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Call Sign : 26-CT-3971 / M7TDV Posts : 686 Times Thanked : 35 Join date : 2021-01-30 QTH or Location : Cirencester, Gloucestershire Equipment Used : Little radios, home-made antennas
Subject: 11m cage dipole Thu May 13, 2021 1:28 pm
Hi all. I am currently using a simple inverted V made using cooker grade electrical wire fed via a 1:1 balun choke. The SWR is lowest just where I want it (top of mid block / lower half of hi block) and usable across the whole of 11m (there's a self plotted SWR curve in THIS thread). It's working just how I wanted it too, it's a very good skip shooter.
I have been thinking about how I can widen the bandwidth a little though. "If" I wanted to run higher power on the lower freebanding frequencies, the antenna would really need a little adjustment. I can actually do that quite easily by clipping on an inch of wire on each end (antenna is in loft so fairly easy to get to). But was thinking of a more permanent solution.
I've come up with lots of ideas, but the one I keep going back to is building a cage dipole, or to be exact it would be a cage inverted V. Not something I have seen people use for CB. I can't see that anyone sells one either.. or at least not now. There is a company that doesn't seem to exist any more that sold one called the THE ELIMINATOR 10/12, which they described as "One antenna that covers all of 10 meters all of 12 meters AND everything in between!". That does seem to be an extraordinarily large bandwidth, but the fact that their quoted gain figures appeared over the top too for what is effectively just a dipole and that they do not seem to be in business now kinda says it all.
However the larger the diameter element - the wider the bandwidth, that's proven fact. So even if the bandwidth is increased just a little from going from a single wire to multi wires in a cage format, that looks good for a try. Having a lot more wire in the construction of the antenna "might" even receive signals a little better?
Has anyone any experience of using a cage on 11m, or even 10 or 12? If so, what is/was your bandwidth like and how many lengths of wire are/were the cages constructed of?
I haven't played with a caged dipole but maybe something on a similar basis. (? Opinions may vary ?)
When I wanted a multi-band antenna for better SWL listening I opted for the Fan dipole rather than a long-wire and it certainly worked as well as expected. Several wires were cut for the bands of interest and I used a simple tuner/preselector/ATU with it. There was a marked difference on reception including alleviating some of the cross band interference I used to get on the commercial SW bands.
My fan array was hung as an inverted V arrangement including zig-zagging in my attic space more to fit it all in than anything.
Moving forward I got back into CB radio but I didn't want a mahoosive antenna sticking out of the house with the chance of villagers pointing their gnarly fingers screeching, "There be a CB'er!!", before turning up with their pitchforks and burning torches!
So I hung up an inverted V in the loft tuned to the CB frequencies and although a useless antenna for local work it did prove itself on the summer propagation, (Germany, Austria, etc.), with low power outputs. That was all the fun I needed to eventually decide I wanted more and took my Foundation.
I then being a cheapskate wanted to see if this antenna would work if tied into the SWL Fan array. (One coax feed then.) It sure did!
Taking it further I also wanted to see if it would be operational for the Amateur bands and a Ham friend lent me a MFJ-259B antenna analyser, (expensive kit but so very useful). It indeed showed me that this arrangement would certainly be workable as a multi-band antenna. So with a volunteer jumping up the loft I read the Analyser and he trimmed the array to better standards. (I wasn't far out considering my original dimensions were made with a tape measure!)
As soon as I was licensed and received my callsign I used this arrangement in earnest and it did indeed work! OK, maybe not the best antenna setup in the world but along with a homemade ATU to handle transmission power it covered every band I had access to in the HF region. Just the job.
In interest I wondered if adding a 10m dipole could be added to this array and hung it as a inverted V next to the CB or 11m dipole. I had expected some interaction, (it certainly did affect the lower frequency dipoles as I added bands), but nope, all worked fine. Despite my utilisation of an ATU, with this taken out of line the CB dipole had a great SWR and popping up to 10m showed that it was also great. That multi-dipole array certainly has a lot going for it.
Now I've seen cage dipoles in efforts to increase 80m bandwidth by Hams who want both sides of the band for CW and Voice. They're certainly not common though and hardly surprising considering the work involved and the proverbial wind sail it would become! The usual ones I've seen are three wire cages.
But I've also seen two wire arrays....they're not exactly cage dipoles but rather two 80m dipoles, one cut for the lower end and one cut shorter for the higher end of the band.
Very similar for what I did with my 10m/11m tied to a common feeder!
