|
Don't know where you can buy a passband filter. Maybe be able to find some
cavity type filters for 50 MHz, but probably only surplus. Building from scratch is easy but takes a network analyzer to tune. A coax stub can be either open or shorted, your preference. Cheapest way is to start with an open stub slightly too long and trim it to length. If you can borrow a signal generator and power meter, then you can tune it that way. It's practical to get about 25 dB of loss with a stub, better is difficult due to losses in the conectors, cables, etc. Rough length of the open stub would be 1/4 wavelength at 55.25 MHz, about 1.35 meters. Accounting for coax velocity factor of 0.66, the stub would be about 0.89 meters long. Start a maybe 5-10 CM longer than that and trim to length. -- Tom "GeorgeF" wrote in message ink.net... 1) Where can one buy a passband filter for 50-52MHz? 2) When talking about coax trimmed to length, are you talking about a coax stub? Such as cut to 1/4 wavelength of the offending freq? If so would be ends be shorted or let open? never worked with stubs yet.... TNX George |
Don't know where you can buy a passband filter. Maybe be able to find some
cavity type filters for 50 MHz, but probably only surplus. Building from scratch is easy but takes a network analyzer to tune. A coax stub can be either open or shorted, your preference. Cheapest way is to start with an open stub slightly too long and trim it to length. If you can borrow a signal generator and power meter, then you can tune it that way. It's practical to get about 25 dB of loss with a stub, better is difficult due to losses in the conectors, cables, etc. Rough length of the open stub would be 1/4 wavelength at 55.25 MHz, about 1.35 meters. Accounting for coax velocity factor of 0.66, the stub would be about 0.89 meters long. Start a maybe 5-10 CM longer than that and trim to length. -- Tom "GeorgeF" wrote in message ink.net... 1) Where can one buy a passband filter for 50-52MHz? 2) When talking about coax trimmed to length, are you talking about a coax stub? Such as cut to 1/4 wavelength of the offending freq? If so would be ends be shorted or let open? never worked with stubs yet.... TNX George |
Don't know where you can buy a passband filter. Maybe be able to find some
cavity type filters for 50 MHz, but probably only surplus. Building from scratch is easy but takes a network analyzer to tune. A coax stub can be either open or shorted, your preference. Cheapest way is to start with an open stub slightly too long and trim it to length. If you can borrow a signal generator and power meter, then you can tune it that way. It's practical to get about 25 dB of loss with a stub, better is difficult due to losses in the conectors, cables, etc. Rough length of the open stub would be 1/4 wavelength at 55.25 MHz, about 1.35 meters. Accounting for coax velocity factor of 0.66, the stub would be about 0.89 meters long. Start a maybe 5-10 CM longer than that and trim to length. -- Tom "GeorgeF" wrote in message ink.net... 1) Where can one buy a passband filter for 50-52MHz? 2) When talking about coax trimmed to length, are you talking about a coax stub? Such as cut to 1/4 wavelength of the offending freq? If so would be ends be shorted or let open? never worked with stubs yet.... TNX George |
"Tom" wrote in message news:YBvjd.2272$bH2.1471@trnddc09... Don't know where you can buy a passband filter. Maybe be able to find some cavity type filters for 50 MHz, but probably only surplus. Building from scratch is easy but takes a network analyzer to tune. A coax stub can be either open or shorted, your preference. Cheapest way is to start with an open stub slightly too long and trim it to length. If you can borrow a signal generator and power meter, then you can tune it that way. It's practical to get about 25 dB of loss with a stub, better is difficult due to losses in the conectors, cables, etc. You may achieve -25dB loss at CH2 video, but unfortunately you will also have high loss at 50MHz, and a VSWR that is out of sight. Build one and see for yourself. Dale W4OP |
"Tom" wrote in message news:YBvjd.2272$bH2.1471@trnddc09... Don't know where you can buy a passband filter. Maybe be able to find some cavity type filters for 50 MHz, but probably only surplus. Building from scratch is easy but takes a network analyzer to tune. A coax stub can be either open or shorted, your preference. Cheapest way is to start with an open stub slightly too long and trim it to length. If you can borrow a signal generator and power meter, then you can tune it that way. It's practical to get about 25 dB of loss with a stub, better is difficult due to losses in the conectors, cables, etc. You may achieve -25dB loss at CH2 video, but unfortunately you will also have high loss at 50MHz, and a VSWR that is out of sight. Build one and see for yourself. Dale W4OP |
"Tom" wrote in message news:YBvjd.2272$bH2.1471@trnddc09... Don't know where you can buy a passband filter. Maybe be able to find some cavity type filters for 50 MHz, but probably only surplus. Building from scratch is easy but takes a network analyzer to tune. A coax stub can be either open or shorted, your preference. Cheapest way is to start with an open stub slightly too long and trim it to length. If you can borrow a signal generator and power meter, then you can tune it that way. It's practical to get about 25 dB of loss with a stub, better is difficult due to losses in the conectors, cables, etc. You may achieve -25dB loss at CH2 video, but unfortunately you will also have high loss at 50MHz, and a VSWR that is out of sight. Build one and see for yourself. Dale W4OP |
