Wonder what this is at 5300Khz? - its always there.
Cant seem to find any reference online as to what it is. There isn't any audio on it, and thought perhaps its an ALE signal, but no. So I suspect it's noise.
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Here is a very similar one in the 16m band
This is almost certainly RFI from an unstable oscillator, probably harmonic from a switching power supply.
Makes sense. I'm using genuine Apple USB 10W power bricks.
I think I might build a linear supply.
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
Most switching power supplies change the frequency of the converter depending on the temperature. Not much, but enough to notice it at the waterfall. If it is not possible to disconnect the power source you are testing from the mains, simply heat it up a little with a hair dryer and look at the signal on the waterfall
I do have a DC battery pack - I will try that and see if the noise is still there. It could also be coming from the loop antenna Bias T as it too runs from an apple brick (separate) - Ill do some swapping around in the weekend.
Check the antenna Bias Tee first.
Many don't have enough filtering built into them.
Regards,
Martin
So, anecdotally, I "think" its the Apple power supplies.
Unfortunately I only have one pure DC supply (battery pack with USB), however when I swap out one of the Apple bricks, the noise almost dissapears. When I switch between the Bias Tee and or the KSDR, the result is basically the same. (looking at the waterfall, the signal is much fainter than when using two Apple bricks) So I suspect there is some harmonic interference that seems to amplify when using two bricks.
I have an ultra low noise linear power supply coming (https://www.ebay.com.au/itm/145022571057?var=444227624373)
Ill mount it in a nice metal box with a couple of USB headers conntected to the output.
It was fairly cheap - so a useful experiment.
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
Make sense. To be honest, the antenna is a cheap MLA-30+ which in fairness, does an excellent job of increasing signals and reducing the noise floor, and given I live in a suburban area, I cant complain for the price.
My next step for an antenna that doesn't piss too many people off is (read; other half)
https://techoman.co.nz/collections/hf-shortwave/products/lwhf-160-hf-160-6-metres-multiband-end-fed-long-wire-antenna
and perhaps coupled with an ATU like:
https://techoman.co.nz/collections/hf-shortwave/products/mfj-956-15-khz-30-mhz-lw-mw-swl-antenna-tuner
I have a reasonable sized section and could run this along a fence line and keep it quite low and out of the locally generated noise.
(Or I will make one - depends on motivation levels and time)
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
Brilliant, really appreciate the advice!
I have moved the loop antenna to the rear of the property away from the house, and I have a small room in the rear of the garage which doesnt have much in the way of electronics in it where the KSDR resides, and I also put that into a metal box (well vented)
The antenna looks a bit boxed in and close to other properties (and noise sources) in that position.
Have you tried it parallel to the fence line I have marked in yellow ?
It doesn't need to be mounted high up, my loops at home are pretty much on the ground and hidden by bushes.
Regards,
Martin
Hi Martin,
That was actually going to be my next option, however I will need to get a good length of coax as a run from there to the garage would be 60 odd meters.
Off to Jaycar this weekend then :-D
Cheers
Sean
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
Dear all,
I also receive such very strange signals on the two Kiwisdr of Trémolat (France, Nouvelle Aquitaine). The following images were taken on the Kiwisdr 2, more sensitive and receiving less interference. These are not interferences coming from the installation. These modulations are captured by the antenna. Their carrier frequency, if there is one, seems very unstable to me. And the signal is sometimes interrupted quite regularly. The reception is not permanent, we do not receive them all the time.
My antenna is a vertical antenna, an isolated 11 meter pylon. It is far from homes. This antenna is installed 250 meters from the Kiwisdr receiver. I use 250 meters of 75 Ohm satellite TV coaxial cable, shielded 5 times. The cable is buried 40 cm.
The last photo shows what I get when I unplug the 11 meter tower. Still connected to the Kiwisdr are the 250 meter cable, the 15 dB amplifier at the base of the antenna, and the impedance transformer. The VLFs pass, because it is the buried coaxial cable that picks them up over such a distance.
Best regards, Philippe
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
Dear Martin, sorry, I didn't have time to answer you earlier. Your method of observing parasites is great. I should do the same investigation (in the workshop, I have a Rohde & Schwarz analyzer that could be used for this. Now, I can't see myself intervening on the installations of the first neighbors who are 250m from the antenna.
to give you an idea, the antenna is at the location of the red arrow in the photo above.
best regards, Philippe
A quick update.
I received the DC power supply, gave it some tests and it seems like a nice stable 5.18V on the output.
I replaced the two Apple bricks, one for the KSDR and one for the Bias Tee, and connected them to the new linear DC supply, and from what I can tell, the "noise" is all but gone on that frequency.
Will monitor and report any additional findings.
Parts used:
Left to do: