Ham Radio - The Doublet. An old but good multi-band single dipole antenna. Part 1
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- Опубліковано 21 лип 2024
- One of the antennas I've wanted to play with for awhile. In this video, we look at the antenna and it's design, and then my build of the antenna.
In part 2, we'll look at it's performance and try it out on the air.
Link to web site mentioned in the vid:
webclass.org/k5ijb/antennas/Al...
Link to the PDF mentioned:
sp5ppk.waw.pl/wp-content/uplo...
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One of the best antenna we have used, after testing we ended up using this antenna as the ONLY antenna for H.F that is worth our time ( we tested it against other antenna such as multiband verticals and yagi's).
Our feed line goes through an open window directly into the antenna tuner ( avoiding using an external balun ).
At first we were worried the metal frame of the window will interfere, but found out that the effect was not felt at all ( even when we close the window onto the line ), but then again, this is the only spot were the balanced line could " see" metal.
Do try this antenna , it's worth the time.
VK4BYE, VK4DJZ , VK4CPR
Most modern tuners now have a 1:1 current balun that does not do any impedance transformation. A 4:1 balun like the ones that used to be in turner which was a voltage balun was very inefficient unless it was feeding a 200 ohms load. Since the load impedance varies widely in this application, the manufacturers have finally got smart and started using the more efficient 1:1 current balun that maintains efficiency over a wide impedance range and also converts the unbalanced output of the tuner to that of a balanced condition - a win win situation !
My 102 feet doublet with 4:1 balun is the best antenna I ever used for sure... Cant believe have many years I messed about with every other antenna going until i tried it out...
This is the optimal antenna for my 5 watt G1M. I fussed around with EFWH, bought Times Microwave RG8X coax and made an "improved" 49:1 balun. But really, ladder line is the way. I use an Em-Tech ZM2 tuner which is also light weight if a bit bulky.
To make mine portable, I built it around a wire wrapper and used really tight fitting banana plugs to make the feed line pack easier. I put it up with a TacMini fiber glass pole (17 feet) and run as inverted Vee.
I wish I could have made it a folded dipole but that just wouldn't be compact enough for a back pack already stuffed with other crap for camping.
Grateful for this video as it helped me get motivated.
I made a doublet by splitting speaker cord into a doublet and using the non-split speaker line as a balanced feedline. I made it on field day 2019 in about 30 minutes and used it to operate using QRP power. What fun that was. I heartily endorse the doublet!
Dude I’m a software engineer and this is so intimidating to me. It’s a pleasure seeing you explain seemingly complex concepts in clear and easy to understand ways.
Kevin is right about the benefits of a doublet. I used one from a 2nd story apartment in Seattle for a few years. Doublet was 42' long (including the 'end drops'), bare #14 copper wire and used with 20' of homebrew open wire feedline. This I connected to a homebrew 'Z-Match' tuner on my bench. Coax was maybe 2' long. The doublet ran kitty-corner from living room to bedroom and dropped down vertically maybe 6' on each end. I worked all over the states and the world- from an apartment, using QRP. I could opeerate on 40 no problem, and even on 80 but had to retune the Z match whenever I moved more than a few KHz. lol. Worked all bands from 80 to 10. And not with a shiny new rig.. it was my Heath SB-101. Haha. Nice vid Kevin. Thanks OM & 73
Cool! That's what makes ham radio fun!
How did you hang the antenna if I may ask? Apartment dweller here, 11th floor, but I think the neighbors downstairs would see my wire hanging if I just hang them from the balcony hehe Thanks!
Great video Kevin - I am a long term fan and user of the simple doublet. It knocks spots off 9:1 random wires in both receive (S/N) and RF radiation. Doublets also work well as long as the length is at least 3/8 wave of the lowest frequency. So 50 ft is ok for 40m and up and 100ft should be fine for 80m and up. The ladderline can also feed into the tuner via a 1:1 current balun if the ATU is not a balanced tuner. The trick here is to keep the coax between balun and ATU as short as possible - less than 10 feet is ideal.
I've been looking forward to this video. I always enjoy these videos and I always learn something and usually quite a bit (mostly limited by my old brain's ability to store new information). I particularly appreciate these technical videos with links to curated articles that keep me from doing the work to search for good articles on my own. That PDF is a keeper. I saved it in my ham info folder. Looking forward to Part 2 for the operation and performance of your doublet antenna and the 700mW CW transceiver.
Something I’ve seen suggested in bringing window line inside through a wall is to attach each side of the window line to the center conductors of two lengths of coax, then bring the two lengths of coax indoors, leaving the shield unconnected. This will keep the feed balanced yet shielded. Also, IIRC, there used to be a form of _”shielded twinlead”_ that might also work.
