Re: Now General RF Issue WAS 160m loop experiment a big failure
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Dear Group,
I apparently have a bigger problem with RF in the shack and it has nothing to do with the loop. I have been running a successful shack on the second floor of my house and as of Friday last week when I installed the loop I have had nothing but RF problems. I thought on Saturday when I removed the ladder line from the shack and coiled it up in the tree far away from the shack that I would be ok and everything seemed to be ok. Anyway long story short, now with only the dipole (alpha delta trapped dipole at 30 ft) connected in the shack I have terrible RF problems and it can occur even barefoot at 100w so I am not pointing to the amp as of yet. I have dropped the antenna and checked that the coax is tight, checked to see if the coax is tight at the lighting arrestor, ran with and without the tuner connected. I have rechecked the grounding that I have in the shack, which after more research is not adequate, and I will be addressing that this weekend. However, I don't think that this will fix it. Right now I am thinking that I have a bad coax line outside of the house. The reason for this is that I had a new propane tank installed and they needed to back the truck up and had to drive over the buried coax. I did put boards down to spread out the load and protect the lawn and also the coax. However the problem has started since this incident. I pulled the coax out of the ground and it has bend marks at the edges where the boards were which to means that it was deformed and maybe it is now crushed. So other than doing a whole new ground setup with more ground rods outside and adding more chokes to the coax, I want to check out the coax that I have this weekend to determine if I have a "crushed" problem. Is there a way I can check it out with my 259b or is it just replace it and see what happens. Anyway, I am off the air until I get this sorted out. Basically now I have to start over, and frankly speaking I am a bit overwhelmed right now so I just need a friendly group to lean on as I really am frustrated right now as my favorite pastime is now no longer possible due to some failure of some kind or another. Thanks in advance for your understanding in a non-elecraft post, but this is the most friendly and knowledgeable group on the net that I belong to so please help me get my K3 back on the air. Cheers Don ~73 Don KD8NNU ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Now General RF Issue WAS 160m loop experiment a big failure
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Don,
You MFJ259B can help you locate the fault. Look at the instructions for the 259B and in particular the Distance to Fault section. Yes, crushed coax can cause severe discontinuities, including actual shorts in the coax - not unlikely for coax being run over by heavy equipment. A shack on the second floor is always a problem for RF. A ground wire to a ground rod (hopefully also connected to the utility entrance ground rod) will provide a good path for AC Mains faults, and may also provide *some* lightning protection, it will not serve well for an RF ground point. The distance between the ground rod and the shack connection will have some reactance due to its length - if it is near a quarter wavelength, it will present a high impedance in the shack - to be effective, an RF Ground point should present a low impedance at the shack location. This may ba a case where the only good solution is he use of "counterpoise" wires. A quarter wavelength of wire on each frequency of interest will present a low RF impedance at the shack end and a high impedance at the far end of the wire. You may have to resort to this 1/4 wave wire as your best solution. Some experimentation may be required. 73, Don W3FPR On 10/20/2011 9:21 PM, [hidden email] wrote: > Dear Group, > > I apparently have a bigger problem with RF in the shack and it has > nothing to do with the loop. > > I have been running a successful shack on the second floor of my house > and as of Friday last week when I installed the loop I have had nothing > but RF problems. I thought on Saturday when I removed the ladder line > from the shack and coiled it up in the tree far away from the shack that > I would be ok and everything seemed to be ok. > > Anyway long story short, now with only the dipole (alpha delta trapped > dipole at 30 ft) connected in the shack I have terrible RF problems and > it can occur even barefoot at 100w so I am not pointing to the amp as of > yet. > > I have dropped the antenna and checked that the coax is tight, checked > to see if the coax is tight at the lighting arrestor, ran with and > without the tuner connected. I have rechecked the grounding that I > have in the shack, which after more research is not adequate, and I will > be addressing that this weekend. However, I don't think that this will > fix it. > > Right now I am thinking that I have a bad coax line outside of the > house. The reason for this is that I had a new propane tank installed > and they needed to back the truck up and had to drive over the buried > coax. I did put boards down to spread out the load and protect the lawn > and also the coax. However the problem has started since this incident. > > I pulled the coax out of the ground and it has bend marks at the edges > where the boards were which to means that it was deformed and maybe it > is now crushed. > > So other than doing a whole new ground setup with more ground rods > outside and adding more chokes to the coax, I want to check out the coax > that I have this weekend to determine if I have a "crushed" problem. Is > there a way I can check it out with my 259b or is it just replace it and > see what happens. > > Anyway, I am off the air until I get this sorted out. > > Basically now I have to start over, and frankly speaking I am a bit > overwhelmed right now so I just need a friendly group to lean on as I > really am frustrated right now as my favorite pastime is now no longer > possible due to some failure of some kind or another. > > Thanks in advance for your understanding in a non-elecraft post, but > this is the most friendly and knowledgeable group on the net that I > belong to so please help me get my K3 back on the air. > > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Now General RF Issue WAS 160m loop experiment a big failure
