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Hi-Q RF filters, anyone?
Hi chaps, I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? Thanks, p. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sat, 26 Jul 2003 12:35:11 -0400, Joseph Legris
wrote: What is the intended application? I want to increase the sensitivity of a radio control rx. To this end, I'm going to build an RF pre-amp, which needs to be highly selective to avoid the probablility of increased ajacent channel interference. Hence the need for a sharp filter in conjunction with the pre-amp. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sat, 26 Jul 2003 12:35:11 -0400, Joseph Legris
wrote: What is the intended application? I want to increase the sensitivity of a radio control rx. To this end, I'm going to build an RF pre-amp, which needs to be highly selective to avoid the probablility of increased ajacent channel interference. Hence the need for a sharp filter in conjunction with the pre-amp. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sat, 26 Jul 2003 17:42:19 +0100, Paul Burridge
wrote: On Sat, 26 Jul 2003 12:35:11 -0400, Joseph Legris wrote: What is the intended application? I want to increase the sensitivity of a radio control rx. To this end, I'm going to build an RF pre-amp, which needs to be highly selective to avoid the probablility of increased ajacent channel interference. Hence the need for a sharp filter in conjunction with the pre-amp. This is a strange way of achieving your aim. You should be going for adjacent channel selectivity in the IF, not the front end. That way you can use a fixed frequency filter, and it can be as lossy as you like - and it will be lossy to achieve these kinds of selectivity with achievable unloaded Q. If you put this filter at the RF stage where it will help with adjacent channel selectivity,m it must be before the first amplifier, and that will have killed your hoped-for sensitivity increase. If you put it after that amplifier, then you may as well leave it where it belongs - in the IF. Radio design is always a compromise between sensitivity, selectivity and large-signal performance. The standard topologies haven't emerged by accident, I'm afraid. d _____________________________ http://www.pearce.uk.com |
On Sat, 26 Jul 2003 17:42:19 +0100, Paul Burridge
wrote: On Sat, 26 Jul 2003 12:35:11 -0400, Joseph Legris wrote: What is the intended application? I want to increase the sensitivity of a radio control rx. To this end, I'm going to build an RF pre-amp, which needs to be highly selective to avoid the probablility of increased ajacent channel interference. Hence the need for a sharp filter in conjunction with the pre-amp. This is a strange way of achieving your aim. You should be going for adjacent channel selectivity in the IF, not the front end. That way you can use a fixed frequency filter, and it can be as lossy as you like - and it will be lossy to achieve these kinds of selectivity with achievable unloaded Q. If you put this filter at the RF stage where it will help with adjacent channel selectivity,m it must be before the first amplifier, and that will have killed your hoped-for sensitivity increase. If you put it after that amplifier, then you may as well leave it where it belongs - in the IF. Radio design is always a compromise between sensitivity, selectivity and large-signal performance. The standard topologies haven't emerged by accident, I'm afraid. d _____________________________ http://www.pearce.uk.com |
In sci.electronics.design, Paul Burridge
wrote: Hi chaps, I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? I've got that deja-google feeling all over again: http://groups.google.com/groups?hl=e...com%26rnum%3D6 I like the idea of downconverting to an IF, filtering using standard IF technology, and (if you want the output to be the same frequency band as the input) upconverting using the same local oscillator as the downconverter. Just change the LO frequency (maybe use a frequency synthesizer for stability) to do tuning. Thanks, p. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
In sci.electronics.design, Paul Burridge
wrote: Hi chaps, I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? I've got that deja-google feeling all over again: http://groups.google.com/groups?hl=e...com%26rnum%3D6 I like the idea of downconverting to an IF, filtering using standard IF technology, and (if you want the output to be the same frequency band as the input) upconverting using the same local oscillator as the downconverter. Just change the LO frequency (maybe use a frequency synthesizer for stability) to do tuning. Thanks, p. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
Take a look at lowband filters and duplexers from CellWave, Telewave, etc. Your filter is going to be a coaxial cavity about 2mx20cm with piston for tuning. I am sure there are some better approaches to your task :) Vladimir Vassilevsky, Ph.D. DSP and Mixed Signal Design Consultant http://www.abvolt.com Paul Burridge wrote: Hi chaps, I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? Thanks, p. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
Take a look at lowband filters and duplexers from CellWave, Telewave, etc. Your filter is going to be a coaxial cavity about 2mx20cm with piston for tuning. I am sure there are some better approaches to your task :) Vladimir Vassilevsky, Ph.D. DSP and Mixed Signal Design Consultant http://www.abvolt.com Paul Burridge wrote: Hi chaps, I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? Thanks, p. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
Paul Burridge wrote in message . ..