*73 de AF6AS*
Yes I made one of these a few years ago, 110 ft long, and it worked well, out performed a 40-80 trap dipole....from Fred in England.
Agree Fred ... I’ve got my 100ft doublet up an average of 15 feet and for 500 miles on 80 and 1,000 miles to 3,000 on 40 it does v well.
Best video I’ve seen on the doublet yet. Very clear and to the point. Thanks!
I use a doublet of ~ 2x12 meters and a tuner, works fine on 160m to 10m.
From the tuner i run double coax through the wall and then window line to the antenna.
The double coax has center wire as "ladder line", braids connected to each other at ends but not to ground!
If there was anything that Leroy B Cebik (SK) didn't know about antennas, it wasn't worth knowing.
Great video Kevin - I like your all your videos as they are very well introduced and explained.
Many, may moons ago, my Elmer talked about the value of Ladder Line and I dismissed its use because it was ugly/messy/sightly and old fashion. I did use it on occasions but was never an enthusiast.
Kevin's presentation and his references shows that I should look for ways to utilize Ladder/Open Lines and it should be foundational especially when operating QRP.
The difference in line loss between coax and ladder line when an SWR is present is amazing.
Another great presentation of practical know-how and experience, with test results, from Kevin.
ThankYou Sir....
Thanks Kevin, I have been using a doublet about 115 feet long since 2016 and have an outdoor remote tuner (with NO balun) that can tune from 80 through 6 meters even though the tuner is not specified for 6 meters. The wire is just THHN house wire with the insulation on. That does lower the velocity factor a little so that helps with the lower frequencies some. Oh, and I just use some 300 ohm TV twin lead to feed it since I bought out a Radio Shack store when they closed and were selling 100 foot rolls for one dollar. The trick to using a tuner without a balun is to float the tuner at RF so it is NOT grounded at RF (It IS grounded at DC). The tuner I am using is an SGC-239 which is NOT an outdoor tuner, but I added my own waterproof NEMA 4 enclosure. I know the loss from the 300 ohm line is greater than the 400 ohm window line, but it is what I had. I may replace it one day or try some 300 ohm window line which is available. I wanted to thank you for this video since I have found it hard to convince people that an antenna can radiate just fine and NOT be resonant. I have been watching your videos at night on my ROKU box for some time, but there is no way to subscribe or like so I finally decided to get on the computer and do both! Keep it up, this is one of the best things I watch anywhere.
How does this, "floating" effect noise floor and what about the risk of lightening strikes?
@@Justin-bd2dg Affordable automatic tuners are susceptible to lightning, even miles away. Reason: It's all active circuitry, only as reliable as the input protection circuit(s), which are skimpy for hobby-quality devices. Mil-spec is another world, $$$... Many I know have the opinion that there is no real protection against a direct strike anyway.... except disconnecting everything, but how do you disconnect a remote tuner from the antenna (conveniently, that is)?
@@avt3216 I'm using lightning arrestors, I don't see how, if wired properly, they wouldn't work? You are providing a shorter path to the ground than the radio?
All good practical stuff Kevin,have been using this antenna for some time with good results,I am now looking at the same antenna build (slightly shorter!)but in the vertical direction as an experiment using a pole with the antenna center fed and window line,should be good fun!
Good vid but SWR causes loss in coax primarily because of higher voltage across the dielectric at the standing wave anti-nodes, and increased current in the conductors at the nodes. Current on the outside of the shield is a separate issue entirely.
Really great antenna. I would recommend that you add a slight twist to the window line, about 1/2 turn per foot seemed to work well for me. It keeps the window line from catching the wind.
Good video. I have only 55ft of horizontal run space on my townhouse roof. I set up a doublet 50 ft horizontal run with ends zigzagged to fit for a total of 105ft. It is fed with about 20ft of ladder line to a 4-1 Balun attached to an LDG remote tuner followed by 100ft coax to the rig. It tunes 80 to 6 m. Tom kp2ch
I have used a doublet fed with ladder line and still do. The advantages I’ve seen are, it’s cheap, it’s easy, and it works very well on every band. The only disadvantage I’ve noticed is it would be impossible to use mobile in motion. Using it from a stationary RV however, would be a different matter entirely. 🙂
If only I had the space. I might get all of a 30' doublet up, maybe 20 high. Not too high or the wrath of the HOA falls on my head. That's why I usually keep it mobile or portable. You video inspires me to try a portable antenna setup for pic-nic parks and such. Maybe I'll try that. You make good videos and I try to see ever one of them. So, keep them coming.
