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Old Dec 26, 2014, 08:09 AM
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Joined Jul 2014
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Winded wire

I have straightened wire with drill tool but it got a bit into a form of screw,
If you slide it with nail it feels like grinder surface.
Does it have any effect on RF performance?
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Old Dec 26, 2014, 04:03 PM
Wait...what?
gbmarsh's Avatar
Canada, BC, Abbotsford
Joined Sep 2010
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Quote:
Originally Posted by Norbit View Post
I have straightened wire with drill tool but it got a bit into a form of screw,
If you slide it with nail it feels like grinder surface.
Does it have any effect on RF performance?
Should be fine. Don't over think this too much, hand straightening the wire is usually enough, wrapping around the former will get rid of some of the kinks as well.

Cheers,
Geoff
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Old Jan 23, 2015, 06:39 AM
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Joined Aug 2014
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Alex how thick does the metal for the ground plane need to be? I have some 3mm perspex that is coated one side with very thin almost foil like copper. But I'm thinking its too thin? or does it not matter?
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Old Jan 26, 2015, 11:35 AM
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Prague, Czech_Republic
Joined Aug 2010
92 Posts
Hi guys!
I'm going to make my first helical for 1258. Because it's my first, maybe I'm taking it too seriously so I want to ensure me:
Is it suitable to use as a support hard paper tube from carpet with diameter 64mm (2.52inch) which is -13% against recommended diameter for wood/paper? It has quite thick walls (~10mm =0.39in).
Or it will be better to use water tubing with outer diameter 75mm (2.95in), which is within the recommended range for PVC tubes? Problem is that these tubes are no longer made from PVC, but from Polyprophylene (PP). Will it signaficantly change calculations?
I'm anyway wondering, if for so wide range of useable outer diameters for PVC tubes (3000/f - 4600/f) isn't really needed to do any change in other dimensions and antenna will perform the same?
Is it generally better to have it thicker or thinner?
Thanks for any ideas and just tell me if I take it too serious .
Roman
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Old Jan 26, 2015, 02:05 PM
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United States, FL, Lady Lake
Joined Oct 2013
641 Posts
Quote:
Originally Posted by texmur View Post
Thanks Martin
I asked because the construction of my new antenna perfect fit to 7,5 turns and I did not want cut it if it is not necessary to have 7 turns


Here some photos: ( I am doctor ant that is why the construction is from hypodermic syringe IT PERFECT FIT TO 5,8gHz

Parameters:
* Design frequency 5800MHz
* 7,5 turns
* Internal diameter 19.5mm
* Wire diameter 2,2mm
* Coil spacing 12,4mm
* Reflector54mm
* Wave Trap size 6.4mmx3.2mm
* Wave Trap spacing from feed point 2mm
Brilliant! Perfect forming and mounting.
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Old Jan 27, 2015, 09:02 PM
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IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
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Quote:
Originally Posted by RBirdie001 View Post
Hi guys!
I'm going to make my first helical for 1258. Because it's my first, maybe I'm taking it too seriously so I want to ensure me:
Is it suitable to use as a support hard paper tube from carpet with diameter 64mm (2.52inch) which is -13% against recommended diameter for wood/paper? It has quite thick walls (~10mm =0.39in).
Or it will be better to use water tubing with outer diameter 75mm (2.95in), which is within the recommended range for PVC tubes? Problem is that these tubes are no longer made from PVC, but from Polyprophylene (PP). Will it signaficantly change calculations?
I'm anyway wondering, if for so wide range of useable outer diameters for PVC tubes (3000/f - 4600/f) isn't really needed to do any change in other dimensions and antenna will perform the same?
Is it generally better to have it thicker or thinner?
Thanks for any ideas and just tell me if I take it too serious .
Roman
Polyproylene is ok. No real change for that. I simply gave a wider range for pipes because the selection is limited. I gave a range for wood former much narrower to illustrate that you can have plenty of error and get a good antenna.

-Alex
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Old Jan 27, 2015, 11:46 PM
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United States, CA, Riverside
Joined Feb 2012
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hey Alex,

i had a quick question , when making the helical antenna does the length of the wire determine the frequency that the antenna is "centered" or is that mainly changed by : diameter of wire ; diameter of center coil "wind size" ; ground plane size ; winding step distance;

i was under the assumption that the number of turns simply changed the gain not the target freq, no less then 3 and more then 10 not much can be gained. If this is not the case can you please shed some light on the subject,

P.S. Thanks for all the DIY threads
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Old Jan 28, 2015, 05:13 AM
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shadowolfs's Avatar
United States, GA, Savannah
Joined Mar 2013
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Frequency is determined by the coil spacing and diameter. If you refer back to his calculations you see the dia and spacing is determined by a number/Frequency.
Also you can go beyond 10 turns but at the cost of efficiency.
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Old Jan 28, 2015, 05:32 PM
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thanks for the response , i was hoping alex would jump in
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Old Yesterday, 03:41 AM
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markus123456's Avatar
Switzerland, LU, Buchrain
Joined Aug 2006
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Quote:
Originally Posted by quadcopter007fpv View Post
hey Alex,

i had a quick question , when making the helical antenna does the length of the wire determine the frequency that the antenna is "centered" or is that mainly changed by : diameter of wire ; diameter of center coil "wind size" ; ground plane size ; winding step distance;

i was under the assumption that the number of turns simply changed the gain not the target freq, no less then 3 and more then 10 not much can be gained. If this is not the case can you please shed some light on the subject,

P.S. Thanks for all the DIY threads
According to my experiance, the overal lenght of the coil does have SOME impact on the target frequency. I never figured out exaclty how since I more or less always build helicals with complete turns, but as you cut the wire in small pieces, the frequency goes up and back down again depending on where on a 360 degrees turn you "cut" the top winding. Its however not the main parameter to determain the frequency. As often with HF things "everything matters". The obvious parameters have the bigest influcence, but the wave trap (asuming you use this to create the impedance match) also has a significant impact.

HTH

Markus
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Old Yesterday, 10:23 PM
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IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
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Quote:
Originally Posted by quadcopter007fpv View Post
hey Alex,

i had a quick question , when making the helical antenna does the length of the wire determine the frequency that the antenna is "centered" or is that mainly changed by : diameter of wire ; diameter of center coil "wind size" ; ground plane size ; winding step distance;

i was under the assumption that the number of turns simply changed the gain not the target freq, no less then 3 and more then 10 not much can be gained. If this is not the case can you please shed some light on the subject,

P.S. Thanks for all the DIY threads
Markus covered this pretty well but perhaps I can explain further:

The length of the wire changes the impedance. However, as you get farther away from the reflector, the wire has less effect on impedance. Remember that impedance does NOT mean resonance. We are targeting RESONANCE. if all we needed was impedance we'd all use resistors and not antennas.

When I refer to "centering" an antenna on a frequency, I am referring to resonance only. You want the antenna to properly capture the rotating wave. If your coil spacing is wrong, then your antenna will not work correctly as the wave will travel faster or slower than your antenna's turn rate. If you are too wide or too narrow, you will have impedance issues.

-Alex
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