3-Band Ham Radio Antenna: StarDuster Off-Centre Feeding Method

I explore how I re-designed the CB / 11m SkyLab StarDuster and made a 15m / 12m and 10m high-gain powerhouse using the technique of off-centre-feeding, I show how I unlocked three-band performance from a single element. Discover how shared radials and element placement can make all the difference for any ham radio setup. Join me as I dive into the science behind off-centre-feeding and learn how to transform your antenna into a multi-band special! Don't miss this exciting episode :) More from this series:
▶️ • The Ultimate CB / 11m ... - The Design
▶️ • Custom SkyLab StarDust... - The "HOLY COW" Build!
More Videos:
▶️ • Antenna Modelling Antenna Modelling
▶️ • Tips and Tricks Tips and Tricks
▶️ • Antennas Antennas
▶️ • Live Streams Live Streams
▶️ • Commander World My Stuff
▶️ • Foundation Training Ham Radio Training

[@Superacerc]

Didn't know that about the tangent curve for off center feeding. Good stuff Cal! I'll keep that in my back pocket for some future builds.

[@DXCommanderHQ]

Well, I don't know for sure - but it makes sense (maybe!)

[@Superacerc]

@@DXCommanderHQ lol. Good enough for govt work. All I need to know is the swr doesn't fluxuate badly if you go off center and it radiates some RF. Might be useful for several situations. I love building new stuff and seeing how it worksand then the less awesome ones I disassemble and make a new one. I've got some new belden 9913 coax I need to use and make another antenna this coming week. Only have 4 running into the shack right now. Also have a Heathkit SB-200 amp coming next week to spruce up and put on the air.

[@mewrongway]

Thats a pretty cool project Callum! 👍

[@shawnbergin8479]

Going to be following this concept to see where it can go. Thank you.

[@DXCommanderHQ]

Yes, we will do a rabuild in the summer.. Need to finish a few jobs and settle the Sig 9 down :)

[@fredsiegfried1707]

Just Stood mine up Friday, have my Stryker 955hpc hooked to it. its Fantastic. 686 in the Keystone State

[@RichardDePas]

Fantastic! I have wondered about running a vertical oriented dipole. Looks like I need to put some more effort into a build like this.

[@DXCommanderHQ]

Go for it Richard!

[@BryanTorok]

In my area we have a local 10 meter net. Also, 11 meters (CB) is having a resurgence. At a hamfest last year I picked up a 43 foot (13 meter) fiberglass pole for cheap. So, I've been trying to figure out how to make an antenna that might work for both and use the pole to get some adequate height for local ground wave. The pole is fairly thin and flimsy up near the tip, so using it raise a conventional antenna wouldn't work. But you have given me some great ideas that might work for this pole. Thanks. And, if you decide to make a commercial version, I may be a customer.

[@acestudioscouk-Ace-G0ACE]

That's really impressive and interesting, thanks. For a long time I've been wondering about something like this for 6m, 4m, 2, and possibly 70cm. The height would help a great deal. 👍😃

[@DonzLockz]

Thanks Callum, more info to cram in my brain🧠 👍🤓

[@DXCommanderHQ]

No worries!

[@ptsmonvideo]

This inspired me to build a linked wire starduster for 10, 12 and 15. I use it on the expedition pole. Not as high as yours but it works!

[@DXCommanderHQ]

Yes it does!

[@alunroberts1439]

Reminds me of my old thunder pole

[@peterlowrie1216]

I've been using the 'starduster' type for years made with wire and compared it with half wave vertical dipole and I have to say I'm heard more on the 'duster' but the half wave hears more. The 'duster' IMHO is much better for skywave propagation.

[@gm1sxwraymond882]

10 extra bananas! Imagine taking it to the beach 😮

[@DXCommanderHQ]

Oh yes!

[@stewpot3971]

Would be interesting to see how 2m and 70cms work on this, I have had quite a few 2m SSB contacts on the classic, I take it with a 10m element resonant on say 28.8 you would have the fifth harmonic at 144.300 for SSB and if you made the element resonant for the 10m FM portion you should be resonant in the 2m FM portion of the band. Great stuff Callum!

