Effect of the MFJ-915 Choke Balun (

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What effect does adding a choke balun (in this case the MFJ-915) have on antenna behavior? The antenna is a two-band trapped antenna (MFJ-17554).
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Комментарии : 142

@larrysclassroom2118 7 месяцев назад

Dave, I suggest you do the same experiment but add a meter to measure common mode current. This will help determine if the choke is actually doing what it is designed to do.

@richardwesterman5773 3 года назад

Placing a Choke at the feedpoint of the dipole reduces common mode current on the feedline during transmit. Placing the Choke at the transceiver reduces common mode current picked up by the feedline during receive. This RX common mode current causes noise, sometimes lots of noise, in the RX. Therefore, a choke is required at both ends of the feedline.

@arconeagain 2 года назад

Do you have a grasp on what a transceiver is?

@peterock8217 3 месяца назад

Isn't both ends of the feedline the same point of the feedline, meaning there's only one feedpoint

@kareneighth6045 2 года назад

This video misses the mark and is sure to confuse many. The whole point of a line isolator is to reduce common mode current. This eliminates some noise picked up by the coax. Also can help with rf in the shack.

@arconeagain 2 года назад

Let's not forget transmit as well. After all, things work both ways with a transceiver.

@frankthetank3342 11 месяцев назад

I was thinking the same thing. Get a field strength meter inside shack and check for common mode, with and without the choke. Oh well.

@ohyeawhosurpoppy 3 года назад

I am a crazy about building my own antennas and stuff. I was using a 49:1 auto transformer on a half wave 20m piece of wire for about 6 months with great success barefoot on a FT891. I notice the horizontal wire antenna was had greater background noise than my built vertical 20m diapole. I built a choke using 240-43 and 17 wraps of RG58 AND left a approx 10ft tail with PL259 on it. Connected the tail to the 49:1 auto-trans and then connected the radio coax to the choke. In my case it dropped the noise floor very noticably, and shifted the SWR because it was no longer using the radio coax as a counter poise. 73 and keep'em coming

@zappatx 3 года назад

You don't know how helpful your videos are!!! Thanki you so much for these resources. I'm not only learning but your videos are more to the point than some of these long "engineer types".. There's a bloke from Germany who also has great info but you have to watch 5 times to get what he's saying.. 73 from Sioux Falls.

@glenmartin2437 3 года назад

Thank you. I have used rf choke baluns on occasion and seen improvement in lower noise levels, not only in radio equipment, but the mass spectrometers I operated. N0QFT

@consciousness1237 3 года назад

Dave what I do is have an actual current balun at the dipole for antenna isolation. Then just before the coax enters the rig I have what you are testing to eliminate RFI picked up on the coax shield it cuts the noise the reciever picks up in half if you live ia a noisy area like me. Your location looks very quiet and peaceful. They also call those with the beads coax line isolator you can use them at the dipole but the work better at the shack end. Best investment for low noise reception. 73's AA4CP Chuck Port Salerno FL USA

@marcelotoniolo4434 3 года назад

Well done David. Another great video that helped me in clarifying a few things.

@popefelix 3 года назад

I built a homebrew RF choke balun out of a couple of FT-240-31 toroids and some #12 wire. I'm fixing to use this on my rain gutters. This video gives me some idea of what to look for to test its effectiveness. :)

@boonesmith9261 3 года назад

I do not understand your concentration on SWR changes, when the primary function of a choke balun is to eliminate common mode RF flowing on the exterior of the coax shield. The presence of common mode RF can be a primary cause of increased receiver noise and spurious received signals.

@forgetyourlife 3 года назад

YES! It seems Dave buried the lead on this item. Its mainly for noise and common mode current to which Dave mentions is only a problem on his PC speakers "that he simply just turns off" How does this video say anything about the intended purpose of the device?

@ne2i 3 года назад

It helps to preserve the pattern of the RX and TX of the antenna. It does almost nothing to vswr....

@SufficientlyScott 3 года назад

Yeah I'd really like more info as to how it affects noise when placed at the antenna vs. the transmitter.

@falsedragon33 3 года назад

He doesnt understand this topic, is why. No mention of skin effect, or that this is a current issue.

