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 Utilising Coax as Antenna Elements

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Victor
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Victor


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PostSubject: Utilising Coax as Antenna Elements   Utilising Coax as Antenna Elements Icon_minitimeSun Jul 17, 2022 10:01 am

Hi All,

Hope you're keeping well and most of all enjoying your radio.


There's a lot of you here at CT that love to play with an antenna or two and I'm always enthralled at the home made varieties.

I do remember someone playing with utilising coaxial cable as antenna elements being able to shorten them by taking the velocity factor into account. It's not something that I've ever tried to do but after reading a couple of articles I'm convinced this might be an avenue worthy of further exploration.

The articles in question that raised my interest are here :-

https://www.hamuniverse.com/17mcoaxmox.html

and

http://on5au.be/content/a10/moxon/n0khq.html


It was the first article I stumbled upon but have seen many antennas written about on HamUniverse so I investigated further. The second article really pricked my ears up due to being written by the venerable L.B.Cebik with a more complete analysis.


The reason it has peaked my interest is that with my FT8 work 17m has been the far more fruitful band for me as far as distances go. I regularly get PSKReporter results back from the USA to Japan but as of yet no responses to my calls. (I've been heard in over 90 countries in total but only worked 43 with QRZ confirmations!?!)

.....and please, let's not have all that FT8 bemoaning here when you can start another topic to do that. Wink

As this type of antenna can be easily constructed at home and the fact it would fit in my loft/attic space it's raised my interest as it might bag me a few more countries. May be worthy of further investigation with antennas for other bands too. (Could help me with the 10m challenge next year!)


So before I go shelling our for a roll of coax to start chopping it to bits has anyone else had some first hand experience with these methods?
I don't necessarily mean with this particular 17m antenna, (although would be useful), but just the method of using coax for antenna elements.

Any help with this would be most appreciated and I look forward to your input.


All the best,
Victor

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Alan Pilot
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Alan Pilot


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PostSubject: Re: Utilising Coax as Antenna Elements   Utilising Coax as Antenna Elements Icon_minitimeSun Jul 17, 2022 12:27 pm

Can't help but will be watching with interest Victor.

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karelgol
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PostSubject: Re: Utilising Coax as Antenna Elements   Utilising Coax as Antenna Elements Icon_minitimeSun Jul 17, 2022 7:46 pm

Don't have the room anymore for a directional antenna, but this would certainly be a possibility. I'm very positive about coax antenna elements as my T2LT and homebrew gainmaster 5/8 are the proud replacements for an A99 and a GPA.

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Victor
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PostSubject: Re: Utilising Coax as Antenna Elements   Utilising Coax as Antenna Elements Icon_minitimeSun Jul 17, 2022 10:27 pm

Hi Karel,

I'm pretty sure it might have been you that posted details about utilising coax antennas on the forum then but not sure. I know I saw it somewhere and CT is my common hangout. There isn't a heck of a lot of information out there which is why I'm grateful for any input that people can give me.

I did come across one article on coax that may have suggested limitations otherwise here :-

http://mail.karinya.net/g3txq/coax_antennas/

Although I respect that work I still have an inkling to explore such things further.


Since then I've had a dig about through my 'junk pile' and come across various lengths of coax including some RG58. With the help of a NanoVNA (still grateful Alan Utilising Coax as Antenna Elements 1f44d ) I've done some basic tests/experiments. I may have just enough cable to recalculate John's N0KHQ antenna to play around with a 2m version and see how it works out.

Sometimes playing around with such stuff leads to maybe disappointment but often something good comes about. My recent doublet and ladder line antenna made from some scrounged lawnmower lead won't make me a DX king but it has got me on air from 80m to 10m with Continental contact and a lot of fun. Was a struggle running through the various methods presented to match such an antenna but I got there in the end.


Often it's just an enjoyable experience to play around, build and discover which for me is just as much radio fun as making contacts.

I always appreciate and admire others that do similar.


Thanks for the input.

All the best,
Victor
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PostSubject: Re: Utilising Coax as Antenna Elements   Utilising Coax as Antenna Elements Icon_minitimeMon Jul 18, 2022 2:54 pm

I built a double bazooka dipole and found no real benefit over using wire other than being a bit shorter. Bandwidth didn't seem to be significantly higher. Seemed an expensive way to build an antenna TBH. Worth a go for an experiment though.