Thanks for sharing. Antennas are always so much fun. Never ending story 😉
Kinda reminds me of the old TV antennas and twin-lead. When we went to coax we had to have a (balun?) to connect to the antenna screws on the TV. I know, that was (I think) 300 ohm twin-lead and 75 ohm coax, but basically the same principle.
Good video explaining theory with references. Thanks a lot sir.
I believe this antenna it’s a better fit for my living area than that end fed. I watched both vids, end fed and doublet and this one seems to fit my situation better since I don’t have to add any counter poise wires. I live on the second floor and there are two tress right in front of my balcony that I can fits a 40 m doublet perfectly. It’s around 70 feet’s between the trees. The middle of the antenna would be right in front of the balcony. I can get away with a short feed line since I’m going to be using the radio from the living room. My only issue is bringing the feed line inside since my door is metal. Or maybe I can use the radio out in the balcony on a small table if I can’t find a way to bring the feed line inside without getting it close the metal door.
I have a ~120 dipole up feed with 450 window line which technicanally means I have a doublet. I terminate the window line with an external balun at 9:1 ratio. It works quite well.
Hi Kevin...yep, window line and a balanced tuner is the way to go for multi-band. I have won quite a few local EU contests with a doublet (and double extended zep with 5/8 each leg on band of choice). In very simple terms it’s a case of getting 90W+ radiated (out of 100W) vs (as low as) 10W radiated with a good quality ‘lossy’ coax system.....
What I have found in my experience with 450 ohm ladder line is that it's okay to go directly across, for example, a metal window frame for a sliding window, but not okay to run it parallel but very close to, for example, an aluminum gutter on your house. The idea is that any metal near the feedline runs the risk of creating an imbalance in an otherwise balanced feedline. Where your metal object encounters the feedline is where the risk of introducing an imbalance is greatest. But, as long as the effect of the metal object is essentially equal to both sides of the feedline - like when you run it across a window frame at 90 degrees, the effect to the balance of the feedline is minimal. On the other hand, when running alongside and parallel to another conductor, like an aluminum gutter or tower support, where one side of the feedline is closer to the conductor than the other, the imbalance is far more pronounced and problematic. This is why I prefer my fiberglass portable masts when using ladder line and my aluminum portable masts when using coax.
Another nice thing about using ladder line is that it is very lightweight and is easily suspended between two supports when feeding a center fed wire antenna, like a doublet. And, I like using a doublet and a tuner because it also makes shortwave listening on non-amateur frequencies more effective.
Thanks, for the video!
73
AI4IJ
Great video and explanations! You did a very good job of explaining it in "laymans terms" Thanks for sharing it with us. Have you considered a video on off-center fed resonant dipoles? There are a lot of people talking about them. 73 & 72 de K7RMJ Frank
A doublet is the best thing for me so far... vertical antennas work so poorly in the desert, the only alternative is a good horizontal. I've determined the performance difference using the fine analytics suite from SOTAbeams, specifically the "simultaneous spots" feature that eliminates time-variability in WSPR spots when testing one antenna against another.
Very enjoyable i am going to build one for Shortwave listening.🐻🤗👍
20 years ago I bought a antenna called an "All Bander". The reason I didn't build it was because I couldn't buy the material as cheap. It included 100 ft of 450ohm ladder line feed line, even insulators and rope on each end. The cost back then $29.95 and after i realized what a deal this was I ordered a 2nd one. I run this antenna everyday mostly on 75m ssb phone and it is a tiger. I run the 450 line all the way into my basement shack to a Palstar 4kAT tuner. It included a 1-1 balun and has been up 20 years with no trouble. I did make stand offs coming down my Rohn 45g tower about 2ft from the tower spaced every 10 ft and twisted the line several times on the way down the tower to prevent catching the wind and keeping it stiff. BTW the 2nd antenna is still in the package safely stored away.
Very interesting , I am a great believer in parallel feed line. Most of my ham friends think coax is the only way. I have a G5RV that makes use of this principal. This video makes it make sense. Thanks. David Byrd KN4BHS
Used the G5RV for years , yet the full doublet ( 450 line to the matcher ) made a BIG difference as it is a real multi band antenna .
Maybe convert to a doublet... I did, there's no comparison, the doublet is way more efficient, and truly all-band (you may have to trim the length of the feeder to make one troublesome band match OK).
Mate, every type of G5RV style antenna doublet, is without out exception the most deat antenna I have ever tried
Great Antenna Set up!!