@katsebua 3 года назад

How does the change in SWR indicate arresting of feedline radiation?

@elpechos 3 года назад

My understanding is such a choke will not have large impact on VSWR but it will have a large impact on radiation pattern if the frequency is high enough. So measuring VSWR isn't telling you whether you are getting a benefit from the choke or not. When driving a balanced antenna from an unbalanced feed line without a balun, the balanced feed line will radiate, messing up your radiation pattern

@Johnyrocket70 Год назад

This video wasted 15 minutes of my life. I have a noise problem on 40m I don't have a swr problem I gotta noise problem using a coil to get on 40

@bluejohnnyonly9770 3 года назад

I was just reading a paper today about having two CMC inline. One near the Antenna for TX and the other near radio to reduce noise pickup in transmission line for RX. Thanks for your videos.

@user-xj8oh6fo2f 3 года назад

BlueJohnnyOnly ! One near the antenna is enough.

@davecasler 3 года назад

Grounding the outer shield before bringing the coax in the house really helps with noise too. I've had personal experience with that.

@user-xj8oh6fo2f 3 года назад

David Casler that could just mean that balun at the antenna end doesn’t have good common mode current attenuation.

@teddysphillips 3 года назад

I use one of these common mode chokes with my mobile screwdriver, upon manufacturer recommendation in the antenna manual. Without this in place, the stray RF causes the SWR to fluctuate wildly and bleed over on nearby electronics. There is little change in noise for me when using the choke, but the stray RF is mitigated and the SWR at the radio stays happy when transmitting and allows my mobile operation. Thanks for the videos.

@BartVanAllen 3 года назад

I have one on my 80mOCF at the antenna and it works excellent to keep stray rf out of the shack. But on the vertical (about 40 feet from the shack) I need one at the antenna and one at the entrance to the shack, which is also shield grounded at the shack entrance and at the antenna, and with buried cable, to stop the rf feedback from going crazy in the shack. I tried one at each end on the vertical, neither of which did the trick although both locations lowered the rf in the shack. Using both, it is working nicely with just a wee bit of the wiggle patterns on one of the computer monitors when transmitting - it is an old monitor!

@jay-rus4437 3 года назад

Okay....gotta admit, as a new ham (tech earlier in 2020, then upgraded to general followed by extra by august).....but why was there such a focus on swr related to the effectiveness of a choke? I watched in hopes of seeing whether or not the mfj choke had any positive effect for white noise or some RFI. So as a newbie am I missing something?

@sw33tgr455 2 года назад

Your coax cable has a copper core and a woven copper shield surrounding it. The copper shield acts as a Faraday cage surrounding the copper core, so the copper core is protected from external interference. This is why we use coax, we can run relatively long lengths of the cable without too much interference. This also means that the copper shielding is picking up all of the interference that is in the environment. A choke balun works by creating a single point of high impedance for the shielding. RF will travel down the path of least resistance and this point of high impedance acts to isolate the coax shielding from the antenna system. If the choke balun is working when transmitting, the signal travels down the copper core with minimal loss then it is transmitted by the antenna only, and not the coax shielding. The shielding of your coax will be picking up RFI, but because it is isolated from the antenna system, the noise signal will not go to your receiver. If the choke balun doesn't work, the shielding will act as part of the antenna during transmit and receive. If you know your antenna is perfectly resonant on a certain frequency you can measure the effectiveness of a balun by watching the SWR. If the SWR is 1:1, then every single watt of energy is being emitted from the antenna at that frequency. If the SWR is higher than that, you know that you are losing power. As long as you have eliminated other issues (bad soldering, conductive materials close to you antenna, etc.) it is probably being lost to the coax shielding for the length of your coax. So by looking at SWR, you are essentially measuring how effective the balun is at isolating your coax shielding from the rest of the system. If the SWR is low then the RFI and noise picked up by the shielding is not making it through the choke to your receiver.

@jay-rus4437 2 года назад

@@sw33tgr455 wow…thank you so much for the informative reply. Exactly why I asked if I was missing something.

@j.r.3215 3 года назад

According to J.T. FT8 is a weak signal mode and not a low power mode.

