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#51
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On Mon, 28 Jul 2003 23:07:59 +0100, Paul Burridge
wrote: Have a look here http://www.ife.tugraz.at/datashts/nsc/h7912.pdf This also looks a possibility: http://w1.859.telia.com/~u85920178/use/rc-prop.htm Might be a contender for the next 'bot, possibly? -- Hello Paul, yes it does. That is a great site. Harry gives you the circuit, the artwork and tells you how he makes his printed circuit boards. Harry explains that he has managed to use that little AM Rx on FM also. I think you plenty of info now Paul. Have Fun, John Crighton Sydney |
#52
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![]() "John Crighton" wrote in message ... On Mon, 28 Jul 2003 10:19:13 +0100, "Hans Summers" wrote: Back to your interference problem. Is your operating channel frequency smack in the middle of the 40 Mhz band? If so, maybe you could try a different set of crystals, so that you operate as far away from everyone else as possible. Or simply just borrow a different set of crystals in case there is a weird mix going on, just to eliminate that possibility. We've recently got wise to that one and I've ordered a pair of xtals from the *last* channel of the band. That's what we'll be running with come the last week in August, when we're due up for the next filming. Not necessarily the solution, I got bitten by that one once some 9 or 10 years ago when I used to fly radio controlled aircraft (in the UK on 35MHz). It bothered me when someone else at the flying field had the same crystal as I did and I had to wait for them to finish flying before I could fly. So bought another pair of crystals, the highest I could find, if I recall that was channel 83 (35.230MHz). Everything was fine for a while but a few weeks later I crashed after losing radio contact with my plane. A little investigation (in between gluing the aircraft bits back together) found the cause. A channel vs frequency listing, compared with the MHz printed on the crystal case revealed that the receivers were single conversion superhets with 110KHz IF. Channel separation was 10KHz. Clearly with that setup, image rejection is practically negligible. So someone transmitting on channel 61, 220KHz away, interferes with channel 83. After that I went back to my crystals on 76 smack in the middle of everyone elses, learnt to be patient if someone was already using the channel, and had no more problems ;-) Hans G0UPL http://www.HansSummers.com Hello Hans, what brand/make was that R/C set that you had? It was a Futaba, I don't recall which one. Very old and battered but worked great. I've been away from aero-modelling for 9 years or so and don't know what's new now - but at that time, the latest control sets were dual conversion (avoiding that image problem) and PCM (Pulse Code Modulation) compared to the old PPM like mine (Pulse Position Modulation). It always seemed to me (perhaps somewhat subjectively) that the PCM tranceivers, which were supposed to be more reliable, were in fact more prone to interference. In the presence of interference the flyer seemed to have no control, presumably because the incoming code was scrambled and the receiver couldn't make head or tail of it. With the old fashioned PPM sets it seemed that often even if interference was causing your servos to twitch a little you still had some degree of control over it, often enough to turn it round and bring it in closer whereupon full control would return and permit a hasty landing. You have reminded me of a silly incident at my model flying club decades ago. One of the wealthier club members was having all sorts of trouble with his model, engine and radio gear so he flung heaps of money at a ready made, ready to fly model with an expensive four stroke engine, and a new expensive all singing and dancing radio control set. First day out with the new model and everything is going well for him, he was doing stunts all over the sky. My models were el cheapo sticks and tissue construction, I couldn't afford nice covering film/material. I was more interested in home built radio control gear. Radio assisted free flight was more my style. When the fuel ran out in my models I didn't mind walking a few hundred yards if necessary to retrieve my model. So I am off for a long walk with my transmitter still switched on as one would. (The receiver gets switched off first then the transmitter.) The rich guy is stunting around and decides to buzz me at low level about 20 feet above the ground. His model flies over me and then nose dives into the ground near by. I could here his servos twitching away as I walked past the wreckage. After I retrieved my model and switched off my transmitter, I stopped by the little gathering at the wreck site. The rich guy was operating his servos OK and scratching his head. " I spend thousands on my model and that ******* John Crighton comes here every weekend with 50 dollars worth of homebuilt junk and flies. It just isn't fair." "Moan...grumble..moan." I