I realize this video is old but I really would like to encourage any viewers to try a doublet antenna. I use a total of 102-feet (51 per side) with 450-Ohm window-line and I have never had a better dipole antenna and it just blows away anything I've done with coax. Now, as far as going through walls with window line: My house has stucco that is attached by a continuous layer of chicken-wire. All I did was part away the chicken wire (as best I could) and run the window-line through the wall (once it exits the wall, I droop it down for a rain-drip) to 2 female banana-jacks that are mounted on a piece of polycarbonate plate. so that either a short jumper of window-line (which then runs to the tuner) is plugged in or, a pair of heavy wires that are hooked to ground--both of these have male-plugs on them. I swept the line with a TDR and SWR and there was no effect with the chicken wire; this is because the window-line runs perpendicular to the chicken-wire.
So, don't let people telling you horror-stories of running balanced line--it is so much more tolerant than is let-on. I will never go back to coax for this type of antenna ever again!
The performance is just astounding! BTW: I use a 4:1 balun and this works with both manual (link-coupled) and auto-tuners on all bands 80-10 meters. Please try it!
I love these. I have Brian's 'True Ladder Line' doublet in 'flat top' configuration.. 125' long. Each leg is a solid wire, no solder points what ever. 600 ohm feed through an Array Solutions surge unit and then directly through the window frame and onto the tuner! Only 2 coax jumpers of 15" between the radio and amp to the tuner. Yes, 450 ohm is window line and NOT ladder line. Many get these two feed lines mis-labeled.
Words. We all know what is meant.
@@rikoski Are you kidding? The difference matters!
I had one of these years ago. It was great for all bands. I cut my ladder line down by the shack and installed RCA jacks. I built a 1', 2', 4', 8' piece of ladder line. By experiment I found the right length to match 50 ohms for almost every band. I used a 1:1 current balun and short coax to the tuner, but often it could stay in bypass. Maybe if you have enough extra ladder line you could do a similar experiment for the channel. The ladder line acts as an auto transformer. Unfortunately, I didn't have any suitable test gear at the time to record quantitative data. I just know it worked a treat up to legal limit! Thanks for your videos and keep up the good work OM.
I have this antenna also (260ft). Do you think your would work for 160m to 6m with out an external tuner?
@@barretto4152 probably wouldn't be a problem. Hardest part is finding the magic feed line length for each band and remember to plug in the right sections each time. Takes some trial and error.
O you have to change it out for every band. I think I'll stick with the manual tuner I'm using . Thanks
Excellent video! This gives me some great ideas for my next antennas project. I am looking forward to your testing results. Is the Balun a current or voltage Bain or does that matter? Thank you , Harvey K5NR
Current type.
I HAVE MADE ONE RESONANT AND WITH GAIN.......THANKS FOR YOUR EPLANATIONS
Im looking to build a doublet that will work best on 160 and 80
You can save money by substituting the ladder line for 300 ohm flat twin lead TV antenna wire, if you can find it.
Good Info , Joe KM6MNS!
Are you concerned about the strain placed on the UHF connector on the RV from the feed line weight and wind load?
I addressed that in the video. I pointed out that this is just an experimental set up and won't be up for long like this.
However, we did have one heck of a wind storm and it survived so far.
i saw doublet like these but one side 11.7m and 2.5m other side and feedline is 7.4m ladder line to short coax
That's an off center fed dipole and won't have the advantage of low loss on the feed line. In fact, being asymmetrical, it will radiate off the feed line.
The doublet is symmetrical, a completely balanced system.
Kevin, as you know I am quite limited on what I can do antenna-wise. I do like the outdoor balun idea. What considerations are there for the ladder line as far how it's run to the antenna? Keep it clear of as much as possible. My gut says it won't do well strunk at or near the ground (which is what I would need to do to keep things out of sight. My shack is in the front of the house, I have some antenna space in the back yard.
--- Joel
Hi Joel, The ladder line should be kept in the clear as much as possible, and avoid running it parallel and close to anything metal.
It's the best performing single dipole I've ever used. If you can get one up, you'll probably love it.
Internal tuner in radio won't handle anything over swr of 3.5.. adding the 4:1 balun will correct this??
Maybe, maybe not. It depends on what the impedance present is at the specific frequency your operating on at the time. What the 4 to 1 balun will do, is bring the high impedance has down closer to 50 ohms, giving a tuner less work to do in many cases. The impedance on this antenna it's going to be all over the place on different frequencies.
Great video! My brother just made one very similar to yours and with the same feed line. I agree.... it worked very well on all the hf bands and now I am thinking of doing the same. Thanks! Btw.... where is that neat vacation spot? Looks like a Nevada or California desert.
