROTECTED] wrote: Sorry this is off topic but there is so much experience here. I've been licensed for only 2 years, my only rig is K1 so I've been QRP CW only (and enjoyed it immensely). I've recently started using a PA to get up to 100W on 3.5 to 21MHz, but RFI problems have started to appear. Here are the symptoms: 50Hz hum on key down on hi fi Similar problem on mains MW radio. Freezing of PC modem on key down. These are all in different rooms of the house and all at least 15 feet away from the rig. The rig is on the ground floor right next to the outside wall where the coax feeder runs out at ground level. Feeder is about 70 feet long and all at ground level until it rises to a multi dipole at 30 feet up, cut for 80/40/20m. Feed point is at least 50 feet from house. The feeder shield is connected directly to the PA ground point and therefore to the mains ground wire. I have no Balun and no RF ground so I guess I've broken all the rules. I suspect RF is on the mains 240V house wiring and can see it on my scope (about 5mV P-P superimposed on the mains). I have a number of things to try but not sure in what order of priority, maybe someone could help, I want to tackle the source of the RFI first, rather than the affected domestic equipment. Here's the list: Make a coax choke balun in the feeder to reduce out of balance currents (quick and cheap) Fit a commercial balun (heavy and pricey) Construct an RF ground in the garden and connect to feeder sheath at entry into the house. (time consuming) Fit a ferrite ring choke to the PA mains lead Build an inductively coupled ATU to avoid connection of feeder sheath to the mains ground. Fit ferrite ring chokes to the affected equipment Fit a proprietary RFI filter to the telephone line (to cure the modem problem) Or maybe I should just go back to QRP hi. Any advice would be greatly appreciated as I don't want to run the risk of causing RFI to the neighbours. Why not take a look at our Web site? http://www.simoncarves.com * The information in this email and any attachments may contain privileged and/or confidential information intended solely for the use of the individual or entity to whom it is addressed. If the reader of this email is not the intended addressee, or the employee or agent responsible to deliver it to the addressee, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify me by telephone or email and delete all copies immediately. * ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com Things that I would try first:- a) Fit a balun (at the center of the dipole) or b) Make the antenna completely balanced by using open wire feeder, and a balanced ATU. You will notice a reduction in received noise as well as RFI reduction. Good luck 73 Stewart G3RXQ ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Elecraft: RFI Problems
The short answer to your problem is - keep the RF inside the coax until it gets to the antenna. With an unbalanced feedline and no balun, you likely have considerable RF on the outside of the coax. Your list of possible cures is a good one, but add one more at the top - run the feedline away from the antenna at right angles for as far as possible - that places the feedline in a position where the fields should cancel and prevents the feedline from picking up radiation from one side of the antenna. Then start at the top of your list and try each item one at a time until you have found what is effective. If your antenna is located close to the equipment you are having difficulty with, as might be the case with a low antenna or an attic antenna, then QRP may be you only solution. Those devices are supposed to be unaffected by an RF field, but we all know what is supposed to be and what really is are two different things. Your neighbors should be further away from the antenna than your own equipment is located, so your local problem should be greater than theirs. 73, Don W3FPR - Original Message - Sorry this is off topic but there is so much experience here. I've been licensed for only 2 years, my only rig is K1 so I've been QRP CW only (and enjoyed it immensely). I've recently started using a PA to get up to 100W on 3.5 to 21MHz, but RFI problems have started to appear. Here are the symptoms: 50Hz hum on key down on hi fi Similar problem on mains MW radio. Freezing of PC modem on key down. These are all in different rooms of the house and all at least 15 feet away from the rig. The rig is on the ground floor right next to the outside wall where the coax feeder runs out at ground level. Feeder is about 70 feet long and all at ground level until it rises to a multi dipole at 30 feet up, cut for 80/40/20m. Feed point is at least 50 feet from house. The feeder shield is connected directly to the PA ground point and therefore to the mains ground wire. I have no Balun and no RF ground so I guess I've broken all the rules. I suspect RF is on the mains 240V house wiring and can see it on my scope (about 5mV P-P superimposed on the mains). I have a number of things to try but not sure in what order of priority, maybe someone could help, I want to tackle the source of the RFI first, rather than the affected domestic equipment. Here's the list: Make a coax choke balun in the feeder to reduce out of balance currents (quick and cheap) Fit a commercial balun (heavy and pricey) Construct an RF ground in the garden and connect to feeder sheath at entry into the house. (time consuming) Fit a ferrite ring choke to the PA mains lead Build an inductively coupled ATU to avoid connection of feeder sheath to the mains ground. Fit ferrite ring chokes to the affected equipment Fit a proprietary RFI filter to the telephone line (to cure the modem problem) Or maybe I should just go back to QRP hi. Any advice would be greatly appreciated as I don't want to run the risk of causing RFI to the neighbours. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Elecraft: RFI Problems