didn't try to explain that his receiver got swamped. His mates put the crash down to pilot error at low level, and that was that. Ha Ha, similar story here. I was a student at the time, had very little money. Serves that rich fellow right for flying so low near you, sounds dangerous. I used to have a Hi-Boy 4-channel trainer with 0.40 cu inch 2-stroke OS engine. When it came to me it had spent at least a decade in a damp garage and required an almost complete fuselage rebuild to clear the rot. Quite likely therefore that by the time I finally flew it, the original dimensions weren't adhered to any longer. A particular weakness seemed to be the nosewheel which was endlessly breaking up during my bad landings. Solution to that one was just to remove it and fly the thing as a taildragger. The OS40 engine worked a treat, perhaps slightly overpowering the model: I used to be able to take off and fly vertically immediately like the jet fighters at air shows. Had SO many crashes with that plane, and came to love it - just glued it back together every time. In the end it was probably more glue than balsa wood. A number of times I had to carry the pieces home in a plastic shopping bag. By the following Saturday it was glued back together and generally caused jaws at the flying field to drop. No-one could believe anything with that much glue in it and such bad aerodynamics could actually fly. The wings (balsa sheet covering polystyrene) had snapped 4 times and been repaired by application of a fibre-glass bandage, adding significant weight of course. It actually flew quite well too, all the aerobatics no problem and I particularly used to like slow low level inverted fly bys at 10 ft or less. Happy days ;-) Hans http://www.HansSummers.com Fun and games, eh! :-) Regards, John Crighton Sydney |
#53
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![]() "John Crighton" wrote in message ... On Mon, 28 Jul 2003 10:19:13 +0100, "Hans Summers" wrote: Back to your interference problem. Is your operating channel frequency smack in the middle of the 40 Mhz band? If so, maybe you could try a different set of crystals, so that you operate as far away from everyone else as possible. Or simply just borrow a different set of crystals in case there is a weird mix going on, just to eliminate that possibility. We've recently got wise to that one and I've ordered a pair of xtals from the *last* channel of the band. That's what we'll be running with come the last week in August, when we're due up for the next filming. Not necessarily the solution, I got bitten by that one once some 9 or 10 years ago when I used to fly radio controlled aircraft (in the UK on 35MHz). It bothered me when someone else at the flying field had the same crystal as I did and I had to wait for them to finish flying before I could fly. So bought another pair of crystals, the highest I could find, if I recall that was channel 83 (35.230MHz). Everything was fine for a while but a few weeks later I crashed after losing radio contact with my plane. A little investigation (in between gluing the aircraft bits back together) found the cause. A channel vs frequency listing, compared with the MHz printed on the crystal case revealed that the receivers were single conversion superhets with 110KHz IF. Channel separation was 10KHz. Clearly with that setup, image rejection is practically negligible. So someone transmitting on channel 61, 220KHz away, interferes with channel 83. After that I went back to my crystals on 76 smack in the middle of everyone elses, learnt to be patient if someone was already using the channel, and had no more problems ;-) Hans G0UPL http://www.HansSummers.com Hello Hans, what brand/make was that R/C set that you had? It was a Futaba, I don't recall which one. Very old and battered but worked great. I've been away from aero-modelling for 9 years or so and don't know what's new now - but at that time, the latest control sets were dual conversion (avoiding that image problem) and PCM (Pulse Code Modulation) compared to the old PPM like mine (Pulse Position Modulation). It always seemed to me (perhaps somewhat subjectively) that the PCM tranceivers, which were supposed to be more reliable, were in fact more prone to interference. In the presence of interference the flyer seemed to have no control, presumably because the incoming code was scrambled and the receiver couldn't make head or tail of it. With the old fashioned PPM sets it seemed that often even if interference was causing your servos to twitch a little you still had some degree of control over it, often enough to turn it round and bring it in closer whereupon full control would return and permit a hasty landing. You have reminded me of a silly incident at my model flying club decades ago. One of the wealthier club members was having all sorts of trouble with his model, engine and radio gear so he flung heaps of money at a ready made, ready to fly model with an expensive four stroke engine, and a new expensive all singing and dancing radio control