South West Arizona.
Loss is = impedance times current SQUARED (plus resistive loss) so the higher the impedance the lower the current (at the same power) so the higher the transmission line impedance (of any kind) the lower the losses and for no other reason.
50 Ohm parallel feedline has about the same loss as 50 Ohm coax.
600 Ohm parallel feedline has less loss than 450 Ohm parallel feedline.
Ron W4BIN
What happens to all those ohms when impedence is transformed from 450 ohm to 50 ohm? On an end fed half wave antenna the mismatch can be around 3 thousand ohms! What happens to all those ohms when they pass through a 49:1 match box?
You cleverly answered your own question..... the impedances match.
Hello Kevin,
Concerning @ 13:00 about standing waves on coax, would those not be knocked down by an Ugly balun, and/or a string of ferrite chokes on the coax?
Secondly, if you had a much firmer center point, heavy pole, tower or tree, would it be better to mount the remote match at the center feed point, then run the coax to the rig?
Thanks &
73 - John - N7GHZ
Sure, making the loss even higher.
Toroid: Only if you chose the correct toroid mix and number of turns. Ugly balun: Not likely, unless you characterize it. In general: Adding a random inductance can make matters worse. Consider you're choking common mode currents on a feeder to a load that's capacitive.... you've just tuned the feeder to pass common mode current *better*.
An rf choke is for common mode current on braid of coax, swr does not travel on braid of coax as incorrectly mentioned in the video
Great explanation of this antenna. What would the losses be like (table 2) with say 40 feet of ladder and 4:1 balun and 100 ft quality co-ax? Glad you covered the main disadvantage with the doublet - the shack needs to be near the centre; can't trail ladder through bushes/trees/outbuildings/along the ground, etc. (That's why the not-very-good G5RV is popular I guess),
My doublet is 19.5m+19.5m at 9m high with 9m 600 ohm ladder, 4:1 voltage balun followed by a ferrite-sleeve coke balun, with 30m RG213 coax to the ATU in the shack. (This doublet antenna with the voltage balun at the base of the ladder feeding the coax to the shack is also known as the 'comudipole' in case anyone wants to do some additional research.)
How significant is the balun core material? I'm using T200 iron dust. Looks like you're using ferrite. Thanks.
Janet Winslow iron dust cores are not great as choke baluns, ferrite of the right mix is far more suitable, I use FT240-31 or FT240-43 cores with great success.
Great video. The link to the PDF now comes back “file not found”. Could you post it somewhere?
Thanks, I found it elsewhere and updated the link.
sp5ppk.waw.pl/wp-content/uploads/2018/08/MultibandCenterfedZepp.pdf
I'm interested. Where did you get that feed line? It looks a lot easier to manage that ladder line.
DX(pensive)engineering. :-)
My Palstar AT2K has an external 4 to 1 balun. I have 25 feet of coax to the balun, then ladder line after that to a loop. I assume the 25 foot of coax is seeing a big loss on high mismatch? I had thought about hooking the balun directly to the back of the tuner, but as you said running ladder line in the house is problematic.
One trick I ran across was making a parallel feeder by using two pieces of coax. Short the shields at both ends together, but do not connect them to anything else. Then use the center conductors as your feeder. The isolation of the shields makes it more forgiving for passing over or along metal.
@@loughkb I will keep that in my memory bank. That plus each coax spaced apart in a separate 1/2 inch pvc conduit might work great. I would just match the spacing of my home made ladder line. ( around 3.5 to 4 inches apart ). Attach them to the floor joists down stairs and out to the wall to my existing ladder line. Thanks.
@@loughkb EXCELLENT TRICK!
Is the window line feeder dangerous to be near or is it only dangerous when attached to the horizontal dipole wires?
No. Since it's a balanced feedline, the field around it should be weak.
@@loughkb okay great, thanks for confirming that. It helps in planning where to put it.👍
Keen on part 2, is it posted yet ?
In a couple of days.
Thanks Kevin. Great video. You are an expert in making complex things understandable. I always used windowline or open wire for my antenas. My hor loop skywire is still up at home QTH since 1995. I will certainly try out the Doublet as you described in our vacation house. I have a Spiderbeam pole over there (40feet ) and plan on doing as you did. Just a question: how high is the feedpoint on the mast ? And what is the lowest the antenna gets groundlevel ?
Many tnx again and good dx ! 73 de Ronald, ON4BBQ / N2YCQ,
Hi Ron, the doublet is on an MGS 30 foot mast. The ends slope down to about 6 feet off the ground.