I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? It'll need to be a crystal filter, and your requirement that it must be tunable means that you will convert down/up to an IF frequency and back up/down again. (Well, you may not have to convert back up again but you don't tell us your application). Problem with the IF and conversion is the production of images. Images won't be a killer problem because your tuning range is really quite narrow. If you wanted to really cheapskate out some ceramic IF filters also seem to meet your stated needs. Tim. |
Paul Burridge wrote in message . ..
I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? It'll need to be a crystal filter, and your requirement that it must be tunable means that you will convert down/up to an IF frequency and back up/down again. (Well, you may not have to convert back up again but you don't tell us your application). Problem with the IF and conversion is the production of images. Images won't be a killer problem because your tuning range is really quite narrow. If you wanted to really cheapskate out some ceramic IF filters also seem to meet your stated needs. Tim. |
On Sat, 26 Jul 2003 21:55:40 +0100, Paul Burridge
wrote: On Sat, 26 Jul 2003 18:50:45 +0100, Don Pearce wrote: This is a strange way of achieving your aim. You should be going for adjacent channel selectivity in the IF, not the front end. That way you can use a fixed frequency filter, and it can be as lossy as you like - and it will be lossy to achieve these kinds of selectivity with achievable unloaded Q. If you put this filter at the RF stage where it will help with adjacent channel selectivity,m it must be before the first amplifier, and that will have killed your hoped-for sensitivity increase. If you put it after that amplifier, then you may as well leave it where it belongs - in the IF. Thanks, Don. I'm aware this is a daft way of doing it, but I don't have much choice. The IF stages of this rx are not accessable and no schematic is available, either. The makers have declined to make them available and threatened any service personel who do so with termination of their contracts. Faced with these obstacles, I don't see any other option, apart from boosting the tx power instead; a solution which just brings a different load of problems. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill Hello Paul, it is time to dump that receiver and start again. It is too small and tiddly and I know you do not like surface mount size components. I would imagine that you have plenty of room inside that robot of yours to take a fairly large die cast box. My suggestion is find a radio control receiver that you can get circuit diagrams for or build one from scratch on large pieces of printed circuit board using "ugly construction" or "dead bug construction". Google those terms and you will see what I am talking about. You can then build the various stages of the receiver on separate boards and try all the different things you have been wishing to do but couldn't due to miniature parts, lack of access and lack of information. After you have a prototype ugly construction receiver working, you can miniaturize if you wish on the the next unit. You will need spares anyway. Heh heh heh......it is fighting machine. Have a look at National semiconductor application notes for radio control receiver, they might even give you half a dozen chips as free samples. Google search for radio control receiver schematics. "Buy" is a dirty word for me, but you might be able to buy a receiver in kit form with all the information on construction and alignment as well as a "how it works" description. Have Fun, John Crighton Sydney |
On Sat, 26 Jul 2003 21:55:40 +0100, Paul Burridge
wrote: On Sat, 26 Jul 2003 18:50:45 +0100, Don Pearce wrote: This is a strange way of achieving your aim. You should be going for adjacent channel selectivity in the IF, not the front end. That way you can use a fixed frequency filter, and it can be as lossy as you like - and it will be lossy to achieve these kinds of selectivity with achievable unloaded Q. If you put this filter at the RF stage where it will help with adjacent channel selectivity,m it must be before the first amplifier, and that will have killed your hoped-for sensitivity increase. If you put it after that amplifier, then you may as well leave it where it belongs - in the IF. Thanks, Don. I'm aware this is a daft way of doing it, but I don't have much choice. The IF stages of this rx are not accessable and no schematic is available, either. The makers have declined to make them available and threatened any service personel who do so with termination of their contracts. Faced with these obstacles, I don't see any other option, apart from boosting the tx power instead; a solution which just brings a different load of problems. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill Hello Paul, it is time to dump that receiver and start again. It is too small and tiddly and I know you do not like surface mount size components. I would imagine that you have plenty of room inside that robot of yours to take a fairly large die cast box. My suggestion is find a radio control receiver that you can get circuit diagrams for or build one from scratch on large pieces of printed circuit board using "ugly construction" or "dead bug construction". Google those terms and you will see what I am talking about. You can then build the various stages of the receiver on separate boards and try all the different things you have been wishing to do but couldn't due to miniature parts, lack of access and lack of information. After you have a prototype ugly construction receiver working, you can miniaturize if you wish on the the next unit. You will need spares anyway. Heh heh heh......it is fighting machine. Have a look at National semiconductor application notes for radio control receiver, they might even give you half a dozen chips as free samples. Google search for radio control receiver schematics. "Buy" is a dirty word for me, but you might be able to buy a receiver in kit form with all the information on construction and alignment as well as a "how it works" description. Have Fun, John Crighton Sydney |
In article , mentioned...
Take a look at lowband filters and duplexers from CellWave, Telewave, etc. Your filter is going to be a coaxial cavity about 2mx20cm with piston for tuning. I am sure there are some better approaches to your task :) How about a helical resonator. They're smaller than a cavity, maybe not as high Q, but still higher than lumped constant tuned circuit. They're tunable, but I'm not sure how much. Vladimir Vassilevsky, Ph.D. Paul Burridge wrote: Hi chaps, I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? Thanks, p. -- -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
Paul Burridge wrote in message . ..
Hi chaps, I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? Thanks, p. Filter at 40 MHz with 40 KHz BW means a very high Q, up to 1000. Cavity filter at 40 MHz is big! You can try active RF tuned stage (at 40 MHz) with a positive feedback, also known as Q-multiplier. In addition to high selectivity this will also result in a high gain, which may overload your actual receiver. In this case you can attenuate the signal at the output of the RF stage. You have to make sure Q-multiplier would start to oscillate. It is an issue by itself. 73, Vlad kb9olm |
Paul Burridge wrote in message . ..
Hi chaps, I've decided to bite the bullet and try to build an RF filter for 40Mhz. This filter will ideally have a very, very sharp characteristic at one single spot frequency +-20Khz and attenuate the crap out of anything either side of this. It'll need to be tunable over a range of say 200Khz. Can anyone give me a steer on what type of arrangement would be best suited to fit this purpose? Thanks, p. Filter at 40 MHz with 40 KHz BW means a very high Q, up to 1000. Cavity filter at 40 MHz is big! You can try active RF tuned stage (at 40 MHz) with a positive feedback, also known as Q-multiplier. In addition to high selectivity this will also result in a high gain, which may overload your actual receiver. In this case you can attenuate the signal at the output of the RF stage. You have to make sure Q-multiplier would start to oscillate. It is an issue by itself. 73, Vlad kb9olm |
On Sat, 26 Jul 2003 21:20:18 -0700, Watson A.Name - 'Watt Sun'
wrote: In article , mentioned... Take a look at lowband filters and duplexers from CellWave, Telewave, etc. Your filter is going to be a coaxial cavity about 2mx20cm with piston for tuning. I am sure there are some better approaches to your task :) How about a helical resonator. They're smaller than a cavity, maybe not as high Q, but still higher than lumped constant tuned circuit. They're tunable, but I'm not sure how much. I'd like to live long enough to see a helical at 40MHz that can 'attenuate the hell" out of signals outside the Fr+/-20kHz channel. |
On Sat, 26 Jul 2003 21:20:18 -0700, Watson A.Name - 'Watt Sun'
wrote: In article , mentioned... Take a look at lowband filters and duplexers from CellWave, Telewave, etc. Your filter is going to be a coaxial cavity about 2mx20cm with piston for tuning. I am sure there are some better approaches to your task :) How about a helical resonator. They're smaller than a cavity, maybe not as high Q, but still higher than lumped constant tuned circuit. They're tunable, but I'm not sure how much. I'd like to live long enough to see a helical at 40MHz that can 'attenuate the hell" out of signals outside the Fr+/-20kHz channel. |
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Paul Burridge wrote:
Thanks, Don. I'm aware this is a daft way of doing it, but I don't have much choice. The IF stages of this rx are not accessable and no schematic is available, either. The makers have declined to make them available and threatened any service personel who do so with termination of their contracts. Please tell us the name of this incredibly awful company so that we may avoid buying their products. -- All relevant people are pertinent. All rude people are impertinent. Therefore, no rude people are relevant. -- Solomon W. Golomb |
Paul Burridge wrote:
Thanks, Don. I'm aware this is a daft way of doing it, but I don't have much choice. The IF stages of this rx are not accessable and no schematic is available, either. The makers have declined to make them available and threatened any service personel who do so with termination of their contracts. Please tell us the name of this incredibly awful company so that we may avoid buying their products. -- All relevant people are pertinent. All rude people are impertinent. Therefore, no rude people are relevant. -- Solomon W. Golomb |
On Sun, 27 Jul 2003 17:14:59 GMT, "Clifton T. Sharp Jr."
wrote: Paul Burridge wrote: Thanks, Don. I'm aware this is a daft way of doing it, but I don't have much choice. The IF stages of this rx are not accessable and no schematic is available, either. The makers have declined to make them available and threatened any service personel who do so with termination of their contracts. Please tell us the name of this incredibly awful company so that we may avoid buying their products. Sanwa. They mostly make radio-control stuff. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sun, 27 Jul 2003 17:14:59 GMT, "Clifton T. Sharp Jr."
wrote: Paul Burridge wrote: Thanks, Don. I'm aware this is a daft way of doing it, but I don't have much choice. The IF stages of this rx are not accessable and no schematic is available, either. The makers have declined to make them available and threatened any service personel who do so with termination of their contracts. Please tell us the name of this incredibly awful company so that we may avoid buying their products. Sanwa. They mostly make radio-control stuff. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sun, 27 Jul 2003 13:46:57 +0100, Paul Burridge
wrote: Thanks for the suggestion, John. It *does* make a lot of sense, I must admit. Hadn't considered that possibility, to be honest. I've never been a fan of dead bug construction - there's no satisfaction in seeing the finished job - so may well have a stab at using regular, proper-sized discretes along the same lines. And yes, there's no shortage of space, either. Way to go over the long term, I reckon. Thanks again. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill Hello Paul, since you are not keen on dead bug construction here is a couple of websites that talk about Micron radio control kits. http://www.micronradiocontrol.fsnet.co.uk/ http://www.norcim.fsnet.co.uk/ I am sure there are other kits around, maybe someone else will mention some. Radio Control Models & Electronics magazine is still around. Years ago there were lots of construction projects. I don't know if the magazine still caters for the do it yourself enthusiast. Decades ago it did. http://www.hhc.co.uk/pages/show/entr...record_flag/59 You could enquire from them about build it yourself radio 40 MHz radio control systems. Here is another site with an article on interference and servo connections and lots of other good stuff. Shows your airtronics/(sanwa) servo connections. http://www.uoguelph.ca/~antoon/hobby/hints.htm No need to change servos with a different receiver. 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. How did you go with Win's soft start motor controller? Regards, John Crighton Sydney |
On Sun, 27 Jul 2003 13:46:57 +0100, Paul Burridge
wrote: Thanks for the suggestion, John. It *does* make a lot of sense, I must admit. Hadn't considered that possibility, to be honest. I've never been a fan of dead bug construction - there's no satisfaction in seeing the finished job - so may well have a stab at using regular, proper-sized discretes along the same lines. And yes, there's no shortage of space, either. Way to go over the long term, I reckon. Thanks again. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill Hello Paul, since you are not keen on dead bug construction here is a couple of websites that talk about Micron radio control kits. http://www.micronradiocontrol.fsnet.co.uk/ http://www.norcim.fsnet.co.uk/ I am sure there are other kits around, maybe someone else will mention some. Radio Control Models & Electronics magazine is still around. Years ago there were lots of construction projects. I don't know if the magazine still caters for the do it yourself enthusiast. Decades ago it did. http://www.hhc.co.uk/pages/show/entr...record_flag/59 You could enquire from them about build it yourself radio 40 MHz radio control systems. Here is another site with an article on interference and servo connections and lots of other good stuff. Shows your airtronics/(sanwa) servo connections. http://www.uoguelph.ca/~antoon/hobby/hints.htm No need to change servos with a different receiver. 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. How did you go with Win's soft start motor controller? Regards, John Crighton Sydney |
On Sun, 27 Jul 2003 21:21:52 GMT, (John Crighton)
wrote: Hello Paul, since you are not keen on dead bug construction here is a couple of websites that talk about Micron radio control kits. http://www.micronradiocontrol.fsnet.co.uk/ http://www.norcim.fsnet.co.uk/ I am sure there are other kits around, maybe someone else will mention some. Radio Control Models & Electronics magazine is still around. Years ago there were lots of construction projects. I don't know if the magazine still caters for the do it yourself enthusiast. Decades ago it did. http://www.hhc.co.uk/pages/show/entr...record_flag/59 You could enquire from them about build it yourself radio 40 MHz radio control systems. Here is another site with an article on interference and servo connections and lots of other good stuff. Shows your airtronics/(sanwa) servo connections. http://www.uoguelph.ca/~antoon/hobby/hints.htm No need to change servos with a different receiver. Thanks for the pointers, John. They are duly noted! 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. How did you go with Win's soft start motor controller? Currently under construction... -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sun, 27 Jul 2003 21:21:52 GMT, (John Crighton)
