All posts by Chris S
Below are all of Chris S's postings, with the most recent are at the bottom of the page.
Ok. Good luck.usually there would be four rows each row with a dipole all fed in phase and having a bigger reflector. The single rectangle might need adjustable size to tune it .
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That's good news Nick . I think that the addition of the reflector gave the main boost to the gain and made the dipole a better match. Not convinced that so many sets of directors relatively close together give much improvement but it works well . So cant knock it! We are getting warm weather again so any interference due to high pressure will be a good test.
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Z beams need to be long in A group ,short at CD . Just like standard Yagis. They were not As broadband as X so were fairly evenly spaced . You might notice that X directors are closer together near the dipole to control the overall aerial bandwidth. Thick or x elements can be around 0.8 as long as equivalent thin elements.
I was an electronics technician . College courses were in telecommunications and radio.
looking at the gain diagrams of the various types if aerial on that aerial website I listed is very educational.
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The old large X in analogue days was no better than an H . THey were just cheaper to make . A bit of a gimmick rather like tri beam aerials are today. The only advantage was that some versions of the X could reduce unwanted reception at 90 degrees from the wanted direction.
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A 27 MHz X would have arms each about 9 feet long ! with a similar response to an H . A quad driven element with quad reflector would have more gain and sharper beam and take up less space.
Nick . an excellent DIY wifi aerial is here Making your own Bi-Quad (Wi-Fi) antenna
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J the coverage checker shows you should be able to get most of the channels from Sandy Heath . You are in range of some other transmitters so you may have to tune in manual mode to be sure of getting Sandy heath . I think a good outdoor wideband aerial is essential in such a complex multi transmitter area.
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Nick . I don't see how you can build better than a parabolic dish ! Unless you look in your book for a really old but efficient aerial a dual rhombic. These are huge for shortwave but not too bad at UHF and above .
You can buy wifi extenders which have the electronics combined with the aerial (look on Amazon) I have one that reaches nearly a mile range. SWR matching is not so important for reception . So you can just guess and use a 1:1 balun for a low impedance dipole or a 4:1 for a higher impedance dipole . A basic dipole is about 73 ohms but adding directors and reflectors brings it lower . So a folded dipole is used which is 300 ohms by itself but adding elements brings it nearer to 75. the Xs are effectively full wavelenth so are high impedance. I found an article that described the tall narrow rectangle that you use as having a low impedance around 50 ohms. Apparently the rectangle is equivalent to one bent half wave dipole stacked on another.
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You can find designs for wifi antennas online . I agree that swr is more important for wifi as it transmits .
The biquad I linked to was calculated for 50 ohms . Maybe the 30mm is the calculated value . The lower figure gives more gain . Perhaps they usually accept a worse SWR than optimum.
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I agree with Chris. The reception should be good . It may not help to check out other aerials in the area because they presumably were selected for the old Sudbury frequencies.
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Wednesday 29 August 2018 3:43PM
Or by multi reflectors do you mean a 5 row grid?