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About Bosse

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  • Birthday 05/05/1962

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    Being a weirdo
  1. Because different receivers and transmitters uses different brands of connectors, and cable connectors wich you might use, comes in different brands, it is not useful to express recommended cable-lenghts in inches or millimetres, reason is the dimensions of the connectors are not completely standardized and exact dimensions are essential, when making a matched transmission cable for use with equipment wich is not perfected. However, for my "old type" lawmate receiver, I have made a goof proof patch and I used Radiall connectors and RG-174 cable from Bedea. Components used are ( in ELFA numbers), you can translate it to yours, I don't have the time to do that for you right now, sorry for that: 46-123-13 46-122-06 55-909-14 Link to ELFA (for reference) is: http://www.elfa.se/en/ The measurement of the finished cable is 170,0 mm, when I put a moderate strain on the cable. Measurement is from nut edge to nut edge. Measurement is NOT proved to be optimal, it just gives reasonable good results. This is to make it possible to get a reference point for some of those who do not like "odd multiples of 1/4 wave-lengths inside the cable with 0,66 x lightspeed factor disscussions" A side note: Recently, I wrote about the loss you should expect, using connectors. I wrote someting about 0,7 dB loss per connector and I wrote that was not too bad. Well, I screwed up, I should have written 0,07 dB. 0,07 dB loss per junction is not a huge amount of loss, concidering you are able to replace the antenna with another one, easy as pie. Best Regards, Bosse
  2. Ok, Feeling like I need to come back to this subject. I have not had the opportunity to make any flight or other tests recently. I am still conviced Bi-quads are great, only remember they are polarized, horizontally or vertically or at some other weird angle inbetween, you migh find great. Bi-Quads are the turbo-version of patch antennas in my oppinion, let it be they are somewhat more awkwarad in design, still they are quite simple but with high gain. Whenever I have some test results, I will come back on this subject. Best regards, Bosse
  3. As I assume Cyber-Flyer means, It is always best to make empirical studies and adjust the setup accordingly. Empirical approach is the final blow on a problem of this kind !!! However, strictly empirical way of looking at a problems, does not give as much feedback as the theoretical way does. Both are completely essential. Best Regards, Bosse
  4. Hello Cyber-Flyer and everone else ! Terry, I assume, you have already found out that you can use a wave-guide also known as a horn, not only as an antenna by itself, but also as the active element in a dish or parabolic antenna, wich is also the truth for some other antenna designs. (they are called parabolic but how many of them are parabolic and not spherical ?). The horn itself has a quite narrrow reception aperture, or beam-witdth as people like to call it. I have no numbers right now but you will easily find out if you look around on the net, I think it is less that +/- 10°. The dish will not widen the the angle, it will restrict it and enhance the gain maximum. The larger you make the dish, the narrower the aperture will be (mostly if the dish is parabolic that is). Now I'm guessing a bit more than usual: By knowing the maximum distance to the transmitter, the sensitivity of your receiver and the field-strengt of the source signal, you can optimize the size of the dish. I do not think you will benefit from a 25 meter dish if the transmitter is only 1000 meters away, to make a funny example. You can make a dish with a customized aperture shape to some degree. Radar antennas and radar reflectors used in aviation typically have an elliptical outline to obtain what I guess you are looking for. Do not forget that a dish will put more strain on your antenna stand and your servo motors. If you want it to move snappy, then the stand must be heavy or be fixed to something heavy, and the servo motors must be powerful enough. Best Regards, Bosse
  5. Bosse

    RC Autopilot Project for PIC

    You are right about the wind, or as I think of it, the turbulence. Best Regards, Bosse
  6. Cyber-Flyer. I think I know the reason of your objection now hehe. I guess you say "work with half wave-lengths" I say (or my source says), "work with ODD multiples of 1/4 wave lengths" Well, it is excactly the same, with one exception: the first multiple, or the first maximum you will find in the cable. Essentially I guess we agree ! Best Regards, Bosse
  7. It is quite possible a transmitter does not have an output impedance of for example 50 Ω, enventhough the manufacturer says so. Same goes for coax-cables. 1/4 wave gp antennas might not have an impedance near 50 Ω just because 1/2 wave ones do. This would force us to carefully adjust cable lenghts unless we use Baluns, wich would require us to know the excact impedance anyway. I wish I could afford a DIP-meter, Field-Strenght meter and a Network Analyzer. I would gladely make exepriments and tell you then. This is old well documented stuff. However, since it is a bit complicated, it requires much effort to get a hold on for laymen like myself. Best Regards, Bosse
  8. Terry, About Di-poles with reflectors. I am sorry I can't tell. However, I do have a extremely strong feeling the reflector, or director, if used, does not change impedance. It should be 73 Ω according to my feelings I guess you have looked at one of those round antennas with a di-pole as driven element and one round reflector as well as a round director ? I think those looks good myself. However, right now (just like the wind changes), I look more at wave guides (horn designs), for my next receiver antenna. Best Regards, Bosse
  9. Last thing I want to do is to make you sour but the "Odd multiples of 1/4 wave-lenghts" rule is what I have read. I could be wrong. (that happens regularly) I would be grateful to be enlightened. Best Regards. Bosse
  10. That's why I was smart enough to add "theoretically" To be safe, it is always best to use theoretically matched cable lengths. If you have access to instruments, you can tweak your setup from that point and get the best results. If you use almost perfect components, cable length will affect performance just like the books says. (just keep lengths short and forget about the millimetres) If you start wrong, from a theoreticl pow, and you can not check your performance with help of instruments, you might find it hard to find the right formula of success. Best Regards, Bosse
  11. I mean, theoretically, if you use Yb2normal's ground plane antenna design, you can forget about excact transmission cable length, just keep it short to reduce loss. Best regards, Bosse
  12. I mean it should be odd multiples of one quarter of one wave-length. Best Regards, Bosse
  13. The length should be odd multiples of one wave-length (approx 20.5 mm). You should concider whole transmision cable as being the whole length (including connectors), that is whole lengt of shielded transmission cable including all connectors, even those in your bought equipement. If the load on the reciver or transmitter is perfectly matched, this is not theoretically important however. Best Regards, Bosse
  14. Only by looking at a ground plane antenna, I get the feeling it is un-balanced. It has at least four ground plane radials and only one radiator. I never try to be smart. I just like to discuss and share what is important to my and yours interests. Best Regards, Bosse
  15. You might wonder why I spend time in investigating why this antenna works so well. I think it is very important to to investigate reasons of good results, thats all. Discussing reasons of less positive results can be interesting too, but this is so much more interesting. Best regards, Bosse