[@DXCommanderHQ]

You've given me some ideas! :)

[@n3ljs399]

I built a diy DXC about three years ago just had the 40m and 20m wires on it. I checked the SWR on 2m and 70cm was both below 1:5. Gets into the repeaters in the area.

[@stewpot3971]

@@n3ljs399 I have have noted similar results, I think that I get 2.1 on 70cms but this changes if I move my radials around or shortening/lengthen the coax but it can easily be matched. Not sure how 70mhz (4m band) works as I don't have a rig that covers this. Would be interesting to know.

[@vincenzofidanza2539]

Hello Cullum, nice work. A question: how long, fold comprise, is the 15m elements? Vince

[@DXCommanderHQ]

I had 2.8m to play with and 15m needs about 3.4m. So we are missing 60cm. However, we need to go longer because the radials were shorter. So let's say we are short of about 80cm. Well, instead of going "up" 80cm (we can't!) we can come back THREE times that amount. So although I don't recall the exact numbers, I suggest the return should be around 0.8 x 3 = 2.4. Which means, we must have come back nearly the whole amount. Honestly, I never measured it - but that rule of thumb seems about right.

[@americaswayout4489]

Cal, some areas in USA use 10 meter phone for local rag chew so height is important for ground wave and also to help get a clearer opening for DX. I do believe offering this version of the DX Commander could find a market, of course using the lower half for lower bands, CBers could also use it, especially when places like the UK, with their FM40, Germany with their lower 40 and New Zealand being at 26.220 up. All of these could be accommodated by adjusting length of radiator or adding a second or more radiators?

[@DXCommanderHQ]

Yes, it could easily be tuned.. I need to get some scaffold poles in the ground for raised guy points, say 1-m off the deck so dogs don't run into them - then we can do this again. It would be an extraordinarly small market - possibly 10 per year as a production run but for crazy folks like me, it could be a good laugh.

[@americaswayout4489]

@@DXCommanderHQ I am living in a hotel while my home is torn down and rebuilt, but for me surrounded by metal roofs getting up is desirable. I do think the 18 meter built like you are considering is preferred. Also while in the hotel, I am thinking of dropping a small wire out the window screen ( I am on 3rd floor) using a 49/1 and tuner at the antenna could work? I also have a ground tuner so the CCI can be handled or a second wire to complete the dipole, except both would be straight down. Fun to try. I do think this 18 mtr pole idea will work for me. When I get back to my home and get over my heart surgery we will try one and find out !!! DX Commander still the best buy in Ham antennas !!!!

[@TheBicycleGuy]

I had my version of this antenna up again a couple of weekends ago for its second test. All the elements were too long the first time so it was easy to shorten everything and I moved the feed point up the mast a bit because I could. I tried a thing were I used 6 radials, three were in between the other three that were attached to the guy cord. So the result was having 3 radials for 15m and 3 for 10m. 12m was just left to figure things out with whatever radial worked. All SWR curves showed very acceptable but 12m was still just a little high. The 10m radials were not even close to being 45 degrees and I may just scrap this whole idea of having 6 radials as it just adds weight and maybe for nothing. I'll be waiting for good weather and a day off to have a go again at round three of testing.

[@DXCommanderHQ]

Interesting.. Yes, I would just share three radials between them..

[@ne2i]

It may be cool to use some sort of field strength meter on your drone to verify your designs in the near field. Don't know how you would pull that one off tho. Just an idea.

[@nandrews8412]

Would need to store GPS position and strength. Then make a map chart on PC with that information.

[@DXCommanderHQ]

Yes, you COULD do that.. Or just measure the plot at zero-degrees say 500m away in a circle. At least we could get a base-line for all antennas... I already have a plan :)

[@ynot6473]

"suck it and see" is more accurately known as the "vacuo-visual technique"! BTW, maybe use some pipe lagging on any posts for radials, i know what dogs are like when they're just arsing about and not looking where they're going.

