Rich Griff Posted January 21, 2023 Share Posted January 21, 2023 Feb edition of the bmfa news arrived about fifteen minutes ago. Briefly glanced thru, some reading cover to cover this evening, reminder, refresh, reset of latest ( in hard copy on paper at any rate ) rules. Please may I ask, if a metal rod, insulated at both ends, touches something made of metal, can/does this cause a "radio interference" at all please ? Even if it's relatively close to the RX, like 6 inches or so away ? Nice to see some electronics, not read yet. I think I need to remind myself of the symbol for a nand gate and ways of configuring an and gate, part numbers as well. Cannot hear any noise from the football pitch so hope they are playing away today. Nice day, nippy but some tree top movement seen. Just hope it's calm enough there, we shall see. Quote Link to comment Share on other sites More sharing options...
GrumpyGnome Posted January 21, 2023 Share Posted January 21, 2023 Dead calm on East Coast of Yorks.... strong sun too so feels quite warm. Sadly I am puppy-sitting 😞 Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted January 21, 2023 Share Posted January 21, 2023 15 minutes ago, Rich Griff said: ...Please may I ask, if a metal rod, insulated at both ends, touches something made of metal, can/does this cause a "radio interference" at all please ? Even if it's relatively close to the RX, like 6 inches or so away ?... If you mean metal to metal noise, can happen when an RF field is present. Particularly if the metal is a resonant length at the frequency in question. Where the two metal objects touch, if they are only in grazing contact any contaminant on the surfaces can cause a semiconductor effect which will cause harmonics to be generated which will reradiate. Even a microscopic ark can occur at the contact point, creating all sorts of RF noise. If the metal parts are small enough, they don't create a large enough antenna to radiate significantly, this is why I never worry about putting a metal clevis on a metal throttle arm. Quote Link to comment Share on other sites More sharing options...
john davidson 1 Posted January 21, 2023 Share Posted January 21, 2023 Certainly used to be a problem on 37 together with noise from electric motors but 2.4 ghz ignores it , thank goodness Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted January 21, 2023 Share Posted January 21, 2023 (edited) 1 hour ago, Andy Stephenson said: If you mean metal to metal noise, can happen when an RF field is present. Particularly if the metal is a resonant length at the frequency in question. Where the two metal objects touch, if they are only in grazing contact any contaminant on the surfaces can cause a semiconductor effect which will cause harmonics to be generated which will reradiate. Even a microscopic ark can occur at the contact point, creating all sorts of RF noise. If the metal parts are small enough, they don't create a large enough antenna to radiate significantly, this is why I never worry about putting a metal clevis on a metal throttle arm. Yep, I reckon that's as good an explanation as any. I remember looking into all this 'metal to metal' noise way back in the 80s when it was a great excuse among us to blame glitches or crashes on it. I did my HNC in electronics 40 years ago, (they'd only just dropped valve technology off the curriculum at the time) but wouldn't claim to be an RF expert as it's a highly specialised subject (maybe even a bit of a 'black art' in years gone by). No matter how I tried, I could never replicate an example of MTM noise by simply having two pieces of metal rubbing together in close proximity to an RX, so possibly something a bit more subtle going on. Edited January 21, 2023 by Cuban8 Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted January 21, 2023 Share Posted January 21, 2023 I saw a fairly extreme example of the phenomenon, where a carbon prop was freewheeling on the shaft of a brushless motor when the nut had come loose. Carbon fibre being conductive acted like metal and the servos went mad. Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted January 21, 2023 Author Share Posted January 21, 2023 Thanks guy's. I was looking at a picture in bmfa news and noticed the longish section of throttle control rod screwed ? Into throttle snake and screwed into plastic clevis, which looked as if it would touch the engine or metal like looking engine mount. The throttle snake on my 40 has some heat damage, half way thro, and was thinking about a metal rod cranked so it would not touch the engine or exhaust. It's grounded, as in not flying, at the moment for this reason and one or two little jobs to do on it, resealing film edges and a bit of wieght saving, quarter inch off each undercarriage clamp bolts, all eight of them. Nice time flying but the drones and helo "disappear" against the trees and thicket surrounding 3 sides of the football pitch. Much windier about treetop level and wind just could not make it's mind up, little gusty from every direction, a trimming nightmare. All good fun and all home safe and sound in one piece. Quote Link to comment Share on other sites More sharing options...
Mike Blandford Posted January 21, 2023 Share Posted January 21, 2023 Pity the electronics diagram shows AND gates when they are actually NAND gates! There should be small circles on the outputs indicating the output is inverted. Mike 2 Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted January 21, 2023 Share Posted January 21, 2023 (edited) 1 hour ago, Mike Blandford said: Pity the electronics diagram shows AND gates when they are actually NAND gates! There should be small circles on the outputs indicating the output is inverted. Mike Not a very impressive design - the litho machines that I worked on years ago used a similar system principle to monitor water level/ flow and would be variable in performance. Eventually changed to an ultrasonic system which worked fine. Edited January 21, 2023 by Cuban8 Quote Link to comment Share on other sites More sharing options...
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