@Lugeix 2 года назад

Back in the good old days, I had a Swan 350 and a d-104 mic. When I tune up the rig on a band the antenna wasn't design for, I got a nifty burning shock from the microphone. Sometime on the mouth. The solution was put a choke on the feed line, and coke on the mic line.

@curtmyersk2cwm477 3 года назад

If mounted outside near antenna (I agree), I am assuming additional weather/water proofing would be desired? For $40, how good can it be outside unprotected (which I assume the reason MFJ suggests mounting it inside hi hi).

@ktmman1503 Год назад

Hey Dave, just came across your video.. and I love your videos.. I do have a question… the choke.. surely it’s not a Balun as you say.. but a RF choke, as a Balun is a device which is for a balanced antenna to unbalanced feed line? Correct me if I’m wrong.. cheers 73 VK3NCR

@walteranderson7889 Месяц назад

The one experiment that always seem to be neglected is: How does the radiation pattern from a balanced resonate dipole antenna change with a balun installed vs NO balun installed

@ths3900 3 года назад

I think that is more for reducing feedline radiation in the shack. Sometimes they call it a line isolator. Put it just out side the house. It is some weight to lift for at the antenna. They do go bad.

@davecasler 3 года назад

The point is to get the common mode reflection off of the outside of the coax. That's why I recommend it be installed near the antenna. Perhaps, because of its weight, it would work best in an inverted vee configuration.

@SNAKERADIOS 3 года назад

Hi Dave. I could not belive when a customer of mine got the 915 and said the destructions stated to put it at the transmitter. I was like what the####?. I told him to ignore that and put it at the feed point. I recommend these to all my customers when doing new setups for 11 meters. We use the double pl 259 for the connections at the antenna feedpoint . I have always used a choke balun on all my base stations.

@lindajensen6889 3 года назад

Good comment here, thank you Snake Radio.

@rangerbud 3 года назад

Was the coax 1/2 wavelength @ 40m & 1 wavelength @ 20m? Given that your vertical run was so perpendicular to the dipole, is a resistive choke even necessary?

@paulc.cowanjr.9499 11 месяцев назад

Dave, What is the Boat Anchor on the 2nd shelf over your right shoulder ?? ?Looking for a tube or Hybrid to start with

@dalependleton6420 6 месяцев назад

If this unit is coax in and coax out it is NOT a balun. It is simply a choke. SWR varies along the feed line if there is not a perfect match at the load. Inserting this unit simply extends the length of the feed line. The correct placement for this "choke" is as close to the feed point of the antenna as possible.

@MrVasile 3 года назад

Thumbs up for the video, and also for the Star Wars shirt!

@joecraft4409 2 года назад

Interesting. I thought a “choke” was supposed to block current mode RF. I use one at the Dipole (Balun) and one at the radio (feed line choke) and chokes on the “mains”. Same ferrite, same # of turns and same circle diameter. I aim for high impedance (resistive) and thousands of ohms. One “choke” usually doesn’t do the trick especially in noisy environments.

@larrysclassroom2118 7 месяцев назад

I f you are saying that you thought a choke was supposed to block common mode current then you would be correct.

@Johnyrocket70 Год назад

If you have noise put it by the radio. One on each end with a non resonate antenna is even better.

@CE3FJK 2 года назад

where I can look to make this choke on my own? I'd like to try this very same shape not squared. suggestions ?

@DerekWitt 4 месяца назад

I recently bought a GA-450. I noticed some significant power supply noise. This antenna has a rechargeable battery that recharges via USB. I do have numerous USB chargers throughout the apartment. I’m thinking I’m picking up the noise from the GA-450’s battery itself. The noise is much more pronounced on shortwave. It seems to level off from around 30 MHz on up. Broadcast FM and up seem to be not as bad. Would a ferrite bead/ring placed on my BNC cable near the antenna’s junction box end help mitigate the noise issue?

@aymansaqer3212 2 года назад

Good day brother ...I have noise from outside the house and I think from the houses near me .. I tried a lot to keep the noise away .. Is this product useful for me...thanks for your support .

@vincentditizio8790 11 месяцев назад

Would an end fed antenna be a better test? I have a Chameleon end fed that drives my Xiegu 125b amp nuts.

