Are switch-mode powers supplies suitable for receivers?
I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding
24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. |
Are switch-mode powers supplies suitable for receivers?
On Mon, 28 Jan 2008 11:27:20 -0000,
Richard wrote in : I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. Some switchers are very good, some aren't very good at all. One friend has the Icom PS-120 (I think) for his Icom transceiver, and finds it to be so noisy as to be unusable .Other friends have other switchers and find them to be OK, and a third group find them somewhat noisy, but tolerable if you don't mind tuning around the birdies. I use a Samlex 30-Amp switcher to drive my Yaesu FT-897D in the shack, and it's just fine above 500 KHz or so. It *does* put out some hash in the 20-500 KHz region; my SDR-IQ receiver's waterfall display shows it quite plainly. You may find a linear-mode supply (xfmr; half-wave, full-wave, or bridge rectifier; filter) to be better for your use; I don't know of a lot of 24V switchers. Certainly a linear supply will be quieter if done well, as the only noise will be from ripple that gets through the filters, and the tiny bit of hash from the rectifier junctions turning on and off. -- I had the largest, strongest tornado ever recorded march by just four miles away in May of '99, I could feel the house breathing from the subsonic pressure wave. It's a Live Thing, like Fire. -- Charly the *******, in rec.org.sca |
Are switch-mode powers supplies suitable for receivers?
On Mon, 28 Jan 2008 11:27:20 -0000, Richard wrote:
I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. You are almost talking about a wall-wart there, aren't you? Or, possibly, a desktop 'brick' PS. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. Just make sure the PS is enclosed. And, use ferrite beads/doughnuts on _all_ input\output wiring. And, it wouldn't hurt to put .001 uF bypass capacitors on that wiring, too, betwix the ferrites and the PS. My venerable IC-551's (6M) internal power supply went kah-kah and I replaced it with a switched-mode PS from Marlin P Jones: http://www.mpja.com/ That was some time ago, but what I bought was similar to: http://www.mpja.com/prodinfo.asp?number=16001+PS My original requirement was _size_. I wanted to stuff the new PS into the same cavity in the IC-551 where the old PS came out. So, having installed the new switched-mode PS _inside_ the rig -- with all the install 'details' I listed above -- I saw no appreciable rise in the no-antenna-connected noise floor. Plus I could 'tweak' the output voltage -- setting it at 13V -- and "amp up" that IC-551 to a blistering 11W or so. HI!HI! I encouraged a feller in Kansas to do likewise with his IC-251 (2M) that had a dead PS, and he reported similar success. Of course, YMMV gl es 73 Jonesy -- Marvin L Jones | jonz | W3DHJ | linux 38.24N 104.55W | @ config.com | Jonesy | OS/2 *** Killfiling google posts: http://jonz.net/ng.htm |
Are switch-mode powers supplies suitable for receivers?
On Mon, 28 Jan 2008 11:27:20 -0000, "Richard"
wrote: I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. Some are, some are not. You have a lot of choices available at 300ma. John Ferrell W8CCW "Life is easier if you learn to plow around the stumps" |
Are switch-mode powers supplies suitable for receivers?
On Jan 28, 3:27 am, "Richard" wrote:
I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. The receiver I'm building uses switchers internally to take 5V down to various other voltages. Total power supplied by the switchers is around 20 watts. They're little open modules. I can "see" the fundamentals (200kHz-700kHz range for these supplies) and the first few harmonics if I go looking for them, but they're certainly not an issue at 144MHz. With enough shielding and bypassing (done right), I suppose any switcher would be clean enough. With a switcher of good design, you won't even need any additional shielding or bypassing. Cheers, Tom |
Are switch-mode powers supplies suitable for receivers?
You can tweak up the power on a 24VDC switcher to cover the headroom for a
linear regulator following the switcher. This is an old technique - and still used. My preference would be an adjustable regulator with the adjust pin bypassed with 10uF. Linear Technologies has some regulator chips that out of the box have noise lower than garden variety LM317/337. You may have to shield the supply -- |
Are switch-mode powers supplies suitable for receivers?
