I need to build two minimalistic antennas for RX/TX at ~433MHz. I have insulated solid core copper wire, but I need to make it perfectly straight. I was thinking of using the type of sticks you set next to plants to support them while growing but perhaps there is a better, less ugly way. What do you suggest?
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$\begingroup$ can you please update your question with more information ? what type of copper wire ? multi-strand/single-strand ? what thickness ? as well as the antenna design you like to build ? and any further information you may volunteer .... help us to help you. $\endgroup$– Edwin van MierloCommented Sep 28, 2016 at 8:38
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$\begingroup$ It is single-stranded wire, 1mm thickness. I need two omnis. $\endgroup$– user400344Commented Sep 28, 2016 at 8:41
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2$\begingroup$ If you're just making an antenna, there's no need for the wires to be perfectly straight. Just a normal amount of straightness is more than sufficient. $\endgroup$– Phil Frost - W8IICommented Sep 28, 2016 at 15:44
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2 Answers
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Based on the information you have given in the post and comments, the simplest way to construct a "omni" for 433 MHz, is by using an SO239-chassis-connector, and solder/screw the antenna elements directly onto the connector. Make sure the ground-plane elements are bended down, to ensure a close match to 50Ohm impendance.
The single-strand/1mm wire will do nicely without supports.
Here is an example:
The dimensions can of each of the wire elements would be 300/433/4 (a quarter wavelength), each element would be the same length.
Start with somewhat longer elements, and "prune" them until you have the lowest SWR for the intended frequency.
If this is not what you are looking for, please update your post with more information.
answered Sep 28, 2016 at 10:09
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$\begingroup$ I do have one question though - another ham told me I'd need at least 1/2 wavelength on both antenna and radials to get resonance. I can do that, with your design ( excellent build btw ), I just need some 2-3mm copper for the radials. Is it worth it in terms of reception? $\endgroup$ Commented Sep 29, 2016 at 4:30
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$\begingroup$ @user400344, all elements of the shown antenna are 1/4 wavelength. so if you measure from the tip of the vertical radiator, to the bottom tip of one of the ground-plane elements, you get 1/2 wavelength... :-) ... for a GP antenna like this you do not use 1/2 wave elements. The advise you were given was wrong $\endgroup$ Commented Sep 29, 2016 at 6:57
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$\begingroup$ So effectively, it is a nice dipole? $\endgroup$ Commented Sep 29, 2016 at 6:58
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$\begingroup$ not really, it works differently, a dipole would be a balanced antenna (and therefore should not be fed directly with coax), while this GP antenna is an unbalanced antenna, and can be fed with coax directly. $\endgroup$ Commented Sep 29, 2016 at 7:00
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1$\begingroup$ if you have questions in regards to what materials to use for antenna building or how to, or techniques of building, why don't you post a new question. short answer; I would not use steel, as the "velocity factor" and "resistance" is quite differently, which may introduce other design criteria. $\endgroup$ Commented Sep 29, 2016 at 7:02
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To straighten single-conductor copper wire, clamp one end in a vice, grab the other end in a pair of lineman's pliers and turn the pliers so that the wire is wrapped around them a bit. Pull to tighten the wire, then hit the wire-end of the pliers with a hammer (going away from the vice). Easier to do than to describe.
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$\begingroup$ I can't post an image inline, but mine is like yours in most respects. I was wondering if I can just cut the tiny coil on the FS1000A 433M TX module, and solder my coax core to that spot. Can I? I am increasing the TX module voltage from 5 to 12, hopefully I can punch through a wall or two then. I am retaining 5V to the data pin, would there be any damage from increasing it when the rest of the module is at 12V? $\endgroup$ Commented Nov 1, 2016 at 13:32
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$\begingroup$ Moderators: yes, I could start a new question, but these are follow-up questions, and others who need the same info may benefit from a single thread. $\endgroup$ Commented Nov 1, 2016 at 13:34
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$\begingroup$ coils add loss - you will get the best signal with the straight piece described in the OP. $\endgroup$– SDsolarCommented Mar 23, 2017 at 8:46