@quaildogusa 6 месяцев назад

I don't understand what symptoms you would be experiencing to indicate that you need the choke assuming that the SWR is fine. Would it be that the return RF causing problems with devices within you house? Thanks, Wayne KV5WLG

@uwegewinner6343 2 года назад

Hello David I think that when you measured the results on this antenna you did not say that the antenna feed line is lamda/2 of the longest operating frequency. MFJ 259 (B) measures also the transformation defects on the feed line and falsifies the measurement results ! To the Coke Balun very close to the feed point of the antenna and one at the tuner or TRX. then I have also QRN by 18 dB at my station lower. I use the Coke from W1JR. 73 from DG1RUG

@TeddyD802 3 года назад

Thanks for the video. I have an end fed antenna with about a 225ft coax run. I have one at the TX. I was wondering about trying one at the feed point of the antenna... what are some disadvantages of coax radiating from an antenna performance perspective?

@joecraft4409 2 года назад

A good counterpoise is almost a requirement on Endfed antennas. If you rely on the coax shielding to be used as a counterpoise, a choke near the coax/antenna junction (at least 25’)

@joecraft4409 2 года назад

Watch this RU-vid “RF man discusses long wire antennas, ununs, rf chokes and antenna towers” uploaded Oct 2020

@thomasmaughan4798 2 года назад

Coax simply becomes part of the antenna system in that situation. Might help, probably not. It changes the radiation pattern and directionality. In some circumstances it can be a bit dangerous to have RF on the outside of the coax, runs down to the radio, through the microphone cord into your mouth and/or hand and you'll get a "bite" it is like an electric shock but at radio frequency it is a sharp little burn.

@livesonjura 2 года назад

At 11:50 in your video you mention that RF current returning on the coax shield is dissapated as heat in the balun. I don't think so. The inductive reactance of the RF choke or "balun" opposes changes in current by creation of an electro-magnetic field and a counter-EMF that opposes current flow. THe choke is not a resistor.

@mdblack98 Год назад

Such a choke will have a slight effect on capacitance due to the extra coax/wire inside it. It should have very little effect unless your coax is very short. You really need a VNA to analyze such a thing so you can see the smith chart. We just tested a 4 turn on 3 inch choke for 6M and the choke had a small effect on the capacitance. A true balun with impedance matching will have more effect of course. You simply have to have the correct Z at the antenna to match your coax. This can be done by tuning the antenna length sometimes or an appropriate impedance matching balun. 200Ohm loops need 4-1. Loop-fed Yagi's should be able to get VSWR 1 with a 2-1 balun (they run 100Ohms).

@timbacchus 3 года назад

Thank you so much for this info. I have been thinking about buying this. Never heard of putting a balun at the transmitter. Wonder if it helps receive at all?

@davecasler 3 года назад

It didn't seem to me to help at the transmitter end of the coax.

@falsedragon33 3 года назад

Common mode current issues aren't an rx issue. Due to skin effect, your dipole turns into a tri pole allowing for current to travel in both directions on a single conductor. The problems will correlate with power. This video will only serve to confuse you more, as it is based on confusion. Watch the balun series by TRX Bench. He explains it all, if you can digest it.

@consciousness1237 3 года назад

Yes big time right before the rig cuts noise in half

@SteveWithnell 2 года назад

@@falsedragon33 Common mode can be an issue for RX, the symptom being a higher noise floor. If you are in an electrically quiet environment, this is irrelevant, but in a noisy urban environment, the impact can be substantial.

@user-mt2qn4yp8w 3 года назад

I have a problem with my SWR at the radio to the tuner. I must use a tuner with the type of endfed I have. The SWR is very good for tuner to antenna. So what can I use from radio to tuner?

@davecasler 3 года назад

That's a very odd problem. Check the cable. Also make sure the radio and the tuner are grounded together. Note that the tuner in the radio should be turned off. You should be able to set the tuner such that the radio SWR reads 1:1.

@vladtepes481 2 года назад

I have used choke baluns on some antennas. Verticals that are somewhat poorly grounded(mobile antennas are are often bad) and off center fed dipoles benefit from a choke balun. Dipoles and verticals with lots of radials not so much so. Incidentally, analysis with an MFJ-259 may not show a problem but applying 100W may give a very different story. I am not convinced your analysis is correct.

