G8JNJ

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

"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

For transmit purposes, it's all about antenna efficiency, and radiating as much of the applied RF power in the direction you want it to go.

For reception purposes, it's all about the Signal to Noise Ratio, and a good transmit antenna may not always be a good receive antenna.

The natural noise floor on the LF bands is relatively high, especially in urban areas, and even quite small antennas can still be performance limited by the surrounding noise floor.

Rather than concentrating on large antennas, you may get better results with a smaller antenna in an electrically quieter location. Some experimentation is required, to get the best results.

Balanced antennas are generally better than unbalanced ones, and end fed wires have a reputation as being noise magnets.

If you do wish to install one, this diagram may provide some suggestions about minimising unwanted noise.

Regards,

Martin

I should have clarified the way it works a bit better.

Pushing the mouse wheel down whilst rotating it enables the opposite mode to the default that has been chosen. in OpenWebRX.

Having the possibility to tune using the mouse opens up other possibilities such as making your own VFO knob, using the optical encoder recovered from a scrap mouse, or buying one of the more expensive ready-made commercial items.

If it could be implemented in a way similar to that of OpenWebRX , then it would still retain the mouse wheel zoom option for those who prefer it, but offer an alternative for folks who would like to use mouse wheel tuning.

Try it and see for yourself.

http://wessex.hopto.org:8060

If you open up the settings pane in the control panel, you should see the "Hold mouse wheel down to tune" tick box. Also set the tuning step size in the controls section, 500Hz or 1kHz is useful for SSB, as most folks use 'rounded up' frequencies.

I'm not specifically requesting this feature, as I don't wish to add to John's already massive workload of much more important issues, but I can understand the appeal of it.

Regards,

Martin

Well done on the TDoA, especially as it doesn't work too well on CW or FSK. I made several TDoA runs during grey line propagation, and initially thought it was from Germany. I should have known better. I used two separate browser instances with my KiWi, with the frequencies offset to produce a composite, but much narrower shift FSK signal, that I could attempt to read with an external decoder. However, the data is encrypted, as you would expect for a military signal.

The pair on 7043/7050 kHz shift to 7041.5/7048.5 kHz

The pair on 7063/7070 kHz shift to 7061.5/7068.5 kHz 

Reports and discussion suggest it's a Russian FSK transmission, with some reports suggesting it's coming from somewhere in the Urals or the heart of Siberia, but one more detailed report suggests that the source is in the Crimea near Sevastopol ( https://youtu.be/zRho2iFfBCE )

--- Text from YouTube video---

Sevastopol; Extremely powerful two channel 20b/7000 Hz FSK paired signals re-appear from Apr 23rd on 40m band ~ 7045cf and 7065.5cf, each channel seems to be 7 kHz from mark and space, chosen for it's immunity from being easily jammed, at times the pair will shift frequency; originating from Eastern EU / Western RU region, now Crimea with transmitters near Sevastopol. The modulation rate of 20b with a shift of 7000 Hz.

 -The signal frame is 17 bits, the first of which is a 0.

 -The superframe is 15 frames (255 bits) and is constantly repeated so it does not appear to carry any useful information 

Military encryption 5N1 use in related signal connection to the conflict between Ukraine and Russia is likely. Contributor ANgazu thank you for your analysis!

---

This link has a similar discussion and explanation as to these signals:

https://reflector.sota.org.uk/t/some-weird-cw-found-on-40m/38289?u=iu1kgs

These are typical of RF welding / Drying / Curing processes. Very high power RF sources are also used during some types of semiconductor manufacturing processes.

Another source, is from the cheap Chinese "Radio Frequency Facial Machine" or "wands". These typically produce between 5 to 25 watts, but some are rated at several hundred watts.

All of the above can usually be observed around most of the ISM allocations, and they are a good propagation indicator on the low VHF bands.

Here are a few that should really be in the 40MHz ISM band, most likely from Asia.

When I used to live in an industrial town, we had one in a factory that welded seams on industrial clothing, that operated on 27MHz, and the Interference Investigators were forever chasing the owners, as they often removed safety covers, so that they could run the machine for longer before it overheated. The stray RF signals and harmonics used to interfere with the 2m amateur band and local taxi services over a very large radius. Once you have heard the distinctive warbling, humming, and drifting signals, you can easily spot them again.

Regards,

Martin

It's a common US HFGCS frequency, and they are sending an encoded Emergency Action Message (EAM)

Nothing to worry about (yet) these are very common transmissions.

But I'm pleased your SNR is creeping up :-)

Regards,

Martin

Good luck.

I don't use mine that much, but if you are interested in radio, it's always handy to have an amateur licence.

In the past, it used to be a valuable "pseudo" technical qualification when seeking employment, but those days are long gone.

Have fun,

Martin

Hi Glenn, I don't disagree, which is why I stated "Any further improvement can only be brought about by using a better antenna, or by reducing the amount of noise present by some other method."

If for example you have a problem with noise induced into the transmission line, amplifying and balancing at the antenna, then attenuating at the receiver, can reduce the noise contribution. This is only one example, but as you have said "sometimes, even if for the wrong reasons, a preamplifier might improve performance".

The point I was trying to make is that by just adding extra gain, it usually doesn't make things any better. It requires considered thought to do it correctly.

Regards,

Martin

That amplifier uses the same Qorvo TQP3M903 device, so I'd assume it's the same circuit too.

As before, the IMD performance isn't really sufficient for use ahead of a KiWi.

SV1AFN produces some good amplifiers that work well.

Although no longer a standard product, on request, he can also produce active splitters using push-pull pairs of FET's that work well. They have been successfully used at the Weston KiWi cluster, where we previously had severe problems with strong medium wave signals from nearby transmitters.

Turn Island Systems also produce a filtered pre-amp, using a Mini-Circuits device. Although the IMD specification is not too good, the use of a shelving and low pass filter ahead of it, minimises the performance issues.

I have no commercial interest in these companies, and do not specifically recommend them. I have simply highlighted them because of their characteristics, which may make them useful to KiWi owners.

Regards,

Martin