kavea

No, dimensions are frequency dependent

Yes, I cut 3 rods of 1m to get four half elements

How do you control the spindle ?

Ok good idea. However it will not properly work if you mix different designs. I would take all dimensions from wb5cxc Yagi, it seems to have a nice performance. Good luck and share the photo when you finished

It will work, not a problem, you will increase the gain if designed in a right way. But with more directors it becomes less and less portable.

To check no, since the scale is just an indication, but if you connect two different transmitters to the same radiating cable or a radiating wire (antenna) you can say wich one inject more power.

Yes it can be used anywhere, the best antenna booster is the antenna itself. You are operating on HF in your car ?

1/ I'am an engineer in antenna design having a PhD, i understand very well how it works. Moreover, the electromagnetic simulation confirms very well the working condition of this antenna (cf. my blog). 2/ Google for "coaxial cable dipole" if you don't believe me. The electrical structure of the driven element is a folded dipole. The center break of one inch ? It's not true and depends on the cable diameter and frequency. If a want an antenna working at 5 GHz its total length will be around 1 inch so you understand that you cannot have a break of 1 inch all the time :) Moreover the impedance depends a lot on the position of the driven element compare to the director and the reflector, there is a electromagnetic coupling between these three elements which modify the S11 parameter.…

1/ I'am an engineer in antenna design having a PhD, i understand very well how it works. Moreover, the electromagnetic simulation confirms very well the working condition of this antenna (cf. my blog). 2/ Google for "coaxial cable dipole" if you don't believe me. The electrical structure of the driven element is a folded dipole. The center break of one inch ? It's not true and depends on the cable diameter and frequency. If a want an antenna working at 5 GHz its total length will be around 1 inch so you understand that you cannot have a break of 1 inch all the time :) Moreover the impedance depends a lot on the position of the driven element compare to the director and the reflector, there is a electromagnetic coupling between these three elements which modify the S11 parameter. 3/ Google for "Yagi antenna". If you electrically connect director to reflector and to the driven element it will not work.Read "Antenna Theory" from Balanis, it's a good book to begin with antennas.

What frequency band you are interested in ? The term SDR is too huge, today it often means just a software receiver. For example i use an "SDR Play" which works from 1 MHz up to 1.5 GHz, and depending on the frequency band i have different antennas, because you cannot have an universal antenna which could cover all this spectrum in an efficient manner. But generally speaking, if your SDR receiver has a 50 ohm input impedance then there is no any difference from any other 50 ohm receiver in terms of antenna requirement, you can use any antenna you want. There are no "SDR antennas". However there are broadband antennas, like Discone, but even so, you would not be able to cover all the band down to 1 MHz..In your case if you want ONE small antenna for all bands, i would …

What frequency band you are interested in ? The term SDR is too huge, today it often means just a software receiver. For example i use an "SDR Play" which works from 1 MHz up to 1.5 GHz, and depending on the frequency band i have different antennas, because you cannot have an universal antenna which could cover all this spectrum in an efficient manner. But generally speaking, if your SDR receiver has a 50 ohm input impedance then there is no any difference from any other 50 ohm receiver in terms of antenna requirement, you can use any antenna you want. There are no "SDR antennas". However there are broadband antennas, like Discone, but even so, you would not be able to cover all the band down to 1 MHz..In your case if you want ONE small antenna for all bands, i would suggest an active antenna (google mini whip). I would be a good trade off but not a perfect solution. Unfortunately small, broadband and efficient (at the same time) antennas don't exist and cannot exist.

If your antenna has a stable impedance of 450 ohm over 3-50 MHz, than you don't need a tuner, otherwise you still need a tuner, but this balun helps a lot to tune wires to 50 ohm. In my case i can easily tune a 5 m length wire to 80 m band with LDG 100 tuner, without this balun i cannot tune this short wire. Another advantage to use the balun is some common mode rejection which decrease the radiation from the coaxial cable. To increase the power handling up to 200 W you need one FT240-61 toroid, it has the same AL of 170 as two FT114-61, so this should give the same result, but with increased power handling.

Nothing special, as usually do not put it near metallic objects and respect the polarization (usually vertical so put the antenna like on first image, connector up or down)

In practice a wifi antenna is made to be matched at both 2.45 GHz and 5 GHz (laptops etc). For home purposes it can be done with horn type antennas since it can provide very broadband response. In these two cases you dont need anything. However if you have two different antennas, one for 2.45 and other for 5 GHz band you will need a switch or a diplexer to isolate two antennas. Otherwise their impedances will be seen in parallel from the receiver.

Your welcome! The monopole should be placed 31 mm from the back and at the middle from the sides i.e. at 43 mm (86 / 2). This position has been optimized in the 3D FEM solver, but theoretically it's lambda/4 from the back . Any metal sheet will work if you respect the internal dimensions of the horn, an other point is the poor conductivity of some alloys which can lower the gain. And not all alloys are solderable. The best choice still copper, but more expensive than brass.

The monopole is exactly 3 cm length, it seems to be longer because of the optical effect ;) Can you clarify your question about measurements ? You are talking about the physical dimensions or the S parameters measurements ?

Yes, the diameter of the wire will change the BW but also the central frequency. However 1mm +/- 0.5mm will not affect a lot the result.