@usernamemykel 2 года назад

Ok, a choke at the antenna end for a dipole. Dipoles are resonant. Where does one place a choke for a non-resonant antenna? Thank you.

@BadHorsie2 3 года назад

Would there be any advantage to running ta choke at the antenna and at the transceiver. I will be in your area for ten days visiting family.

@BadHorsie2 3 года назад

Never mind you answered my question.

@g0fvt 3 года назад

I enjoy your videos, however the subject of common mode chokes is more complex than it first appears, I have messed about with them for a few years now and still have unresolved issues with them. There is definitely a case for using more than one and there are definitely "nodes" on the feeder where they work best. The best ferrites for the job are somewhat lossy, you don't want a high Q loading coil effect which could in fact increase common mode current. (depending on feeder length and frequency). SWR measurements don't give the information you want, perhaps you could build a simple toroid and diode arrangement to examine the common mode current on your feeder? Where you are likely to see gains are in reduced noise levels and reduced RFI to other electronics. The heating of the ferrite is dependent on the common mode impedance of the choke and how much common mode current you have. Digital data modes such as FT8 etc are weak signal modes, not automatically low power modes.... but that will set the cat among the pigeons..73

@nevellgreenough404 2 года назад

The MFJ-854 RF current meter will tell you the common mode RF current running on the outside of the coax. The coax must fit inside the coupling transformer. This would be a fun experiment. --73, N2GX

@KD5XB Год назад

@@nevellgreenough404 Yeah, if you can get the clamp open!!!

@flateartheffect 2 года назад

Does anybody know where I can send my old DX-394 Radio for repair? Thanks

@DickGJ61 2 года назад

I'm a newbie so I'm sure this will be a dumb question...would there be any improvement if you put one of these chokes at both ends?

@j.b.5348 2 года назад

It's actually a very good question. Yes one at both ends would be ideal in eliminating common mode current at the shack and at the antenna. 73.

@JohnHill-qo3hb 3 года назад

Whether on purpose or unintentional, the misuse of terms and the incorrect application of the unit being discussed, one thing is true about this video... it has succeeded in generating conversation. Many of the terms in our hobby are misused and misunderstood. I'm sure Mr. Casler would agree that he is no expert and is subject to making errors, he is doing us all a service in spite of any errors in his videos as those errors generate discussion and in a discussion, people learn, well done Mr. Casler Using the term Choke Balun is inaccurate, the unit is a choke, what it is not is a balun. A balun is a type of wide band transformer designed to transform one impedance into another different impedance. A choke is exactly as the name infers, it chokes off something, in this case unwanted RF energy. Positioning of the choke depends on the type of antenna in use, a balanced antenna would make use of the choke AT the antenna feed point whereas an unbalanced antenna such as a long wire with a suitable type of transformer at the feed point would use the choke at or near the rig it serving two purposes, first, as the coax shield would be acting as a counterpoise the placement (where it is in the length of feed line), the choke would affect the SWR of the long wire antenna and second, any RF on the shield would be choked (blocked) from entering the rig. Best example here would literally be a "Hot mic", I'm sure most of us have had the "joy" associated. The above is my understanding of the use of the Common mode choke, I could be completely wrong or I may have a part understanding. I'll find out in a few weeks when I install a EFHW antenna at my antenna restricted new QTH. The most important thing to take away from this video is to discuss things that don't jive with our understandings, after all, the level of general ham competence is all in the title of what we are AMATEUR radio enthusiasts. Keep making stuff. de VE3KKQ

@davecasler 3 года назад

I stand by my assertion that it is a balun. It connects a balanced antenna to an unbalanced feedline regardless of its connector type. It uses the technique of removing the unwanted power from the exterior of the feedline. The function of the device is that of a balun. The ARRL Antenna Book calls them baluns for the same reason I do. The Rothammel's Antenna book from the German equivalent of the ARRL (DARC) says the same. BTW, the purpose of a choke is an inductor that passes DC but not AC.

@davecasler 3 года назад

BTW, the term "amateur" in amateur radio is from the English usage at around the turn of the 20th century and means unpaid or done by self-funded people who are nonetheless very good at what they do. Think of "amateur athletes" in the Olympics--for many decades paid athletes were banned from the games.

