Hi All,
Not sure if this is the right place to put this, however...
Just a quick question to run by you all - does anyone suffer any interference on HF from having cable Internet (for those that have both in the same room)
The reason I ask is - I'm considering getting rid of my ADSL and having BigPond cable installed, however I'm wondering if there might be potential for interference as the cable for the Internet would run directly parallel to my antenna cables.
Does anyone have any problems at all with interference on HF? I primarily use 80, 40 and 20 metres
Regards,
Brayden
Cable Internet and HF Interference
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VK3ZFS
Re: Cable Internet and HF Interference
I would check the freq spectrum of the Telstra cable, up and down channels. aprox 5 to 50Mhz uplinks, 80 to 700Mhz downlink, its not a perfect RF tight the cable system, so expect some leakage RFI.
Re: Cable Internet and HF Interference
Brayden
I have had Foxtel plus Big Pond Cable for some years and there definitely is some radiation from the coax feeds into the property and then to the respective IQ box and Big Pond cable modem. I have tried ferrite clip-ons on the coax outers at the splitter point in the termination box on the outside wall but it doesn't seem to change the level of radiation much. I suspect that it is direct radiation from the coax outer that I am hearing and the only way I reduced it slightly was to run an short earth wire from the splitter body down to a small earth stake directly below the termination box. Probably a no-no as far as Foxtel/BP is concerned, but it did help a bit here.
It manifests mainly as a broad band noise and video buzz on HF, mainly evident on 3.5 and 7 MHz, peaks around 4-5-6 MHz and nothing too obvious above 10 MHz. Nothing significant on the higher bands like 14, 21, 28, 50 MHz etc - more computer-related noises and LAN pulsing evident on them.. Preset your NIC to 10MB/s to minimise LAN noises in the shack !
How bad the QRM is will probably be determined by the physical spacing of your HF antennas from the coax cable signal feed and whether these feeds are run through ceilings or along the bottoms of the outside walls and then through-the-hole directly to the Fox/BP termination. Coax-to-coax induction isn't likely to be too bad provided you have baluns on the centres of dipoles or V's (ie any unbalanced feeds to balanced antennas) so that, on the coax feeds to your radios, the outer does not play any real part - except for providing the shielding effect on the inner, skin effect on the inside against the poly/foam dielectric etc..
P.S. : You do get used to the noises over time.... even if you don't want to.
I have had Foxtel plus Big Pond Cable for some years and there definitely is some radiation from the coax feeds into the property and then to the respective IQ box and Big Pond cable modem. I have tried ferrite clip-ons on the coax outers at the splitter point in the termination box on the outside wall but it doesn't seem to change the level of radiation much. I suspect that it is direct radiation from the coax outer that I am hearing and the only way I reduced it slightly was to run an short earth wire from the splitter body down to a small earth stake directly below the termination box. Probably a no-no as far as Foxtel/BP is concerned, but it did help a bit here.
It manifests mainly as a broad band noise and video buzz on HF, mainly evident on 3.5 and 7 MHz, peaks around 4-5-6 MHz and nothing too obvious above 10 MHz. Nothing significant on the higher bands like 14, 21, 28, 50 MHz etc - more computer-related noises and LAN pulsing evident on them.. Preset your NIC to 10MB/s to minimise LAN noises in the shack !
How bad the QRM is will probably be determined by the physical spacing of your HF antennas from the coax cable signal feed and whether these feeds are run through ceilings or along the bottoms of the outside walls and then through-the-hole directly to the Fox/BP termination. Coax-to-coax induction isn't likely to be too bad provided you have baluns on the centres of dipoles or V's (ie any unbalanced feeds to balanced antennas) so that, on the coax feeds to your radios, the outer does not play any real part - except for providing the shielding effect on the inner, skin effect on the inside against the poly/foam dielectric etc..
P.S. : You do get used to the noises over time.... even if you don't want to.
Doug VK4ADC, QG62lg51
http://www.vk4adc.com
http://www.vk4adc.com
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VK6ZRY
Re: Cable Internet and HF Interference
The cable will suffer no ill affects.
However your cable and adsl modems will.
Upon inspection of these modems you will notice they have plastic cases and the lines and cables in and out are not shielded in any way.
RF from your transmissions will affect them if too high a wattage.
