Interference Signals
Good morning....
I have two Kiwisdr versions 1 and 2 connected to two magnetic loop antennas of different brands, on both kiwisdr on the same frequencies for almost the entire reception band I find
interference signals spaced about 15 kHz.
I attach files as a confirmation, can anyone tell me what kind of signals they are and maybe how to solve them?
Thanks for your collaboration
Comments
This seems to be a characteristic spectrum of a 15 kHz impulse or perhaps high odd harmonics of a 7.5 kHz square wave. These kinds of signals are often from fast edges of SMPS power sources coupling into receive systems.
If you could forego the waterfall or augment it by showing a full 0-30 MHz spectral display instead it might be possible to say more about likely coupling mechanisms.
Waterfalls are remarkably un-useful for this sort of diagnosis.
The most visible and annoying disturbances start around 4.5 MHz and end around 7 MHz
Then from 10.6 to 21.9 Mhz there are the disturbances reported in the initial post.
And subsequently towards 23.9 Mhz I have this disturbance.
I don't know what the source is, as in my opinion it's a variety of disturbances. One piece of information I can add is that in recent months they have activated a DAB FM signal repeater about 500 metres away as the crow flies, but the transmission power cannot be found.
As useful as this may be, this is still the entire cascade of my receiver.
The series of waterfalls is not as useful as a series of spectrum plots, as suggested by Glenn.
However, apart from the interference I can see no obvious short wave signals, so how is your receiver and antenna configured ?
Is this just the KiWi with no antenna, with just a bias tee, or with the loop amplifier, but with no loop connected ?
The noise bands are almost certainly from some sort of switched mode power supply, or charger, and I suspect that if you listen to the signals around 10.6MHz, using AM you may hear some 50 Hz component.
Can you provide further information regarding your receiver and antenna configuration ? What type or make are the antennas, where are they located, and how are they connected to the KiWi.
How is the antenna powered and how is the KiWi powered ?
Regards,
Martin
As both Martin and I have been suggesting, please present a spectrum plot so any similarly spaced lines, particularly down near the low end of a Kiwi's range, might be discovered.
Very low frequency ingress will not be by way of (inverse square) radiation. Rather it will come in by direct injection. As Martin suggests, knowing the configuration helps diagnose this. There might even be evidence of few-kHz region ingress, depending upon the mechanism. If there isn't but there still is sign of it at relatively low frequency it may be near-field coupling of some sort.
Discovering and identifying, or even ruling out these other ways and causes of QRN is part of the cure.
I'll start by saying that I don't speak English and sometimes I don't understand the technical terms used. Maybe if we start from this problem it will be clearer if I don't answer on topic.
My receiver setup is a Kiwi v.2 and a powered MFJ loop antenna.
Both devices are powered by two +12 and +5 power supplies
[iFi iPower Low Noise DC Power Supply - actively removes unwanted electrical noise introduced by noisy power strips or wall plugs to provide a more stable and reliable DC to the device]
the antennas are about 10 meters from the ground on a balcony, the double-wrapped connection cables are divided by an aluminum sheet for the ground cable and are about 5 meters to reach the receiver
As for the [spectrum] I hope this is what is requested:
The predominant signal in the photo is a STANAG
this is the full spectrum instead.
I hope I answered all your questions, if so let me know I will try to add more details,
Thanks for your cooperation
OK understood.
If the antenna is on a balcony in an apartment block, it's very difficult to get away from sources of interference.
However, all the signal levels seem to be very low.
Do the wanted signals and interference levels change when you rotate the antenna ?
What model of MFJ loop antenna are you using, and happens when you remove the DC power feeding it ?
Regards,
Martin
...this is the situation when the antenna is in East/West direction.
this is the situation when the antenna is in South/North direction
this is the situation with the antenna not powered
the antenna is a MFJ-1886X
I'll leave it to Martin since I know little about MFJ-1886X but it appears that not only are signals very low but that there are very few below mid-HF.
Since most places in the world have AM or MW broadcast stations nearby, it rather looks to me like there is improper low-frequency coupling between the antenna and the Kiwi.
Since there is definitely a difference between powered and un-powered, I suspect some kind of RF connection issue to the Kiwi. The un-powered levels seem reasonable.
At these levels it may be that the signals you asked about are from ground loops or these same system problems.
I might add that it could be useful to use the WF:Autoscale function to spread what signals there are over the Y axis to make visibility better.