Tnx Kevin ! 73 !
I may have missed it but nobody addresses grounding this thing! Summer thunderboomers are a fact of life here so I would probably go w/ the balun outside the house to stick my ground into the section of coax from balun to tuner.
Is the balun a current or voltage ?
Current.
Bless the guy who always votes your videos down
I can't decide if its because it adds a bit of strange character, or if its just base funny
You Kevin!:
As usual GREAT video! Taught me a bit more about antennas! I am of the opinion that the length of open ladder line DOES matter. Just me & my opinion. You know of my interest in 160 mtrs right? Would a 4:1 or 9:1 Baluns help load up my G5RV (dipole) on my aut6 tuner that covers 80-10 mtrs?
Great video, can't wait for the 700mw video!
73's!
de seeker/Jeff WA7LFP
I thought that it did, Spent a lot of time researching looking for a specific length. No suggestions in any of the articles covering the "Dipole Doublet."
Kevin, I’ve been reading on line that an automatic tuner such as a LDG will not work on a doublet. If my memory serves me that is the tuner you are using. My thoughts are that if you feed the doublet through a short coax and a 4:1 BALUN it shouldn’t have any problem. Keep the videos coming, very informative. 73.
I think that using an external 4/1 balun fixes that alleged problem.
What about the balanced ATU , no balun required , less loss ! Thanks for putting up your film. Carl.
boxingday11 Some very clever balanced ATUs have been built but mostly by people who have not thought about the problem.
I have a Double Extended Zepp Antenna each leg is 0,64 wavelenght so since it is optimized for 80m band its a fairly long 328 feet or 100m. This antenna works great on all bands from 160 - 10m. Feed it with ladderline to my MFJ Tuner. So you should do fine with your antenna Kevin. Unfortunatle I have it in my summer house so no room for this antenna at my home in Söderhamn since I live in apartment. Thanks for your videos. 73 de sm3uwz/Lars
Is your Double Extended Zepp collinear? (the two legs fed in phase) If so, how did you do the phasing?
No its fed like a dipole.
What gage copper wire do you use coated or uncoated?
It doesn't matter very much really, but I'm using 14ga solid wire with a jacket on it.
Thanks.
very good. 73 - VA2SOB CLAUDE (stupid me I bought one already done but I like that manufacturer)
Isn´t it necessary to use a 1:1 Current-Balun when you want to use a Doublet Antenna as a Multiband-Version?
No. It must be a current balun, and you can use a 1:1 if you want. The impedance is going to vary quite a bit depending on frequency, but will usually be quite high. A 4:1 will bring it down a bit so the tuner has less of a mismatch to deal with, resulting in less loss in the tuner.
@@loughkb thank you very much for your answer. So I can use it for my new antenna system. 73 de Mike....
This was really interesting. As a newbie/returner I need to learn whether power I save by using a doublet will be lost at the ATU. Is ATU loss going to be less than co-axial loss?
Loss in the transmatch depends on the degree of mismatch it's dealing with. Higher mismatch, more loss.
@@loughkb That follows, I see the logic. Thanks Kevin.
@@acestudioscouk-Ace-G0ACE any reflected power loss is due to feeder attenuation not the tuner absorbing power as its reflected back to the antenna at the tuner with no loss at the reflection point
@@Pioneer936 Thanks Paul, I thought wherever you have a coil, you have a loss, however small. Thanks for putting me right.
@@acestudioscouk-Ace-G0ACE the book reflections by Walt Maxwell explains this subject in detail
Good video. I always learn something from you.
I have a MFJ 1778 G5RV. It's a 102 foot dipole which matches the design of your doublet, except it is slightly shorter, and the length of the ladder line makes it balanced, giving 50 ohms at the coax connection point. I've read that the ladder line is part of the antenna, so it's specific length (32.6 feet) gives it the 50 ohm balance.
So from your video I gather that extending the ladder line makes the antenna unbalanced again. Is the 102 feet length too short to convert this to a doublet for 80 meters? This assumes I'd add a balun (my tuner only accepts coax).
Thanks Ed.
In the G5RV, the length of the window line is specific to create a 50 ohm point. It's similar, but not the same design philosophy. I probably should have mentioned it in the video. I'm sure I'm going to get a lot of comments from other people that may confuse the two antennas.
Kevin Loughin Too short to convert to a doublet?
@@edneely No. and it would probably still work ok on 80. But why? Doesn't it work well as it is?
Kevin Loughin It seems to work well, but I have about 100 feet of coax to get it into my house. I wonder how much loss I have. Hard to say.