wrote: Hello Paul, since you are not keen on dead bug construction here is a couple of websites that talk about Micron radio control kits. http://www.micronradiocontrol.fsnet.co.uk/ http://www.norcim.fsnet.co.uk/ I am sure there are other kits around, maybe someone else will mention some. Radio Control Models & Electronics magazine is still around. Years ago there were lots of construction projects. I don't know if the magazine still caters for the do it yourself enthusiast. Decades ago it did. http://www.hhc.co.uk/pages/show/entr...record_flag/59 You could enquire from them about build it yourself radio 40 MHz radio control systems. Here is another site with an article on interference and servo connections and lots of other good stuff. Shows your airtronics/(sanwa) servo connections. http://www.uoguelph.ca/~antoon/hobby/hints.htm No need to change servos with a different receiver. Thanks for the pointers, John. They are duly noted! 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. How did you go with Win's soft start motor controller? Currently under construction... -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
On Sun, 27 Jul 2003 22:33:48 +0100, Paul Burridge
wrote: How did you go with Win's soft start motor controller? Currently under construction... -- Hello Paul, you are dragging the anchor a bit. That was months ago! :-) Have a look here http://www.ife.tugraz.at/datashts/nsc/h7912.pdf Page 9. Application hints, has some good reading on how to play around with the input transformer. Is Henry's Radio still around? They used sell sets of IF coils for hobbyists and experimenters. My Henry's catalogue is a bit old. A nice Indian gent in an electronics junk shop in Edgeware Road gave it to me in 1973. I should come over there and get a more up to date copy. Are the electronic disposal shops still there? Maybe rob some 455 KHz IF coils out of a dud transistor radio if necessary. Save some dosh. Get that Dalo etch resist pen out, bottle of ferric chloride and sharpen your old soldering iron. You have a good Tek CRO and a Signal Generator. Do I sound like I am pushing you? Heh heh heh.... Regards, John Crighton Sydney |
On Sun, 27 Jul 2003 22:33:48 +0100, Paul Burridge
wrote: How did you go with Win's soft start motor controller? Currently under construction... -- Hello Paul, you are dragging the anchor a bit. That was months ago! :-) Have a look here http://www.ife.tugraz.at/datashts/nsc/h7912.pdf Page 9. Application hints, has some good reading on how to play around with the input transformer. Is Henry's Radio still around? They used sell sets of IF coils for hobbyists and experimenters. My Henry's catalogue is a bit old. A nice Indian gent in an electronics junk shop in Edgeware Road gave it to me in 1973. I should come over there and get a more up to date copy. Are the electronic disposal shops still there? Maybe rob some 455 KHz IF coils out of a dud transistor radio if necessary. Save some dosh. Get that Dalo etch resist pen out, bottle of ferric chloride and sharpen your old soldering iron. You have a good Tek CRO and a Signal Generator. Do I sound like I am pushing you? Heh heh heh.... Regards, John Crighton Sydney |
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 |
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 |
On 28 Jul 2003 07:13:56 GMT, (Michael Black)
wrote: John Crighton ) writes: Maybe rob some 455 KHz IF coils out of a dud transistor radio if necessary. Save some dosh. It would be interesting to have some tests done on the original receiver. If I remember the start of the thread, the receiver is not sensitive enough. I can't help but wonder if it's insensitive or it's too sensitive, leading to overload in the front end. That would be just as bad (in terms of operational range) as an insensitive receiver. Likewise, if one had an idea of the IF bandwidth, it would be easier to know if the problem really needs fixing, or there is some other issue. If the thing is using some sort of ceramic filter, looking at the board would hopefully say what type (unless the markings have been sanded off), and then the specs could be found. Assuming it's a standard IF frequency, maybe one could find a narrower filter that would drop right in. For all we know, it may have too wide an IF, and that's causing the