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+--- Thread: Another New Site Review. (/showthread.php?tid=2241)
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RE: Another New Site Review. - Benedict.Smith - 2017-07-27
(2017-07-27, 00:39)allsorts Wrote: Nothing wrong with a linear power supply and 7805. The lack of noise is a positive advantage. Lower effciency is the draw back but what is a couple of Watts?
The only problem is 7805 regulators normally only handle up to 1A and even then need a heat sink, there are other similar ones that have higher current ratings (I can't recalls he type numbers off the top of my head), why not just add a decent LC filter network, that is what I have done and it is as quiet as you could wish.
Ben.
RE: Another New Site Review. - allsorts - 2017-07-27
1 A is ample for a Blitzortung controller, if I remember correctly a controller draws 400 to 500 mA. Disipation in a 7805 is dependant on the voltage drop across it and the curent flowing through it. Minimum supply voltage is 7 V so it's dropping 2 V @ 0.5 A = 1 W dissipation, don't think that would need a heatsink. Feed it 12 V the disipation rises to 3.5 W, that probably will...
A post supply filter stops the noise getting to the controller via the power lines but doesn't stop the noise being radiated from the PSU itself or other wires connected to it. I'll admit I have post supply filter but I use PoE so don't (easily) have the option of a linear supply.
RE: Another New Site Review. - Benedict.Smith - 2017-07-29
(2017-07-27, 22:26)allsorts Wrote: 1 A is ample for a Blitzortung controller, if I remember correctly a controller draws 400 to 500 mA. Disipation in a 7805 is dependant on the voltage drop across it and the curent flowing through it. Minimum supply voltage is 7 V so it's dropping 2 V @ 0.5 A = 1 W dissipation, don't think that would need a heatsink. Feed it 12 V the disipation rises to 3.5 W, that probably will...
A post supply filter stops the noise getting to the controller via the power lines but doesn't stop the noise being radiated from the PSU itself or other wires connected to it. I'll admit I have post supply filter but I use PoE so don't (easily) have the option of a linear supply.
Yes, you are correct, I was thinking more along the lines of the Raspberry Pi projects I have that need 2-3A, a 7805 should be fine for Blitzortung, I don't worry too much about the PSU radiating noise as it is only one if around 20 in the same room and I don't plan on changing everything to linear supplies.
RE: Another New Site Review. - allsorts - 2017-07-29
The only Raspberry Pi project I have that got me searching for a PSU that could supply a real 4 A is the media player. The Pi doesn't use it, it's spinning up the 2 T byte USB HDD.
Wandered about the house the other day placing the antenna of a SW receiver close to anything I thought might be radiating RF noise. Found three big offenders, two LED light bulbs and the electronic ballast for the aquarium lights. One of the light bulbs is Luminous brand from CostCo (UK), the other an unknown "brand" from the local hardware store. We have a mix of light bulbs in use, from tungstenm CFL, LED chip to LED filament. RF wise tungsten is silent, CFL noisy, LED chip significantly noisier, LED filament, quieter than CFL but not silent.
The many wall wart SMPSUs were on a par with CFLs, maybe a bit quieter. I know that some of them have noisy outputs from setting up my station. At some point I intend to invest in a multiple output CCTV power supply, these are a single box conatins a 12 V 10 A (or more) PSU and distribution for individually fused outputs. Need to check what everything actually lives off, if something wants a lower voltage I have some LM2956 based DC-DC convertors that I hope don't radiate too much.
Aquarium? Need to investigate that, it's double insulated so has no ground connection for starters.
RE: Another New Site Review. - pasense - 2017-07-30
The worst source of noise I have detected so far is an induction plate we use for cooking. It generates strong magnetic stray fields which have unfortunately a frequency exactly in the range we need to detect, so these signals cannot be filtered out. I will have to move the ferrite antenna as far away from the kitchen as I can.
RE: Another New Site Review. - allsorts - 2017-07-30
Well I'm not surprised an induction hob is a noise source, after all it uses a powerful magnetci field to heat the pan... I will have to see what our single ring portable one shoves out. At least a induction hob is off far more than it is on, unlike light bulbs. B-)
RE: Another New Site Review. - pasense - 2017-07-30
Distant second in terms of (magnetic) noise is the aircon unit (the indoor part), but this problem will certainly also be solved when I move the antenna.