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A closer look at G3TXQ on common mode chokes.
- Thread starter Marconi
- Start date
Do I think this website helps me
I'm still working figuring out what size diameter and how many turns for 11 meters. Searching through the threads for an answer can be confusing with so many voices giving their interpretation of how to make a RF Choke for whatever frequency.
Maybe if there where reference thread files from the administrators or/and members they can trust and can commission to make such threads for reference only for those who are searching for the facts. At least,where to go to find such information would make it easier. These reference threads would closed but accessible to study. I spend most of my time Googling for info instead of searching this site's threads unless Google redirects me back to this website. But then even with that I check,double check, and triple check to make sure I got my info right. I recently bought the 22nd edition of the ARRL Antenna Handbook. I see in it a lot so far of what I've been googling because some of the book's contributing authors have posted their own write ups on different sites.
Overall,I say that Worldwide Radio Forum has a wealth of info. You just have to keep digging and gaining knowledge and experience.
I'm still working figuring out what size diameter and how many turns for 11 meters. Searching through the threads for an answer can be confusing with so many voices giving their interpretation of how to make a RF Choke for whatever frequency.
Maybe if there where reference thread files from the administrators or/and members they can trust and can commission to make such threads for reference only for those who are searching for the facts. At least,where to go to find such information would make it easier. These reference threads would closed but accessible to study. I spend most of my time Googling for info instead of searching this site's threads unless Google redirects me back to this website. But then even with that I check,double check, and triple check to make sure I got my info right. I recently bought the 22nd edition of the ARRL Antenna Handbook. I see in it a lot so far of what I've been googling because some of the book's contributing authors have posted their own write ups on different sites.
Overall,I say that Worldwide Radio Forum has a wealth of info. You just have to keep digging and gaining knowledge and experience.
Several years ago I was discussing coax chokes with Bob85. I also might have been trying a choke I made for my Sigma 4 at the time, but it was not based on this article by G3TXQ below...even though it might have been close to one suggested. Common-mode chokes
During those email contacts I discussed an idea I had that came to mind during my testing for Common Mode Currents. The idea was based on my noticing that feed line length seemed to have a noticable effect on the symptoms for CMC, and the same was true for the tune. I felt what I was seeing simply happened upon adding more feedline with the choke. I did not make a choke using the existing feed line, which would not have added feed line. If I'm right that obviously might have made for totally different results.
I also made a remark to Bob that I had earlier seen my best tuning results for my I-10K when I used a 50' foot piece of RG8 with FPE foam dielectric and a reported vf somewhat over 80%. At about the same time we both were complaining that our I-10K's were not showing the best SWR at resonance, and we didn't know why. But, after using this 50' foot coax and seeing the problem go away...I told Bob what I had experienced.
Look, I'm not claiming these two events were connected in my thinking or my work, but at some point I was excited about the prospects for what it might be suggesting. I told Bob that maybe Jay in the Mojave had a point in his manual suggesting the type and length of the coax to use to tune his I-10K without seeing this split in the match anomaly we were seeing.
I've also raised the same issue several times since, but not much was decided one way or the other. This is the account of my anecdotal tidbit for today.
Now I ask you folks to consider G3TZQ report if you find favor with the information. Check out the table below his chart that shows a range of coax lengths from 20ft to 70ft that may or not be helpful in mitigating common mode currents to a point where they do not manifest TVI type symptoms and suggesting if and when a choke is needed. Doesn't that suggest that feed line length is important in regards to CMC? That is what this table is suggesting to me.
Do you see 50' feet of feed line coax showing "no need for a choke?"
I have on several occasions written comments or made a thread about my idea here, and I did not get much response. I also provided links to W8JI that suggested worst case scenarios related to height and line length associated with CMC. That too did not produce any interest.
Here is yet another published anecdotal piece of evidence that might help some connect the dots who are considering the use of a choke. I said I did not make the connections before, but now I think Bob and I were experiencing CMC that skewed the match at the feed point on our I-10K's, and we didn't realize it or maybe we weren't even considering for CMC.
Then I saw my solution, the 50' foot feed line seeming to make sense, and later I saw this evidence along the same line of thining.
This should be easy for some of you to duplicate, and it would be nice to see if the ideas here could possibly be effective in mitigating CMC symptoms.
During those email contacts I discussed an idea I had that came to mind during my testing for Common Mode Currents. The idea was based on my noticing that feed line length seemed to have a noticable effect on the symptoms for CMC, and the same was true for the tune. I felt what I was seeing simply happened upon adding more feedline with the choke. I did not make a choke using the existing feed line, which would not have added feed line. If I'm right that obviously might have made for totally different results.
I also made a remark to Bob that I had earlier seen my best tuning results for my I-10K when I used a 50' foot piece of RG8 with FPE foam dielectric and a reported vf somewhat over 80%. At about the same time we both were complaining that our I-10K's were not showing the best SWR at resonance, and we didn't know why. But, after using this 50' foot coax and seeing the problem go away...I told Bob what I had experienced.
Look, I'm not claiming these two events were connected in my thinking or my work, but at some point I was excited about the prospects for what it might be suggesting. I told Bob that maybe Jay in the Mojave had a point in his manual suggesting the type and length of the coax to use to tune his I-10K without seeing this split in the match anomaly we were seeing.
I've also raised the same issue several times since, but not much was decided one way or the other. This is the account of my anecdotal tidbit for today.
