Success! 20m and 40m on same element - Amazing Result!

[@Capt_Duffy]

Hi Cal, I just wanted to share my recent experience. After watching your video on the short 40m vertical, I decided to erect one using whatever materials were readily available to me. I had a bamboo mast of around 20ft, so I built the antenna with a center loading coil using 17ft of the mast. I increased the turns and made it resonant at 7.1 MHz, but the bandwidth was slightly low due to the coil. I wanted to avoid linear loading due to mechanical issues, so I conducted an experiment and installed three piano strings in the shape of a flower to create a capacitance hat. This dramatically reduced the resonance well below 5.6 MHz, and to make it resonant again, I gradually reduced the number of turns on the coil until it was almost half the original amount. The bandwidth is now fine, almost 1.5 all over the band, and the efficiency appears to be better, as noticed by FT8. I just wanted to share this experience.

[@DXCommanderHQ]

Beautiful!!

[@Superacerc]

Fantastic experiments Cal! I did my first park activation with the dx commander yesterday. Did a loop on the ground with an ldg 4:1 balun out of 20ft of wire as well in my icom 756 pro II receive antenna port. Dead silent receive and great signal reports using about 40w from the dx commander. Absolutely loving it!

[@DXCommanderHQ]

Fabulous! Don't forget an eHam review :)

[@Superacerc]

@@DXCommanderHQ qsl cal. Will do

[@mully89]

This is what I love about your channel Cal instead of selling snake 🐍 oil you are happy to do honest real world comparisons, fair play brother 👏

[@DXCommanderHQ]

I appreciate that!

[@skinnyflea2628]

This was interesting! About a year ago I accidentally ended up making one similar. I was trying to load a vertical on 40, but only had a 20ft mast. I remember scanning it with my SWR meter and being confused on how I managed to get both resonant! This explains it some more! Thanks!

[@DXCommanderHQ]

Amazing.. There's a few of us that have stumbled across this.. Thinking about it, I can start to understand what's going on - but it took me a while!

[@T.M.G2014]

yes i think these should be manufactured and shipped in little dx commander pull string bags with logo, very handy for a quick activation use , and to have various ones made up of course a pack could be sold with 6.5m dxc pole included or sell them individually , prices would be reflected on the manufacture and branding costs then varied price with pole and wire combos or individual added on top

[@johnnorth9355]

I have been messing with coils for months - sometimes with good effect and sometimes not so much. My excuse - no science involved just trial and error. Now I feel much less like a wizard stirring the pot !

[@SteveBrace]

Thanks for all your hard work Cal... An off-topic question though: Now that this solar cycle enables fantastic propagation, how do we gently persuade Italian and other KW+ stations to turn it the F down?!!

[@DXCommanderHQ]

Good question Steve.. Some of our Italian friends are fabulous operators with top-notch gear. Others seem to have missed the class when we discussed etiquette and operating styles!

[@tincanblower]

Looking forward to watching this properly later. Thanks for all your hard work Cal. I might email you with an idea of something to model - it's been in my head for years! 73, Matt M0PTO

[@davidportch8837]

that's great Callam... I love your generousity in sharing all of this with us... what other manufacturer would say things like... you can build this yourself if you wish... Dave KPZ

[@DXCommanderHQ]

Well, I suppose so.. Thing is, very often people make the stuff - then come to us for the genuine kit - so pointless really making it all secret. It's jolly good fun!

[@corradoQC]

I would have liked to see how you add coils on traps in MMANA.

[@DXCommanderHQ]

There's a screenshot at exactly this time-stamp: kzbin.info/www/bejne/a6PXXmxnnpKKqNE - check the "Use Loads" button and place your coil as you would a source and your inductor value in the box where I put in 40. Alternatively, watch the previous videos. Or even read the manual for the software.

[@alunroberts1439]

Am going to try this on the back of the work shop roof.

[@pribeiro]

Thanks for sharing your experience with antennas with us! Regards

[@DXCommanderHQ]

My pleasure!

