Does this PSU seem adequate for two KiwiSDR's?
While testing a new KiwiSDR + BBG, I've been powering it with this PSU:
https://www.amazon.com/gp/product/B07T44S4MV
The output amperage is stated differently in several places, but it appears to be 3.5A.
I'm planning to add a second KiwiSDR. Does the above PSU seem as though it would be adequate for two? I see it stated here that the receivers peak at about 1.5A each.
Comments
While that might work for two Kiwis, especially if they start at different times, some of us have turned to an inexpensive alternative. While these run from DC rather than mains AC and one has to provide that separately, and while they are SMPS so do have fast edges capable of QRMing a Kiwi, they run at ~ 1MHz and in practice can work very well.
You might want to consider trying these, one per Kiwi, from whatever inexpensive ~12V DC supply you might have battery or otherwise before going the route you ask about. SUch a solution could be more flexible and cheaper.
Thanks, I've seen those mentioned, and they're certainly inexpensive to try.
Are certain bands known to be affected more by noise from the buck converters?
PS noise is generally due to conducted, common mode noise current. The Kiwi is pretty impervious to differential noise so more C's or series L's don't usually help.
These small, cheap supplies have a high switching frequency and because they are small and by design most circulating currents are contained within them rather than injected on the input and output lines.
It's not uncommon to not be able to even find the ~960 kHz fundamental or its harmonics anywhere in an operating Kiwi. I use them on receivers that reach or exceed the ITU propagated noise floor.
I suggest identifying the frequency of the line and verifying that it is not an impairment to Kiwi operation at first but other than setting the V to 5.25VDC or so ahead of time and perhaps shrink tube wrapping the whole thing (takes a larger diameter shrink to fit but they are pretty small so should be available) it's not necessary to do much.
On the original PSU question, I have a similar (internal transformer) linear and it would run two standard Kiwi's without issue but as n6gn highlights, the issues are most problematic at boot so if you have a momentary power failure there is a small chance that one or more would not boot due to the strict power control on the BeagleBone.
The UK listed version calls it a 25W PSU but says don't add anything else after 3.5A,5.1V (17.85W) which is more realistic (and fine for two BBG Kiwi's).
I think I also went down the small DC-DC (MP1584 based) after seeing it mentioned on here and they are remarkable considering the cost and size. I fed them from "AnyOld" 12V linear supply or 12V lead acid from solar, knowing the supply to them can be up to 28V (I think) gives a nice level of protection.
Don't be tempted to "Upgrade" to the larger DC-DC (LM2596) with multiturn pots and up to 35V input, 3.5A out as they are much noisier in my experience.
Thanks, I'll try using the 5V 3.5A PSU with the two KiwiSDR's for now, then work with the buck converters. It would be nice to consolidate all 12vdc and 5vdc devices to use a single power source.
Hi All,
A bit of an old thread, but I've just go around to putting my home KiWi inside a screened metal box in order to try and cut down on the overall amount of RF noise in the workshop.
As part of this I thought I would try one of the MP1584 DC-DC convertor boards previously mentioned. I had already used some similar board for other projects, but I wasn't quite prepared for just how small these ones are.
After some load tests on the bench, just to make sure they worked as advertised, I decided to connect one with my KiWi. The plan was that if this worked, I could get rid of the separate 5v power supply and just run it from my big 12v power supply that already feeds everything else.
I mounted the board inside a small screened metal box I'd made by solding together sections of brass sheet.
Some quick tests revealed that it was producing quite a bit of broadband noise on frequencies up to about 1MHz, with a strong carrier at just below 1MHz, which was very noticeable.
Adding some 10uF 25v ceramic SMD capacitors directly across the input and output -ve and +ve terminals reduced the level of this carrier by about 25dB, and it also dropped the level of the broadband noise by a significant amount too.
Adding some 22uH (low resistance moulded chokes I found in my junk pile) series connected input and output inductors on the +ve supply rails, and another pair of capacitors to ground on the input and output side of the inductors, was used to form a Pi section low pass filter. I then used some thin coax to take the DC in and the DC out to the existing KiWi input DC voltage connector. However I took the -ve screen of the coax directly to the KiWi 0v rail, as everything else was directly grounded, and I didn't want to place a short across one section of the balanced input choke, as this would affect the choking action.
Doing all of this has brought the level of emissions down still further, and I'm now able to place the DC-DC convertor board, directly inside the screened box that the KiWi resides in.
With a 50 ohm load on the KiWi input, I now cannot detect the approx 1MHz switching carrier, and the broadband noise is almost completely gone. There are a couple of low level warbling carriers at around 2MHz, which I've not so far been able to trace the source of, but apart from that it's all pretty good. Once an antenna is connected, all of these interally generated signals just get lost among all the other directly received interference, so it's not really a problem.
The current draw at 12v is surprisingly small (in comparision to the current draw at 5v) at around 300mA, so overall I'm pretty pleased with the end result.