@@edneely Ed, I generally recommend to anyone who uses a G5RV to cut off the matching section and run ladder line all the way from the center insulator to the tuner. The G5RV has very high SWR on a number of bands so you're losing quite a bit of signal in the coax on those bands due to the mismatch. As noted by the chart in the video, the ladder line will exhibit very low loss under those same conditions.
I am not sure why but somehow the G5RV has, over the years, become somewhat mystical in its abilities. It's actually cheaper to make a doublet than it is to buy a commercially-made G5RV (especially when the cost of a long run of coax to the G5RV is added) and the low loss of the ladder line will allow the doublet to be a better performer on nearly every band.
Great job, but there are lengths that should be avoided depending on which bands you want...
use one myself...its now my goto antenna
This highlights the importance of using good quality coax with a high velocity factor. Excluding the effect of high SWR any decent coax these days should be better than =
Why a 4:1 balun and ot 9:1? Seems to me that 9:1 would get 50 ohms closer to 450 ohms. I must be missing something... 🙄
I think I have that tuner. :) It's 9:1 impedance.
The 450 ohm is for the ladder line itself. The actual ohm the tuner sees or in this case the balun sees will vary from band to band, see the video part comparing coax vs ladder line, the ohms can be as high as 5000 . The 4:1balun in this case is there to interface the ladder line to coax and help the tuner out a little. Note some people recommend a good 1:1 choke aka current balun because as you can see in the chart in video sometimes the ohms can be low on certain freq so stepping down the ohms with a 4:1 or higher would not be desirable since most tuners are more efficient with tuning higher impedances
@@Gabagabe1 thanks... so much to learn
Lol
Man, if you're The "Old" Tech Guy, I'm Methuselah Tech Guy. *lol*
lol I was always thought he was kind of a young tech guy myself
@@mikemcdonald5147 Yeah, he doesn't know old, yet.
Several parts of my body are much older than the calendar says they should be. :-)
@@loughkb haha I know that feeling well LOL
I have not yet read the papers you cite. But my understanding of the thing is different. First: The leader line has such low loss even at high SWR simply because it has very low dielectric loss. The dielectric of leader line is basically air and air has low dielectric loss. That is why low loss coax usually comes with foam dielectric.
The feed line will actually radiate some power. The G5RV and its derivatives like the ZS6BKW uses a similar "trick" when used on a non resonant frequency of the dipole part. These antennas just try to keep the dimensions in a ratio so that multiple resonant frequencies occur across the dimensions of the dipole and feeder combination. Hence they are usable without tuner on these frequencies.
So this antenna is just simply plain a non resonant dipole, forced to match the impedance of the TRX by a tuner. The bad SWR will cause high losses on the feed line, which is mitigated by using a very low loss feed line, i.e. leader line.
You can get about the same by placing the tuner right at the feed point of the dipole without any leader line. But this is inconvenient as you need a weather proof, remote controlled tuner.
Read the papers. They're an easy read and clear a few things up.
Kevin where did you get your 60 ft. Mast?
When done properly the open-wire/ladder line does not radiate, this is a strange but popular myth, the G5RV and derivatives use the line as a matching section. Unfortunately often without any effort to reduce common mode current.
There is merit in carefully choosing the length of a doublet to avoid wildly high impedances at the feedpoint.
@@g0fvt Yes. After putting some more more brain cells into the problem I agree that the ladder line should not radiate. Common mode current is still a problem. That's why you should put a common mode choke or balun at the feed end of the ladder line. Not to match impedance, but to suppress common mode current. If there is a suitable antenna tuner at the feed end of the ladder line it also suppress common mode current. I read recommendations to add a common mode choke or balun to a G5RV or ZS6BKW. I did such a modification to a G4RV but I still have to test it.
@@56932982 it has to be said that the baluns incorporated in many tuners are not very good, since the impedance of the doublet can be all over the place I have decided not to use an impedance transforming balun. Most ATUs struggle with very low impedance loads, and are more efficient with higher Z so I am using just a common mode choke "1:1" the ATU will not flash over readily (7kV capacitors). It is handy to have an HF antenna that is compact and versatile, I have no interest in HF beams at present. VHF though is a different matter..
Re watching this it tells me that if your antenna is resonant good coax can match 450ohm window. But if you're using a single wire multi band, window can't be beat unless you ran coax with the tuner at the feed point. That's going to look funny.
So why doesn't everyone use ladder line as a feed to center fed antennas? Because there are some problems with keeping it truly balanced and therefore display it's good side. First, it hates anything that upsets it's balance. Like rain, dew, or snow. Or any metal nearby to it. Second, it is hard to verify the balance condition- no simple device like an SWR bridge in the case of coax. It was these problems that led hams to so readily adopt coax feed, since coax does not have these problems.
