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Re: MORE CMC SINGLE CORE DATA
Dave,
I can't resist replying again, and challenging some of your points. Coaxially wound CMC are not true common mode chokes.I differ on that point. I claim that they are true CMCs, just like bifiliarly wound ones. They do suppress common mode current on a coax cable just as well as on a bifiliar one. Thus they tend to force the currents on both conductors to be of the same amplitude and opposite phase, regardless of whether the two conductors are arranged side-by-side or one-around-the-other. They offer aI would like to simply do away with the distinction between currents on the outside or the inside of the outer conductor, because it's irrelevant. We cannot separate them at the ends. And anyway, whenever the operating frequency is low enough, and the outer conductor is thin enough so that it's thinner than the skin depth, there physically isn't any separate current, but just ONE SINGLE current in the outer conductor. And a CMC wound with coax cable can work both below and above the limit frequency above which separate currents can exist on the outside and inside of the outer conductor. Furthermore the distinction is irrelevant for this reason: At high frequencies and with thick outer conductors, the current on the inside of the outer conductor automatically is equal and opposite to the current on the inner conductor, regardless of whether or not there is a CMC. The CMC will then suppress current on the outside. And at low frequencies in a coax cable having a thin outer conductor, there is just one current in the outer conductor, which can be different from the current on the inner conductor, but a CMC will force them to be the same. So, the end effect is that regardless of whether those separate currents can exist or not, the CMC works the same. We just don't need to care about where exactly the outer conductor's current flows. As such, they function as a currentI can't agree with that logic. I can't see how a CMC, by itself, can turn CM energy into DM energy. Anyway energy involves voltage and time in addition to current. Letting the time aside, which means disregarding the confusion between energy and power, to talk about CM energy we need some external conductor (usually earth) to complete the circuit. As soon as such an external conductor is involved, we can no longer talk about the CMC doing anything, because it's the whole circuit that's doing it. It is a bilateral device.Yes. Any CMC is. A bifilar wound CMC accomplishes the function of aI absolutely disagree on that. There is nothing in a CMC wound with bifiliar line that would force such balance. At least not in a "clean" CMC that works reasonably free from parasitic effects. If you connect one port of a balanced-wound CMC to a ground-referenced signal source, and the other end to two different load resistors to ground, then the ground-referenced voltages on those two resistors will NOT be equal.Just the currents will be the same. And if you do the same exercise with a coax-wound CMC, you will get the same results. Except if you have such strong parasitics (such as stray capacitance) that they dominate over the desired effects. But in that case you have a badly designed CMC. This 'feedback' mechanism whichI disagree! The truth is that DM current causes no flux in the core, while CM current does cause flux, and that this happens regardless of whether the two conductors are side-by-side or coaxially arranged. For that reason the winding impedance of a CMC opposes the flow of CM current, while having no effect on the DM current. Again without any distinction between coax and parallel line. The true CMC works on the same principle as parallel wire transmissionI believe that what you are trying to point out here is that with parallel wire the core does have some effect on the transmission effects along the line, while with coax cable it doesn't, given that parallel line has much of its field outside around the conductors, while coax line has it all confined inside. That's true. But the effect of this is mainly that the core will affect the impedance of the parallel line, if it's wound with the conductors very close to the core, while a coax cable is immune to this. It doesn't cause any effect on the fundamental action as a CMC. CMC using parallel line should be wound with a reasonable spacing between the conductors and the core, to avoid increasing the transmission loss, and changing the line's impedance. Coax cable instead can be tight-wound around the core without a loss penalty nor a change in impedance. Of course only as long as its bending radius doesn't end up too small, but that's yet another effect that has nothing to do with what we are discussing here... So I maintain that a winding of coax cable on a magnetic core makes a fully valid CMC, that even has some advantages over a CMC wound with parallel line. I don't accept that using parallel line to wind a CMC fundamentally produces any additional balancing effect. Manfred |
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Re: MORE CMC SINGLE CORE DATA
Does anyone know if G3TXQs numbers are the same for 8x as for 58? I.E. can I sub 8x for 58?