[@chrisbartlett6022]

Interesting. These coils are very useful. Still using my 12.4 as we discussed. Looking forward to what happens with more elements.

[@DXCommanderHQ]

Well, I have got 15 and 10 now working too :)

[@chrisbartlett6022]

@@DXCommanderHQ Thats interesting. So 40, 20, 15 and 10 on a fairly short pole. Bet that will be attractive to quite a plot of folks.

[@DXCommanderHQ]

Basically, it's the "Rapide" with only 3 x elements.

[@FromthehamshackwithNJ4Z]

Great Video Cal and inspired design. You have me thinking of trying this concept on a 80/40 vertical. That might very interesting on a 12m pole. I need to work out some of the maths.

[@DXCommanderHQ]

I think on a 12m pole John, it would work well.. It's like the Signature 12.4 where I do 80 and 30 - but the coil would (I guess) be higher up - around 6-8 feet from the top.

[@JimBobbyJoJo]

Even better if 2 well placed coils could get you 80/40/20 on one wire on the taller poles. Maybe go really crazy and try to sneak a 3rd coil on there to get 10. 4 bands with one wire to string would be a hell of a thing. Doesn't seem like they work as traps so it may be a pipe dream.

[@DXCommanderHQ]

Mark.. OK, so I can't find the "next harmonic" - it's probably up high somewhere.. And too many coils spoils the broth anyway :) !

[@paulsengupta971]

It would be a great experiment! Not sure I'd like to do the maths!

[@MopH3ad]

I've just started building coils for a shorty 80 due to limited space, this idea is excellent

[@DXCommanderHQ]

Yes, watch for the harmonics - then adjust the coil to suit the one you're after.

[@HawesJohn]

This is very intriguing Callum, thanks for sharing. I have tried out short verticals in my /A backyard before. I haven’t tried multi-banding them though, that is handy if you can do it. Yours looks very simple in practice but for me it is rather more complicated to analyse and understand. I have spent a fair bit of time with XNEC2 trying to get your parameters to work with a small radial counterpoise over sommerfield ground but haven't had much luck. So I messed around trying to do something similar from scratch and came up with something that looks like it works in a similar if not the the same way. Two things appeared from my early efforts. Parallel capacity in the inductor (which could be parasitic capacity) has a noticeable effect even if very low (eg 5pF). The self resonance in fact is somewhere in the vicinity quite possibly, so trap-like behaviour can be seen with some higher values of inductance. And if the inductive reactance is much more than the wire surge impedance, it looks like it chokes off the current at those frequencies. And the top loading effect of the fold back is essential. So my redesign adopted top loading to a greater degree with a couple of “T” like elements at the top, although I sloped them down to be like wires running down guys. That is the sort of thing I have tried before. More top loading allows a smaller loading inductance at a higher point than otherwise. Mine ended up as two wires sloping down 1m and out .8m from the top of the 6.5m element. My loading coil is 4.7uH with 5pF to represent a reasonable self capacity. I started with higher inductance and less loading but I think these values are likely to be less fiddly to get working in practice. This gives a super 7MHz response with the current well up the wire like a conventional quarter wave. As you raise the frequency there is a high impedance resonance about 10MHz or so, and then it comes back to a broad match at 20m. There the current looks more like a quarter wave with the top bit acting like a very short half wave with the current swallowed up in the loading inductor. As such I would hope it’ll work as well as yours seems to. Best regards, John G8CQX

[@DXCommanderHQ]

Hello John.. Ah-ha. Very interesting!

[@richarde735]

another great video Cal

[@DXCommanderHQ]

Much appreciated! Thank you.

[@mewrongwayKOCXF]

Awesome Callum!! 👍

[@DXCommanderHQ]

Legend!

