Surprised by interference.
I know I am in an urban area, however with my loop aerial fixed on the chimney stack I am quite surprised that it is still prone to so much interference eg from SMPS's. I thought the offending SMPS would need to be quite close to the loop, but maybe that isn't the case.
I do have quite a lot of SMPS's in my own house, but I don't believe the problem lies with them. I have turned most of them off & the problem is still present. The only ones I can't turn off at the moment are the 2 for the router & the ONT box, if I unplug those I won't have any internet to feed to the Kiwi. I don't have any battery power packs or linear power supplies to use yet.
Obviously I can rotate the loop, this reduces the SMPS noise, but there seems to be 2 different sources of the noise, each at different frequencies & in different directions. The LW noise is worst in the N/S direction, whereas the noise from 400Khz to about 750Khz is worse E/W. I do have the VDSL noise much higher up as well. I have tried common mode noise chokes etc, they don't make much difference. I assume getting to the noise source is the only way to reduce it ?
Many thanks.
Trevor
Comments
Hi Trevor,
I don't think your situation is quite as bad as you think it is.
I'd suggest sorting out the main issue first.
Your loop is providing quite high signal levels, and the two strong medium wave stations on 693 & 1053kHz are almost certainly causing some intermodulation products over the rest of the MW band, and maybe beyond.
Try adding 10dB of attenuation and see if this improves things.
In fact, you could probably add as much as 20dB, without degrading the Signal To Noise Ratio.
The antenna only needs to raise the noise floor by 6 to 10dB on the quietest of frequencies, which are probably those above 25MHz.
Adding 10dB of attenuation should reduce all the signals by 10dB, if some reduce by a greater amount, or disappear completely, then they are likely to be false signals produced as intermodulation distortion.
If intermodulation products remain, then the loop amplifier is being overloaded, and a smaller loop may be required.
Regards,
Martin