[EMAIL PROTECTED] wrote: 50Hz hum on key down on hi fi Similar problem on mains MW radio. Freezing of PC modem on key down. My suggestions, in order: 1) Try wrapping the speaker leads of your hi fi around ferrite rods or toroids. If this doesn't clear it up, try wrapping the mains cord from the hi fi around a ferrite as well. Try to get as many turns as possble. The clamp-on beads are not effective at HF. 2) Treat the radio in a similar fashion. 3) Use an inline telephone filter (such as the k-com or similar) on your modem phone line. Also wrap the power wire to the modem around a ferrite. 4) Add a balun of some kind to your dipole. There's a lot more that you can do, but this basic stuff should help. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Elecraft: RFI Problems
Martin: I have a few thoughts on your EMI problem. First, keep in mind that an antenna produces three different kinds of fields, the induction field, the near field and the far field. The induction field vanishes within inches of the antenna. The near field, the cause of many emi problems, has non-trivial strength out to about 1/6 of a wavelength. The far field is the one that gets out, and behaves like a nice predictable travelling wave. The near field turns out to be extremely sensitive to boundary conditions, and simple acts like opening or closing a door can change the boundary enough to change the pattern of the near field. This is one reason for the seemingly magical properties of emi. My reason for making this disclaimer is to make you appreciate the fact that any of the very sound advice you get on the reflector may or may not help you to overcome your particular emi problem. I would encourage you not to give it up; your problem (or set of seemingly unrelated problems) can be solved. Second, you have not mentioned what bands give you the emi problem. You should check for all the symptoms on all the bands. There is a good possibility that part of your house wiring is perversely resonant in one of the ham bands, and is acting like an antenna that captures and reradiates your near field. Of course, if the resonance occurs on 80 meters, you might also be resonant on all the harmonically related ham bands. Anyway, it is worth checking which bands cause which bad effects. Third, having no RF ground is a big nono. The problem is that the RF that is on the chassis of your rig has to go somewhere. If you do not provide it a low impedance path to ground (where RF is converted to heat) it will find its own path, and the one that it finds will not make you happy. The power system ground has very high inductive reactance (A straight wire has an inductance of 10 nanohenries per inch. A 10 foot length of wire has an inductive reactance of 26 ohms at 3.5 MHz in the absence of mitigating capacitive effects. ) In other words, from your rig to the power system ground rod the overall impedance is probably on the order of hundreds of ohms, and virtually none of your RF energy is finding its way to the ground rod. If you're lucky (in your case you're not) the energy will be turned into heat in the losses of the wiring. Otherwise, it gets coupled into your other equipment. Since you are physically at ground level, I would strongly recommend that you install an 8 foot copperweld ground rod as close as possible to the rig, and feed through the shortest possible number 6 solid wire. (Solid has lower inductance than stranded or braid.) This is not an expensive solution, but it may solve your problem. Going from the shield of your cable direct to the ground rod may solve your problem and it may not. The emi problem may not be caused by radiation emanating from the outside of your shield. To avoid the creation of ground loops, and new emi problems, it is considered best practice to use a single point RF ground. Connect the rf grounds of your auxiliary equipment to your antenna tuner ground if you have one or to your transmitter ground otherwise. Make sure the ground connections are done in a star configuration (no loops in the ground wire), with short direct connections of solid wire (braid has higher inductance; avoid it) with your rig or tuner ground being the center of the star. To that single point at the center of the star connect the lead to the RF ground. This is a compromise configuration that tries to balance many conflicting tradeoffs, but it is the one that typically results in the fewest emi problems. The 8 foot copperweld ground rod is not really that good an electrode at HF, but it is better than nothing and vastly better than what you have now. In fact, there is no good ground electrode at HF. All of them have non-trivial inductive reactance. The least electrically bad ground electrode is a long solid copper wire (I prefer number 6; it has good physical strength and is not too hard to handle) at least a half wavelength at your lowest frequency and buried just deep enough that your lawn mower does not hit it, but preferably less than an inch deep. Every 8 feet or so along the wire you should connect the wire to a 12 inch ground rod. The wire does not need to be in a straight line. It can meander all over the yard, turning corners as necessary, but no corner should be tighter than 90 degrees. Obviously this is not practical to install during the winter. Nevertheless, when you can install such a ground, it is worth the trouble doing. BTW, a cheap trick that often works in place of an RF ground is to use an MFJ (or equivalent) artificial ground to a length of wire running along the floor as an RF counterpoise. The idea is that the reactive elements in the box tune out the reactance in the counterpoise and create the effect of a low
