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 Slingshot antenna

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PostSubject: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeSat Feb 11, 2023 10:11 pm

Has anyone made a slingshot antenna for any band?

It's not a common antenna design, but I came across it on the net and it looked simple to make, with the right measurements one could quickly be knocked up for PMR, 70cm or 2m. Hamuniverse have published designs for a couple of bands and a scan the original April '89 73 magazine with the article it was derived from is also on the net if you do a search.

In short it's a sort-of dipole antenna. 3/4 wave length for each leg. A 1/4 wave each side set horizontal and the final 1/2 wave bent up vertically. In the texts it's said to be directional off the ends with a null broadside. I modelled it, won't bore you with the details, but confirmed the texts.. it has a little gain off the ends being 1.something dB and an equal sort of null broadside. Polarization vertical for the main part. Sort of pattern you could expect from using 2x 1/2 waves and a phasign harness.

I thought it would be a good one to build and try out this Tuesday night on the 70cm FM contest, and was then just going to bend the end half wave sections horizontal and run it like that for the later SSB contest.

Won't be using it. I have spend over 4 hours off and on today going up and down the loft ladder trimming and bending wire, but could not get it good enough to work for me. Below is what it looked like after countless bends and trimming. The black Y is not part of it, just using my upright V antenna frame to hold the wires up.

antenna - Slingshot antenna Slings10

The lowest SWR I could manage was 1.5:1. I'd be just fine with that, but I couldn't get it to that in the 432MHz region, it was always way over 2.0:1 in that area. I changed the bend positions multiple times, trimmed and added wire, and changed the spacing between the elements at the feed point a number times ranging from a few mm up to 5cm, but I could not get it right to use for 432 Mad

Am a bit sad. Such a simple design that would only need 90 degree turning angle to point wherever I needed. I know it wouldn't have the poke of a 3 or even 2 element beam, but just wanted to use something different this time for the contests.

Anyone made one before? Any suggestions? I don't have time to play with it again before Tues, but if there are any good ideas then I might try make another one for next month.

For this one I have stuck my wire 2m j-pole up again. It's currently sat horizontal across the top of that black Y frame and directed E / W. The black Y is on top 2 sections of my fibre glass mast and so the antenna is a touch higher than it was slung across the roof rafters and I can reach just inside the loft without having to climb right in to turn it just like I had planned with the slingshot. What I don't get is although I am firing London one way and south Wales the other way, why I am reaching France, Guernsey and Belgium with it. I'm happy obviously, but nothing is making sense to me today.

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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeSun Feb 12, 2023 10:24 am

Hi Neal,

All frustrating this antenna malarkey isn't it?! Wink


I've got to admit I had more 'failures' when I first started playing around with antennas (especially at VHF/UHF) than I care to admit. They were all a learning experience in the end though. antenna - Slingshot antenna 1f44d 

Nowadays if I come across an unusual antenna design that very few appear to have built I stop to think why that might be. There's a myriad of 'armchair' designs out there accompanied with various charts, facts and figures but if they haven't got a photo of a finished design in use I simply move on. (There's tonnes of those!)

Extended Double Zepps (5/8th dipoles) have worked out well for me at all frequencies, HF usually with my ATU's and VHF/UHF with 1/8 wave feeders (for 50 ohm coax connectivity). Nice simple gain to be had from those. The most fun I had at those high frequencies was with Yagi-Uda's, (narrow banded), Bow-Tie reflectors, (wide banded), as well as the simple 'corner reflector' which works well no matter how poor your construction abilities are. For the latter my first was a cardboard reflector with aluminium cooking foil glued on! Very Happy

I've now come to realise that everything sort of 'works' but it's a case of whether it works well enough for you or is too much of a faff to get working.


Keep playing and experimenting, keep having fun (even when frustrated!) and enjoy it all.

I'll bet like me you've run through a fair bit of wire, rods, tubes and anything conductive to repurpose as an antenna! Very Happy


All the best,
Victor

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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeSun Feb 12, 2023 12:12 pm

Thanks Victor. This one looked so simple though, how could it not just work lol. I had to force myself not to get ahead myself again as for some days I have been thinking of making this same antenna for 2m, but with the addition of parasitic elements for 70cm in the centre of the 2m 1/2 wave uprights to focus the 70cm signal more on the horizon. Just as well I didn't. Maybe I should just of made it out of pipe like the plans said, it might just of worked then, though if it did then who knows why.

I use a lot wire and bits, yes, but recycle a lot too literally from bits people are throwing out (cooker grade wire from builders skip at work for this one) to recycling items from my own experiments. I love it when things come together and work, but I do get a slant depressive after spending a long time on something that should work but just won't.

I might just try this one with pipe.. who knows, it might make a difference even if there is no logical reason why.