@thomasmaughan4798 2 года назад

@@davecasler "I stand by my assertion that it is a balun. It connects a balanced antenna to an unbalanced feedline regardless of its connector type." It is not a balun; but it can usually be used where you might prefer a balun. A real balun isolates the ground and each leg of a dipole antenna (for instance) has exactly the same voltage and current distribution as the other. Merely choking the coax does not force the antenna to be balanced. It *does* prevent the coax from becoming part of the antenna system and without it, the center pin sees a different antenna length as compared to the shield connection which sees not only half the dipole but the outer surface of the coax as part of the same conductor. So it achieves a similar purpose. A choke can sometimes resonate with the shield-connected portion of a dipole, and if it is not long enough it is capacitive and this can form a series resonant circuit with the inductor or choke and suddenly you are worse off than before. The antenna current will then prefer to use the shield of the coax. More words abused: "Common Mode". If I had a dollar for every time this phrase was used incorrectly I'd buy a Tesla. Or a nice oscilloscope and some other gear. Common mode means simultaneously induced in two or more conductors. That won't happen with coax.

@PaulaBean 3 года назад

In what way, in your opinion, warrants naming a RF choke a 'balun'? Where in this thing is a unbalanced input (coax) converted to balanced output (dipole wires)?

@davecasler 3 года назад

@PaulaBean 3 года назад

@@davecasler Interesting. In general, could we say that any device which connects a unbalanced feed to an balanced antenna is a balun, regardless of operation or efficiency?

@lindajensen6889 3 года назад

Dave's views are quite a bit different than Callum, DX Commander. Hard to tell which approach to use . . . As in so many topic areas in ham radio, the reader/user doesn't know who to believe and you end up having to figure it all out by experimentation.

@thomasmaughan4798 2 года назад

"In what way, in your opinion, warrants naming a RF choke a 'balun'?" Way too many people do the same thing to try to fix it at this point. But I try anyway.

@thomasmaughan4798 2 года назад

@@lindajensen6889 "As in so many topic areas in ham radio, the reader/user doesn't know who to believe" It often does not matter, until it matters! But yes, the amount of not-really-that-way radio theory overwhelms good science. For instance, you'd think that radio engineers had somehow overlooked the miraculous EFHW for the past 100 years. No, they are extremely difficult to use (1). Then there's a debate whether you need a "counterpoise". Why is there debate? There must be a circuit, some place for the electrons to GO. If you don't provide a counterpoise, guess what? It will use the coax. Oh, you say, but I have a choke! Well, your 200 ohm choke isn't going to do much when the feedpoint impedance is already 4000 ohms. It is absurd to use or think you are using a "balun" with an end-fed antenna. The whole point of a balun is that it is in the exact center of a dipole, hence, "balanced". So you read/listen/study and eventually find a source that is usually correct and hopefully understandable at the same time (an unlikely combination). 1. Difficult EFHW: Extremely frequency specific endpoint impedance. Compare to a dipole that has about 35 ohms (each leg 70 ohms but they are in parallel). A bit "off" on length doesn't change this much. But EFHW is at a "node", a high voltage, low current node. Zero current and infinite voltage, or at least it would be but it radiates and thus does not reach infinite volts. But a few inches of difference and suddenly your 4000 ohm feedpoint impedance and 69 to 1 transformer (also improperly called a "balun") should be 45 to one or something like that. A few more inches, now the correct transformation is 9 to 1.

@eddy2561 3 года назад

OOOPS Dave, a typo? You show an MFJ-17554, it should read MFJ-17754 ..... great stuff as always, 73 k6sdw

@davecasler 3 года назад

Ouch! Good catch!

@Graeme_Lastname 2 месяца назад

I''d really like to know what happens if you got rid of or at least used the least possible length of the short bit of cable feeding between the antenna and balun. 🙂

@davecasler Месяц назад

Well, give it a try! The short piece of cable is a tiny fraction of a wave length.

@Graeme_Lastname Месяц назад

@@davecasler I wish I could but circumstances do not allow. 😭

@pathdoc 3 года назад

Do you know how many ohms it is rated?

@paulhastings3109 3 года назад

With balun at antenna. How would you trim the 20, than 40. Would that not work.