John Ferrell wrote: On Mon, 28 Jan 2008 11:27:20 -0000, "Richard" wrote: I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. Some are, some are not. You have a lot of choices available at 300ma. John Ferrell W8CCW "Life is easier if you learn to plow around the stumps" I tried one that created all kinds of interference. I was able to solve the problem by installing caps in parallel with the rectifiers, . 005uF disc I think. Jimmie |
Are switch-mode powers supplies suitable for receivers?
On Jan 28, 10:27 pm, "Richard" wrote:
I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. Their noisy period, but you might get away with it on 2m. But you will still be QRM'ing everyone else... Hold AM transistor radio next to it, have a listen as you tune across the band....not nice, lots of spurs with rich harmonic content... Its your choice. The dark path or the light path of Radio Karma.... Andrew VK3BFA. |
Are switch-mode powers supplies suitable for receivers?
On 28 Jan, 11:27, "Richard" wrote:
I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. I use a 12V switcher with my FT-817D, it's very quiet. Leon |
Are switch-mode powers supplies suitable for receivers?
On Feb 4, 10:13 pm, Leon wrote:
On 28 Jan, 11:27, "Richard" wrote: I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. I use a 12V switcher with my FT-817D, it's very quiet. Leon You were lucky - you got a quiet one. And its the luck of the draw, unfortunately. How come we have all been conned into these switchmode things? - by their very nature, without a lot of effort, they are noise generators. Their cheap to make, thats their only advantage - everything else is part of the spin cycle. And if it works on 2m and above, fine - you will just be adding to the already horrendous RF pollution from thousands of the bloody things already on HF - the suburbs are getting unbearable, S9 plus noise, every night, on 80m.....160 aint to crash hot either... I refuse to have to work on a power supply to get it quiet enough to be used with a radio. I am interested in the radio, not fixing shortcomings in design of things that , by their very nature, are unsuitable to be used near radios. That sucks. Linear technology is far easier and quieter... Andrew VK3BFA. |
Are switch-mode powers supplies suitable for receivers?
On Feb 4, 3:55 am, Andrew VK3BFA wrote:
On Feb 4, 10:13 pm, Leon wrote: On 28 Jan, 11:27, "Richard" wrote: I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. I use a 12V switcher with my FT-817D, it's very quiet. Leon You were lucky - you got a quiet one. And its the luck of the draw, unfortunately. How come we have all been conned into these switchmode things? - by their very nature, without a lot of effort, they are noise generators. Their cheap to make, thats their only advantage - everything else is part of the spin cycle. And if it works on 2m and above, fine - you will just be adding to the already horrendous RF pollution from thousands of the bloody things already on HF - the suburbs are getting unbearable, S9 plus noise, every night, on 80m.....160 aint to crash hot either... I refuse to have to work on a power supply to get it quiet enough to be used with a radio. I am interested in the radio, not fixing shortcomings in design of things that , by their very nature, are unsuitable to be used near radios. That sucks. Linear technology is far easier and quieter... Andrew VK3BFA. There's another advantage of a switching supply that is very important to some of us: efficiency. The receiver I've been working on runs from 5VDC, but I have to supply power at 1.0V, 1.2V 1.8V, 2.5V and 3.3V, and each one of those uses a switcher. A linear regulator to 1V from 5V will result in a supply that's 20% efficient. The switcher I'm using for that supply is about 87% efficient under its operating conditions. If I tried to run all my supplies with linear regulators, I'd have to supply over twice the power; it would come close to violating the power rating of the 5V supply, and power dissipation in the receiver would result in excessive heat rise. But even with all those switchers, the only spurs greater than about -145dBm (antenna-input-referred) and greater than 1.5MHz are from digital circuits, not the power supplies. -145dBm is, I believe, 20dB _below_ S1 by usual definition of the S-meter units. Even the power supply fundamentals are only at about S1. And the supplies are not themselves shielded. (The receiver RF circuitry is, of course, as is the whole receiver module.) I would be much more circumspect about using a switching supply in a homebrew receiver that was going to be used where power dissipation wasn't an issue, but then I'd do a lot of things differently than I have for such a receiver. It wouldn't keep me from using switchers; I'd just look at the whole design in a different way. On the other hand, finding ones that would be adequately quiet for a 144MHz receiver should not be difficult at all. Cheers, Tom |
Are switch-mode powers supplies suitable for receivers?
