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| Slinky Antenna for SWL | |
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| Tweet Topic Started: Thursday, 21. January 2010, 19:54 (4,457 Views) | |
| Firetrap | Thursday, 21. January 2010, 19:54 Post #1 |
26CT100
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Anyone ever head of making an antenna from a slinky? they are 67 feet long when stretched and apparently make ideal antennas for SWL. I suppose they act like a Long Wire Antenna. Does anyone have any information on this or a guide as to how to make it and get the best results? Im definetly going to try it! Cheers |
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| 2EC837 | Thursday, 21. January 2010, 20:21 Post #2 |
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Slinkys can be used as antennas.It can be as simple as attaching your feedline to two slinkys or the much more involved.People do use them for transmitting as well but any change in the length from wind will make the SWR fluctuate.They are availble purchase assembled but I fell it it's a waste and more fun to roll your own.![]() List of components: 2 Slinky coils 1 hard-PVC (Schedule 40 sprinkler pipe) T-piece, ¾ inch Ø, 2½ inch long 3 hard-PVC plugs that fit the T-piece 3 eyebolts 3 nuts for eyebolts 6 washers for eyebolts 3 locknuts (nuts with nylon insert) for eyebolt 1 BNC jack (through-hull, not screw-on) 1 washer + lock washer + nut for BNC jack 50 cm of insulated heavy gauge multi-strand copper wire 20 m of nylon or dacron cord (pre-stretched is best; slinky coils are not self supporting so you need to use a messenger line to support the weight of the coils) Tools required: soldering iron + solder large pliers regular pliers drill + drill bits socket wrench + small sockets (for nut on BNC jack and eyebolt locknuts) sand paper Construction notes: 1. drill hole in center of each PVC plug (2 to fit an eyebolt, 1 for the BNC jack). 2. install the eyebolts (nut + washer on outside, washer + nylon self-locking nut on inside of plug and of the T-piece) 3. install the BNC jack (washer + washer with solder lip + lock washer + nut on inside of PVC plug) 4. drill hole next to eyebolt and BNC jack, into the plug. Avoid hitting the washer/nut 5. take 2 pieces of 25 cm of heavy gauge insulated multi-strand copper wire. 6. strip off about 5 mm of the insulation 7. solder wires to center conductor and ground (solder lip) of the BNC jack 8. insert the wires and plug with the BNC jack into the center hole of the T-piece 9. press in tightly with large pliers (no glue required!!) 10. run each wire through the hole in one of the 2 remaining PVC plugs 11. insert the two plugs into the T-piece, and press fit. 12. pull out the wires 13. VERY carefully bend half of the final turn of each Slinky coil (both ends of each coil), such that it is perpendicular to the cross section of the coil. See pictures. Use a bending radius of about 1 cm. The steel wire is very brittle. You can only bend it once, and only if you use a sufficient radius. 14. were the bent part of the coil separates from the rest of the coil, sand the surface of the coil and of the bent part over a length of about 1-2 cm. Solder. 15. open each eyebolt and hang the bent part of one end of each coil in it. Close the eyebolt. 16. strip about 6-7 cm of insulation of each wire 17. sand the surface of the first turn of each coil over a length of about 1-2 cm. 18. solder 1-2 cm of the stripped wire that is closest to the insulation, to the coil. 19. wrap the rest of the stripped wire around it, and solder. See photo below. 20. compress each coil, and run about 6 m of 3 mm Ø nylon cord through it, and tie it off to the eyebolt. 21. suspend the T-piece from the eyebolt on top. 22. run the nylon messenger (support) wire through the coils, from both sides of the T-piece to whatever (tree, wall, ...), and tie off. If desired, end-insulators can be used. E.g., traditional egg-insulators or tie-wraps (simple & cheap). 23. Leave enough support wire to run back to the end of the stretched coil. 24. stretch the coils both coils to the same length (up to 4.5 m), and tie off the bent turn of each coil. See photo below. 25. attach coax to the BNC jack. 26. ready for operation! Performance notes: 1. As a receiving antenna, signals are about 30 - 40 dB stronger than with a thin 5 m multi-strand wire (no tuner). 