I am new to this, having just set up my station. I have "very bad" QRN on 40m: S9. Here is the setup:
- High density suburb with flats and houses
- Yaesu FT450D with fan dipole at 6m-9m above ground (sloping), this is lower than a building with flats to the North East. Wires for 40/20/10m, nicely resonant, checked with NanoVNA.
- 1:1 Balun (ie choke) at feedpoint. 15 turns on FT240-52. No evidence of RF in shack.
- 22m RG58 run back to station which is on first floor
- Station earth dropping about 3m from 1st floor to 1m driven ground stake (I realise this may not be effective, as run is too long)
These are the things I have tried:
- 40m QRN is consistently > S8 mostly S9 during the day. Grainy white noise.
- 20m and 80m are only S3.
- Noise drops slightly at night but only 1S unit.
- Turning off all power in house with radio on battery reduces it to ~S7.5 so about 1 S-unit. Still a long way from level on 20m and 80m.
- I have tested calibration of S-meter on all bands with signal a generator and a 40db Attenuator. It's within spec acc to the service manual.
- There are some "VDSL" (UK broadband) training tones giving me a "birdie" every 4kHz. But this is only on some days and appears not related to the background S9 "grainy white noise floor".
- Our own broadband line runs almost parallel to the dipole (I have put as much angle as I can but it's < 20 degrees). But turning our router off (as above) doesn't remove the "main" source.
- I cannot detect the "VDSL guard bands" at 5.2, 8.5, 12Mhz
- Noise appears solid across all of 40m, ~6Mhz to about 8Mhz
- I can make contacts on 40m but only with "booming" stations.
Edit: additional info from discussion in comments below To test for radiated vs conducted noise I also performed these tests:
- I have a second FT240-52 toroid with 10 turns of RG58 at the radio end about 10 inches before the PL259. It was spare so I thought I would add it. Made no difference.
- The radio running on battery without antenna is totally quiet on all bands.
- With linear 12V power supply it is also totally fine without antenna.
- As soon as I plug in the antenna I get S9 noise on 40m.
- The same even with a "random 5m wire thrown out the window and shoved into the centre of antenna connector on the back of the radio."
Also: I was taking HTs for a walk with my son today, and we walked past one of those green (UK colours) Telecom boxes about 100m (?) from my dipole. The interference coming off that thing was enough to break through the squelch of our Baofeng HTs tuned to 2m. On FM! Similar cabinets around the neighbourhood showed no sign of interfering with the radios, even with the squelch fully off. Could be a lead?
What is my logical next step?
Run around the neighbourhood with a portable HF radio and a directional loop antenna? Requires some investment? How about a NanoSA, which might be a useful tool anyway?
If I find source, what are options: 1. work with neighbours 2. use a phasing noise canceller?
Any tips much appreciated
Update: I am in the process of building this loop: https://ka7oei.blogspot.com/2021/02/rfi-radio-frequency-interference.html The pre-amp is built and tested. Have made a wooden frame for the loop. Just needs putting together. I am hoping it will help me understand if I have one or many (major) noise sources. There is an 11kV distribution transformer about 40m from dipole, which would be a great candidate!
Update#2: Loop is built and seems to be working. I can receive distinct signals on the tinySA (see above link) and the loop is definitely very directional - able to completely null strong signals. What does it mean? I don't know yet. There is a contest on, so 40m band is drenched in "wanted" signals. :-) -- I may need another amplifier stage to look at the "noise" in more detail, but I suspected that, and left room for it on the circuit board. TBC... If anyone has experience in using such a loop with spectrum analyser please comment or add answer. I have a feeling operating the loop in a structured way to get meaningful results is going to be key.
And the tinySA showing the signal from the amplified loop standing under the dipole.
The loop is clearly working and showing signals. And these can be nulled by rotating, but it does not show the "raised floor". Why? I am not sure how to interpret this.