set. First day out with the new model and everything is going well for him, he was doing stunts all over the sky. My models were el cheapo sticks and tissue construction, I couldn't afford nice covering film/material. I was more interested in home built radio control gear. Radio assisted free flight was more my style. When the fuel ran out in my models I didn't mind walking a few hundred yards if necessary to retrieve my model. So I am off for a long walk with my transmitter still switched on as one would. (The receiver gets switched off first then the transmitter.) The rich guy is stunting around and decides to buzz me at low level about 20 feet above the ground. His model flies over me and then nose dives into the ground near by. I could here his servos twitching away as I walked past the wreckage. After I retrieved my model and switched off my transmitter, I stopped by the little gathering at the wreck site. The rich guy was operating his servos OK and scratching his head. " I spend thousands on my model and that ******* John Crighton comes here every weekend with 50 dollars worth of homebuilt junk and flies. It just isn't fair." "Moan...grumble..moan." I didn't try to explain that his receiver got swamped. His mates put the crash down to pilot error at low level, and that was that. Ha Ha, similar story here. I was a student at the time, had very little money. Serves that rich fellow right for flying so low near you, sounds dangerous. I used to have a Hi-Boy 4-channel trainer with 0.40 cu inch 2-stroke OS engine. When it came to me it had spent at least a decade in a damp garage and required an almost complete fuselage rebuild to clear the rot. Quite likely therefore that by the time I finally flew it, the original dimensions weren't adhered to any longer. A particular weakness seemed to be the nosewheel which was endlessly breaking up during my bad landings. Solution to that one was just to remove it and fly the thing as a taildragger. The OS40 engine worked a treat, perhaps slightly overpowering the model: I used to be able to take off and fly vertically immediately like the jet fighters at air shows. Had SO many crashes with that plane, and came to love it - just glued it back together every time. In the end it was probably more glue than balsa wood. A number of times I had to carry the pieces home in a plastic shopping bag. By the following Saturday it was glued back together and generally caused jaws at the flying field to drop. No-one could believe anything with that much glue in it and such bad aerodynamics could actually fly. The wings (balsa sheet covering polystyrene) had snapped 4 times and been repaired by application of a fibre-glass bandage, adding significant weight of course. It actually flew quite well too, all the aerobatics no problem and I particularly used to like slow low level inverted fly bys at 10 ft or less. Happy days ;-) Hans http://www.HansSummers.com Fun and games, eh! :-) Regards, John Crighton Sydney |
#54
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In (rec.radio.amateur.homebrew), Hans Summers wrote:
Had SO many crashes with that plane, and came to love it - just glued it back together every time. In the end it was probably more glue than balsa wood. A number of times I had to carry the pieces home in a plastic shopping bag. By the following Saturday it was glued back together and generally caused jaws at the flying field to drop. No-one could believe anything with that much glue in it and such bad aerodynamics could actually fly. The wings (balsa sheet covering polystyrene) had snapped 4 times and been repaired by application of a fibre-glass bandage, adding significant weight of course. It actually flew quite well too, all the aerobatics no problem and I particularly used to like slow low level inverted fly bys at 10 ft or less. From RFC 1925: "(3) With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead." -- Mike Andrews Tired old sysadmin since 1964 |
#55
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In (rec.radio.amateur.homebrew), Hans Summers wrote:
Had SO many crashes with that plane, and came to love it - just glued it back together every time. In the end it was probably more glue than balsa wood. A number of times I had to carry the pieces home in a plastic shopping bag. By the following Saturday it was glued back together and generally caused jaws at the flying field to drop. No-one could believe anything with that much glue in it and such bad aerodynamics could actually fly. The wings (balsa sheet covering polystyrene) had snapped 4 times and been repaired by application of a fibre-glass bandage, adding significant weight of course. It actually flew quite well too, all the aerobatics no problem and I particularly used to like slow low level inverted fly bys at 10 ft or less. From RFC 1925: "(3) With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead." -- Mike Andrews Tired old sysadmin since 1964 |
#56
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Watson A.Name - 'Watt Sun' wrote in message ...