I honestly don't know what's going on, but something doesn't seem to be correct.
The signal levels seem incredibly low, although there is some variation when you rotate the loop.
The loop amplifier is very simple, and uses two GALI-74 MMIC devices, I'd assume the current draw would be around 160mA, and I think it's worth checking if the amplifier is consuming something like this level of current.
The circuit can be found here
https://cdn.shopify.com/s/files/1/0289/7782/3843/files/MFJ-1886_Loop_Schematic.pdf?v=1586534117
However, even when there is no power to the amplifier, there is still some low level interference present, which must be being conducted into the RF antenna path somehow.
When I'm comparing KiWi's I tend to set the waterfall gain to manual, with the minimum at -110dB and the maximum at -30dB. This accommodates most variations in antennas when swapping between different KiWi's.
However, in your case the signal levels are so low, it may be better to use the Autoscale function, as Glenn suggested, so that we be able to see some signals.
Regards,
Martin
this is the spectrum in automatic mode with
and without power
That's a bit more helpful.
I think you have a few problems, and I'm not sure if there is an easy solution.
The noise floor is relatively bad, but I think it would look a lot worse if the MFJ loop had a flat frequency response. The relatively high value of amplifier input impedance is favouring the HF bands, and this can be seen in the way the noise floor increases above 10MHz.
Other loop amplifiers such as the Wellbrook or LZ1AQ have a much lower value of input impedance on the LF bands, and this improves the sensitivity on those frequencies, but it wouldn't be much help for you, as it would just show up more of the LF band noise, that you can't currently see.
The second problem is that the wanted signals are at a very low level, and even the normally very strong (in Europe) broadcast signals, that can be seen around 13, 16 & 19MHz are very low. On my KiWi's, I have actually had to include notch filters for these bands, as without them, I often observe the KiWi overloading during the evening from these signals, and I'd estimate that they are 30 to 40 dB lower in level than I'd expect from an external antenna. As a result, I think it would be worthwhile checking the DC power consumption of your loop, just in case one of the amplifier devices has somehow gone faulty.
However, if the antenna is working correctly, I suspect the problem may be associated with a steel frame construction of our apartment block, or some other method used in the construction that has produced a RF screen.
Can you try different antennas, possibly poked out from the balcony or a window, just to see if this gets them outside the screen being formed by the structure of the building ? This may also reduce the level of the interfering signals too.
Regards,
Martin
I have a similar issue (bearing in mind this is mid-Sunday morning here and QRM is at its finest. ;-)
However, from later in the evening though to 6am it's quite clean and bearable. However, as you can see there is a lot of noise down the lower end of the bands, and no idea what that is. Most of it cleans up at night. (I go from 9db SNR to 20+ SNR in the evenings)
I am using the kiwi produced MW filter, hence the "dead spot" down the MW band.
I also added an FM filter, which seemed to knock off a number of spurs.
Furthermore, I haven't made my antenna rotatable (perhaps next version) however I am using two loops which I can switch between.
All that being said, I live in a very urban area and have all but settled on the fact this will always be the case, unless I put my Kiwi in a remote location away from human interference.
...I tried another loop antenna positioned one meter away from the other always on the same position, a
[Bonito MegaLoop FX - active amplifier for loop antennas in reception]
this is the result below: the first image with power inserted, the second without power
[BONITO GigActiv GA3005 - 9 kHz to 3 GHz Active Antenna]
the third image with power on, the fourth without power
[Diamond D-130 DISCONE ANTENNA for reception 25-1300 MHz - 50/144/430/1200 MHZ TX]
the fifth image with power on, the sixth without power
the last image is made with a 10m antenna wire placed on the balcony
Interesting.
The Bonito MegaLoop FX seems to be producing the best signals, but a lot of the noise is still present with the power removed.
When power to the antennas is removed, I wouldn't expect to see such high levels of noise and interference.
If you could figure out how this noise is being introduced, probably by means of the interconnecting cables or power supply, you may be able to further improve reception.
The rest are predominantly unbalanced antennas, that will be using something in your property as the "missing half" of the antenna, which is where the majority of the noise is being introduced, regardless of other factors.
Balanced low impedance antennas, such as loops, are most likely to be the better performers under such conditions.
I think you need to experiment with your cable placement, power supply types and connections, removing earth loops, and adding some decent ferrite choke baluns.
Regards,
Martin