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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeTue Feb 14, 2023 7:52 am

SangueG wrote:
Thanks Victor. This one looked so simple though, how could it not just work lol. I had to force myself not to get ahead myself again as for some days I have been thinking of making this same antenna for 2m, but with the addition of parasitic elements for 70cm in the centre of the 2m 1/2 wave uprights to focus the 70cm signal more on the horizon. Just as well I didn't. Maybe I should just of made it out of pipe like the plans said, it might just of worked then, though if it did then who knows why.

I use a lot wire and bits, yes, but recycle a lot too literally from bits people are throwing out (cooker grade wire from builders skip at work for this one) to recycling items from my own experiments. I love it when things come together and work, but I do get a slant depressive after spending a long time on something that should work but just won't.

I might just try this one with pipe.. who knows, it might make a difference even if there is no logical reason why.
Hello, I trust my response finds you in good fettle and well comfortable.
I have a Yaesu 221R lying in my workshop the very first Boat Anchor puurchased via eBay (Germany) never really had the interest in firing up. Would love to Qrp. I`m currently using FTDX10 however really interested in your exploits and ask politely for results should you venture in the 2m antenna construction. Would appreciate your assistance. I reside long term Bulgaria and passed my Ham exam during the covid dilemma. Sincerely looking forward to your response. CiAo for now from across the pond. Paul (Onyer¬Edson)
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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeTue Feb 14, 2023 9:52 am

I havn't tried that particular design but the main thing I see missing from any such experiment is a meaningful choke at the antenna feedpoint.  (Don't believe 'wind coax on a pipe' ! etc)

Two turns of the feeder through a large (10mm dia + for RG58) ferrite clip on choke or ring suitable for suppression at the operating frequency (so for VHF UHF fair-rite mix 61 for example) placed right below the antenna will change the antenna characteristics as seen at the end of the coax significantly.     When you get very 'near' check if moving the choke a few cm makes it better or worse 

(Once you have it working you can try to downgrade to other materials or chokes if you wish as you have then made yourself an easy choke-test-bench)
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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeTue Feb 14, 2023 11:07 am

I'll definitely try making one of those, but as suggested, with a choke at the bottom. 
Thanks for posting,
Tim
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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeTue Feb 14, 2023 11:49 am

SangueG wrote:
Has anyone made a slingshot antenna for any band?

[...]

Won't be using it. I have spend over 4 hours off and on today going up and down the loft ladder trimming and bending wire, but could not get it good enough to work for me. Below is what it looked like after countless bends and trimming. The black Y is not part of it, just using my upright V antenna frame to hold the wires up.

[...]

Hi there!

I have a question regarding the black material you mention above that is the Y-shaped support for the antenna. What material is this made from?

Cheers,
Jan
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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeTue Feb 14, 2023 12:49 pm

I made a similar antenna years ago but, like SangueG, the SWR was never any goodYes, I've been up and down ladders, trimming and bending wires to no avail.  If it worked at one end of the 2m band it would suddenly stop working mid band or SWR was so much 'out' it wasn't worth messing around with it.  As Victor said, antennas can be very frustrating sometimes!

73s

John
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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeWed Feb 15, 2023 8:08 am

Paul.. If I manage to make any unusual antenna types work for 2m, then yes of course I will share details on this forum. What do you use for 2m at the moment? I use a 2m j-pole made from 300ohm window/ladder line which works very well both vertical or horizontal. The details of construction for that  one can be found all over the net if you want to try.

Bruce and Tim.. I don't know if the choke will help, but it might. Thanks for your suggestion and the mention of the mix 61 ferrite. I do have clip on ferrites as a not well thought out choke which are probably doing nothing, and might even be causing a problem (1x mix 43 ferrite and 2x unknown mixes I took off a couple of comms cables from a decommed IBM zSeries server). Doesn't seem to have any bad effect for my 2m j-pole on 2m or 70cm.

Jan.. The black used to make the Y is PVC piping. Very cheap if buying new. I've recently found some white off cuts in the loft, nothing to do with me, but I'll make use of them. The Y construction can be found here:
https://charlietangodxgroup.forumotion.com/t4023-upright-v-antenna

John.. When you made a similar one, did you use wire or pipe? My thinking is that a 1.5:1 swr which I managed on another part of the band is a workable figure, and construction from pipe would wide band the results a little. Ygritte (my 11m 1/4 wave made from copper pipe) is laying on the loft floor unused... I might chop her up Twisted Evil

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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeWed Feb 15, 2023 11:41 am

Greetings SangueG

I used some thick single-core earth cable that I found in a box.  I can't even recall what mm size it was, but it was thick stuff.

I had it up in the loft.  It was a very old house and I did wonder at the time if other metalic objects up there were affecting SWR. I never did sort out the issue and the antenna is probably still there....I moved a couple of years ago.