initial problem. Knowing the bandwidth of the existing filter would also make it easier to figure out a complete replacement for the receiver. In this day and age, ceramic or crystal filters are the way to go, not a bunch of IF transformers. Pull parts out of a cordless phone, at least the 49MHz type, and you'll get a filter suitable for narrow deviation FM and a crystal for converting from 10.7MHz to 455KHz. If FM happens to be the operating mode, then pull out the whole IF strip. If that filter is too wide, pull the 455KHz ceramic filter out of a am BCB radio, or for something narrower, a CB set. The possibilities are endless. Michael VE2BVW Hello Michael, you are correct, there are many possibilities. I would like him to do some tests also. The main stumbling block for Paul is no information on the present Sanwa receiver and an understandable reluctance to poke around and then kill it accidentally, especially if it is borrowed or belongs to a mate. I suggested building a new Rx that is physically big so that experiments and mods are easily done by Paul. If the CRO probe slips.....no big deal. :-) We know of this LM1872 http://www.ife.tugraz.at/datashts/nsc/h7912.pdf that we can all look at and help out with suggestions. Do you know of anything else we can all see on a website? Regards, John Crighton Sydney |
On 28 Jul 2003 07:13:56 GMT, (Michael Black)
wrote: John Crighton ) writes: Maybe rob some 455 KHz IF coils out of a dud transistor radio if necessary. Save some dosh. It would be interesting to have some tests done on the original receiver. If I remember the start of the thread, the receiver is not sensitive enough. I can't help but wonder if it's insensitive or it's too sensitive, leading to overload in the front end. That would be just as bad (in terms of operational range) as an insensitive receiver. Likewise, if one had an idea of the IF bandwidth, it would be easier to know if the problem really needs fixing, or there is some other issue. If the thing is using some sort of ceramic filter, looking at the board would hopefully say what type (unless the markings have been sanded off), and then the specs could be found. Assuming it's a standard IF frequency, maybe one could find a narrower filter that would drop right in. For all we know, it may have too wide an IF, and that's causing the initial problem. Knowing the bandwidth of the existing filter would also make it easier to figure out a complete replacement for the receiver. In this day and age, ceramic or crystal filters are the way to go, not a bunch of IF transformers. Pull parts out of a cordless phone, at least the 49MHz type, and you'll get a filter suitable for narrow deviation FM and a crystal for converting from 10.7MHz to 455KHz. If FM happens to be the operating mode, then pull out the whole IF strip. If that filter is too wide, pull the 455KHz ceramic filter out of a am BCB radio, or for something narrower, a CB set. The possibilities are endless. Michael VE2BVW Hello Michael, you are correct, there are many possibilities. I would like him to do some tests also. The main stumbling block for Paul is no information on the present Sanwa receiver and an understandable reluctance to poke around and then kill it accidentally, especially if it is borrowed or belongs to a mate. I suggested building a new Rx that is physically big so that experiments and mods are easily done by Paul. If the CRO probe slips.....no big deal. :-) We know of this LM1872 http://www.ife.tugraz.at/datashts/nsc/h7912.pdf that we can all look at and help out with suggestions. Do you know of anything else we can all see on a website? Regards, John Crighton Sydney |
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? 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. Fun and games, eh! :-) Regards, John Crighton Sydney |
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? 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. Fun and games, eh! :-) Regards, John Crighton Sydney |
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On Mon, 28 Jul 2003 07:02:53 GMT, (John Crighton)
wrote: On Sun, 27 Jul 2003 22:33:48 +0100, Paul Burridge wrote: How did you go with Win's soft start motor controller? Currently under construction... -- Hello Paul, you are dragging the anchor a bit. That was months ago! :-) Have a look here http://www.ife.tugraz.at/datashts/nsc/h7912.pdf You'll have to forgive me here, John, as i'm battling with a duff display on the computer I'm using at the moment and I was only able to glimpse the data for a few seconds, but this chip doesn't seem to be suitable for 40Mhz FM, does it? I'm sure your general solution to the problem is an excellent one, though, if a suitable chip can be found. -- "I believe history will be kind to me, since I intend to write it." - Winston Churchill |
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