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73, and thanks, Dave (NK7Z) ARRL Volunteer Examiner ARRL Technical Specialist, RFI ARRL Asst. Director, NW Division, Technical Resources On 2/9/21 9:09 AM, Dragan Milivojevic wrote:
/g/NanoVNAV2/message/1147 |
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Re: RF Sampler
On Tue, Feb 9, 2021 at 10:01 AM, Wa4kfz wrote:
Mark, thanks for posting this (you beat me!). Looking at the drawing in your first link, it's possible that my copper foil connects to the RF line rather than ground as I had described it. Unfortunately, that tap is back at my house in Silicon Valley, so I can't verify. Here, at my "portable 6" QTH, my tap has no foil because a flat response isn't important to me for signal monitoring. - Jeff, k6jca |
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Re: RF Sampler
Bob Albert
I made a poor man's sampler.? I just put a loop around the coax and connect it to the scope.? There is plenty of rf even when operating barefoot.?
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Bob K6DDX On Tuesday, February 9, 2021, 10:01:48 AM PST, Wa4kfz <wa4kfz@...> wrote:
This is an example of an RF tap used for sampling a signal. 73, Mark WA4KFZ On Feb 9, 2021, at 12:47 PM, David Eckhardt <davearea51a@...> wrote: |
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Re: RF Sampler
Max, how much power are you driving?
I hate winding toroids, so for my transmitters in the 100 watts range, I just make a simple voltage divider (e.g. 10K & 50 ohms). 1 watt for the 10K should be fine for 100 watts continuous (brick on key) xmit power (the 10K's dissipation will be 0.5 watts if your transmit power is 100 watts into a matched load ), and the attenuation is 52 dB, assuming the 50 ohm lower-leg of the divider connects via coax to a 50-ohm terminated device (e.g. o'scope), which gives plenty of signal for my oscilloscope. There will be some tilting of the sampled-signal's frequency response. If you need a flat response, I flatten mine over the HF range by placing a bit of grounded foil near the body of the 10K resistor (I use a piece copper-foil tape (with Kapton tape over the foil as an insulator), but you could try experimenting with a piece of insulated wire). Use your NanoVNA in S21 mode to adjust the foil's (or wire's) placement for a flat response. I build mine into Pomona boxes. - Jeff, k6jca |
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Re: RF Sampler
This is an example of an RF tap used for sampling a signal.
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73, Mark WA4KFZ On Feb 9, 2021, at 12:47 PM, David Eckhardt <davearea51a@...> wrote: |
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Re: RF Sampler
If you just want to monitor what your antenna is radiating, a 24" clip lead
formed in a loop works fine for RF pickup into an o'scope. Connect one end of the clip lead to the BNC backshell and the other to the center of the BNC. While it is not a quantitative sampler, it will capture plenty of energy to assess the quality of your radiated RF energy. Otherwise, the Collins Radio solution looks pretty spiff and easy to build. Dave - W?LEV On Tue, Feb 9, 2021 at 3:07 PM Max via groups.io <kg4pid@...> wrote: I need an RF sampler of some sort for monitoring my RF signal. This might-- *Dave - W?LEV* *Just Let Darwin Work* |
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Re: MORE CMC SINGLE CORE DATA
/g/NanoVNAV2/message/1147
On Tue, 9 Feb 2021 at 17:59, Max via groups.io <kg4pid@...> wrote: Sorry for the confusion on my part. I had forgotten about your |
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Re: MORE CMC SINGLE CORE DATA
Sorry for the confusion on my part. I had forgotten about your measurements being for the bifilar wound CMC, not a coax choke one.
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G3TXQ said the RG-58 could be replaced with RG-400 with little change in performance. That's what I use. I can't remember its power rating but it's likely more than I'll ever need.? One thing I don't understand is how to tell if the CMC choke is resistive at the frequency of interest. Max KG4PID On Monday, February 8, 2021, 03:29:04 PM CST, David Eckhardt <davearea51a@...> wrote:
RG-58 is not appropriate for US amateur legal power.? I don't use it. This is one of the main reasons I have chosen bifilar wound CMCs. I have enough RG-142 (Teflon silver coated and double shielded 50-ohm coax that will take power) to try one good choke wound in the manner of your referenced presentation.? I can try that and present the results. Dave - W?LEV On Mon, Feb 8, 2021 at 7:33 PM Max via groups.io <kg4pid@...> wrote: ? Your finding don't compare well with the data found here.-- *Dave - W?LEV* *Just Let Darwin Work* |
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RF Power Splitter Using Two Ferrite Toroids
Ken Moorman
I believe that someone on this group sent an email to the group several days ago with an attachment which showed the schematic of and a photo of an rf power splitter using a couple of small ferrite toroids. I have managed to misplace that message and wonder if the original sender (or anyone who might have saved it) would send it to me or provide me with the link to find it on the groups.io site. My email address is nu4i AT cox.net. Thanks.