@davecasler 3 года назад

A choke balun does indeed work a little differently on different bands, but you can still tune the 20 and 40 independently on the MFJ-17754.

@davidrimanich5050 3 года назад

What would be the result if you used one one the line & one near the transmitter?

@eddycuypers7621 3 года назад

It is good practice to have one right by the antenna and You can also put one behind the transceiver. That way You can add the attenuation from both chokes.

@davecasler 3 года назад

It probably wouldn't make much difference.

@pipesmokercowboychris 2 года назад

Ok Dave here's an interesting question. What if your antenna has a bulan and still have RF in the shack?

@SteveWithnell 2 года назад

Baluns have to be of the correct design to impact on the common mode. Guanella types are so called "current baluns" and are effective. Voltage baluns don't impact common mode much at all. Further, chokes need to be designed for the frequency of use - a great choke on 80m might be ineffective on 20m and harmful on 6m.

@thomasmaughan4798 2 года назад

The coax IS an antenna even with a choke at the antenna. That is why chokes at both ends are suggested. A hundred watts a few inches from the coax at the antenna end will simply couple into the coax bypassing the choke, at least partly, and depending on how you lay the coax. If it comes down a pole precisely between the legs of the dipole it should be mostly immune from that phenomenon. .

@beekeeper8474 2 года назад

Kenwood ts520 on the top by the sky buddy helicraft?

@modex20 3 года назад

How does VSWR have anything to do with chokes and common mode current?

@davecasler 3 года назад

Yes, common mode current on the outside of the coax can cause the SWR to behave strangely.

@subramanianr7206 3 года назад

@@davecasler No. You are preaching the wrong stuff. SWR and common mode current are two separate phenomena. SWR is due to impedance mismatch at the feed point. Common mode current arises due to 1. Unequal length of the arms of the Dipole 2. One of the arms of the Dipole being closer to the feeder 3. One of the arm's end nearer to the ground (in case of an inverted V configuration) 4. One of the arms of the Dipole has some RF absorbing structures like concrete building, trees or even a bunch of birds sitting on the wire..😁 You should have a clear idea of the two different phenomena before making the video and suggestions.

@kenslimmer5251 2 года назад

@@subramanianr7206 100 % correct. @David Casler, you should edit your video to provide the correct information.

@ve3pcp 3 года назад

It's a choke, not a choke balun. A balun couples unbalanced to balanced feedline. Both end if the choke are unbalanced so it is not a balun, just a choke.

@davecasler 3 года назад

@ve3pcp 3 года назад

@@davecasler We can agree to disagree.

@ve3pcp 3 года назад

@@davecasler I have the exact same choke on my Hustler 4BTV vertical and it is an unbalanced antenna so I guess it can be considered dual purpose if you insist on referring to it as a balun. In the case where I use it, it is simply a choke to stop common mode current on the feedline and is installed at the base of the antenna.

@davecasler 3 года назад

Good point, although I'm surprised that grounding the radials at the antenna wouldn't do the same. My vertical is well grounded (with some buried bare radials and a ground rod) and the shield is again grounded at the station ground just outside my shack. Certainly the MFJ device would work well in your application.

@davecasler 3 года назад

Agreed. Thanks for your continuing interest in my channel.

@twohandsandaradio 2 года назад

Putting the choke at the antenna.... depends on what type of antenna. If you do that to an EFHW that uses the coax as part of the system you just shut down the EFHW. Best advice would be follow the directions and experiment with your type of antenna to what works best....not a one size fits all comment of put it at the antenna.

@peterock8217 3 месяца назад

I tried to use one well its still on, but to my dismay its really not doing anything, all seems the same to me!!! Using a full wave delta loop horizontal, homemade ladder line to a 9:1 unun, to a lightning arrestor grounded to some coax, maybe 5 ft to the radio( rf choke) then the radio. Here's alink to my video with any differences if you can tell!!! Thanks for all you other vids and info!!! Awesome!!! 73's N3WUB

@clems6989 Год назад

While common mode current can effect SWR somewhat. SWR is not an indicator for common mode. Nor vice versa. .

@miker8379 Год назад

Funniest looking Balun I’ve ever seen. Looks like a Unun to me.