On Feb 5, 3:52 am, K7ITM wrote:
On Feb 4, 3:55 am, Andrew VK3BFA wrote: On Feb 4, 10:13 pm, Leon wrote: On 28 Jan, 11:27, "Richard" wrote: I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. I use a 12V switcher with my FT-817D, it's very quiet. Leon You were lucky - you got a quiet one. And its the luck of the draw, unfortunately. How come we have all been conned into these switchmode things? - by their very nature, without a lot of effort, they are noise generators. Their cheap to make, thats their only advantage - everything else is part of the spin cycle. And if it works on 2m and above, fine - you will just be adding to the already horrendous RF pollution from thousands of the bloody things already on HF - the suburbs are getting unbearable, S9 plus noise, every night, on 80m.....160 aint to crash hot either... I refuse to have to work on a power supply to get it quiet enough to be used with a radio. I am interested in the radio, not fixing shortcomings in design of things that , by their very nature, are unsuitable to be used near radios. That sucks. Linear technology is far easier and quieter... Andrew VK3BFA. There's another advantage of a switching supply that is very important to some of us: efficiency. The receiver I've been working on runs from 5VDC, but I have to supply power at 1.0V, 1.2V 1.8V, 2.5V and 3.3V, and each one of those uses a switcher. A linear regulator to 1V from 5V will result in a supply that's 20% efficient. The switcher I'm using for that supply is about 87% efficient under its operating conditions. If I tried to run all my supplies with linear regulators, I'd have to supply over twice the power; it would come close to violating the power rating of the 5V supply, and power dissipation in the receiver would result in excessive heat rise. But even with all those switchers, the only spurs greater than about -145dBm (antenna-input-referred) and greater than 1.5MHz are from digital circuits, not the power supplies. -145dBm is, I believe, 20dB _below_ S1 by usual definition of the S-meter units. Even the power supply fundamentals are only at about S1. And the supplies are not themselves shielded. (The receiver RF circuitry is, of course, as is the whole receiver module.) I would be much more circumspect about using a switching supply in a homebrew receiver that was going to be used where power dissipation wasn't an issue, but then I'd do a lot of things differently than I have for such a receiver. It wouldn't keep me from using switchers; I'd just look at the whole design in a different way. On the other hand, finding ones that would be adequately quiet for a 144MHz receiver should not be difficult at all. Cheers, Tom Hi Tom, all points noted, and readily conceded - if the things didn't have SOME advantages besides low cost, well.... You've got yours down to S1 - mm, well,......so thats the noise floor you are limited to. And thats probably on a small range of frequencies, gawd knows where else it is radiating...(and adding to phase noise in your receiver...) And, lets be honest, if it isn't causing ME QRM, on the frequency I want to operate, then its OK......fine for VHF/UHF unless a spur is on your IF frequency... The only application I can see for them is, as you say, where low power consumption/efficiency is paramount - but if you can plug your switch mode power supply into a source of AC power, then whats the problem with lugging a quiet linear supply as well as the generator required to run it? To me, they are a flawed technology, and in a better place would not be allowed to be used because of their inherent design flaws... Andrew VK3BFA. (PS - I do a good "back in the good old days" rant if you like.....) |
Are switch-mode powers supplies suitable for receivers?