Ken, NU4I |
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RF Sampler
I need an RF sampler of some sort for monitoring my RF signal. This might be used with a scope or TinySA or ...
Is something like this what I need? If so I'd prefer to build by own if I can get some info on the core type and number of turns and such. If this isn't what I need, what would this be used for exactly? Thanks Max |
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Re: MY CMC MEASUREMENT
#measurement
On Mon, Feb 8, 2021 at 03:02 PM, David Eckhardt wrote:
David, Thanks for: "our measurements look much like mine." Followed Yours and K6JCA, W2DU, G3TXQ and other Experts recommendations... only with my nanoVNA " Miro, OK for "MnZn" it was my tipomistake Please read my post again.I only and only talked / wrote about the voltage and power of the peaks.At the peaks,the toroid and the coils are loaded with this voltage and power. The dog is buried there. This is the maximum and real stress that the choke experiences at the peaks.The arcing between wires is always on the peaks. PA - Tube with 1900 volts on Anode/ 0.5 A plate current (DC) when the PI filter is set to max output power on 3.65 Mhz.. LOAD - 250 watts non-inductive load up to 3 Ghz on a solid radiator (I had to pause so as not to blow it) is heated to 80 degrees Celsius for 30 seconds Nonstop test.The Choke NO - it remained relatively cold. KEY DOWN ON CW is very good test....Nothing less, nothing more.. I can't say Best Regards ! Thanks for the Comments ! |
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Re: CMC MEASUREMENTS - PDF'ed & SIZE REDUCED
OMG!!
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No topic drift, no politics, no name calling, just chat about our favorite topics! There _are_ some reasonable people left alive!! I have found my nirvana on groups.io... What a wonderful group to have found, thank you all! 73, and thanks, Dave (NK7Z) ARRL Volunteer Examiner ARRL Technical Specialist, RFI ARRL Asst. Director, NW Division, Technical Resources On 2/8/21 4:02 PM, David Eckhardt wrote:
Don, I absolutely love your tongue-in-cheek (well, I do understand) |
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Re: CMC MEASUREMENTS - PDF'ed & SIZE REDUCED
Don, I absolutely love your tongue-in-cheek (well, I do understand)
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response! I really do!!! Some of us had to suffer through learning calculus and then applying it to electromagnetic theory and antennas and transmission lines. My references now are graduate level. Yes, we suffered, but at this end of life, I'm glad I *once* (stress: ONCE) did. You are to be commended in your response which reflects the audience to which I attempted to target. If I can't pass along some of the knowledge I gained in formal education followed by decades of seat-of-the-pants learning during my career applying what I learned while suffering, I'm ready for the pine box. Thank you for your reply!!!!!! You should take up satirical writing. Dave - W?LEV On Mon, Feb 8, 2021 at 11:53 PM Don - KM4UDX <dontay155@...> wrote:
As a non-engineer (of any type) like other nano-users, the simple mission --
*Dave - W?LEV* *Just Let Darwin Work* |
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Re: CMC MEASUREMENTS - PDF'ed & SIZE REDUCED
As a non-engineer (of any type) like other nano-users, the simple mission was to wind some coax or wire around a ferrite donut installed on our OCFD and stop the nasty, dreaded, feared, sneaky and often discussed common mode current from creating shack mayhem.
The intended process? Copy the designs of others and validate with our nanos. The actual process: sink into a putrid pit of RF theory, irreconcilable contradictions, arcania, mystery with misery, and a odd desire to plunge an ice pick in our eye because it would feel better than trying to understand how to (a) build a CMC and (b) measure our newly minted CM choke effectiveness over the lowly average ham bands (say 80-10m) with our beloved nanos. I, and others, read and study Dave's (W0LEV)'s work like Orthodox study the Talmud - every letter, every grouping of words, even the space between words, has intense meaning to the lost, abandoned and hopeless neophytes. All this is to say thank you Dave, and others. Your work is light to sheep lost in inky blackness. My favorite professor would say at the end of every lecture to a class clearly dazed, befuddled and confused: ..."okay, clear as mud?" Followed by "Good, see you next week!" Don Km4udx |
Gary W9TD
Frank K4FMH
Don - KM4UDX
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