[@timgoad5750]

Sir Callum, Would you be kind enough to do a video on how you inserted the coil into the antenna in MMANA software model? I cannot figure out how to do this for a project that I am toying with. Thanks, Tim KA9AMO

[@DXCommanderHQ]

Yes I will.. But for speed.. Go to this video and freeze the v ideo exactly here.. kzbin.info/www/bejne/a6PXXmxnnpKKqNE and check the 40uH box (lower right) and also (important) check the box "Use Loads". Remember to add the coil as you do the source, so if you want a coil half way up element number 1, type in W1C (which means Wire 1, Centre).

[@timgoad5750]

@@DXCommanderHQ many thanks sir.

[@the_mad_swimbaiter455]

First. Nice work! This helped me figure out a problem i was having with a 20/30/40 trapped efhw...thx!

[@DXCommanderHQ]

Glad it helped!

[@the_mad_swimbaiter455]

@@DXCommanderHQ your words and experiments often lead to great insight and understanding in and of our HAM radio hobby, bully to anyone that says otherwise; they're nitwits.

[@ka2rwp]

That's good for limited space crunch it into a coil.

[@DXCommanderHQ]

Yes, I didn't think it would work :) !

[@che59v]

Great Video, as for myself, I rather go with an excellent radiator (no traps, no coils, even non resonating) rather than a having my focus on the great SWR. Antenna tuners never put me off as the loss on them plus the 30m of GOOD quality coax attached is very low, much lower than many hams dare to think.

[@DXCommanderHQ]

Just the coax loss to worry about. Unless you are balanced line. Great.

[@che59v]

@@DXCommanderHQ 100%, and if good coax is used (and the run is relatively small) than problem solved. Thank you for a great video and great products. Thinking and making things keeps any man young.

[@ke8wlw]

Kinda like what the atas does on 40m. If I could make my atas higher off the ground, it'd work even better.

[@W9HJBill]

Nice Cal. Odd question ... since you have 40M will that also give you 15M as a harmonic 40M?

[@DXCommanderHQ]

Bill, when you place a coil in the circuit, the harmonic drops in frequency. Yes of course on the full version, we get 21 from 7. BUT you need to watch the video on End Effect from last week.

[@holgerrudolph8906]

Hi Cal. Vy interesting project, thank you! What about putting this shorter 7m pole on the roof on my small house? That way i could keep it clear of obstacles! This ANT would be smaller than my cushcraft R8!! My question would be: if i had some elevated radials, how much would i need? Or should i rather place some radials right on the roof? Vy 73, Holger, DG7MA

[@DXCommanderHQ]

Radials right on the roof. You are close enough to the ground that they should couple just fine.

[@holgerrudolph8906]

Tks Cal! Vy73

[@Aussie_Ham_Radio]

Interesting what you say about traps and harmonics. It made me wonder if you had a wolf river coil type reversed so the coil was at the top how that would perform. The hard part would be the weight high up.

[@DXCommanderHQ]

I don't know about wolf river.. But its just a coil.. Can't be too hard 😀

[@matthewweaver1123]

Good morning, speaking of possible interaction, when tuning any DX commander in general, does tuning any one band affect the others as well, or do you pretty much just tune them one at a time and not worry that much about it? Hope my wording makes sense. 73 Matt W3MMW

[@DXCommanderHQ]

Matt, Good question. Once all the elements are on, a small change in one will rarely affect any other. When I'm doing my R&D, I only notice a small change when I make drastic length cut or extension to another element.

[@matthewweaver1123]

@@DXCommanderHQ thanks Callum. I'll hopefully be buying one this year, maybe before field day if I'm lucky. Hope to hear you on the air sometime, 73

[@PatAutrey]

So if the coil of 35 uH is at 5.5 meters above the ground, after the coil, how much higher does the antenna wire go up? what is the total height of the wire, and then what length of wire did you foldover - thanks!

[@DXCommanderHQ]

Pat, I can't remember. I haven't measured it out yet.

[@PatAutrey]

@@DXCommanderHQ very curious once you do!

[@DXCommanderHQ]

After the coil, it goes up about 1m - then back down another 80cm - like a foldback.

