G8JNJ
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Business survival and the ethics of Open Source
This is a thorny subject, and I could write a thesis on it. I have already made my position clear to John, but I'll raise a few points here to further the discussion.
Open-source / FOSS is generally a great concept, kids these days like having stuff for free. Music streaming is perhaps one of the best examples. However, the problem is how to make money from it, and many small artists are still arguing about that one.
The principle of collaborative free software is good, as long as everyone contributes, less so when one person does the work, and everyone else sits back and makes use of it. In the workplace, most people know who is actually doing the bulk of the work, and who is just doing the bare minimum, or "clock watching".
John is in a difficult position, where the Opensource software, supports hardware, which he sells to make an income.
When you buy a KiWi you also get for free, a superb level of support from its enthusiastic developer (John), and unfortunately competing products like this, building on his work, but sold at low cost, for short term gain, will impact the long term survival of his business, including the other services he provides, such as TDoA, which run on his servers, at no additional cost to users.
By contrast, most of the previous KiWi clones have fallen by the wayside, despite assurances from the companies producing them, that they would not stop supporting their products. They try to make a quick "buck", then loose interest as sales decline.
The current competitors have used the KiWi code, and introduced some innovations in their own product, but these really only benefit the competing hardware, they do not directly feedback into the KiWi code, product or features. Their software is flaky, and response to significant bugs is usually patchy at best.
I don't think John can compete on the hardware side. Designing, building and selling hardware will always be difficult when competing against certain regions of the world. Low production costs, scale of manufacturing, circumventing import taxes and duties when shipped to other countries, and lack of respect for IPR, all add into the mix.
However, the time and effort he has put into developing the KiWi, since it's original fork from OpenWebRX, needs to be rewarded in some way, and I don't think that in future that can be achieved through the manufacture and sales of the hardware. Some way needs to be found to protect his IPR, provide a source of income, and cover the costs of him providing aftersales support, software updates, and the running costs of the services he provides for free such as TDoA and proxies etc. A subscription for support services, could be one way of achieving this, but in the meantime, protecting the parts of his code that he can, without infringing the Opensource parts, should definitely be considered.
Personally I'd risk doing this, and wait to see what happens, if someone objects then just fix the bit that is problematic, but in many cases it would be "the pot calling the kettle black", so I don't think it would be a major issue.
I'm all for respecting the law, and various formal or informal Open source agreements, however this shouldn't allow an individual to be taken advantage of, especially if they are good-natured and willing to go above and beyond what is required to make a profit, for the benefit of the community as a whole.
That is not fair, and should not be accepted by anyone with a social conscience, or sense of justice.
I could say an awful lot more, but this summarises my position, and I hope it will lead to a more meaningful debate.
Regards,
Martin
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Attenuators before or after the pre-amp?
Ideally, you should place attenuators between the LNA and receiver, this ensures the best overall Noise Figure.
However, there is a trade in LNA design between strong signal handling and Noise Figure.
Most cheap LNA's don't have a sufficiently good enough strong signal handling performance, and they produce Intermodulation products, which typically show up around the MW broadcast band and either side of the 160m Amateur band.
The Intermodulation performance of an amplifier is usually specified by the second and third order intercept points that are typically measured at the amplifier output. This is a theoretical value where the Intermodulation products rise at a faster rate than the original signals, and if you plot all these levels against each other, you will find points at which they intersect. Once you have such a graph, you can then work backwards, to see what maximum level the input signals can be, before the Intermodulation products start to rise above the receiver noise floor.
I use a copy of the DXE-RPA1 pre-amplifier and have measured the IOP2 at +92dBm, and the IOP3 at +45dBm, and this is just about acceptable when connected to a decent antenna.
For comparison, a single PGA-103+ amplifier (still decent, and better than most) measured an IOP2 at +48dBm, and the IOP3 at +36dBm, but this does produce noticeable IMD products.
The Kiwi typically has a Noise Figure of 14dB at 30MHz, which is just about adequate. If you add an LNA with a better noise figure, that will improve the sensitivity on the upper HF bands. But every dB of attenuation, you place before the LNA, will degrade its Noise Figure by the same amount. Placing attenuation after the LNA, does not degrade the system NF to the same extent. There are various cascade Noise Figure calculators on the web, if you wish to investigate this for yourself.