The frequency you transmit on is also a factor as certain lengths of wire in the comms system will "pick up"
more RF than other frequencies.
So on 40M it might be fine and on 20M it may suffer. It will only become apparent when you TX.
The modem will have errors and may fail, with the red flashing light on the modem indicating a signal fail from the exchange.
Goodluck.
Yes I work for The Big T.
I suggest all leads (audio & data) have a Faraday shield, a metallic shield only earthed at on end will provide safety from RF.
This is how we protect all data connections in a Telephone exchange, all data jumpers and cables have shields with earth only at one end.
All the RF from DC switches and flouro fittings are negated.
I have terminated thousands of them, making absolutely sure one end is insulated and no earth loops are created.
However your cable and adsl modems will.
Upon inspection of these modems you will notice they have plastic cases and the lines and cables in and out are not shielded in any way.
RF from your transmissions will affect them if too high a wattage.
The frequency you transmit on is also a factor as certain lengths of wire in the comms system will "pick up"
more RF than other frequencies.
So on 40M it might be fine and on 20M it may suffer. It will only become apparent when you TX.
The modem will have errors and may fail, with the red flashing light on the modem indicating a signal fail from the exchange.
Goodluck.
Yes I work for The Big T.
I suggest all leads (audio & data) have a Faraday shield, a metallic shield only earthed at on end will provide safety from RF.
This is how we protect all data connections in a Telephone exchange, all data jumpers and cables have shields with earth only at one end.
All the RF from DC switches and flouro fittings are negated.
I have terminated thousands of them, making absolutely sure one end is insulated and no earth loops are created.
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VK3VBR
Re: Cable Internet and HF Interference
Hi VK6ZRY,
I'm looking to have cable installed very shortly as my ISP (Internode) has just been bought out - that and I want 100mbps (max) speeds - currently on 8mbit ADSL. (I thankfully do not have any issues with interference to my existing ADSL.)
I have made a note of all you have said re shielding etc. However, my main concern at this point is the potential to interfere with Foxtel boxes in the house. I personally hardly watch the thing, but there are others in the house that live on it! We have four (one unused) outlets in the house, with my Internet outlet adding another for a total of 5. The Telstra and antenna cables will be literally about 10cm apart running parallel down the wall. (There is currently a foxtel & phone outlet hybrid plate on the wall in my shack, next to my antenna runs, however there is no actual cable running to it - possibly re-ran to one of the other outlets. However, there's both a Foxtel iQ satellite dish and cable running into the house - we use the cable - why there is both is anyones guess and I am unsure what the outlet on my plate is.)
I was reading on the BigPond site that if there are more than three outlets - an amplifier is required. Do you have any comment on the possibility of this increasing the likelihood of interference?
I am hoping there won't be anything getting in to the Foxtel boxes/my modem once it's installed, but I will have to wait and see - I have asked fellow amateurs who have Optus cable and they have reported no issues - but I hear Telstra and Optus use different HFC frequencies. I will admit I am fairly green in this area - so will probably call in here for some assistance if there is trouble after it's installed.
Thanks for your input thus far!
Regards,
Brayden - VK3VBR
I'm looking to have cable installed very shortly as my ISP (Internode) has just been bought out - that and I want 100mbps (max) speeds - currently on 8mbit ADSL. (I thankfully do not have any issues with interference to my existing ADSL.)
I have made a note of all you have said re shielding etc. However, my main concern at this point is the potential to interfere with Foxtel boxes in the house. I personally hardly watch the thing, but there are others in the house that live on it! We have four (one unused) outlets in the house, with my Internet outlet adding another for a total of 5. The Telstra and antenna cables will be literally about 10cm apart running parallel down the wall. (There is currently a foxtel & phone outlet hybrid plate on the wall in my shack, next to my antenna runs, however there is no actual cable running to it - possibly re-ran to one of the other outlets. However, there's both a Foxtel iQ satellite dish and cable running into the house - we use the cable - why there is both is anyones guess and I am unsure what the outlet on my plate is.)
I was reading on the BigPond site that if there are more than three outlets - an amplifier is required. Do you have any comment on the possibility of this increasing the likelihood of interference?
I am hoping there won't be anything getting in to the Foxtel boxes/my modem once it's installed, but I will have to wait and see - I have asked fellow amateurs who have Optus cable and they have reported no issues - but I hear Telstra and Optus use different HFC frequencies. I will admit I am fairly green in this area - so will probably call in here for some assistance if there is trouble after it's installed.