[@DXCommanderHQ]

Well, I have made the decision to dig in some short scaffold poles. Sometimes it's not that he doesn't look where he's going, we literally DOESN'T look and just jumps backwards (say). He doesn't hurt himself, but it annoys the heck out of my R&D! LOL :)

[@andylinton2798]

An end-fed half wave has a feed point impedance of 2450R. That's why folk use a 49:1 transformer to feed it. I prefer to use a 1/4 wave stub to match mine, which is then actually 2 double-Zepp as I have two 1/2 wave wires. Works great, but is single band.

[@DXCommanderHQ]

Yes, 3,000 was an approximation since 64:1 also matches nicely.. I like the idea of a 1/4 wave stub Andy!

[@davidbridge3542]

Hi Cal. Once again some interesting stuff. When your swr ing the 3 vertical wires, do you have to work on 1 wire at a time, or do you fix all 3 in position and then do the checking? What I want to know really is there any interaction between the 3 ? Cheers

[@DXCommanderHQ]

I did all three.. Once minor change on one element has no bearing on the others.. Good question.

[@DXCommanderHQ]

(to clarify, I did all three at once - then re-checked the numbers afterwards - normally it just works)

[@TRIPPLEJAY00]

I use the app called Amateur Radio Toolkit, which is very handy. However, it doesn't cover all my needs. This is when Callum comes in to educate me even better. Have a fantastic weekend with the family and dog's.

[@TRIPPLEJAY00]

Sorry, I forgot to say thank you.

[@DXCommanderHQ]

Great tip!

[@mjrtude]

Reminds me a bit of a GAP Vertical. I have never seen a GAP Modeled, can you put it on your list of things to do for us? GAP DX Titan .. thanks! K9IC

[@DXCommanderHQ]

Yeah, I know NOTHING about GAP. Centre fed loaded dipoles basically.. But a LOT lower to the ground. Interesting concept.

[@kirbymcd1]

I wonder if it could work on one of those 7m (more like 6m usable) fishing poles for portable setups?

[@DXCommanderHQ]

Why not.. It's just lower down though so not as impressive.

[@n3ljs399]

If you would put one of your antennas on a apartment flat roof. Use normal radials how would that effect the performance. Do u have any customer that has a similar setup.

[@DXCommanderHQ]

Actually I never thought that would work - and then folks started sending me pictures of theirs on flat roofs, apartment buildings, all sorts.. With radials... Amazing..!

[@MirlitronOne]

Hi Callum, nice video! Would it help the tri-bander to cut each radial a slightly different length, one for each band?

[@DXCommanderHQ]

Well. I suppose we COULD but ideally in pairs else the pattern would go cock-eyed. So we would need 6. But hey, it works like this anyway. Good question though.

[@americaswayout4489]

I watched again, just noticed 75 ohm at feed, just what is needed to use my 3/4 inch cable co hardline. Do you have any 18 meter poles? Is more like a true vertical dipole which natively IS likely 75 ohms so with one of my 75 to 50 transformers inside the match would be good. My heart surgery will not be done so no extended rehab time necessary which with my home rebuild now finished I DESIRE TO GET back on air. KD4MAO!!

[@DXCommanderHQ]

Yes.. We have 18m poles in stock.. So do DX Engineering. We just shipped them a ton more recently.

[@rayhill1855]

Very interesting. I was wondering how a DX commander would react to Elevated radials? Cal with expertise, Would it require the same amount and length as ground radials?

[@DXCommanderHQ]

No. Being very high up, like a V-2000 from Diamond, you only need two actually. I don't believe for one instance we could do this low down..

[@rayhill1855]

@@DXCommanderHQ Thank you sir, Love your videos and your knowledge never ceases to amaze me with your never ending pursue to improve your products. Thanks Cal.

[@briantrask8173]

If you were going to make that for just 10 meters would the vertical wire be 5/8 wave with the 3 radials being 1/4 waves?

[@DXCommanderHQ]

Erm.. Yeah, OK.. so build it 4m lower to the ground..? I don't fany that - and the matching issue. I have looked at a pair of J Poles mounted one above each other. But only gives maybe 2.5dB extra - and a lot of effort.

[@louisblock1006]

i wich i have the dimentions in meter for the antenne on 27,205 mhz , so i can bild 1

[@DXCommanderHQ]

Easy.. 300 / 27.35 *.92. That's a quarter wave. Same for radials.