Pre-amplifiers should ideally only have enough gain to overcome any system losses. As a simple test, if you connect a 50 ohm load in place of the antenna, and note the level of the noise floor at 30MHz, then connect the antenna back up, you should aim for a 6dB increase in the level of the noise floor. Any less than this and you are missing some signals, and any more than this, you are using up the KiWi's valuable dynamic range, which is not desirable.
Regards,
Martin
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Maximum possible number of simultaneous users
In addition.
If you have more than the specified number of users trying to connect, the additional ones can "queue" to wait for the next free slot, or "camp" where they can "piggyback" onto an existing user and hear just the audio.
This is useful when you have a lot of users all wanting to listen to the same thing, such as a popular amateur radio net.
The maximum number of campers can be defined in the "Control" admin page.
Regards,
Martin
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Quiet switch mode power supply (SMPS) for KiwiSDR
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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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Quiet switch mode power supply (SMPS) for KiwiSDR
I recently did a bit more research into the various DC filter boards that can be bough cheaply from China.
I've previously mentioned the simple type with two separate inductors.
Simple DC Filter
But I wanted to compare it against some of the larger types with an additional common mode choke using a dual winding. All of these seem to use the same printed circuit board, but populated with different types of inductors.
Green rectangular core common mode choke, and black core inductors
With toroidal common mode choke and yellow / white core inductors (Type 26 Iron Powder)
Differential Mode attenuation - direct noise from the power rails
All the filters are pretty effective. The simple type is slightly worse, but I doubt you would notice much difference between them in "real life"
Common mode attenuation - conducted noise, usually via a ground path
The Green and White cored filters are much more effective. The White cored filter would be slightly better at reducing low frequency <1MHz switching noise from Switched Mode Power Supplies, but the Green cored version provides much better overall attenuation.
Note that the values of attenuation were measured in a 50 ohm system, and the actual amount of attenuation will depend on the circuit impedance. However, using 50 ohms does at least provide a standard reference for comparison purposes.
Regards,
Martin
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Business survival and the ethics of Open Source
I'd also suggest emphasising the "works straight out of the box" aspect of the KiWi.
One competitor is making an attempt at this, so far unsuccessfully, but the majority of previous competitors have not been able to achieve this. Other options, such as OpenWebRX (moderate pain) or PhantomSDR/Plus software (really painful), are still in their infancy, and require a fairly extensive knowledge of Linux to get running initially, and then update and maintain.
Regards,
Martin
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Hackers be hacking..
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Antenna Considerations / Do's and Don'ts
When using an MLA-30, I don't think you can have too much gain :-)
Auto waterfall settings can have you chasing your tail. So I tend to set the KiWi waterfall & Spectrum display to manual, zoom fully out to see the whole spectrum, then set the maximum waterfall level to -20dB and the minimum to -110dB. This gives a good baseline for comparison with other KiWi's when the same settings are used on them too.
Don't worry about the noise increasing, you should see some, especially in an urban environment.
Just aim for a 6dB increase in the noise floor on the upper HF bands 20-30MHz, when the MLA-30 is powered up.
As I said before, turn the bias tee control to maximum gain, and then just use the amplifier gain control to achieve the best overall performance.
Regards,
Martin
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Any plans to move to OpenWebRX Plus? [not possible, makes no sense]
"Seems the interface is a bit slicker."
Not really, it's just different, and has as many "quirks and foibles" as the KiWi (sorry John).
OpenWebRX + is more orientated to the VHF / UHF bands, and is good at the modes that can be found there, and I operate both.
However, the developers are not as responsive as John, and the admin interfaces and configuration processes require a good degree of skill to set them up and make them function correctly.
By contrast, the KiWi works pretty much straight out of the box and is generally stable, OWR+ is more of a work in progress.
This may suit folks proficient in Linux, who enjoy spending many hours resolving problems, but some of us just want something that works, with minimal hassle.
Regards,
Martin