Posted: 2/2/2015 1:10:32 PM EDT
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I didn't want to high-jack the "New Antenna" thread, so I am starting this with questions about this post:
Quoted:
Remember, start at 33%, tune the length for 1:1 at about 3600MHz, then start moving the feedpoint around to bring the other bands in. It's best if you set up the ends so they can easily be lowered and adjusted for length. Leave an extra 15' of wire rolled up on each end to facilitate that. How does the extra rolled up 15' of wire at each end affect the tuning? What diameter loop should it be rolled into? Which leads me to ask: Is there a way to "trim" wire length without cutting until the optimum length is found and then making a single cut? Possibly some method that helps you find the "one trim too far" without actually cutting the wire. |
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Quoted:
I didn't want to high-jack the "New Antenna" thread, so I am starting this with questions about this post: Quoted:
Remember, start at 33%, tune the length for 1:1 at about 3600MHz, then start moving the feedpoint around to bring the other bands in. It's best if you set up the ends so they can easily be lowered and adjusted for length. Leave an extra 15' of wire rolled up on each end to facilitate that. How does the extra rolled up 15' of wire at each end affect the tuning? What diameter loop should it be rolled into? Which leads me to ask: Is there a way to "trim" wire length without cutting until the optimum length is found and then making a single cut? Possibly some method that helps you find the "one trim too far" without actually cutting the wire. The idea behind rolling it up is a way to trim without cutting. That's the entire point. I roll it up in about a 6" diameter and secure it with Velcro. It doesn't affect tuning at all. Here is a photo of how I secure my wire to insulators. I don't use any hardware, just that knot you see. Just un-tie, move the wire through the insulator, and re-tie. 
Here is a photo of an antenna in progress. This is before I started using the securing method shown above. Once you are done you can cut the entire coil off, or leave a few feet coiled up for future fine tuning. 
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Quoted:
The idea behind rolling it up is a way to trim without cutting. That's the entire point. I roll it up in about a 6" diameter and secure it with Velcro. It doesn't affect tuning at all. Here is a photo of how I secure my wire to insulators. I don't use any hardware, just that knot you see. Just un-tie, move the wire through the insulator, and re-tie. https://farm8.staticflickr.com/7507/16170320535_c59c562485_c.jpg Here is a photo of an antenna in progress. This is before I started using the securing method shown above. Once you are done you can cut the entire coil off, or leave a few feet coiled up for future fine tuning. https://farm4.staticflickr.com/3907/14708256042_65ea268ca8_c.jpg Quoted:
Quoted:
I didn't want to high-jack the "New Antenna" thread, so I am starting this with questions about this post: Quoted:
Remember, start at 33%, tune the length for 1:1 at about 3600MHz, then start moving the feedpoint around to bring the other bands in. It's best if you set up the ends so they can easily be lowered and adjusted for length. Leave an extra 15' of wire rolled up on each end to facilitate that. How does the extra rolled up 15' of wire at each end affect the tuning? What diameter loop should it be rolled into? Which leads me to ask: Is there a way to "trim" wire length without cutting until the optimum length is found and then making a single cut? Possibly some method that helps you find the "one trim too far" without actually cutting the wire. The idea behind rolling it up is a way to trim without cutting. That's the entire point. I roll it up in about a 6" diameter and secure it with Velcro. It doesn't affect tuning at all. Here is a photo of how I secure my wire to insulators. I don't use any hardware, just that knot you see. Just un-tie, move the wire through the insulator, and re-tie. https://farm8.staticflickr.com/7507/16170320535_c59c562485_c.jpg Here is a photo of an antenna in progress. This is before I started using the securing method shown above. Once you are done you can cut the entire coil off, or leave a few feet coiled up for future fine tuning. https://farm4.staticflickr.com/3907/14708256042_65ea268ca8_c.jpg You sure that's not an end-loaded coil? |
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Quoted:
You sure that's not an end-loaded coil? Quoted:
Quoted:
Quoted:
I didn't want to high-jack the "New Antenna" thread, so I am starting this with questions about this post: Quoted:
Remember, start at 33%, tune the length for 1:1 at about 3600MHz, then start moving the feedpoint around to bring the other bands in. It's best if you set up the ends so they can easily be lowered and adjusted for length. Leave an extra 15' of wire rolled up on each end to facilitate that. How does the extra rolled up 15' of wire at each end affect the tuning? What diameter loop should it be rolled into? Which leads me to ask: Is there a way to "trim" wire length without cutting until the optimum length is found and then making a single cut? Possibly some method that helps you find the "one trim too far" without actually cutting the wire. The idea behind rolling it up is a way to trim without cutting. That's the entire point. I roll it up in about a 6" diameter and secure it with Velcro. It doesn't affect tuning at all. Here is a photo of how I secure my wire to insulators. I don't use any hardware, just that knot you see. Just un-tie, move the wire through the insulator, and re-tie. https://farm8.staticflickr.com/7507/16170320535_c59c562485_c.jpg Here is a photo of an antenna in progress. This is before I started using the securing method shown above. Once you are done you can cut the entire coil off, or leave a few feet coiled up for future fine tuning. https://farm4.staticflickr.com/3907/14708256042_65ea268ca8_c.jpg You sure that's not an end-loaded coil? When I cut the coil off the end nothing changes. Having a little inductance at the end of the wire really makes no difference. It's not like a capacitance hat or the like, and it's not a vertical. And the coil is not exactly an organized, serious inductor, it's just a random ball of wire, not a real "coil". Now inductance in the middle or beginning of the wire, that's another story... |
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Quoted:
If it's bare wire you're good to go but if it's insulated you're adding an unknown inductance to the equation. Quoted:
You sure that's not an end-loaded coil? If it's bare wire you're good to go but if it's insulated you're adding an unknown inductance to the equation. I'm using 14GA insulated THHN and it doesn't seem to make any difference. |
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Quoted:
I'm using 14GA insulated THHN and it doesn't seem to make any difference. Quoted:
Quoted:
You sure that's not an end-loaded coil? If it's bare wire you're good to go but if it's insulated you're adding an unknown inductance to the equation. I'm using 14GA insulated THHN and it doesn't seem to make any difference. Anytime you add a coil in an rf circuit you're going to add induction. Maybe this isn't showing up on an swr meter but look at it with an antenna analyzer and you'll see the change in inductance as well as in the reactance. Hence the efficiency will drop. Remember.. a dummy load presents a 1:1 swr. Antennas can be physically shortened for a specific frequency by adding induction coils as is the case for many mobile antennas for HF freqs.. Dipoles can also be shortened somewhat. Just remember.. Everything is a trade-off.. Here's a linkie for a loaded dipole for 80. http://www.qsl.net/vk3jeg/loadpole.html Good luck & have fun tinkering... |
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Quoted:
For clarity, aa...I was being funny. Now he says something! You know, I used to take the extra and lay it along the wire like everyone else, but it was just too much of a pain to manage, with cable ties and whatnot to secure it. So one day when tuning an antenna I just rolled it up and not only did it work, it was so much easier. |
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In your lowest band, 80 meters, you want to tune to 3.55 mhz (lowest SWR). That will make the
other ham bands line up with the harmonics of the fundamental freq. That is, 7.1 mhz, 14.2 mhz, 17.75 mhz (and still good for the 18 mhz 17 meter band), 21.3 mhz (if you have a split that will support use of 15 meters), 24.85 mhz (and still good for 12 m), 28.4 mhz (just fine for 1 meters). Actually, the higher bands will all tune a little higher than that quoted above due to end effects, and thus, even better aligned with the ham bands. If a 66' OCFD, adjust it for 7.1 mhz. With an OCFD don't just trim one end, or trim both ends the same amount. Trim the longer end about the same proportion as the longer is to shorter. If you have a 1/3-2/3 split, and want to take off 6", then take 2" off the shorter end, and 4" off the longer end. |