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Quiet switch mode power supply (SMPS) for KiwiSDR
Getting rid of differential noise is fine, though the power management IC regulators in the Kiwi's BB is so good that this is seldom to never a problem, in my experience. (Try deliberately introducing differential noise and check the Kiwi's response. I haven't done this for a while but I think even 100 mV tends to be pretty invisible)
But just looking the schematic of this typical linear regulator and wondering ...
What would happen if we built a PS, either linear or SMPS and then added another series pass device in the 'GND' leg of the output to raise the impedance and reduce CM current? Against typical CM source/load impedances, would it significantly improve the situation in real circumstances?
It likely might not since typical total CM impedance may be in the 100's of ohms territory and well above the effective resistance of the series pass devices, but it wouldn't be difficult to try.
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Quiet switch mode power supply (SMPS) for KiwiSDR
@IK8SUT , I don't have a diagram. This is a classic power supply consisting of a step-down transformer, a diode bridge and a 1084 linear stabilizer.
I used a toroidal transformer from a BBK household amplifier. The secondary windings of this transformer had too much voltage, so I simply wound two windings on top with a thick stranded wire of 12 and 5 volts. I used four diode bridges to power three 5 volt channels and one 12 volt channel. After the diode bridges, I installed electrolytic capacitors and linear stabilizers. One 7812 and three 1084. (I bought some MP1584 high frequency converters. I'll test them for noise later). After linear converters, I used filters from inductors and capacitors. I'll attach some photos.
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Quiet switch mode power supply (SMPS) for KiwiSDR
If anyone is interested, I use a linear transformer power supply. I have three SDR receivers. One KiwiSDR, one FlydogSDR and one RSP1A running Orange Pi4 lts. I also use a Microtik LTE router, an ethernet switch, and active loop antenna and a downconverter. Depending on user activity, the total electricity consumption is 60 watts per hour.
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Quiet switch mode power supply (SMPS) for KiwiSDR
All the broadband routers I have had provided, have had noisy Switched Mode "Wall Wart" type power supplies as standard.
They produced far more interference than the routers, which generally tended to be of good construction and had been EMC tested as part of the design process.
The power supplies always seemed to be an afterthought, and may have been sourced differently from the actual router, depending on local electrical regulations and requirements.
It is likely that the power supplies have been chosen on the basis of cost, and we all know what happens then.
Because of their small size, it is usually not possible to add extra filtering, and such internal modifications can also result in safety and insurance issues.
I tend to look in Charity (Thift) stores or at Car Boot sales for older, cheap electronics, with separate linear power supplies. As it's difficult and expensive to buy new linear power supplies, especially since the audiophiles are willing to pay silly prices for them. The rest of the electronics are useful for parts too.
On an incidental, but related subject
A friend of mine, who allows me to host a KiWi at the historic Goonhilly satellite earth station in Cornwall UK, was good enough to resite the KiWi to a new location on the site, in an attempt to resolve some long standing interference problems. However, he couldn't get it to connect properly to the network. He could see it acquired a DHCP address, but he couldn't ping it. He then transferred the KiWi back to the original location, and it still didn't work properly.
Thinking that somehow the build had become corrupted, we arranged for him to return the KiWi to me, so that I could fix it, upgrade the OS and take the opportunity to check things like the fan (which as expected was stuck solid).
The actual fault was the Switched Mode Power supply, which seemed to be working correctly, as the output voltage was correct when checked with a multimeter, it would also still happily deliver 5A output.
However, I noticed that the output voltage dipped just a bit more than I would have expected when on load, but only by about 0.2v.
I took the power supply apart and discovered that the main high voltage DC storage capacitor (150uF at 450v) had dried out over time, and was completely open circuit. This is why the DC regulation was so poor, and also why the KiWi was having difficulties.
Replacing the capacitor fixed the problem, and the KiWi was back to working as normal.
Most of my past KiWi problems have been power supply related in one way or another, so my rule of thumb now is:-
If your KiWi is misbehaving in any way, check the power supply first, and pay close attention whilst you do it.
Regards,
Martin
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Waterfall/Spec smearing when zoomed to WF14 on 4-channel mode [fixed in v1.695]
Thanks for reporting this.
It seems the rx4_wf4 FPGA file was incorrectly updated when the v1.692 changes were reapplied in v1.694. But I don't understand why that would of caused this problem. I'll have to go find out.
This will be fixed as part of v1.695
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FT8 6m Autorun [fixed in v1.695]
Yes, I can do that. Added to my infinite list of things to do..
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FT8 6m Autorun [fixed in v1.695]
I think the question was reasonable since it was "using down converters". For this reason using a frequency converter/extender such as the 0-2 GHz transverter I use here suggests the value of having many additional bands listed as options.
Amateurs have already made a great deal of use of narrow band modes above HF, particularly WSPR on 2m and shorter wavelengths.
6m FT8 is very active now in the Northern Hemisphere as we are in the midst of the sporadic E season. With the LO offset JKS has added, the KiwiSDR already natively supports all-modes on all-bands. Adding FT8 support and even all-extension support makes a lot of sense to me.
Why not support it all in a Kiwi?
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v1.694 [hopefully a working version of the failed v1.691,692 update]
Okay, let's try this update again. Hopefully it won't cause your ATM machine to stop giving you cash.
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Private use of a KiwiSDR receiver in France
Hi Andy,
I understand the points you are making, but having previously discussed this with Philippe, I think there are some valid concerns, that may discourage other people, in other countries, from operating a KiWi.
If a simple fix, which John has already implemented, can help remove some of these barriers, then surely it is a good thing ?
Some countries are extremely sensitive about some aspects of the radio hobby, and to be honest, if I was living in one, I wouldn't be running a KiWi. It's easy to forget this when living somewhere that is more "relaxed" about such things.
Callsign piracy has always been an issue, and using an alpha-numeric string (or emojis) to identify an individual doesn't mean that they are who they say they are. However, I can understand the problem for the KiWi admin, if someone else decides to use your callsign, and you, the legitimate owner, find out, and then blame the admin for something that he has no control over. This may sound unlikely, but I have experienced similar problems when we had the "Chat" facility enabled on one of our websdr's, which caused so many issues we, (like most other websdr admins) removed it. Any public site, that has the ability for folks to anonymously post comments, no matter how brief in content, will unfortunately be abused.
Andy - "they" already know, who you are and where you are :-)
Regards,
Martin - G8JNJ ( or am I )
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Javascript not working since the last update [fixed in v1.695]
@studentkra many many thanks, now working :)