So finally, getting to my point after a long winded affair....
Maybe it might be worth experimenting with your original Inverted V by adding another to it tuned slightly up or down accordingly?
Anyway, sorry for all the waffle but I thought the history of how I came about it all might be useful. I am more of a practical/experimental man with a smattering of theory preferring that to jerking myself off silly over antenna modelling software.
Thank you Victor. We obviously think alike on certain aspects of radio. A fan dipole was one of my thoughts as I have also had a such an array or wires up in the loft just for listening on. Slightly ironically all that wiring is currently down so that I could get as clear a signal out of the V for the skip season.
I had thought about connecting another V with the best SWR set at the lo lo block calling frequency, and had theorized that it would either create a longer low SWR or at worst a W with a low middle if plotting out the readings. But at the same time I had thoughts that it just wouldn't work and mess with the original V. Learning the output of your previous trials does make me think I should give it a go.
I'm still getting a pull to build a section of Russian woodpecker to operate from though The good thing with doing stuff like this in the loft, as you know, is that it doesn't have to look pretty and doesn't have to be strong like it would outside.. though I do get quite a draft up there. I'll probably end up trying both at some point.
Your road to Ham by the way is interesting. I should really pull my finger out and go for it properly one day. Radio has been in my life for almost ever, few examples... had wired walkie talkies between bedrooms as a young child with morse buttons on, built first crystal receiver with long wire before I was 10, modified a low power toy that transmitted on FM broadcast to increase range and ran a pirate music station in early teens, and whilst doing the CB and freebanding thing first time around used a couple of FM rigs connected to transmit data between a couple ZX speccies I think before even the BBC tried it. I did actually start an online course a year ago like many other people during Covid, but I gave up. It's the boring (to me) but necessary bits like learning callsign types that just made my mind switch off. I'll do it one day. It's something people can poke me on when the colder months come back around again
You're spot on there Neal, a double dipole certainly does produce that flat middle W SWR plot.
Love your 'Russian Woodpecker' idea too, plenty of cages there. The Russians certainly came up with some weird and wonderful inventions, been toying with a corner reflector antenna for VHF just recently. Stick that whole shebang on a bearing table, point and squirt that RF!
I agree completely, indoor antennas whether in a loft or strung across a room can be worthwhile and as you say having no exposure to the elements means you can knock them up out of all sorts. (My first Moxon experiment was with electrical wire taped in place on a big piece of cardboard....worked too!)
I'm not knocking things like modelling software at all, but unfortunately a lot of the practitioners never actually build antennas or stop experimenting because the software says 'no'. Such a shame really, get the wire out and start building to your hearts content is way more fun and you learn a lot whilst enjoying it all.
TBH Neal I never thought I'd bother with my ticket after having a bit of a shameful response by some Hams as a youngster.
I was initially the little radio whizz-kid like you when I first attended a Ham club meeting out of interest but was soon shunned for my unlicensed experiments and committed the most heinous of crimes by having an illegal AM CB! That really put off that young impressionable lad I was. The same attitudes can still be found today displacing the young experimenters with their easily available, (and affordable), Chinese tech and lack of 'old-school' respectability.
Luckily, not by all. The 'baton' shall be respectfully passed on regardless of what some may think.
I love your passion for it all Neal and you got up to the same sort of radio antics a lot of experimenters did. "FM Transmitter? Nah M'lud. Pirate radio station? I was just experimenting."
I eventually went for it all because I had the time to discover a wonderful place like this here Charlie Tango. Hams, CBers and experimenters, (mostly), getting on with each other? What a wonderful world. Wished I discovered it much sooner!
Like you I was a bit 'meh' about the hoops you had to jump through but at least it was available online in your own comfort. Just getting through the nonsense of knowing how high up the ionosphere layers are, (in km? still befuddles me!), to pass that exam was just a case of biting the bullet. Now I get to experiment with a lot more frequencies and modes!
It just makes me laugh when I get the "Well done, an M7, now you'll have to do your Intermediate!" Yeah right, "Congratulations, you've passed your car test, now you can do your PSV and move onto HGV!"
Then what do you do when you get that 'HGV'? Start riding a bicycle! (Full licence progression to then sit on a hill running QRP? )
If you're going to do it Neal, do it for yourself. I finally got my ticket just so I could get back to experimenting with radio and I'm thoroughly enjoying myself.
I know one thing, I'd enjoy a QSO with the likes of yourself transmitting on your home-made wire concoctions and modified radios.