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Victor
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PostSubject: Re: Utilising Coax as Antenna Elements   Utilising Coax as Antenna Elements Icon_minitimeMon Jul 18, 2022 4:00 pm

Hi Conor,

Thanks for the input, really appreciated.

Getting some unusual readings vs calculations so far (doesn't seem to match the velocity factor) but having fun playing around with it all. I have an inkling that you may be right as so far it looks like I may have a reduced bandwidth and not making so much of a space saving. It could be an expensive folly with a full build but luckily a 2m version will just use up what coax I had in the junk pile.

Always worth a play if for nothing else than the learning experience.


All the best,
Victor
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Alan Pilot
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PostSubject: Re: Utilising Coax as Antenna Elements   Utilising Coax as Antenna Elements Icon_minitimeMon Jul 18, 2022 5:31 pm

You have started something now Victor.
Got coax all over the back garden now lol.
Only success is a T2LT i just made lol getting frustrated with the other one not doing what it should so i though i would walk away for a bit and try something else.
Bugger all on 27/28 now but i might just put that t2ly in the big car with the telescopic pole and dig the Mk1 Lincoln out ready for a good day and then go up the hill well Holyhead mountain just a hill to me.

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Victor
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PostSubject: Re: Utilising Coax as Antenna Elements   Utilising Coax as Antenna Elements Icon_minitimeTue Jul 19, 2022 6:51 am

Hi Alan mate,

I'm sure you don't need much of an excuse to start getting out bits of cable to have a play around there being far more aspects to radio interests than straight DX'ing. Wink

I'm all for a bit of experimentation as well as learning along the way and often different methods can be a great answer to situations. (The T2LT or shrouded dipole lends itself well to end feeding an antenna.)

Unfortunately so far, although I can reduce the size of the antenna with coax, (I landed up building a 70cm version.....very tricky trimming that b*gger!), there are losses in comparison to a straight wire version using a field strength meter to compare them. It looks like Steve G3TXQ was right in as far as losses introduced with such a method. There are however some merits to it by utilising it into a two element beam to make up for losses but I'm not sure that its all worth it for just size reduction alone. (Quite a lot of reduced bandwidth too!)

It was definitely worth a play with but I'm not convinced enough to fork out for a roll of coax for a bigger version.

Still, it's all for the learning and someone may just find it a good solution for their needs.


Well, back to the drawing board. Wink


Thanks to all for your input it was much appreciated and certainly worth filling my time with.
(Better than rotting in front of the 'box'. Very Happy )

All the very best,
Victor

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Call Sign : M0GVZ / 26CT1760
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Join date : 2019-11-13
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PostSubject: Re: Utilising Coax as Antenna Elements   Utilising Coax as Antenna Elements Icon_minitimeTue Jul 19, 2022 7:03 pm

Always worth experimenting and having a go even though you know it's probably going to be pants. I've done slinky antennas, coax antennas, tried loading up a set of step ladders and mesh garden fencing. When I first got a SGC230 antenna coupler I hooked anything metal up to that just for the laugh of seeing what I could make contacts on. 

Opening something boxed is OK if you're wanting fairly guaranteed results but what I think are my most rewarding achievements have been from stuff that I think just simply shouldn't do what it does. Working Argentina with 1W SSB for example is what I personally consider my best QSO.

Victor, in regards to a "small" wire beam you will find it hard to beat the Moxon Rectangle. Building from insulated wire will reduce it's size by ~4%.

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Alan Pilot
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Alan Pilot


Call Sign : 163-CT-220...MW7TTA
Posts : 2518
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Join date : 2019-11-19
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Equipment Used : Yaesu FT-991A,,Yaesu FTDX-10,,Icom ic-7300,,Anytone AT-D878UV PLUS",,LINCOLN II+.
Age : 150

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PostSubject: Re: Utilising Coax as Antenna Elements   Utilising Coax as Antenna Elements Icon_minitimeTue Jul 19, 2022 7:32 pm

I was about to hook up to the mesh link fence after seeing a video online.
Then i remembered it was plastic coated lol.
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