@Andy2e0ree 3 года назад

When I did my one I had made a chock 8feet from the antenna and I got 1-1 all bands

@davecasler 3 года назад

That is particularly true at higher frequencies. Neither 40m nor 20m show much loss. The 50' coax is actually RG-213, so it's pretty low loss.

@hotpuppy1 3 года назад

Saw several online priced at around $40. I think a person could build their own for less since MFJ looks like they bought all their parts at the hardware store.

@BurrowsNE 3 года назад

A choke is very simple to build, the basic idea is to use as many wraps as possible. I use random ferrite cores and usually works out fine.

@paulkazjack 2 года назад

Lol!😂

@thomasmaughan4798 2 года назад

if you use ferrites, be aware they are very frequency specific depending on their "mix". Air wound chokes don't have that problem but do take a lot of coax depending on the frequency.

@gooberminther3tik25 2 года назад

OF Course you know an unbalanced Coax feeding any antenna requires the choke at the antenna; and, a balanced antenna with balanced ladder line feed requires a choke at the unbalanced radio, and before the tuner if used. For the benefit of the audience I'll cut it short: The common current return flow on both inner and outer surfaces of the shield must be halted at the feed point of the antenna. That didn't take 14:32 minutes to read. While you speak of your superior grounding, not everyone is so inclined.

@steveschroder8782 3 года назад

Dave, check out ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ExUkjhcCr3Y.html. The author makes the case for putting the choke at the transmitter. Noise reduction is a notable benefit.

@arnecarlsson9740 3 года назад

BALUN implies balanced to/from unbalanced (coax). This is a unbalanced to unbalanced device in other words an UNUN???

@davecasler 3 года назад

Yes and no. It has coax coming out the top, but it's designed to be directly connected to a balanced antenna (the dipole). So it really is a balun.

@eddycuypers7621 3 года назад

You are right, it is an UNUN. It is just a straight piece of coax with two connectors and some beads over the coax. To be a balun. this choke should have a balanced line out, like two bolts, for direct connection to the dipole. This is the wrong choke for a dipole. It looks more like a choke for in between a coax.

@arconeagain 2 года назад

Chasing your tail here. This is because common mode current may give you false SWR readings. So what is the point of this exercise other than to flex some BS ham license/apparent knowledge?

@BulletButle 3 года назад

What i conclude is, don't bother to purchase it. It makes no noticable difference. But is it better than ugly balun, just piece of coax wrap around a pvc pipe?

@davecasler 3 года назад

Actually, I think you're right--a simple "ugly" balun does about the same thing. But it takes about 25 feet of coax, and coax is more than a dollar a foot, so the price differential isn't so huge that way.

@SteveWithnell 2 года назад

@@davecasler Nope. An ugly balun does not do the same thing at all. An ugly balun relies on resonance to create the common mode impedance, this makes it a single frequency device. You need ferrite (see K9YC cookbook) to create resistive impedance across a broad range of frequencies. The MFJ choke will have resistive impedance across a frequency range. I haven't a clue about how much and where. The ugly balun will reduce the common mode impedance at some frequencies, making any CM issues worse not better.

@oldbassist60 Год назад

Not sure of the purpose of this presentation in your series of generally good videos but this one misses the point completely. You can't measure CMR choking effectiveness using an SWR meter because you're using a cheap, insensitive directional coupler on an imbalanced system. Check out any of the instructional videos posted by TRX Labs et al, on using the NanoVNA to measure CMRR effectiveness of line chokes. And remember that an antenna presents a complex impedance not a pure resistance as in the lab. If you want to use clip-on beads to help with RX or LF broadcast noise, place a number of them at both the feed point and random points along the line and some at the rig. It may help reduce RX noise, but they make a lousy CM current choke. Want a good choke? Make a 2-core Guanella choke. A W1JR or Reisert choke is ineffective as a true Guanella choke. Just because it's popular doesn't make it good. And, yes, anything will work - somewhat - even a steel bolt.

@carlpoore4691 10 месяцев назад

Better to build one yourself

@paullalli7774 2 года назад

I think this video is just a "filler", doesn't provide specific 'fixes' for a significant problem...product review only. Not a good reason to go buy one. Sorry...