Well, probably true. Don't transmit through it! The computer with the
shorted-stub spreadsheet on it is broken, so I can't look at the loss vs. frequency. It's a simple Excel sheet that models the complex transmission-line equation (including loss) of the stub against the feedline. Hoped it wouldn't be that bad at 10% separation, but am flying blind until I can get access to it and run the numbers. -- Tom "Dale Parfitt" wrote in message news:jZAjd.2538$bH2.1351@trnddc09... "Tom" wrote in message news:YBvjd.2272$bH2.1471@trnddc09... Don't know where you can buy a passband filter. Maybe be able to find some cavity type filters for 50 MHz, but probably only surplus. Building from scratch is easy but takes a network analyzer to tune. A coax stub can be either open or shorted, your preference. Cheapest way is to start with an open stub slightly too long and trim it to length. If you can borrow a signal generator and power meter, then you can tune it that way. It's practical to get about 25 dB of loss with a stub, better is difficult due to losses in the conectors, cables, etc. You may achieve -25dB loss at CH2 video, but unfortunately you will also have high loss at 50MHz, and a VSWR that is out of sight. Build one and see for yourself. Dale W4OP |
Well, probably true. Don't transmit through it! The computer with the
shorted-stub spreadsheet on it is broken, so I can't look at the loss vs. frequency. It's a simple Excel sheet that models the complex transmission-line equation (including loss) of the stub against the feedline. Hoped it wouldn't be that bad at 10% separation, but am flying blind until I can get access to it and run the numbers. -- Tom "Dale Parfitt" wrote in message news:jZAjd.2538$bH2.1351@trnddc09... "Tom" wrote in message news:YBvjd.2272$bH2.1471@trnddc09... Don't know where you can buy a passband filter. Maybe be able to find some cavity type filters for 50 MHz, but probably only surplus. Building from scratch is easy but takes a network analyzer to tune. A coax stub can be either open or shorted, your preference. Cheapest way is to start with an open stub slightly too long and trim it to length. If you can borrow a signal generator and power meter, then you can tune it that way. It's practical to get about 25 dB of loss with a stub, better is difficult due to losses in the conectors, cables, etc. You may achieve -25dB loss at CH2 video, but unfortunately you will also have high loss at 50MHz, and a VSWR that is out of sight. Build one and see for yourself. Dale W4OP |
Well, probably true. Don't transmit through it! The computer with the
shorted-stub spreadsheet on it is broken, so I can't look at the loss vs. frequency. It's a simple Excel sheet that models the complex transmission-line equation (including loss) of the stub against the feedline. Hoped it wouldn't be that bad at 10% separation, but am flying blind until I can get access to it and run the numbers. -- Tom "Dale Parfitt" wrote in message news:jZAjd.2538$bH2.1351@trnddc09... "Tom" wrote in message news:YBvjd.2272$bH2.1471@trnddc09... Don't know where you can buy a passband filter. Maybe be able to find some cavity type filters for 50 MHz, but probably only surplus. Building from scratch is easy but takes a network analyzer to tune. A coax stub can be either open or shorted, your preference. Cheapest way is to start with an open stub slightly too long and trim it to length. If you can borrow a signal generator and power meter, then you can tune it that way. It's practical to get about 25 dB of loss with a stub, better is difficult due to losses in the conectors, cables, etc. You may achieve -25dB loss at CH2 video, but unfortunately you will also have high loss at 50MHz, and a VSWR that is out of sight. Build one and see for yourself. Dale W4OP |
"Dale Parfitt" ) writes: "Tom" wrote in message news:YBvjd.2272$bH2.1471@trnddc09... Don't know where you can buy a passband filter. Maybe be able to find some cavity type filters for 50 MHz, but probably only surplus. Building from scratch is easy but takes a network analyzer to tune. A coax stub can be either open or shorted, your preference. Cheapest way is to start with an open stub slightly too long and trim it to length. If you can borrow a signal generator and power meter, then you can tune it that way. It's practical to get about 25 dB of loss with a stub, better is difficult due to losses in the conectors, cables, etc. You may achieve -25dB loss at CH2 video, but unfortunately you will also have high loss at 50MHz, and a VSWR that is out of sight. Build one and see for yourself. Dale W4OP So you get a crystal cut for the channel 2 carrier frequency, and find a place to connect it in the receiver chain. This sort of thing was done apparently in repeaters forty years ago, to keep the transmitter out of the receiver. I do think one would have to modify the receiver because the crystal might not be able to handle the transmitter signal. Michael VE2BVW |
| All times are GMT +1. The time now is 10:38 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com