30 feet of PVC pipe and around 260 feet of wire yielded him a good antenna for 1830kHz. So I am willing to bet using a bit more wire slightly more closely wound would provide a usable 30 foot antenna for down on 1710kHz or the other popular 1610kHz frequency that pirates and part 15ers alike use.
I am really considering trying to build this as it sounds like it would be fun to at least try and compare to my 30' high x 60' long windom antenna I currently use for broadcasting on the AM dial which performs great as is and covers the whole town with 10 watts.
Also I can see where a helix would benefit me since I could set it up in a part of my yard where it would be quite surreptitious and just run coax out to it.
I currently have a roll of 100' of 16 gauge speaker wire that I could split and make 200' of. That won't be enough but I could still make a temporary test antenna that resonates at a higher frequency and then just use an antenna tuner to tune up to it right? (I'm asking because I don't know if it would properly tune up with helix type antennas)
Also I wonder just how much voltage would be induced near the top when running 10 watts carrier into it? I really don't want to be making a giant Tesla coil lol but it sure would be interesting if the antenna lights itself up with sparks. Probably wouldn't be healthy for my amplifiers finals Definitely will have to get out a florescent light bulb and wave it near the top just to see if it glows!
Well has anyone here heard of any AM pirates using this type of antenna? I wonder if I will be the first to try?
Bahhh.. just realized the slinky antenna is technically a helix antenna which has been used by pirates. Anyways I figure 1/4 wavelength would be more suitable than 1/2 wavelength of wire, so make that 130' to 150' of wire will be needed. I am a newb when it comes to helical antennas so any tips or ideas are greatly appreciated.
www.lpam.nl have an helical with a matching top hat that works well for the am band, the site is in dutch but you can use google to translate it into english, from memory the aerial is 2metres in height.
Well the more I think about this the more I realize it was just a neat idea but I don't have the money or parts I need at the moment to try it. Maybe in the near future I will grab a few slinkys and hook them together, and use some plastic line or twine and put it through the slinky antenna to hold it up so it doesn't continually stretch in the wind. Problem is I rather get the groundwave signal out there instead of skywave, so for me I rather go vertical.
There's little info on helical antennas likely because they are such a pain to get right when you're shortening an antenna below 1/10 wavelength. They are more related to mini Tesla coils in this range because of the insane voltages that can develop on them, not to mention vary narrow BW, requiring tuning before every broadcast. (I used to have one for a LowFER operation)
Slinky or helical dipoles are MUCH easier in that they don't require perfect grounds and unbalanced currents are easier to deal with.
Post by sonofpigmeat on Jan 18, 2015 22:21:38 GMT -6
I agree with cm. You need to fashion a capacitance hat for the thing, lay out a bunch of groundwires, 120 is the usual standard, and build an antenna tuner/match. Then you've got to screw around tweaking it for your frequency of choice.
Even running 10 watts into the thing will generate enough voltage to bite you several feet away, especially if the ground is wet.
I speak from experience, I've melted several lengths of pvc trying to build them. I do like them as a receiving antenna for the lower HF bands in quiet areas. You can use a couple of wires as a counterpoise if you want. They receive low angle sigs very well, picking up dx stations up to a good hour before a dipole or a longwire will.
The helical dipole is favorite of mine for transmitting and receiving. All you need is a rope and some wire, (lots of wire wound tight around the rope.) You cut the wire in middle, attach some ladder or tv line, run it to your tuner and you're ready to roll. A solid performing wideband antenna.
Beware of neighborhood heathens. I made a helical dipole for listening at home. Some SOB stole the thing in the middle of the night. I guess he needed the rope?
Thanks sonofpigmeat for the info. Welcome to the forum! This is one project I still haven't got around to yet. Now I have renewed interest after thinking on it again. Only issue atm is that I don't have enough wire right now to accommodate the many wraps needed to make a helical for those low of frequencies. When I get the parts and wire this is definitely on my to-do list since I always wanted to use my MW rig for operation while camping or other places where a full sized T or inverted L takes too much to setup.
I've used helicals of various sorts on mediumwave, and they're a complete pain. The bandwidth is inherently small, so you have to use a capacity "hat" and you still have to mess with the modulation to get any treble through the system! The wider the bandwidth, the lower the efficiency - it's a no-win, I'm afraid. They're horribly inefficient. The same amount of wire used for a Windom or an inverted-V will give much better results!
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