Interference spikes on 40 metre band.

Mike Steventon

I am getting spikes showing up on 40 metre band, at intervals of exactly 4khz. They start roughly at the beginning of the band, say, 7.080mhz, then carry on up to 7.200mhz. I thought it might be within the receiver, but I think I can exclude a fault inside as when I plug in a dummy load to the antenna, the spikes disappear. This is also the case if I unplug all antennas.
The spikes show up quite strongly on the panafall. I wonder if anyone else has similar problem, and to suggest possible source of interference? I have excluded all household appliances by way of major shut-down of all house circuits except the (traditional) old fashioned LINEAR power supply. I have currently a vertical, and a long wire antenna. I have recently gotten a 6600M and was initially very worried that it was a "Flex-Fault", but I think I can exclude that from my deliberations!!! Apart from that, wow, what a radio!! Very happy bunny.

WK2Y

All the time or some particular time of the day?

Dave K5OZ

Mike, give us a screen shot of the 40M band. It may help us analyze. Here’s a few more questions that others and I may need to Troubleshoot:

1) Is your 6600M connected to your LAN? If so does your router have a UPS?

2) Is your rig grounded?

3) Do you have neighboring houses close by?

4) Do you have a ferrite core on your antenna coax at the rig?

5) Is 40M the only band that has this interference?

Dave

Mike Steventon

Thanks for your replies!! I have only had the rig for less than 24hrs, so will monitor 40 metres. I have attached a jpeg image of the display. The 6600M is solo. No ups. Yes, I am on an estate. I have a balun designs 1:1 current balun about 2 metres from the antenna input to alleviate common mode currents. All power to the house has been eliminated from the search. The only thing that I cannot disconnect is the smart-meter fitted by the power suppliers. I will see what things are like over the next 24 hrs and report back.
Cheers. Mike.

Dave K5OZ

Mike,

if you have a 12 volt car battery, try that? The sharp spikes look like harmonics from a microprocessor (maybe in the linear PS smart meter). What is the manufacturer and model number of the PS. I would also but a Toroid on the coax at the input of the rig

Dave

Mike Steventon

Yes, Dave, I think you may be correct. I cannot disconnect the smart meter, but I may well try to shield the electricity supply box with Faraday-type screening just to remove doubt. It is odd though that it only occurs on the 40 metre band. Another possibility is to take the gear into the country-side and power it from the car battery to see if that takes care of it. For the time being, I will keep an eye on it and update this chat-line as-and-when...

John KB4DU

Usually these interference items were always there, but went unnoticed without the panafall. Starting point is much like suggested above. Operate the flex with a battery and turn of the house power. If the interference remains,it is probably external to the house. Tricky part is to run SSDR without ac. I use a laptop for this, but an iPad or a ups will also work.

KD0RC

I use an RSP1 A SDR receiver and a loop antenna to sniff out RFI. I walk around the house with it looking for signal maximums. In my case, I found the RFI outside - it was my neighbor's security cameras. This technique lets you keep your electricity on as you wander around looking for the source. You will be amazed at how much RFI is produced by modern electronics. So much for FCC Part 15 protection...

Mike Steventon

Thanks all for your input. It has been 24 hrs of more or less continuous monitoring and the spikes have not gone away. I have dug out my old super-het and have confirmed the regular pattern of the interference, so have proved to myself that it is not the 6600M. I have shut ALL power to the house and still have the same problem. It can only therefore be generated from nearby houses, possibly broadband?, or it could be anything, really. It is just an unfortunate coincidence that it smothers the 40 metre band only, at every 4khz. I would not have cared less if it was "out-of-band".......
Yes, John, I have only become completely aware of my problem now that I have a panafall display. It reveals far too much!!!
If I ever find the cause I will post my findings on this excellent forum.
73 de G4GWH

Erik Carling EI4KF

According to the RSGB, 4khz spikes on the 40m band are due to so-called 'training carriers' from VDSL. You might check if any of your neighbours have such a system.

Mike Steventon

Thanks Erik. I have just read the RSGB article, and now am firmly of the conclusion that it is VDSL interference. The RSGB article does also confirm the 4khz spacings that I have observed. I have unplugged my internet connections and it still manifests itself, so it must be radiating vie the ground wiring. We are on a housing estate so there are many others enjoying super fast broadband in the immediate area. I recently invested in a DX Engineering NCC-2 antenna phasing unit, but I am still experimenting with it and have yet to set it up properly. My hope is that I will be able to reduce the spikes by electronically rotating my receiving antennas using the DX box.

John KB4DU

Maybe try setting a TNF notch filter on one of them to test. If the signal is a carrier only, it will be pretty narrow so the TNF may not block too much of the band. These filters work in the audio chain, not the rf chain so if the signals are strong enough to affect the agc, the TNF won’t help that. I live next to an army base that generates a lot of rf spikes and the TNF helps a lot. They are pretty easy to create and delete.

Mike Steventon

Yes, the TNF does have a good effect, and I can of course expand the filter to my will, so at least I have some control on it. There appear to be a lot of reports on the web regarding the problem in the UK. I have some useful news to report: I have crudely rigged up my NCC-2 antenna phase box with a couple of lash-up antennas (bits of wire, actually!) and was amazed to see and be able to drop the spikes by a considerable margin without removing desired signal. The effect is sufficiently broad-band to not require adjustment when moving across the band (40metre is the worst here). Now waiting on delivery of DXE pre-amps to install in the unit to give me more power to my elbow. British Telecom do not appear to be interested in resolving the problem. When we eventually all have fibre to the property internet, I assume the problem will just go away.

John KB4DU

Does the NCC box give enough of a direction to trace the source? Also, the flex has internal 32dB preamp. Due to the noise floor below 20M, i don’t use any preamp on those bands, just makes the noise worse.

Mike Steventon

Hi John. I am planning to use a couple of low noise low gain receive-only passive vertical antennas, so I figure that there will be the need for pre-amps in the NCC-2 to help things on their way. You do have a good point about directionality, as of course I might be missing out on rare DX by way of eliminating the spikes in a particular direction. I at the moment do not have a clue as to how to interpret the phasing as a way to determine the source. All these thing I can live with, as long as I can destroy the vision of horrible spikes splattered across parts of the hf bands I am interested in, right across the panafall. The nicest thing to see is the vertical lines disappear also for the waterfall display. They show up on 20metres also, by the way, and can be made to disappear by re-tuning the NCC-2, with very little detriment to the signals received. I did nor realise the extent of the issues until I got my Flex 6600m!! Cheers.