To Choke or not to Choke? (
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- čas přidán 15. 05. 2021
- Damian, VA3CYC, is working on building a copper pipe VHF antenna, and wants to know how he should do the chokes? How many? Is one ferrite choke equal to another?
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using a 2 inch toroid, with coax coiled inside it, down about 19.2 inches below the antenna contact point will keep rf off the coax shield, and should help with the matching!
My first antenna was a home built jpole. Very satisfying to make a QSO on it! 73, Tom k2bew
Good stuff, thanks. I'll pitch in one of these days soon...
This is a great channel!
Love the 'On Screen Graphics' whiteboard - it works great!
Hello Dave, the LMR-400 equivalent we have from Radioworld up here is an ABR product, which is a good alternative as I understand. This is probably what VA3CYC has. 73 de VE3GKT
ABR is in Houston, Texas. I had a great interaction with them.
There is a you tube channel named TRX labs, the guy is from Germany or Austria, he is very technical and very good. He has a series on BALUNs, Videos 100-103 where he goes through the theory and builds a common mode choke Balun, he also builds a X:1 balun (I don't recall x) in another video based off of the choke BALUN (you will need to search for it ), I have repeated the testing and measuring he does in my lab and have built the BALUN(s) to great success, it is well worth the time to watch for anyone interested in this subject.
His methods and materials are spot on. I built two using his technique and same hardware. SWR was less than 1:1.1 on 1.8 - 60mhz and close to 50 ohm impedance throughout the range. Verified on a vector analyzer.
His methods and materials are spot on. I built two using his technique and same hardware. SWR was less than 1:1.1 on 1.8 - 60mhz and close to 50 ohm impedance throughout the range. Verified on a vector analyzer.
Dave, I noticed that for some reason I was not subscribed to you when I watched the other day and just thought it was my big thumbs. I saw Cal from DX Commander put out a notice asking his subscribers to check and see if they were still subscribed as a CZcams thing had happened and unsubscribed a bunch of his people. I now believe this is what happened to me in your case so recommend you put out a similar notice.
Cheers from Moose Jaw. Tim
CZcams does not like us "thinkers" they prefer sheep. Do you get any "aw snaps"s?
Interesting. However, you never addressed his [other] question about using ferrites on the feedline...? I'm assuming by his inquiry, he was asking about some type of decent quality "snap on" ferrite, but you never answered/indicated whether or not that was an option...?
Moreover, I [personally] wouldn't use the RG-8X for anything at VHF, it's just too lossy. I really like the LMR-400 UF ("Ultra-flex"). I use it exclusively in my shack for patch cables and such. Quite a bit easier to bend than the regular LMR! Cost is about the same, but a bit easier to handle.
Thanks for your videos! Always good stuff.
Alan
W0ARM
Also consider using an antenna with gain which does not generate common mode currents.
So would a lighting arrester stop CMC? And is there another alternative to wrapping a choke? Maybe use a clip on ferrite choke instead? Thanks
Agreed on genuine LMR, but I needed a 15' premade patch cable for a mesh network, and next week will see if "enigma 400" can work well enough.
I'm often contrary...the objective is to reduce the common mode current. Therefore it makes little difference in whether its LMR400 or RG400 wound around a Toroid. The negative side is not the same as the positive side? Am I right?
Is a 4:1 balun also a choke. I am using balun but was wondering if adding a choke would reduce any common Mode Current that I may have.
I built a choke per G3TXQ, for 80 meter resonant dipole - and swr went right through the roof.
Hi, you mentioned the lightening arrestor? I have a comet gp3 on my roof with DX Eng 400max Coax running into my 2nd floor bedroom where my radio is set up? So, the coax never goes near the ground. Don’t I just put a lightening arrestor on the coax prior to it entering into the bedroom and run a 10 awg copper ground wire to a 4’ rod that is in the ground ? Also,my antenna is no where near the highest thing in my yard. Antenna is About 40’ but pine trees are easily 80-100’, do I even need to do this?
Can the lighting arrestor be installed at the base of the antenna. Between the antenna and lmr-400? I installed my 1/4 wave this way thinking I wanted the lighting ground at the highest point. Then I have #6 awg bare copper ground cable to the ground.
Thanks -wros246 (GMRS)
will adding ferrites beads ( 5 or more ) along the coax next to tx/rx do the same thing as a choke?
I agree. Try it without a choke first.
No need to anticipate problems that may not be existent.
Disagree. You don't know the difference is you don't know it exists. Every unbalanced coax fed antenna needs a choke. To negate the noise created by a third line, the coax; where the electrical feed on the shield is on inner skin and outer skin of the shield. A mobile radio with snap-ons would benefit having 200 ohms of combined resistance.