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In reply to this post by KD8NNU
On 10/20/2011 6:21 PM, [hidden email] wrote:
> I apparently have a bigger problem with RF in the shack and it has > nothing to do with the loop. Hi Don, Your email, and some of the solutions offered, reflect some common misconceptions about RFI, including an earth connection as a solution (it is NOT), and SWR as a cause (it is NOT). The usefulness of noting changes from the original SWR values is that it tells you SOMETHING HAS CHANGED in the antenna, so that you know to go looking for something that is broken. I strongly suggest that you download and study my tutorial on RFI for Hams. Nearly all problems blamed on "RF in the shack" are really caused by Pin One Problems in equipment where the RF is detected, and by antenna systems that put RF on the outside of the coax. Study http://audiosystemsgroup.com/RFI-Ham.pdf One question to ask is, "What ELSE, besides that coax, might have changed between before when everything worked, and now, when I have RFI." Think about cable connections between equipment in the shack that might be acting as antennas to bring that RF that your antennas are radiating into the equipment. And think about this -- your antennas SHOULD be putting a lot of RF in your shack -- they must do this if they are working as antennas. Any cables connected to your equipment will act as receiving antennas. When equipment has a Pin One Problem, the RF current those antennas (interconnect cables) receive will flow into your equipment. Sometimes you can modify equipment to correct the Pin One Problem, but usually the better fix is simply make the cables a lousy RX antenna by adding a common mode choke to them. That's what you're doing when you wind some turns of the cable through a ferrite cores. Study the tutorial to understand this. And when I say "study" I mean STUDY, don't just read it through once. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Don Wilhelm-4
On 10/20/2011 8:24 PM, Ron D'Eau Claire wrote:
> I wholeheartedly endorse Don's comments. I do too. > > A good practice with any antenna installation is to check the SWR on each > band for which it is used, and make a note of that. While in Comm Officers' School at Keesler AFB many years ago, I was active in the radio club [K5TYP]. We had a tribander up about 40 feet or so that never worked. We borrowed some test equipment and measured the impedance on 20, 15, and 10, and it was almost exactly 50 ohms [and the same on all bands which should have been a clue]. After several weekends of work including several trips up the tower, one of the guys said, "Let's do this one more time," and cranked the frequency of the impedance bridge down to 20m again. Nothing changed. The bridge saw 50 ohms at 14 MHz, 15 MHz, 18 MHz [which wasn't a ham band then], ... everywhere else, including 80m. We finally figured out we had the longest 50 ohm dummy load in Harrison County. I'm not real clear on how faulty coax could cause his RFI symptoms, unless maybe none of the power is actually getting to the antenna and is "backing up" [a technical plumbing term] into the shack. That it started with the propane tank episode is certainly suspicious. OT's may remember the old adage, "Note carefully from which corner of the chassis the smoke comes, that's where you want to begin troubleshooting." 73, Fred K6DGW - Northern California Contest Club - CU in the 2012 Cal QSO Party 6-7 Oct 2012 - www.cqp.org ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by KD8NNU
As Jim Brown says: if all these problems came on suddenly, focus on what parts of the installation have CHANGED. You may well have identified one: > >Right now I am thinking that I have a bad coax line outside of the >house. The reason for this is that I had a new propane tank installed >and they needed to back the truck up and had to drive over the buried >coax. I did put boards down to spread out the load and protect the >lawn and also the coax. However the problem has started since this >incident. > >I pulled the coax out of the ground and it has bend marks at the edges >where the boards were which to means that it was deformed and maybe it >is now crushed. > Is there any chance that the shield has been pulled apart, and is now completely open-circuit? A broken shield connection can be a major cause of RFI, as RF currents can appear in very odd places in their search for a new return path. How would a TDR respond to a broken shield? "Installation-dependent", I suppose... -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Take a antenna analyzer and put it at the end of the coax. Regardless of the reading, run your hand up and down the outside of the coax. If the shield is open or bad, the readings will go all over the place.
