G8JNJ

"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

You only need sufficient attenuation to take the strongest broadcast stations down by just enough to prevent ADC overloads from occurring. I generally try to keep all signals across the 0-30MHz spectrum below -30dB.

If you have an existing band stop filter, with too much attenuation, you can connect a 1K ohm variable resistor between the input and output of the filter, and then adjust the value until you have enough attenuation to prevent overload occurring at night, but still allow some signals to pass through at a usable level.

Even on a receive site where I had strong signals from local medium wave transmitters, I've not had to introduce more than 20dB of band reject filtering to fix the problem. In most cases, a simple 10dB slope frequency / amplitude equaliser provides a good compromise.

This and other techniques have been discussed in many previous threads, so it's worth searching for those.

Regards,

Martin

Hi Frank,

That looks clean, and the distribution of noise looks to be correct.

The fun starts when you connect your antenna, mainly because of introducing other conducted paths for noise to ingress.

As a further test, connect just the ground from your antenna connection cable to the ground of the KiWi, and see what changes.

Then try and fix / resolve any additional noise you can see, before fully utilising the antenna.

Common mode chokes, galvanic isolation, and additional filtering of the power supply, network and GPS cable may all help.

Regards,

Martin

I'd be tempted to have a chat with your neighbour, mine have always been interested in finding out what could be causing such interference, but perhaps I'm lucky that many of them seem to be ex-engineers.

As previously mentioned, it's most likely a Chinese battery charger or similar, that hasn't got the mains filter components fitted.

Also, don't discount your own property, try and drop the main breaker if you can, whilst monitoring using batteries. It's surprising what can be overlooked.

Regards,

Martin

I tend to set the supply voltage at the DC connector, with the KiWi powered and running at 5.4v.

This gives 5v at the internal header due to various voltage drops.

As a result, I don't think 5.66v is likely to be outside the limits, but your issue may be more associated with the rise or ramp up time of the power supply itself, or the way it responds to a load being initially connected.

An old trick to reduce the voltage is to place a silicon power diode in series with the +ve DC supply. Depending on the diode, and the current being drawn, this could introduce anything from typically 0.6 to 1.2v voltage drop.

Regards,

Martin

You can place attenuation ahead of an LNA to improve strong signal handling, but the amount of attenuation needs to be chosen carefully, to take into account the LNA gain and Noise Figure, in order to ensure that the overall system Noise Figure is not any worse than the basic receiver alone.

If you search though the forum you will find many posts on the subject of equalisers, filters and notches.

Here is one example

https://forum.kiwisdr.com/index.php?p=/discussion/comment/5723

For a more detailed analysis of how equalisation can be applied in order to reduce the noise contribution due to intermodulation effects without affecting the basic Signal to Noise performance, see if you can find a copy of this paper on-line.

https://digital-library.theiet.org/doi/10.1049/ree.1977.0028

Regards,

Martin

Personally, I think the internal attenuator is more trouble than it is worth.

An external attenuator controlled by the KiWi, as a separate accessory, may be a better option for those that need to handle day / night propagation changes.

However, in most cases, an amplitude / frequency slope equaliser and / or Broadcast band notch filters can fix most problems, without having to dynamically change the overall gain distribution once it has been initially set. Having a fixed system gain, makes it easier to observe changes in propagation and noise levels.

Regards,

Martin