K0MB
Although the issues you mention are certainly possible, they pose much less of a problem than one might think. I've used ladder line with a number of antennae for years with no ill effects. As long as the ladder line crosses metal at at 90 degree angle and/or for only short distances the effect is negligible. In fact, I run it into the eave of my roof (near some aluminum siding) all the way into my shack. If the feeder were to become unbalanced I would notice RF getting into nearby devices - something I've never noted. As far as rain or ice is concerned, their impact can be alleviated by using true ladder line (parallel wires with plastic or other non-conducting standoffs between them) as opposed to window line which can 'bridge' rain or ice between the wires.
I was convinced for many years that ladder line was just about useless because of the many stories I'd heard about it. However, once I began to use it I realized that the problems I had heard were very much the exception rather than the rule. In any case, I think the ladder line vs. coax decision comes down to one thing - how much loss is a person willing to tolerate? If the antenna is constructed such that it presents a 50 Ohm impedance (or nearly so) at the desired frequency, then using coax is fine. If, however, the antenna impedance is significantly higher or lower than 50 Ohms, then the use of a balanced feedline will provide significantly improved performance because of its low loss.
@@BrianEsche I used window wire as feedline for about 30 yrs when I lived in the dry climate of the Colorado high desert and was quite happy with it's performance. But about 12 yrs ago we moved to central PA, where the more frequent precipitation has rendered the window wire feeds unusable much of the time. I now include the OCD in my arsenal of wires for wet-weather use.
The ARRL antenna book shows a simple way to measure imbalance: Couple a field strength meter to a ferrite toroid with a few turns of wire through the center, then put the ladder line through the toroid. You at least get a relative balance reading, so you can change the one leg length or positioning to get a (better) balance. My take is that yes, the feed line will radiate a little because the antenna is going to be a little imbalanced.... but so what? Nobody expects a perfect pattern!
Like Jamie Smith said earlier, why 4:1 instead of 9:1?
astrorad2000 it doesn't matter much, it just gets the impedance in the right ball park. Note that most 9:1 are ununs. Note the balun used here has two cores wound seperately, many 4:1 baluns are poor designs and don't address common mode current. The baluns in nearly all commercial antenna tuners are junk too. An open wire fed doublet is a great versatile antenna if done right.
@@g0fvt Thank you for the info. I forgot that this is a balanced antenna. It will be nice to see the results of Kevin's testing it out. Bill, WB9NYI
@@astrorad2000 I use a current balun to do similar. The doublet was extremely popular in the past, but the popular use of coax has driven us to antennas that are close to 50 ohms. The issues with the baluns built into most ATUs is that they have some phase shift between the windings and the legs of the feeder are not driven quite 180 degrees apart. They are also voltage baluns so the current in each leg is not automatically going to be equal and opposite leading to feeder radiation and possibly issues with RF in the shack. The object of the two core 4:1 baluns is that they behave as a common mode choke forcing the current in each leg to be equal and opposite.
Wrong! The length of the feedline is critical.
One thing I can never understand is why when you measure wavelength in metric people insist on using feet for antenna dimensions.
To be honest I don't really care which system of measurement I use (I'm british, we use both all the time anyway) but it's much easier to stick with one! As ham bands are defined in metric wavelength I have only ever played with antennas in metric
Ever tried to buy a metric tape measure? Or a metric ruler?
@@avt3216 try buying any tape measure here that dosn't have both?
Got some ideas from here Kevin... 73 de ThReeZa DW3TRZ Mabuhay PHILIPPINES
Heh. You made the same mistake they made on the Today Show: your Earth rotates the wrong direction in your opening. :-) But the video is cool!
I knew that when I found the animation. I left it that way for two reasons. One, it sort of fit the old time look of the opener. (They often made mistakes like that in the past) And two, I was curious to see how many people would notice and point that out. You're only the second one in three years. :-)
Yo!
8:28 You said that the coax between the tuner and the radio needs to be short due to the high SWR. I think this is a blooper. Between the radio and the tuner will be matched to 50 ohms at 1.1:1 SWR, or as close as you can get to it. I think you were thinking about is where you run the window line from the antenna and into a 4:1 balun and then use a short piece of coax to bring the coax into the camper to the back of the tuner. That short piece of coax will have high SWR. Once the tuner tunes it, the SWR from the tuner to the radio will be really low.
ua-cam.com/video/tLMAStiaAxU/v-deo.html
Nano vna setup