@@gooberminther3tik25 I'm a firm believer in "If it ain't broke, don't fix it." 🙂
The term: "Every unbalanced coax...needs" referring to 'required' is not so, but I could understand "recommended or suggested" -and then only if there is a significant difference achieved.
Thanks Greg for your opinion. However, that is not where a choke UnUn is more greatly needed. The labor of lowering and again raising a base station antenna is not so simple as adding snap-on ferrites onto a mobile antenna coax. I put either an "Ugly Balun" or a coax wound Toroid 1:1 common mode choke every time. It won't hurt, save for a poorly constructed choke, to add the noise reducer before raising it the first time.
The neighbors appreciate the absence of RFI, otherwise created by the 18-50'+ of coax radiating interference. This can be especially true if running upwards to legal max power output.
Second to RFI on the base station is RX noise cancellation. I find the difference is > 3 S units, less noise in the receiver; which is the primary objective with mobile radios.
@@gooberminther3tik25 While what you state is perfectly reasonable, the fact remains that if there is no inherent problem then there is no apparent need to fix anything.
The difference you observe at your unique location is not necessarily ubiquitous. It's terrific that you get better results at your QTH by using such measures, -but if it is not raining then it would be frivolous to walk around with an umbrella just because it is raining somewhere else. -'73
The HRO here carries ABR400, is that an acceptable facsimile of LMR400?
I have some genuine LMR-400 and I was surprised how flexible it is. I also have some LMR-900 and that is very stiff.
Times Microwave makes multiple types of LMR-400, some stiff, some more flexible.
@@davecasler Hmm, interesting! I previously understood LMR-400 to be just of one type. I've even seen the label 'Ultraflex' for it. So why are there other versions? What advantages do they have?
73 de M0PTB
@@NoiseWithRules LMR400 and LMR400 ultraflex are not the same
@@JosephVE3GKT Hi Joseph. This is getting even more interesting! I bought LMR-400 for low loss. It seems I got Ultraflex by accident. But the question is still why are there other versions? What advantages do they have? And how to tell which version I'm buying?
73
@@NoiseWithRules I have never purchased LMR400 myself, so I am not at all well-versed in the varieties and pros/cons of each. I hope someone with more knowledge can enlighten us further. 73 de VE3GKT!
Hello Dave, thank for your information on chokes. Can I as a supplementary to this video? If you are on HF, say 14.1mhz instead of UHF, would you use a toroid choke, how do you identify the mix, size and turns required? Thanks for all your assistance to the community, Frank. VK4FEM
Where do I buy real LMR-400 coaxial cable. The vast majority of the LMR-400 that I see sold is the LMR-400 equivalent.
I’ve also thought about using 1/2” hard line for my off-center feed HF 24 foot flagpole antenna. The coaxial cable run is about 65 feet. I wonder if there is a quality 1/2” hard line coaxial cable and a cheap knock off version.
I’ve also heard that a 4:1 balun near the antenna should be separated by about 15 feet of coaxial cable to the RF choke. Is it a good idea to separate the 4:1 balun and RF choke?
Dave KY0L
Could you offer some objective means to determine frequency vs diameter vs count vs cable spec, that is more than just "should work" kind of guidance? Thanks in advance...
I can tell you what works for me (very well): 8 turns @ 8" diameter of RG8x OR RG58 as near as practical to the feedpoint w/ a PL259 coupled to a double female SO239 (barrel) coupler. It is NOT frequency critical (one size pretty much fits all - nothing fancy). Make your run to the shack w/ another PL259 connected to the free female of the SO239 at the feed-point (below the coiled choke). This will choke off most of any feedline radiation back to the shack and minimize most of any pattern distortion. If you're OC/ anal put a couple more turns in the choke). Been doin this for years. If you're stingy on funds, delete the PL259/ SO239 coupler and just wind your choke coil and run it to your station - I've done that too. Works great.
I watched this.
RG8X has foam dielectric, and consequently is not a good candidate for looping. Ferrite beads are a better bet.
Dave, a "copper tube antenna" doesn't have to be a "J-pole". Check out John Portune, W6NBC, his 2m "Slot-Cube" antenna was an easy build and tune for me and makes a great project for anyone interested in building and learning about antennas.
Is there such a thing as too many chokes?
Ether on the power wires or signal cables?
Hmmm... I'm always wondering if I have enough.
Depends on how you measure. If they are anything but free, yes.
Can this be done or used with HF SSB?
Yes
Is Davis RF cheap chinese knockoff as you suggest?
Wagon burner