One key takeaway from all of this is that if your KiWi is still in its original plastic enclosure, spend a bit of time finding a metal screened case for it. It's made a huge difference to the overall noise floor in the workshop, and is much less likely to be contributing to the general level of received interference I hear on my KiWi in its urban setting.
My thanks to folks for recommending these DC-DC convertor boards, which I'm sure I will use elsewhere, with a bit of care and some additional filtering :-)
Regards,
Martin
Hi Martin,
My apologies for not having seen your post until now.
Your comments certainly inspire me to improve the shielding of my KiwiSDR. Do you have any photos of your screened metal box? That might give me some ideas.
Also, you mentioned using inductors and capacitors to form a Pi section low pass filter. I'm not clear on the filter's purpose. There's a noise source above the frequency range your Kiwi covers?
Thanks much,
Frank
Hi Frank,
Here's a quick snapshot.
I moved the position of the DC-DC convertor box around until I got the least spurs and interference when the RF input was terminated with a 50 ohm load. It ended up being soldered to the lids of the lids of the GPS and RF stage. I also had to add some short wire links between the coax sockets on the box and board, as there was too much of a current / voltage differential between them when just the pre-made short coax cables were being used alone.
The DC filter is a 10uF SMD cap to ground, a series 22uH choke and another 10uF SMD cap to ground. This was to filter off any remaining 1MHz switching frequency and noise / harmonics that may have been carried by the DC in and out cables. I also used screened cable for the DC connections in order to minimise any other cross coupling between the cables.
I hope this provides you with some further ideas.
Regards,
Martin
Thanks! It does indeed.
Hello @G8JNJ
Are you still using the mP1584 + filter ? Would any > 22uH value help ?
Thanks
I think anything would help, as long as they will handle the current with some margin to spare, but that's what I had to hand.
You may have to experiment with the grounding arrangements, to achieve the lowest noise floor.
Regards,
Martin
Could you tell me how many caps and inductors in total, values and placement ? if i understood correctly, they are being used like so:
?
Hello,
it's too imprecise to pronounce. If the internal resistance of the 12 Volt generator is low, its voltage drop for 3A will be low. So, when there is a high intensity, it will heat up. the regulation device will have to dissipate 20 Watts, a boiler !
On the other hand, if the internal resistance of the generator is quite high (1 ohm for example), that is to say a less powerful transformer, the regulation will dissipate less heat. It's a nice balance to find.
Another possibility is to choose an output filtering capacity, based on the appropriate time constant. If the 3A current only lasts for a single second, a filter capacitor can handle this current based on its time constant in the circuit. This will avoid having a powerful, heavy and large transformer.
The time constant determines the time required to charge the capacitor to 62 % of the source voltage (product of load resistance and capacitance). the calculation is complex, because the capacitor empties while being powered. what motivates us to choose a capacity of around 20,000 micro Farad. Such a capacity is not reasonable, Except for audiophile power amplifiers. You must limit yourself to 2000-3000 micro farad and take a fairly large transformer (50 VA minimum).
Another alternative is to connect a regulation battery, 6V lead acid for example, to the output in parallel. I do this to protect server hard drives. You need a battery that charges at constant voltage. The battery contributes to the regulation of the output voltage and assumes current peaks up to 5 Amperes. (depending on the mounting of the regulator, anti-return diode or not, for 7805 diode, for 2N3055 no diode).
As for the 22 microHenry anti-ripple coil, it's too weak to be useful. It would take a minimum of 10mH with big wire and a good core to cancel out the 50-60 Hz... Too heavy. I have some in stock here, it weighs 900 grams!
Best regards, Philippe
Philippe's comments are valid, but more related to Linear convertors / regulators.
This is what I did, but it is for a switching DC-DC convertor running at around 1MHz.
The capacitors were 10uF 25v SMD and the inductors were axial 22uH that I had lying around.
If running with a 12v input, the input inductors can have a lower current rating than the output inductor.
The whole circuit needs to be enclosed in a tinplate or brass box, and the capacitors need to be directly where the wires enter and leave the box.
Note that in this instance, the input negative is 'floating', but if you connect everything to the ground, then omit the input inductor in the -ve rail.
Regards,
Martin
Alright!
>and the capacitors need to be directly where the wires enter and leave the box
So then the inductors are gong to lie outside the box, correct ?
Everything is inside the box as shown by the dotted line.
Dear All,
oops, I thought the topic was about a linear power supply. Sorry. I had read it wrong.
Best regards, Philippe
Hi Philippe,
The thread is pretty general, so it's easy to become confused.
Incidentally, I forgot to mention, if you are planning running two KiWi's from the same supply, as the original question. Use separate inductors and capacitors on the output filters, but don't duplicate the capacitor on the regulator output.
This helps to improve the isolation between KiWi's and reduces the current passing through the output inductors.
Regards,
Martin