Andrew VK3BFA wrote:
On Feb 5, 3:52 am, K7ITM wrote: On Feb 4, 3:55 am, Andrew VK3BFA wrote: On Feb 4, 10:13 pm, Leon wrote: On 28 Jan, 11:27, "Richard" wrote: I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. I use a 12V switcher with my FT-817D, it's very quiet. Leon You were lucky - you got a quiet one. And its the luck of the draw, unfortunately. How come we have all been conned into these switchmode things? - by their very nature, without a lot of effort, they are noise generators. Their cheap to make, thats their only advantage - everything else is part of the spin cycle. And if it works on 2m and above, fine - you will just be adding to the already horrendous RF pollution from thousands of the bloody things already on HF - the suburbs are getting unbearable, S9 plus noise, every night, on 80m.....160 aint to crash hot either... I refuse to have to work on a power supply to get it quiet enough to be used with a radio. I am interested in the radio, not fixing shortcomings in design of things that , by their very nature, are unsuitable to be used near radios. That sucks. Linear technology is far easier and quieter... Andrew VK3BFA. There's another advantage of a switching supply that is very important to some of us: efficiency. The receiver I've been working on runs from 5VDC, but I have to supply power at 1.0V, 1.2V 1.8V, 2.5V and 3.3V, and each one of those uses a switcher. A linear regulator to 1V from 5V will result in a supply that's 20% efficient. The switcher I'm using for that supply is about 87% efficient under its operating conditions. If I tried to run all my supplies with linear regulators, I'd have to supply over twice the power; it would come close to violating the power rating of the 5V supply, and power dissipation in the receiver would result in excessive heat rise. But even with all those switchers, the only spurs greater than about -145dBm (antenna-input-referred) and greater than 1.5MHz are from digital circuits, not the power supplies. -145dBm is, I believe, 20dB _below_ S1 by usual definition of the S-meter units. Even the power supply fundamentals are only at about S1. And the supplies are not themselves shielded. (The receiver RF circuitry is, of course, as is the whole receiver module.) I would be much more circumspect about using a switching supply in a homebrew receiver that was going to be used where power dissipation wasn't an issue, but then I'd do a lot of things differently than I have for such a receiver. It wouldn't keep me from using switchers; I'd just look at the whole design in a different way. On the other hand, finding ones that would be adequately quiet for a 144MHz receiver should not be difficult at all. Cheers, Tom Hi Tom, all points noted, and readily conceded - if the things didn't have SOME advantages besides low cost, well.... You've got yours down to S1 - mm, well,......so thats the noise floor you are limited to. And thats probably on a small range of frequencies, gawd knows where else it is radiating...(and adding to phase noise in your receiver...) And, lets be honest, if it isn't causing ME QRM, on the frequency I want to operate, then its OK......fine for VHF/UHF unless a spur is on your IF frequency... The only application I can see for them is, as you say, where low power consumption/efficiency is paramount - but if you can plug your switch mode power supply into a source of AC power, then whats the problem with lugging a quiet linear supply as well as the generator required to run it? To me, they are a flawed technology, and in a better place would not be allowed to be used because of their inherent design flaws... Andrew VK3BFA. (PS - I do a good "back in the good old days" rant if you like.....) We use a couple of homebrew regulated DC-DC boost converters during Field Day, one to run the HF xcvr (13.8VDC @ 25A peak) and one to run the laptop PC for logging (16VDC @ 4.5A), from a 12V wet cell battery "pack"*. Prior to use, they were "sniffed" (at no load and also full load) with an HP spectrum analyzer. The analyzer showed only a few very weak spurs in the HF spectrum that we couldn't hear at all, even on 80m. Of course, they were properly designed with this use in mind... good decoupling and shielding. Switching rate is 500KHz; efficiency is in the neighborhood of 90%. * Battery "pack": http://img22.imagevenue.com/img.php?...122_1054lo.jpg Bryan WA7PRC |
Are switch-mode powers supplies suitable for receivers?