.... How about a helical resonator. They're smaller than a cavity, maybe not as high Q, but still higher than lumped constant tuned circuit. I think that's a popular misconception. The resonator Q is essentially the same as the Q of the same part used as a shielded inductor, and the shield actually lowers the Q from what it is with an inductor in free air (so long as it's not large enough to radiate significantly). They're tunable, but I'm not sure how much. They're certainly easily tunable over a few percent, if you need that... But the problem as originally stated implies a filter of fairly high order and low in-band attenuation, which in turn implies resonators of very high unloaded Q. 20kHz bandwidth at 40MHz in a single tank is a loaded Q of 2000, and to keep attenuation low, the unloaded resonator Q should be perhaps 5 times that much. It would be worse for a multi-pole filter. All this tells me it's silly to even think of an LC filter. Add to that the extreme difficulty of getting a set of resonators to tune together. (To get Qu=10000 in a coaxial resonator at 40MHz would take an air-dielectric line nearly half a meter in diameter! Just plain silly.) I'd opt for a front end with very high dynamic range (esp. low third-order intermod products), into a good IF filter, etc., and a communications protocol that optimized whatever performance measure I needed. Talk to the people who build RF communications sytems that go on aircraft carriers. Or talk with hams who design receivers with third order intercepts up in the +50dBm region and higher. By the way, you may do well by putting an ATTENUATOR on the front end, if interference (distortion products), and not desired-signal-strength, is the problem. Distortion products will go down faster than the inserted attenuation. Cheers, Tom |
#57
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Watson A.Name - 'Watt Sun' wrote in message ...
.... How about a helical resonator. They're smaller than a cavity, maybe not as high Q, but still higher than lumped constant tuned circuit. I think that's a popular misconception. The resonator Q is essentially the same as the Q of the same part used as a shielded inductor, and the shield actually lowers the Q from what it is with an inductor in free air (so long as it's not large enough to radiate significantly). They're tunable, but I'm not sure how much. They're certainly easily tunable over a few percent, if you need that... But the problem as originally stated implies a filter of fairly high order and low in-band attenuation, which in turn implies resonators of very high unloaded Q. 20kHz bandwidth at 40MHz in a single tank is a loaded Q of 2000, and to keep attenuation low, the unloaded resonator Q should be perhaps 5 times that much. It would be worse for a multi-pole filter. All this tells me it's silly to even think of an LC filter. Add to that the extreme difficulty of getting a set of resonators to tune together. (To get Qu=10000 in a coaxial resonator at 40MHz would take an air-dielectric line nearly half a meter in diameter! Just plain silly.) I'd opt for a front end with very high dynamic range (esp. low third-order intermod products), into a good IF filter, etc., and a communications protocol that optimized whatever performance measure I needed. Talk to the people who build RF communications sytems that go on aircraft carriers. Or talk with hams who design receivers with third order intercepts up in the +50dBm region and higher. By the way, you may do well by putting an ATTENUATOR on the front end, if interference (distortion products), and not desired-signal-strength, is the problem. Distortion products will go down faster than the inserted attenuation. Cheers, Tom |
#58
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#59
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#60
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On Tue, 29 Jul 2003 23:04:00 +0100, Paul Burridge
wrote: On Tue, 29 Jul 2003 04:12:43 GMT, (John Crighton) wrote: Or find, beg, borrow, "buy used," or build an ordinary AM R/C transmitter. Ten quid should get you an old style metal cased Futaba transmitter. Hi John, I've already got an AM tx and rx set-up, but am loathed to use it due to the much increased risk of interference from the speed controllers, motors, etc., which as you will know, is far more likely with an AM system. Keep thinking! -- Hello Paul, I would try out your old AM set for sure. You never know your luck. If the servo connections are compatible it will only take a short time. What brand/model? I agree with you that the AM set has an increased risk of interference from your own motors but you said some time ago that your robot works fine at your place but at the venue with other competitors and their transmitters around, the interference is bad for you with your present Sanwa FM set. Even if you do not fit the AM set to the robot, take the working AM set in a box to the venue and see if the servos misbehave in that electrical noisy environment. Regards, John Crighton. Sydney |
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