Antennas for limited spaces - 80m spiral loop

Hi All,


Recently a member of CT, Alan (Alan Pilot), asked about any ideas on an antenna for the 80m, (3.5MHz), band that would be able to fit in a small plot.

I made mention that I was using my 44 foot Doublet down on 80m,  (supposed to be 40m to 10m), with the use of my homemade ATU. However, I'm using homemade open ladder line as a feeder with not many being au-fait with such arrangements and even indeed some 'learned' gentlemen on this very forum scorning me for utilising such 'archaic' practices.

So in the spirit of 'inclusivity' and doing my best to bring some ideas forward for Alan to possibly explore as well as maybe others, I scoured the old internet for possible 'coaxial' solutions.

Didn't take long and came across the following resource :-

https://www.nonstopsystems.com/radio/frank_radio_antenna_SM0VPO.htm

Lots of pretty pictures and graphs as well as build details there for anyone to enjoy.


There's also a good video of Mike, M0MSN finalising such a build and testing it out on air :-

https://www.youtube.com/watch?v=Dceg_QXZT_M

Seems he was quite impressed with it and worth searching out his other videos on the build as well as many other projects.


There'll probably be some that can't justify the possibly expensive variable capacitor required for such projects let alone the fact that their availability is somewhat limited. Well, on the first link I've provided further down the page there are details of a homemade variable capacitor made with a couple of pieces of copper clad PCB type board. There are also other 'antiquated' methods such a 'book capacitors' and worth doing an internet search for.

One idea that springs straight to mind is using pieces of coax as capacitors, (30pf per foot don't you know). You can parallel these together to add up your capacitance and even add them to commercially manufactured fixed capacitors to get the exact capacitance you require. Not even remotely variable but you can clip down the coax piece to get an exact capacitance to tune such an antenna to a fixed frequency......the 3.573MHz FT8 frequency seems like a good option.


So there you go, there's always options especially if you enjoy self builds but you may be limited with the clicking 'buy it now' route as I don't think anyone has a commercial version of this.

I hope that's of help to Alan or gives him some ideas to explore and maybe even help one or two of you other readers.  

Have fun and enjoy your radio.


All the best,
Victor

Thanks for that info Victor.
You now have me looking at 3D printers lol.
First link not working for me.
Got me thinking and i have loads of wire ?????????/.

Not sure why you're scorned, anyone using a G5RV, probably about the most commonly used antenna on the planet, has used ladder line to feed it.

Must admit I never had a lot of luck with my G5RV, and ended up giving it away long ago, and had better luck with dipoles, trapped or otherwise, or a ground mounted vertical.

However, the tiny commercially available ladder line is just too modern for me these days, my vertical open wire ladder line feeder is Copperweld (steel cable enamelled with copper), and is a 14ft long 11 inch spaced ladder line using ex-MoD Admiralty pattern 9418 porcelain rods, then split North-South with legs of 66ft @20ft AGL using marine grade stainless steel pulleys and polypropylene 4mm rope, and insulated at all points with 4" and 7" Pyrex Dog Bones (7" where the voltages are highest as I've had flash over and plastic dog bones melt and catch fire in the past).

So very much an old school antenna here, even the Butternut HF-9V has a short matching 75 Ohm section of Coax that radiates, to give 50 Ohms at the transmitter, indeed it's inevitable that some signal is radiated from any feed line, and in my case with the wire antenna here, its desirable to have a vertical component in my antenna to provide a horizontal radiation pattern to assist with line of sight and ground wave at longer wavelengths.

I'd ignore the detractors Victor, you know far more about such matters than most, including humble me.

Hi Alan,

Had hoped this might come in handy and rather than just shoot you a PM I thought others may benefit from such notions hence the posting.

3D printers? Not my cup of tea but many have fun with them.

Just checked the links again and they seem to be working at my end.

Can just see you now fiddling with lengths of pipe trying to feed copious amounts of wire through them!


All the best mate and do have fun. (Let us know what you get up to. )

""Not sure why you're scorned, anyone using a G5RV,""
I think the thread title might answer that Wayne.

Hi Wayne,

Oh, we did have someone lose the plot a while back about the notion of ladder line and balanced feeds with quite the tirade on the forum. Luckily another very knowledgeable CT member gave me a push in the right direction concerning such techniques. Learned a lot since.

I remember well commenting on one of your antenna postings impressed with your porcelain rods and pyrex dog bones. Awesome stuff.

I'm still very much learning, hoping that never stops and just being an 'Amateur' as in the passionate interest meaning, (for the love of). Besides, anything that can get me on the air despite my 'gammy' leg and limited resources is all good and a bonus if it can help anyone else too.

I'm far from any sort of 'expert' and rather leave charts, numbers, facts & figures to those presenting business meetings or impressed with such things. I like the 'fun' stuff.


All this was just a posting to hopefully assist our Alan with resources available online.

All the best.

Link working now strange.
Edit.
Link very interesting and doable.
Next is the station commander == get her in a good mood as she pulls a face if i mention the word aerial lol.
Not sure when i will get it done but it won't be for the want of trying.
Thanks Victor.

Hee! Send my apologies to Linda for me mate - I'm a bad influence!

Be good to catch you on 80m.

One day my good friend one day.