On Feb 5, 4:46 pm, Andrew VK3BFA wrote:
On Feb 5, 3:52 am, K7ITM wrote: On Feb 4, 3:55 am, Andrew VK3BFA wrote: On Feb 4, 10:13 pm, Leon wrote: On 28 Jan, 11:27, "Richard" wrote: I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. I use a 12V switcher with my FT-817D, it's very quiet. Leon You were lucky - you got a quiet one. And its the luck of the draw, unfortunately. How come we have all been conned into these switchmode things? - by their very nature, without a lot of effort, they are noise generators. Their cheap to make, thats their only advantage - everything else is part of the spin cycle. And if it works on 2m and above, fine - you will just be adding to the already horrendous RF pollution from thousands of the bloody things already on HF - the suburbs are getting unbearable, S9 plus noise, every night, on 80m.....160 aint to crash hot either... I refuse to have to work on a power supply to get it quiet enough to be used with a radio. I am interested in the radio, not fixing shortcomings in design of things that , by their very nature, are unsuitable to be used near radios. That sucks. Linear technology is far easier and quieter... Andrew VK3BFA. There's another advantage of a switching supply that is very important to some of us: efficiency. The receiver I've been working on runs from 5VDC, but I have to supply power at 1.0V, 1.2V 1.8V, 2.5V and 3.3V, and each one of those uses a switcher. A linear regulator to 1V from 5V will result in a supply that's 20% efficient. The switcher I'm using for that supply is about 87% efficient under its operating conditions. If I tried to run all my supplies with linear regulators, I'd have to supply over twice the power; it would come close to violating the power rating of the 5V supply, and power dissipation in the receiver would result in excessive heat rise. But even with all those switchers, the only spurs greater than about -145dBm (antenna-input-referred) and greater than 1.5MHz are from digital circuits, not the power supplies. -145dBm is, I believe, 20dB _below_ S1 by usual definition of the S-meter units. Even the power supply fundamentals are only at about S1. And the supplies are not themselves shielded. (The receiver RF circuitry is, of course, as is the whole receiver module.) I would be much more circumspect about using a switching supply in a homebrew receiver that was going to be used where power dissipation wasn't an issue, but then I'd do a lot of things differently than I have for such a receiver. It wouldn't keep me from using switchers; I'd just look at the whole design in a different way. On the other hand, finding ones that would be adequately quiet for a 144MHz receiver should not be difficult at all. Cheers, Tom Hi Tom, all points noted, and readily conceded - if the things didn't have SOME advantages besides low cost, well.... You've got yours down to S1 - mm, well,......so thats the noise floor you are limited to. And thats probably on a small range of frequencies, gawd knows where else it is radiating...(and adding to phase noise in your receiver...) And, lets be honest, if it isn't causing ME QRM, on the frequency I want to operate, then its OK......fine for VHF/UHF unless a spur is on your IF frequency... The only application I can see for them is, as you say, where low power consumption/efficiency is paramount - but if you can plug your switch mode power supply into a source of AC power, then whats the problem with lugging a quiet linear supply as well as the generator required to run it? To me, they are a flawed technology, and in a better place would not be allowed to be used because of their inherent design flaws... Andrew VK3BFA. (PS - I do a good "back in the good old days" rant if you like.....) Oh, well, the receiver is 100kHz (nom.; actually is -3dB at about 18kHz) to about 38MHz. It also alternately does 70MHz IF at 36MHz bandwidth, at about the same sensitivity. Noise figure on HF is around 9dB at max sensitivity; since switchers are not stable sources, their output becomes broadband noise by the time you get to bandwidths low enough to see -145dBm (e.g., 100Hz), and there's essentially no indication of increased noise floor at the harmonics (past maybe the third) of any of the supplies, even with lots of averaging. The master clock is a low phase noise VCTCXO, and it IS run from a linear supply, with scrubbing added. That oscillator really does set the system phase noise. There are no other oscillators to worry about in the signal chain. You're welcome to rant about the "good old days," but I probably won't hear it. I'm too busy enjoying the "even better new days" to bother looking back. Cheers, Tom |
Are switch-mode powers supplies suitable for receivers?