Thanks for your input thus far!
Regards,
Brayden - VK3VBR
Re: Cable Internet and HF Interference
Hi Brayden
My first remark is, you have my sympathy !
The advice given to you so far has been pretty good, re earthing the outer of the co ax of the service provider. I agree with lack of shielding of the terminating gear as well. All good stuff.
Fortunately some of the most effectively remedies that can be applied are under your control.
First and probably the most effective, use a balanced antenna system as far away from the house as you can. Using an unbalanced antenna without inducing rf into the house wiring is very difficult if not impossible on H. F. That means using a good Balun, and co ax.
Treat the coax of your antenna the same as the service providers co ax. Earth it as it enters the house on its own earth away from the other service provider earth. Earth your radio to this earth. As well as any other equipment associated with your gear such as power supply, atu & etc. Your earth should be physically separate from the house wiring and as close as you can make it to the entry point of your co ax. Ideally it should be a galv or copper earth stake, the galv or copper surface provides a good contact with the ground. If you can put several in. It is not a good idea to use one of those painted fencing stakes. Be aware that if you use different types of metal stakes such as copper and galv separate them with a good capacitor to prevent electrolysis. If it is feasible earth the water system to your earth as well but remember to use a capacitor if it is a different type of metal. A good capacitor is a disc ceramic or mica or similar. Xc should be less than ten per cent of operating frequency.
!Make sure that antenna is properly matched as well. This also reduces the rf on the outer of the co ax.
In addition you could wind the co ax around a ferrite rod. This should be inserted between the antenna and your earth stake.
Finaly just use as much power as necassery for the contact at hand ! You don't need a kilowatt if they are 20 over!
By all means discuss your problems further. Here, or by email, call sign @wia.org. Unfortunately the reality is we do not know the layout of your station or you house hold. Some of the advise we may have given may just not be practical.
But there are ways and means! One of my more memorable QTHs was a 2 story building with thirty rooms, each had a TV set ( and viewer), and a very drunk and volatile dutch neighbor. However I used to work 40 mx, relatively safely!
Like a lot of other Hams I have operated from a lot of situations. There is a lot of experience out there so keep asking.
Lots of Luck
Helen.
My first remark is, you have my sympathy !
The advice given to you so far has been pretty good, re earthing the outer of the co ax of the service provider. I agree with lack of shielding of the terminating gear as well. All good stuff.
Fortunately some of the most effectively remedies that can be applied are under your control.
First and probably the most effective, use a balanced antenna system as far away from the house as you can. Using an unbalanced antenna without inducing rf into the house wiring is very difficult if not impossible on H. F. That means using a good Balun, and co ax.
Treat the coax of your antenna the same as the service providers co ax. Earth it as it enters the house on its own earth away from the other service provider earth. Earth your radio to this earth. As well as any other equipment associated with your gear such as power supply, atu & etc. Your earth should be physically separate from the house wiring and as close as you can make it to the entry point of your co ax. Ideally it should be a galv or copper earth stake, the galv or copper surface provides a good contact with the ground. If you can put several in. It is not a good idea to use one of those painted fencing stakes. Be aware that if you use different types of metal stakes such as copper and galv separate them with a good capacitor to prevent electrolysis. If it is feasible earth the water system to your earth as well but remember to use a capacitor if it is a different type of metal. A good capacitor is a disc ceramic or mica or similar. Xc should be less than ten per cent of operating frequency.
!Make sure that antenna is properly matched as well. This also reduces the rf on the outer of the co ax.
In addition you could wind the co ax around a ferrite rod. This should be inserted between the antenna and your earth stake.
Finaly just use as much power as necassery for the contact at hand ! You don't need a kilowatt if they are 20 over!
By all means discuss your problems further. Here, or by email, call sign @wia.org. Unfortunately the reality is we do not know the layout of your station or you house hold. Some of the advise we may have given may just not be practical.
But there are ways and means! One of my more memorable QTHs was a 2 story building with thirty rooms, each had a TV set ( and viewer), and a very drunk and volatile dutch neighbor. However I used to work 40 mx, relatively safely!
Like a lot of other Hams I have operated from a lot of situations. There is a lot of experience out there so keep asking.
Lots of Luck
Helen.