[@Paul_VK3HN]

So the L loads a 6.5m wire to look like a quarter wave on 40. Surely on 20 it's making it look like a half wave, which would have feed point impedance of a few k ohms. What am I missing? 🤔

[@DXCommanderHQ]

Conventional theory was telling me that too.. Honestly Paulo.. Just build one and slide that coil up and down and watch the harmonic.. I am currently getting 13.8 to 14.6 on a 1.5:1 bandwidth with 50 ohms. The radio thinks it's seeing a 3/4 wave.

[@Paul_VK3HN]

@@DXCommanderHQ Fair enough, if it works it works, I'll try it sometime. Getting a resonant 40 and 20m antenna on a 6.5m pole without links or a tuner is ideal for a portable or SOTA station. Adding additional wires on higher bands would make it a winner.

[@corradoQC]

Yesterday I made a 35uh coil with 50 turns of 1mm enameled wire on a small section of 34mm PVC pipe. The total length is less than 75mm. I found your coil quite long for 35uh.

[@DXCommanderHQ]

You can do the math. 25mm, 135 turns across about 33cm is 33 uH.

[@corradoQC]

@@DXCommanderHQ I'm not doubting the value, I'm just saying if people want a shorter coil 34mm PVC pipe and 1mm enameled wire would do it.

[@DXCommanderHQ]

Yes. Even a 50mm / 2-inch pipe. COrrect - and enamelled wire even less.. I used what I had which is about 2.5mm per turn.

[@fredsiegfried1707]

Do you remember the Super Scanner antenna

[@DXCommanderHQ]

Yes! Interesting concept.

[@75ohmHAM]

Was the Brown marker okay?

[@DXCommanderHQ]

It died :(

[@cfsyoutube5799]

Before you know it you'll have added another half dozen coils and invented the Dxcomander all band cp-6s :-)

[@DXCommanderHQ]

Woops!

[@Trent28888]

On the 40M leg if that was about 5M long u will have 80M so it could be done like a lonked dipole to swap between 40 and 80

[@DXCommanderHQ]

Lonked dipole! Don't worry - I knew what you meant :)

[@genoa1979]

compliment karl :)

[@DXCommanderHQ]

Thanks! 😃

[@1shARyn3]

my calcs show 34 microhenrys -- validates your guess

[@DXCommanderHQ]

Haha - yeah, I checked that this morning just before I launched the video.. I think I saw that too!

[@charlieoscar09]

You will be very lucky to get away with this adding elements without interaction.

[@DXCommanderHQ]

Oh, it will interact, of course - but it'll just be a case of making a couple of adjustments. I mean, it's not like I'm new to this LOL! :)

[@CliveMilton]

Can someone tell me how do I add a coil in mmana please

[@DXCommanderHQ]

Yes. See here: drive.google.com/drive/folders/1dJAOeSnLjk6irT657TSNrunCB0HzLpVX?usp=sharing - Click the "Use Loads" radio button. Place the coil where you want it (in this case, centre of Wire 1 - left of pic "W1C" ) and then put the micro-henrys in the box where mine says 5 (5uH). Take the output with a pinch of salt. Sometimes SWR curves can be more sever (worse) than wanted. In the field they are better.

[@electronics.unmessed]

😎👍

[@bassangler73]

👍

[@edcozart9916]

I've been planning on a Rapide for pota and im liking what i see Callum. I'm going to make this wire and see how it works aginst my mono band wires I have been stringing up in the tree so yes I've been getting out every band i switch but its worth it low SWR now I have something to mess around with 40 and 20 on the same wire😯😯😯 de W9US

[@DXCommanderHQ]

Ed, the Rapide would work for this perfectly. Just use 3 holes / elements and you can operate all bands inside 5 minutes.

[@OCDASDA]

Hi Cal do you give out your email address, i have some questions on the Kenwood TS990S

[@DXCommanderHQ]

Gary, it's on the dxcommander website and also the channel About page.. Happy to receive your email - thanks for letting me know. PS - If I don't reply, just kick me again - something probably went wrong..