[@cuisinartOH1]

Cal, I’ve been hoping you would sell these as an accessory for the 18m Nebula. Do you have the bits to make me a Starduster kit? If so, I would like to purchase a Nebula + Starduster ASAP. This would be a super fun antenna for Field Day. Please let me know. 73

[@DXCommanderHQ]

Ed.. Let me get the parts drawn up.. The parts shouldn't be too expensive. All we really need is the correct sized plastic spacer and a trimmed down plate-set that we can reduce the weight with. Give me a few weeks..

[@cuisinartOH1]

@@DXCommanderHQ This will be fun. Thanks! One question, do you have a device that collects/holds the 10m & 12m elements near the top? Thanks

[@DXCommanderHQ]

Ed.. Sorry for late reply.. I've not got around to this yet..

[@cuisinartOH1]

@@DXCommanderHQ we still have three months’til Field Day. There’s still time! 😀

[@nommy11]

would a 3m wire up and 3 1m radials do the job for 11m band

[@DXCommanderHQ]

You are a little off on the tangent curve I mentioned - my opinion...

[@hootcrichton2173]

sir i have been wondering about top loading your signature for 75m ,,,do you think that would work?

[@DXCommanderHQ]

It probably would, yes.. But you would need a fair amount of loading. Probably best to start a bit lower down, it'll need a good few turns.. Check out the user guide for Signature 12.4 to gain inspiration.

[@hootcrichton2173]

@@DXCommanderHQ I will thank you

[@michaelrosebud]

Wouldn't it be great, if someone could take an old Super Scanner CB antenna, and make one radial 1 ham band, a second radial a third ham band, and a third radial, a third ham band. It was a fantastic antenna, you could use a rotor, it had a lighted switch panel for inside the house. it was awesome. I am just thinking that if someone had three bands they used more so than not, they could tune the antenna and just use one antenna.....just a thought, if you could find one, or duplicate it.

[@DXCommanderHQ]

Well, we don't need to do all that.. We can just share the radials with all the bands, no problem.. 20m might be stretch, that's all.

[@9z4bm]

Hi Cal and hello from the Caribbean .. By chance any MMANA file available for this antenna ? Tnxs ...... de 9Z4BM

[@DXCommanderHQ]

This one..? It's pretty easy to make but I probably have one at home (in office now). Drop me an email to me and that will prompt me to stick it up on a google drive! Email on this channel OR on qrz. Good idea!

[@9z4bm]

@@DXCommanderHQ I use MMANA a lot now , sonetimes more than EZNEC , and would love to play around with it in software .... TNXS , I will email you

[@jelspencer]

Thank you, Cal. Always appreciate the scientific explanations. Antennas often come over as a bit of a dark art, so breaking it down into drawings and showing us how things work is a massive help. Happy Birthday. de M7COT

[@DXCommanderHQ]

Great point!

[@richarde735]

I’d like to make one and hoist it up into my 90’ oak trees

[@DXCommanderHQ]

Gosh - amazing!

[@bassangler73]

👍

[@KrunkTheMadMan]

When is Sharpie going to sponsor your channel Mr Callum?

[@DXCommanderHQ]

That would be fun!

[@edcozart9916]

great stuff Callum hope you had a pint for me last night and make sure you drink some water this morning cause we are getting older nowdays 😎😎😎

[@DXCommanderHQ]

Ed, I accidentally had one more than I should have had!!

[@Allthingsradio]

Ok if you have a massive garden

[@DXCommanderHQ]

And that

[@crazyham]

Very Nice Work Mate ⚡🙏⚡ It looks like you will get a similar take off angle on each of your bands too 👌👌👌 Great for DX due to higher angle than straight dipole.

[@DXCommanderHQ]

Yes.. Did you see the build video? Don't worry - you got the idea anyway! :)

[@9z4bm]

Hello again Callum , i finally got a 5 band version designed using MMANA with the radials = 3m ... Sent the file to you via email , and i am hoping you have time to improve / tweak and even go out and build it .............. Tanks for this video that inspired and guided me quite a bit ............... de 9Z4BM / Leon

[@DXCommanderHQ]

I hope I helped.. That was a while ago. Just found your comment, sorry.