G8JNJ

Which KiWi is your own KiWi, where is it located, and is it public ?

Thinking about this, as this forum only allows limited information to be included in our profiles, it would probably be a good idea for folks to include their KiWi URL(s) in relevant posts.

Regards,

Martin

http://wessex.zapto.org:8074

http://websdr.uk:8060

Two or three times an actual MW broadcast frequency is often observed when very strong local transmitting stations are present.

In this case 3 x 1278kHz = 3834kHz

Sometimes these are actual harmonics being radiated by the transmitter, sometimes they are externally generated by objects such rusty wire fencing, that is rectifying and re-radiating signals, and sometimes they are produced somewhere in the reception chain.

Many times it can be a combination of all of the above.

Placing some attenuation, or better still an amplitude / frequency slope equaliser ahead of the affected KiWi can often help to minimise such problems.

Regards,

Martin

Hi Philippe,

That looks like a switching supply to me, probably more than one.

See if the bands of interference repeat at regular intervals, typically at harmonics of the actual switching frequency, 60, 100, 160kHz.

Unfortunately, if carried by the mains supply they are connected to, the radiated noise can be propagated over a large area, and you will find peaks and troughs in the radiation pattern, depending on the length of wire that are attached to.

I have recently been trying to locate some broadband VDSL interference centred on 3MHz, that is emanating from houses at least 0.5km away from the KiWi site, but fed with overhead copper phone lines.

I've been using SDR Angel and its "heat mapping" option, to perform "drive by" surveys of the area.

I use a magnetic mount active whip and GPS antennas, connected to an RTL SDR V4 dongle and laptop.

The more orange / red or brighter the "blob" plotted on the map, the stronger the signal level.

The KiWi probably has most of the required hardware to be able to do this, but KiWi recorder may be more suited.

Regards,

Martin

I use 75 ohm, foam filled, all copper satellite TV coax, with braid and foil for my active antennas.

Low loss and effective screening, don't worry about the slight impedance mismatch to 50 ohms.

Something like WF100 costs around £30 for 50m.

Don't use stuff with air spacing, or aluminium foil, or copper clad steel.

Regards,

Martin

They are most likely pirates, probably fishermen.

They often like to find "private" frequencies in order to conduct their "private" conversations, and these tend to be on frequencies with number sequences that are easily remembered.

There tend to be lots of them speaking all sorts of Asian languages, and frequently performing lots of chanting.

5 to 12MHz seems to be the most used frequency ranges, but they can pop up almost anywhere.

Regards,

Martin

As I said previously, the majority of Bias Tees have very poor filtering between the DC line and the RF path.

Nearly all the circuits you find on the internet tend to be outlining theoretical designs, that concentrate on providing the least attenuation and impedance "bumps" in the direct RF path, but don't worry about what happens with RF entering via the DC path.

The better designs for our reception purposes, incorporate additional filtering components in the DC path, in order to reduce this problem. But very large values of L and C are required in order to be effective at the low frequencies, especially at less than 100kHz.

Regards,

Martin

Check the antenna Bias Tee first.

Many don't have enough filtering built into them.

Regards,

Martin

I have noticed a problem, where folks stay connected or a long period, but they are only viewing the waterfall or spectrum display, and maybe doing something else.

So the frequency and mode they have selected, are sometimes misleading with regard to the purpose the KiWi is being used for.

This is usually indicated by being fully zoomed out e.g. z0

Regards,

Martin

Before swapping supplies, make sure that it is the Apple power brick that is causing the problem. It may well be something else.

The signal will most likely change its characteristics if the power supply load is altered in some way.

Try a different make of supply and see if the interference on that frequency changes or goes away completely.

Regards,

Martin

There are so many amateur digital modes these days, it is often very difficult to say what is being used.

It is around the frequencies typically being used for SSTV, and it could be Digital SSTV, but that is just a guess on my part.

The Signal ID Wiki is a good place to start when trying to ID unknown signals.

https://www.sigidwiki.com/wiki/Signal_Identification_Guide

Regards,

Martin