All the best to you mate, Victor
rabbi, glenn dog, Pappy Nick and SangueG like this post
I went your route Victor and added a 10m inverted V to the 11m one. Didn't go smoothly for me. Up and down the loft ladder for 2 hours folding, trimming, and moving positions of wires around until got them in a sweet spot. But not sweet to look at. It certainly is not a what you'd call a fan dipole now. With two dipoles fed from the 1:1 balun of pretty much equal lengths, in something that only vaguely resembles inverted Vs, it's more of an open ended droopy and twisted bow tie antenna
As far as SWR goes, it shows very wide usable bandwidth of < 3:1 over a massive span of 4.5MHz. Almost perfect from 28.300 to 28.640MHz. And under 1.5:1 on UK FM, Hi and Mid block.
Does it work? Yes! Today had a contact to Italy on 11m and my first legal contact on 10m to Lithuania LY4A
Still pondering a cage though. In my mind I can't see that the bandwidth would increase much more than the mess of wires I have created is showing. But the radiation pattern has got to be nicer and.. even though most places I have read about cages say the following is not true, a voice in my head keeps telling me that more metal up in the air will capture more signals and may possibly put out a touch better signal than a thin V. Probably will be a winter project by the time I think about it more.
Call Sign : 26-CT-4145 Posts : 90 Times Thanked : 1 Join date : 2021-06-03 QTH or Location : Chatham, Kent Equipment Used : Includes :- AT-878UV, FT474Gx, AT-5555N, FT-818, DNT M40 (RT Factory, Manpack config), Midland Portapack, IC-211E, TS700G, TS2400, MAXCOM 16E, unbranded 40 channel Japanese 49 & 2.4Ghz transceivers (supposedly Uniden, but unlikely) Age : 53
Subject: Re: 11m cage dipole Tue Jun 22, 2021 12:17 am
Personally I hold any spec of a wideband or wider than usual bandwidth antenna commercially marketed with unrestrained contempt knowing most antenna specs represent no actual tests and are just speculative (best case) 'up sell the positives' rewording of a classic reference design.
So anything array or array like is best built DIY where you'll have to fine tune and adapt as part of the process.
As for widened (talking moderately) b/w designs like caged dipoles etc, irrespective of which you try, if it's not raised/located suitably, proximity effects will alter it's response pattern both BW wise as well as it's acceptance/firing pattern.
But anything dipole and unity gain+ is worth a hit at building for trying to make a design usable over a few MHz or so across a few harmonics. But unless you go into directional designs, gain on unity+ dipole based won't go much over 6dBd with any ease if you want bandwidth and at least unity gain.
If it's not dBd gain rated and above or equal to unity, it's only a gain in performance if it's better than the 6-11 dB lossy short typical verticals.
Thankfully, caged and fan types are fairly cheap and easy to make, so worth a hit.
About the only notable quality a true long wire has is it has a good, when tuned per frequency change, capture tendency. Most 'long wires' aren't as they don't meet the criteria of random too long to be naturally resonant across the wavelengths in the HF spectrum. I mean a true long wire is in the order of a mile/km in unspoiled length typically and that's still EL short when you talk about LF/MF/VLF.
I wouldn't go to the hassle of building a cage dipole when you can achieve what you want just by using a wider diameter element.
Bandwidth is affected by the diameter of the radiating element, the larger it is the wider the bandwidth. The idea of a cage dipole is to make a radiating element that appears as one single very large diameter element to RF using wire and typically they'd what you'd use on 80m and 160m where even a thick wire may not give you full band coverage.
Even just rebuilding your current antenna but using two 9ft lengths of 10mm diameter copper pipe would more than achieve what you want.
Couldn't leave it alone, need to play some more To play around with diameters I got myself some ladder line as it's cheaper than getting more copper pipe in. 450ohm so nearing an inch wide.
Without a long waffle for now.. Took down the mess I had created and put up a single inverted V again using the ladder line as radiator element in the exact same spot as I had mounted the original V. It has about 700kHz additional bandwidth over the single wire V. That's great. But also is bringing in a lot less unwanted noise, which is also amazing.. but I don't understand why. A good S2 at least of noise reduction over the single wire V. Wanted incoming signals still same level, have listened to a couple of locals to check.
Any ideas of why there is less noise? The ends of the lines are as below. High voltage tips on left, single wire joins on right fed into balun.
Happy with the results, but would love to understand how the noise has reduced.