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Recent content by Tesla23

  1. T

    C++ is there a way to define a function that takes any size variable?

    One way to do this in c++ would be to derive all types you want to pass from one base class, e.g. MyObject enum { OBJECT1 = 1, OBJECT2 = 2}; class MyObject { public: virtual int Type() = 0; }; class Object1 : public MyObject { public: virtual int Type() {return OBJECT1;} }...
  2. T

    8 bay TV Antenna question

    If the assumption of 300 ohms for the bowties is correct, then this is how you combine them: All the transmission lines are 300 ohms (D/d about 6), except for the quarter wavelength either side of the balun connection at 'B'. If you make this line 424 ohm (D/d about 17), then that will...
  3. T

    8 bay TV Antenna question

    Assuming that the feed impedance of one bay is 300 ohms, then you would run 300 ohm line to where they join, and when you join them in phase, the impedance would be 150 ohm as you say. If you want 300 ohms at the junction (to use your standard balun), then what you could do is make the last...
  4. T

    8 bay TV Antenna question

    You won't be able to optimise your antenna simply by assembling snippets of information. In an array like this the items interact, of particular significance when you want broadband operation. You have taken a commercial design (which may or may not have been reasonably optimised), and tweaked...
  5. T

    8 bay TV Antenna question

    You need a fairly broadband antenna to cover the UHF channels (510 - 640MHz), and you want to throw in a couple of VHF ones as well, down to 79MHz. This means that you have to be careful in taking a narrow-band design, like that ARRL collinear, and using it for likely dimensions. Spacing to...
  6. T

    8 bay TV Antenna question

    Another thing that occurred to me is that comparing the two feeding arrangements you show in your first post, one advantage of using open wire feeder to combine the arrays: is that you know that you are combining the two arrays in phase. When you use separate baluns like this: you run the...
  7. T

    8 bay TV Antenna question

    The fact that this combiner: gave you a significant increase in signal strength means that your impedances are nothing like you expect. But unless you have a network analyzer, or want to mess around with antenna modelling software, you really have no way to find out. If it interests you...
  8. T

    8 bay TV Antenna question

    I just roughly measured this splitter: which looks identical to yours, and the transmission to the two ports are matched to around 0.2dB and less than a degree of phase difference. Also they have about 20dB of isolation. This would be good to combine your antennas, hopefully yours is similar...
  9. T

    8 bay TV Antenna question

    This splitter: is a dead ringer for one I have (with different branding), but the fact it states 3.5dB insertion loss means it isn't resistive. Hopefully it is a reactive in-phase splitter (where if you use it as a combiner the two inputs are added in-phase), so I would try it first. I'd be...
  10. T

    8 bay TV Antenna question

    If you double the number of elements and get everything right you may get 3dB extra gain less the loss in the extra combiner, whereas if you double the height you should get 6dB from increased field strength! (with a few caveats on local terrain.) Going up 40% should get you that 3dB. Just...
  11. T

    Need an accurate oscillator on 15.186667MHz

    These are the folk I have used, decades ago! **broken link removed** The web suggests they may still be in business - no guarantees..
  12. T

    TL071 Audio Amplifier with 6 channel mixer.

    Your hearing loss reminds me of my late father's, almost completely deaf in one ear and a rapid rolloff above 1kHz in the other. About 20 years ago he presented me with a graph like yours and his initial request was to help him hear the TV, without deafening everyone else. I made him an...
  13. T

    How do transmitter & receives work these days with no LC circuit?

    It's amazing what they can integrate these days, check out the ADF5355 https://www.analog.com/media/en/technical-documentation/data-sheets/adf5355.pdf it's got a VCO that tunes from 3400MHz - 6800MHz (with Ls and Cs on chip), along with a PLL, and frequency doubler and dividers so it can...
  14. T

    calculation dilemma

    This type of problem can also be solved with the Extra Element Theorem: https://en.wikipedia.org/wiki/Extra_element_theorem by inspection: \[ Z_\infty = 50||70 = 350/12 \] \[Z_e^\infty = 60||60 = 30 \] \[Z_e^0 = 20||30 + 40||30 = 204/7 \] \[Z = \frac{350}{12}\frac{10 + 204/7}{10 + 30} =...
  15. T

    RF skin current

    I had a quick look at that, and I'm sceptical. There appears to be no justification for the statement "At the same time the radiation resistance is raised considerably while only raising the IR losses slightly". I can't see any reason why the radiation resistance should rise, I suspect it stays...
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