Mel ________________________________ From: Ian White GM3SEK <[hidden email]> To: [hidden email] Sent: Friday, October 21, 2011 1:12 PM Subject: Re: [Elecraft] Now General RF Issue WAS 160m loop experiment a big failure As Jim Brown says: if all these problems came on suddenly, focus on what parts of the installation have CHANGED. You may well have identified one: > >Right now I am thinking that I have a bad coax line outside of the >house. The reason for this is that I had a new propane tank installed >and they needed to back the truck up and had to drive over the buried >coax. I did put boards down to spread out the load and protect the >lawn and also the coax. However the problem has started since this >incident. > >I pulled the coax out of the ground and it has bend marks at the edges >where the boards were which to means that it was deformed and maybe it >is now crushed. > Is there any chance that the shield has been pulled apart, and is now completely open-circuit? A broken shield connection can be a major cause of RFI, as RF currents can appear in very odd places in their search for a new return path. How would a TDR respond to a broken shield? "Installation-dependent", I suppose... -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Now General RF Issue WAS 160m loop experiment a big failure
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In reply to this post by gm3sek
On 10/21/2011 1:12 PM, Ian White GM3SEK wrote:
> Is there any chance that the shield has been pulled apart, and is now > completely open-circuit? A broken shield connection can be a major cause > of RFI, as RF currents can appear in very odd places in their search for > a new return path. I also like the broken shield hypothesis, Ian. > > How would a TDR respond to a broken shield? "Installation-dependent", I > suppose.. It should. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Now General RF Issue WAS 160m loop experiment a big failure
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Is this a helpful list, or what?
Wayne On Oct 21, 2011, at 1:21 PM, Jim Brown wrote: > On 10/21/2011 1:12 PM, Ian White GM3SEK wrote: >> Is there any chance that the shield has been pulled apart, and is now >> completely open-circuit? A broken shield connection can be a major >> cause >> of RFI, as RF currents can appear in very odd places in their >> search for >> a new return path. > > I also like the broken shield hypothesis, Ian. > >> >> How would a TDR respond to a broken shield? "Installation- >> dependent", I >> suppose.. > > It should. > > 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by KD8NNU
If you can see the board impressions in the coax, it's toast. Replace it. You didn't say what kind of coax it is, but 9913 is very easily crushed. According to Mosley, the maker of many military antennas, that's why the military doesn't use it on the ground or in the ground. They use RG213, which will not crush when run over by vehicles with tires. On Thu, 20 Oct 2011 21:21:02 -0400 (EDT), [hidden email] wrote: [snip] >Right now I am thinking that I have a bad coax line outside of the >house. The reason for this is that I had a new propane tank installed >and they needed to back the truck up and had to drive over the buried >coax. I did put boards down to spread out the load and protect the lawn >and also the coax. However the problem has started since this incident. > >I pulled the coax out of the ground and it has bend marks at the edges >where the boards were which to means that it was deformed and maybe it >is now crushed. > 73, Tom Amateur Radio Operator N5GE ARRL Lifetime Member QCWA Lifetime Member ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Amateur Radio Operator N5GE
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Re: Now General RF Issue WAS 160m loop experiment a big failure
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On 10/22/2011 9:33 AM, [hidden email] wrote:
> According to Mosley, the maker of many military antennas, that's why the > military doesn't use it on the ground or in the ground. They use RG213, which > will not crush when run over by vehicles with tires. That information is probably rather dated. Although RG-numbers used to be a specification for cable (MANY years ago), they are now no more than a generic description of size and impedance. You must get to a manufacturer's part number and data sheet to know what a cable really is. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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The point made by Mosley was that the 9913 *style* coax can be crushed easily due to the material used for insulation between the center conductor and the shield. RG213 *style* coax does not suffer from that deficiency. I suppose I could have looked up the MIL STD number of both the coaxes and referred to them in that way, but if I had done so, only experts in reading MIL STD numbers would have got the point. Thank you for passing on your knowledge regarding coax, Jim. 73, Tom Amateur Radio Operator N5GE ARRL Lifetime Member QCWA Lifetime Member On Sat, 22 Oct 2011 09:42:17 -0700, Jim Brown <[hidden email]> wrote: >On 10/22/2011 9:33 AM, [hidden email] wrote: >> According to Mosley, the maker of many military antennas, that's why the >> military doesn't use it on the ground or in the ground. They use RG213, which >> will not crush when run over by vehicles with tires. > >That information is probably rather dated. Although RG-numbers used to >be a specification for cable (MANY years ago), they are now no more than >a generic description of size and impedance. You must get to a >manufacturer's part number and data sheet to know what a cable really is. > >73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Amateur Radio Operator N5GE
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Re: Now General RF Issue WAS 160m loop experiment a big failure
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On 10/22/2011 1:02 PM, [hidden email] wrote:
> The point made by Mosley was that the 9913*style* coax can be crushed easily > due to the material used for insulation between the center conductor and the > shield. RG213*style* coax does not suffer from that deficiency. Understood, Tom. And yes, right on target. 73, Jim ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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