2. With 25½ m (84 ft) of RG58A/U coax and the slinky coils stretched to 4.25 m (14 ft) each, I can easily tune to SWR lower than 1.5 on all bands 10 m through 80 m + 6m (can't get it tuned on 160 m). With 10 m (33 ft) of coax, I get significantly more output (per the power/SWR meter of my tuner) on 40 m, but very sharp tuning peaks on 20 m. 3. I have added a W2DU-style balun at the antenna base (this is actually a ferrite-loaded coaxial RF-choke that just happens to yield the same result as a 1:1 current balun). It is made of 24 ferrite beads (Amidon FB-77-6301) on a 25 cm (10 inch) piece of RG400 coax. The beads fit snugly on RG400, whereas RG58 is too thick (use 3 dozen FB-73-2401 beads instead). Without the balun, SWR is 1:2 on 20 m, and 1:1.4 on 40 m. No change on the other decade bands. I do not use a station ground. 4. I still have to try out this antenna with twinlead feed line or "ladder line" plus a 4:1 balun, as I have already done with my "¼ size" Cobra folded dipole. |
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| Firetrap | Thursday, 21. January 2010, 20:25 Post #3 |
26CT100
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Thanks for taking the time to post this! Ill have a read after some food! Do you mind if i put this in the "How To" forum as a separate topic for others to use? Cheers! Lee |
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Charlie Tango DX www.cbradiouk.com | www.charlietango.co.uk Domain Names For Sale V5Bid.com | Ypsi1.com | 041183.com | Hiya.Mobi | Oddiz.com | DoddP.com Life is not a Conspiracy - Enjoy it, don't be consumed by The Conspiracy Effect | |
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| VoG | Thursday, 21. January 2010, 20:26 Post #4 |
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I'm probably going to show my arse here and display my total ignorance... BUT . . . If you're running ladder-line to the centre-fed dipole surely it is balanced? So why would you need a Balun? |
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| 2EC837 | Thursday, 21. January 2010, 20:27 Post #5 |
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![]() ![]() With Ugly Balun ![]() ![]()
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| 2EC837 | Thursday, 21. January 2010, 20:30 Post #6 |
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This was a cut and paste, but It is at the shack end to transform the ladder line to 50 ohm coax for the radio. |
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| VoG | Thursday, 21. January 2010, 20:32 Post #7 |
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Ahhh, now I understand. Fine, if there's a co-ax link to the rig it makes sense. Thanks |
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| Deleted User | Thursday, 21. January 2010, 23:16 Post #8 |
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I'm sure running 300 or 450 ohm ladder line ,the best way would be to put it to a balanced line tuner and as long as the "Slinkys" are the same length this would work.I took the "Silly" coax off my Full size G5RV and putt 300ohm ladder on it in the same way.......worked Far better.Only thing is don't run ladder near metal objects as this can "Jigger" the good work it does.Just my "Humble View" on the subject .........good luck.........and if it works poor you can always play with it on your stairs Lee!!!! :lol:
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| Deleted User | Thursday, 21. January 2010, 23:23 Post #9 |
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Another good tip for any "Would be" antenna builders.....better than spending money on pointless things.........invest £30-£40 on the ARRL antenna hanbook.Its as thick as a Chinese telephone directary.....I have one,best money I spent,this shows you all the antennas and how to build Quads,Yagis,Marconi "T",Slopers ect.......read this and enjoy the DX!!!!!
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| HomerBB | Friday, 22. January 2010, 00:20 Post #10 |
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2 Charlie Tango 004
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Considering the slinky is not a straight wire how do you determine the proper length? And what would it be for 11 meters? |
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2CT004/2WR183 | |
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| 2EC837 | Friday, 22. January 2010, 03:15 Post #11 |
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Very well said.I personally would not use the slinky for TX but it will work.For SWL it should work as well as a wire. |
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.........good luck.........and if it works poor you can always play with it on your stairs Lee!!!! :lol:
8:37 AM Jul 11