Now I ask you folks to consider G3TZQ report if you find favor with the information. Check out the table below his chart that shows a range of coax lengths from 20ft to 70ft that may or not be helpful in mitigating common mode currents to a point where they do not manifest TVI type symptoms and suggesting if and when a choke is needed. Doesn't that suggest that feed line length is important in regards to CMC? That is what this table is suggesting to me.
Do you see 50' feet of feed line coax showing "no need for a choke?"
I have on several occasions written comments or made a thread about my idea here, and I did not get much response. I also provided links to W8JI that suggested worst case scenarios related to height and line length associated with CMC. That too did not produce any interest.
Here is yet another published anecdotal piece of evidence that might help some connect the dots who are considering the use of a choke. I said I did not make the connections before, but now I think Bob and I were experiencing CMC that skewed the match at the feed point on our I-10K's, and we didn't realize it or maybe we weren't even considering for CMC.
Then I saw my solution, the 50' foot feed line seeming to make sense, and later I saw this evidence along the same line of thining.
This should be easy for some of you to duplicate, and it would be nice to see if the ideas here could possibly be effective in mitigating CMC symptoms.
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Well LY, you voted this site had creds with you, so all you can do to gain some confidence and answer if the ideas here work..is to try it. If you know what your looking for and expect to see, then life is easy. If not, then you're like me sometimes chasing my tail.
When you get that Vector up, depending on where you are located, you might have a worry about CMC. If you are out in the sticks, then not to worry unless the pattern is skewed so bad it effect your results.
If you are looking for the Holy Grail you will be disappointed. I suggest the answers are a lot closer than you expect. If and when you have to tune your Vector antenna you should be so close to on the money, that maybe an adjustment of <1/16" is all you'll need. That is how close I'm suggesting things can be with these new Sirio antennas. Sirio does a good job of instructions and building kits that work for the users.
If you study old Rube a little you will get a little lesson in what he does. We see his projects as a whole objects, big and complicated, but he sees his projects as many very small projects that are simple and all work together effectively.
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Yea,but which tail?! LOL!
1/16" you say. I'll need something better than my plastic duck(MFJ-207). I'm gaining knowledge and experience on the CP Antenna project. Lou at CBC International - books plans kits modifications repairs for CB radios has his antenna plans for the CP Antenna setup for CB'ers but also provides equations for any other frequency. However,he mentions only using a SWR meter to set up the gamma matches on this antenna and not an analyzer. I guess he's keeping it simple and sellable to the masses. When I do setup my V4000 I want it to sing(resonant).
I found out that that area of the mountains has a 2 for soil conductivity,just like down here in this sand.
1/16" you say. I'll need something better than my plastic duck(MFJ-207). I'm gaining knowledge and experience on the CP Antenna project. Lou at CBC International - books plans kits modifications repairs for CB radios has his antenna plans for the CP Antenna setup for CB'ers but also provides equations for any other frequency. However,he mentions only using a SWR meter to set up the gamma matches on this antenna and not an analyzer. I guess he's keeping it simple and sellable to the masses. When I do setup my V4000 I want it to sing(resonant).
I found out that that area of the mountains has a 2 for soil conductivity,just like down here in this sand.
Do you think that 2 ms/meter will hurt you?
Back in the day of CB radio, I use to talk to several of the strongest long distance stations I could hear on the West Coast on a regular bases. They were all clustered in an area in the Mojave desert, and that is all sand out there as you can imagine.
One of the guys had a meat market with a big billboard sign you could see for 10 miles in both directions he said. On this sign he had written, "Randy's Meat Market, you can't beat my meat" and he had a land-office business.
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I'm not well versed in how to make one yet. I was looking for a quick and easy solution to make one and didn't see where it says how many turns. Got the core diameter down pat though.
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LY, G3TXQ's site below has this chart. On the right hand side is a list of chokes. The first column indicates the number of turns (T=# of turns). The next column is the kind of coax used. The rest is a discription of the type. size, or ferrites used for the choke, and for me is pretty self-explanatory. You applications would most likely be found in the Air Cored section.
I think to really use this chart effectively...you obviously need to know something about how these color-code values apply to your particular antenna's feed point. Some probably just take a guess which to use and select a higher value.
Note: IMO, most guys probably ignore the negative consequences of using such a device, and thus they depend on just being lucky.
Does this help?
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If it's just for CB use then 5 turns off RG58 or 213 on a 4.25" diameter form is the way to go, why 4.25"? That's simple, in the UK our household sewerage system has a pipe that is 4.25" diameter, any off cut can be bought for pennies, I bought a 4' length just to use as a former for chokes and large mobile loading coils 
If it's just for CB use then 5 turns off RG58 or 213 on a 4.25" diameter form is the way to go, why 4.25"? That's simple, in the UK our household sewerage system has a pipe that is 4.25" diameter, any off cut can be bought for pennies, I bought a 4' length just to use as a former for chokes and large mobile loading coils
35, have you used one of these ideas before, and did it do the job you were expecting?
The thing about all these chokes is that they are all bench tested designs with an AIM4170C vna, they are guaranteed designs built on solid principles. The big caveat with any air core choke is that small variances in design and length can quite quickly have an adverse effect and make matters worse, even promote CMC. Back to your question, I use simple home built toroid chokes on all my Yagi antennas, I don't suffer RFI issues at home, so either I didn't have any in the first place or the chokes work. The one antenna that does cause me grief is my hustler 5BTV multiband vertical, but then I'm expecting the choke to work from 10 through 80m and that just isn't going to happen, a good job all my HF DXing is currently mobile, be that in the car or on foot.
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