FT736R noise nil there's a pre-amp/converter at the antenna. Even with a hypothetical zero-noise pre-amp, you'll still have 1200K of noise. The important thing to grasp is that there is nothing you can do about this noise. Zero kelvin is total silence, water freezes at 273K, boils at 373K and 300K is a nice day. Let's just use 1200K for now.īy the way, K means kelvins. In some conditions it may be less, but usually it's a lot more. The noise temperature on 145 MHz is of the order of 1000K-1500K. It's the temperature of a 50 ohm resistor that, if connected to the radio instead of the antenna, would make the same racket.
To quantify noise we use a measure called noise temperature. I haven't even included noise of the receiver as it's usually swamped by the forgoing. Transport, appliances, weather, Sun, sky, QRM, splatter, tele-switches, computers the list is endless. Noise arises from almost everything electrical you can think of. I don't think there is much disagreement about this. In some places it's so noisy as to be virtually unusable. What's the reason for this surprising result? The answer is simple. If you had to choose between your huge 145 MHz downlink antenna, and a tiny 60cm lightweight, compact, suitcase sized, no-tune, elegant dish that you could genuinely hitch to a balcony which would you have? No contest, is there? And will you also believe me when I tell you that this little dish still worked excellently indoors, through a closed window? And the transponder signals effortless copy, noisefloor included. Sure enough, the Oscar-13 mode-S beacon was at least as strong as the 145 MHz beacon. So to prove it, I built a 60cm dish antenna from a spun aluminium lampshade I picked up when a local furniture store closed down. Will you believe that the answer is a puny little two-foot diameter dish! Yes, it surprised me too. A 2 metre dish? 4 metres? Several 55 element loop yagis? No idea?
Given that, what size antenna do you think is needed to receive the beacon comfortably? As comfortably as at 145 MHz. The transmitter outputs 1 watt to a 5 turn helix.
#DOWNLINK RUBBER BANDS PLUS#
Consider this Oscar-13 carries a mode-S transponder plus beacon. I have seen the future, and it works! Now it's your turn. Please don't read this article with a cynical smile and a "Oh here's just another wire-head evangelist on his soap box showing off". I will not make my case with airy-fairy hypotheses. S-band in practice is far simpler, cheaper and far more efficient than 145 MHz. I will dispel the myths that S-band requires special knowledge, enormous expense, huge dishes and a "techie" mentality. I will show why S-band (2400 MHz) is an infinitely better proposition. In this article I want to make a case for abandoning 145 MHz Phase III satellite downlinks. I will tenaciously defend any proposition that is a demonstrable fact, that can be supported and extended by reasonable analysis. If I don't know about something I keep quiet. I have never been given much to arguing matters of a speculative nature. Government Health Warning facts can seriously damage your health.
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