On Feb 6, 5:50 pm, K7ITM wrote:
On Feb 5, 4:46 pm, Andrew VK3BFA wrote: On Feb 5, 3:52 am, K7ITM wrote: On Feb 4, 3:55 am, Andrew VK3BFA wrote: On Feb 4, 10:13 pm, Leon wrote: On 28 Jan, 11:27, "Richard" wrote: I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. I use a 12V switcher with my FT-817D, it's very quiet. Leon You were lucky - you got a quiet one. And its the luck of the draw, unfortunately. How come we have all been conned into these switchmode things? - by their very nature, without a lot of effort, they are noise generators. Their cheap to make, thats their only advantage - everything else is part of the spin cycle. And if it works on 2m and above, fine - you will just be adding to the already horrendous RF pollution from thousands of the bloody things already on HF - the suburbs are getting unbearable, S9 plus noise, every night, on 80m.....160 aint to crash hot either... I refuse to have to work on a power supply to get it quiet enough to be used with a radio. I am interested in the radio, not fixing shortcomings in design of things that , by their very nature, are unsuitable to be used near radios. That sucks. Linear technology is far easier and quieter... Andrew VK3BFA. There's another advantage of a switching supply that is very important to some of us: efficiency. The receiver I've been working on runs from 5VDC, but I have to supply power at 1.0V, 1.2V 1.8V, 2.5V and 3.3V, and each one of those uses a switcher. A linear regulator to 1V from 5V will result in a supply that's 20% efficient. The switcher I'm using for that supply is about 87% efficient under its operating conditions. If I tried to run all my supplies with linear regulators, I'd have to supply over twice the power; it would come close to violating the power rating of the 5V supply, and power dissipation in the receiver would result in excessive heat rise. But even with all those switchers, the only spurs greater than about -145dBm (antenna-input-referred) and greater than 1.5MHz are from digital circuits, not the power supplies. -145dBm is, I believe, 20dB _below_ S1 by usual definition of the S-meter units. Even the power supply fundamentals are only at about S1. And the supplies are not themselves shielded. (The receiver RF circuitry is, of course, as is the whole receiver module.) I would be much more circumspect about using a switching supply in a homebrew receiver that was going to be used where power dissipation wasn't an issue, but then I'd do a lot of things differently than I have for such a receiver. It wouldn't keep me from using switchers; I'd just look at the whole design in a different way. On the other hand, finding ones that would be adequately quiet for a 144MHz receiver should not be difficult at all. Cheers, Tom Hi Tom, all points noted, and readily conceded - if the things didn't have SOME advantages besides low cost, well.... You've got yours down to S1 - mm, well,......so thats the noise floor you are limited to. And thats probably on a small range of frequencies, gawd knows where else it is radiating...(and adding to phase noise in your receiver...) And, lets be honest, if it isn't causing ME QRM, on the frequency I want to operate, then its OK......fine for VHF/UHF unless a spur is on your IF frequency... The only application I can see for them is, as you say, where low power consumption/efficiency is paramount - but if you can plug your switch mode power supply into a source of AC power, then whats the problem with lugging a quiet linear supply as well as the generator required to run it? To me, they are a flawed technology, and in a better place would not be allowed to be used because of their inherent design flaws... Andrew VK3BFA. (PS - I do a good "back in the good old days" rant if you like.....) Oh, well, the receiver is 100kHz (nom.; actually is -3dB at about 18kHz) to about 38MHz. It also alternately does 70MHz IF at 36MHz bandwidth, at about the same sensitivity. Noise figure on HF is around 9dB at max sensitivity; since switchers are not stable sources, their output becomes broadband noise by the time you get to bandwidths low enough to see -145dBm (e.g., 100Hz), and there's essentially no indication of increased noise floor at the harmonics (past maybe the third) of any of the supplies, even with lots of averaging. The master clock is a low phase noise VCTCXO, and it IS run from a linear supply, with scrubbing added. That oscillator really does set the system phase noise. There are no other oscillators to worry about in the signal chain. You're welcome to rant about the "good old days," but I probably won't hear it. I'm too busy enjoying the "even better new days" to bother looking back. Cheers, Tom Hey - I agree - I like the modern DDS chips as well, fantastic things. (Note - AD specify separate ANALOG supply for them...Mmm?) I try again - my point is, why bother to stuff around getting a "new" technology to work when an "old" technology is cheap, easy,simple, and it works with no extra fiddling. And if you need a spectrum analyser to check your power supply for suitability, - that is a bit ludicrous, isn't it? Mad Scientist in attic room / Tony Hancock sketch sort of thing. Why make things so difficult? KISS. Never said there were no quiet switchers - just that the majority were not....Google on SMPS noise to prove..... Andrew VK3BFA. |
Are switch-mode powers supplies suitable for receivers?