73s

John

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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeWed Feb 15, 2023 8:33 pm

I decided to sacrifice some wire and time on this.   Tried it on UHF to save wire  antenna - Slingshot antenna 1f600  

Quickly cobbled the design together on a table top with thin stranded insulated wire, cork spacers to keep the wire off the wooden surface and BNC to terminal adapter to connect to a free standing 600MHz VNA 

antenna - Slingshot antenna Slings10

Notes:

The BNC adapter has a vertical section for each terminal of about 35mm which will have some effect on matching etc (effectively a 35mm long by c 20mm wide matching section of a few hundred ohms impedance) but as this could be conveniently replicated directly or replaced by equally long /spaced long coax flyleads it's presented 'as is' 

In layout 1, The VNA is connected at the end of the BNC socket and calibrated at the plug connection point plane.  No space, attempt or need for a choke in this case.

I found the best match at 440 MHz was with the total bottom width between the upstanding wires  of 190mm  and two upstanding wire lengths of 380 mm 

The SWR in this case (layout1) was under 1.5:1 from 433.4 to 445.8 with 1.05:1 at the 440.0 centre.




In layout 2 I tried adding some coax with two 61 material (VHF /UHF) chokes just a little way down the Coax, (layout 2) this just made things worse (1.57:1 at 440)  


For Layout 3 The chokes were moved about 450mm from the adapter (Layout 3) at which point an under 1.5:1 bandwidth of 430 - 442 was seen, but now with a new centre of 435 MHz at 1.1 : 1SWR 



In either case   Typical feeder losses at UHF will of course make this appear a better match and wider SWR bandwidth


Conclusion.   Very fussy antenna, on proximity, shape, dimensions, coax length, choke placement etc.   

Clearly it CAN match well with test equipment, patience, plenty of spare wire  and several attempts , but not sure the performance gain is worth the effort !

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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeThu Feb 16, 2023 8:17 am

Thank you Bruce for putting in the time, resource and efforts to have a go at this. It's clear by both your results and the notes by John that there is no reason for me to chop up Ygritte for some copper pipe to wide band as wire can do the job.

Very interesting too about the different results adding and moving ferrites produced, there clearly is interaction with the coax shield.

I will definitely have further attempts at making one in the near future. I agree with you about the performance gain probably not worth the effort (for many people), but for me the tiny bit of gain, size and very small turning circle for directivity is a plus and also I like to be a bit different... I think it would be fun to have antenna types like 'slingshot' or other strange ones listed on the 2m and 70cm contest submissions to breakup the plethora of multi-element beams and white stick collinears. I'm not out to win, just have a bit of fun, and using something different and homemade does that for me Smile
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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeThu Feb 16, 2023 11:00 am

A footnote,   

The Choke and it's position has a marked effect on the 'tune' frequency and that effect is fully in place along with a nice match and narrow but symmetrical 10MHz (n.b. only 2% @1.5:1)  bandwidth with the choke about 1/4 wave down the coax. 

So no choke  = 440MHz 1.1 :1   
Choke at 1/4 wave and beyond  = 435MHz  1.1:1 
Choke closer to the BNC connection = 440 tune but with poor 1.6:1 SWR at best)

In my mind this confirms that the coax braid is 'active' in this design (not unexpected) which is significant as it means that, without a choke to define the end of the active antenna, coax position, loops, length etc will all affect results to some extent

So some will be lucky and pick a coax length that 'works for them' but the advantage of a Choke here is that having the choke means the run of cable from Choke to Radio should no longer be affecting the tuning etc.

I would add the usual disclaimer that match and good SWR provide no evidence at all of an efficient antenna; but for what it's worth it allowed solid access to a repeater 10 miles away using 1 watt from it's random position on the dining table.  This delicate layout/ construction didn't allow any test of directivity 

Anyway I will leave scaling-up and repeating all this on 27MHz to anyone who wants to try it.  (I think a rigid construction will be essential!)

antenna - Slingshot antenna Layout12

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PostSubject: Re: Slingshot antenna   antenna - Slingshot antenna Icon_minitimeTue May 09, 2023 2:39 pm

Officially putting this one to bed, at least for a long good while. Off and on I have been playing with wire trying to get it to work, like you Bruce although I finally got descent enough readings to use it, just moving the antenna slightly the way it is orientated or elevated, changed the readings drastically. I can't use an antenna that changes how it is matched to the transceiver by turning it just 90 degrees, which is all I actually wanted from it.

At lunch I repurposed some of the wire and made a simple full wave delta loop for 70cm, a 2 minute job. No matching unit of any type needed using the squashed loop dimensions in the photo below. Almost perfect match across the band. Theoretically it should be good for horizontal polarization the way it is orientated in the photo, and vertical with it laid on it's side.. even though it really doesn't look right for a vertical with it laid down. It hits the repeater 15 miles away like that, so must be doing something right. Hopefully will get a few contacts this evening on the FM and UKAC contests.

antenna - Slingshot antenna Deltal10

Not as impressive as a slingshot, but at least it's homemade unlike the shop bought white sticks and yagis most use for the contests.

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