Andrew VK3BFA wrote:
Never said there were no quiet switchers - just that the majority were not....Google on SMPS noise to prove..... Sure... but SMPS noise is categorically NOT about "the luck of the draw" (as you claimed a few days ago). It's all about skill and care in the design - above all, the input and output filtering. Done correctly, there are no problems, as proved by the many base-station HF transceivers that have a mains SMPS built in. When you buy a separate SMPS, don't trust to luck. Be an intelligent consumer: read the reviews, specify what you need, ask what has been done to minimize the noise levels, and be prepared to return the unit or walk away. The only real "luck" is about the SMPSes in other things that your family and neighbours may buy... -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Are switch-mode powers supplies suitable for receivers?
On Feb 6, 8:25 pm, Ian White GM3SEK wrote:
Andrew VK3BFA wrote: Never said there were no quiet switchers - just that the majority were not....Google on SMPS noise to prove..... Sure... but SMPS noise is categorically NOT about "the luck of the draw" (as you claimed a few days ago). It's all about skill and care in the design - above all, the input and output filtering. Done correctly, there are no problems, as proved by the many base-station HF transceivers that have a mains SMPS built in. When you buy a separate SMPS, don't trust to luck. Be an intelligent consumer: read the reviews, specify what you need, ask what has been done to minimize the noise levels, and be prepared to return the unit or walk away. The only real "luck" is about the SMPSes in other things that your family and neighbours may buy... -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)http://www.ifwtech.co.uk/g3sek MM, well.....ok., I will add a rider to the "luck of the draw" - if you have the knowledge of the things in the first place, it is axiomatic that you would need to check it out before you buy it - get test data, spectrum analyser screen shots, copy of CE certification' load test data, a copy of the service manual for future reference...probably a few more things as well, I forget. The rest of us, well.........we basically know bugger all about them, and we havent been hams long enough for someone to tell us "Brand X" is useless. SO we go and buy it, and wonder what the hell went wrong. And I been fixing the things for 20 years now as a lowly service tech - horrible things, havent seen a quiet one yet.. AND AND...its going to get worse. Plasma TV's radiate to buggery - they have big, and good, filters on the SMPS power supply, but they are S9 at 5 miles.......LCD is better - EXCEPT for the plug pack SMPS type 12v etc power supply hanging off them...had one in for repair, the only sign it was polluting was that the (non ham) owner complained it was interfering with his AM radio reception. (That was interesting in its own right - he had contacted the relevant authority, they had sent him a "do it yourself" booklet, and he found it...I thought that was a pretty good effort) And the "Brand X" (still on sale, still selling in the shops) - one hapless inexperienced amateur asked me to "modify" - ie quieten it down. Plastic from and rear panels. Bugger all input filtering - and virtually none anywhere else. On 160m, spot frequencies, it was S9+. I got it down to S3, then gave up in disgust. So, Ian - love your columns, in awe of your knowledge about practical, real radio. I certainly havent got all that much. But this is the view from the trenches, as it were - everyday practical pointy end servicing - so,if I may, I humbly beg to differ. No offense meant, to anyone, and none taken. (Yep - its true - I don't like them...) Andrew VK3BFA |
Are switch-mode powers supplies suitable for receivers?
On Feb 4, 10:13 pm, Leon wrote: On 28 Jan, 11:27, "Richard" wrote: I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. I use a 12V switcher with my FT-817D, it's very quiet. Leon You were lucky - you got a quiet one. And its the luck of the draw, unfortunately. How come we have all been conned into these switchmode things? - by their very nature, without a lot of effort, they are noise generators. Their cheap to make, thats their only advantage - everything else is part of the spin cycle. And if it works on 2m and above, fine - you will just be adding to the already horrendous RF pollution from thousands of the bloody things already on HF - the suburbs are getting unbearable, S9 plus noise, every night, on 80m.....160 aint to crash hot either... I refuse to have to work on a power supply to get it quiet enough to be used with a radio. I am interested in the radio, not fixing shortcomings in design of things that , by their very nature, are unsuitable to be used near radios. That sucks. Linear technology is far easier and quieter... ======================================== When using a switcher (in a metal sealed enclosure and with noise supressors ,as recommended by some in this thread), put a sealed lead acid battery in parallel. If still noisy you then can switch-off switcher when rx-ing . Frank GM0CSZ / KN6WH |
Are switch-mode powers supplies suitable for receivers?
How come we have all been conned into these switchmode things? - by
their very nature, without a lot of effort, they are noise generators. Their cheap to make, thats their only advantage - everything else is part of the spin cycle. Other advantages include much better power efficiency and much lower weight. It's not particularly difficult to make a switcher with very good (meaning very little) noise output, but relatively few applications call for it, and given how incredibly competitive the power supply arena is, it's not surprising that a lot of companies drop a few components to reduce their costs at the expense of noise. |
Are switch-mode powers supplies suitable for receivers?
On Feb 21, 4:58 am, "Joel Koltner"
wrote: How come we have all been conned into these switchmode things? - by their very nature, without a lot of effort, they are noise generators. Their cheap to make, thats their only advantage - everything else is part of the spin cycle. Other advantages include much better power efficiency and much lower weight. It's not particularly difficult to make a switcher with very good (meaning very little) noise output, but relatively few applications call for it, and given how incredibly competitive the power supply arena is, it's not surprising that a lot of companies drop a few components to reduce their costs at the expense of noise. re power and weight - I was having a rant, so deliberately left out the inconvenient facts.....(Yes, I thats unusual, isnt it - I must reprimand myself) And yes, will readily concede the " they can be well designed bit"... But they are not. The percentage? - dont know. All I can do is hear them, on air. Went away at Xmas, remote caravan park, MILES away, looking forward to HF radio . Nope, surrounded by modern caravans with 12v systems, run from noisy SMPS power supplies/battery chargers....it was better, 80m QRM was S3 instead of S9+ Gosh, modern electronics IS wonderful, isnt it.... My point stands. Andrew VK3BFA. |
Are switch-mode powers supplies suitable for receivers?
"Richard" wrote in message ... I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding 24V @ about 300mA. Are switch-mode powers supplies alright or are they too noisy to be used for receivers? TIA. Many years ago I designed a switching power supply for aircraft Nav and Com VHF radios. The switcher was 100% shielded and line filtered to get the radio to pass FCC and FAA TSO certification. Even though the Com and Nav radio's are VHF, they were placed next to an ADF radio (low frequency) without problems. Testing was performed not only for electro magnetic emissions, but also for line current emissions, with a line stabilization network, into the radio from the aircraft power. Even if the switcher is 100% shielded, this will not prevent radiation along the input power line. You need to consider methods to eliminate pulsed current along the input power line caused by the switcher. This may be hard to achieve, especially for high efficiency switchers. A good choke will help, but it will also introduce additional switching losses. So yes, a switcher can be used; but, IMHO it must be designed for use in an RF environment. |
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