|
New to Ham Radio?
My Profile
Community
Articles
Forums
News
Reviews
Friends Remembered
Speak Out
Strays
Survey Question
Operating
Contesting
DX Cluster Spots
Propagation
Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers
Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net
|
|
1-10 of 10 messages
|
Page 1 of 1
|
|
MAINS FILTER REQUIRED ? & RFI problems pls help !
|
Reply
|
|
by G7IVJ on November 4, 2009
|
Mail this to a friend!
|
Hi all
And greetings from London - thanks for any help and advice in advance.
The shack is a seperate building to the house, on a seperate fused ring main about 100foot away from the house.
I am using an FT-897 for HF, an LDG AT-1000 autotuner, and the antenna installed is a 186foot doublet, centre fed with 450ohm feeder - feeder about 100foot long with a balundesigns 4 to 1 current balun with a ten feet piece of good quality coax connecting it to the LDG ATU as this matcher only accepts coax.
The 186 foot doublet is up 40 feet above ground level at its highest point and drops to about 20 feet above ground level on each end, and it is set up as an inverted V in a straight line.
I have quite an extensive earth system - from the ATU to the first 8 foot copper rod which is connected using thick half inch wide tin multi stranded earthing wire which is only 6 foot length from the ATU to the first ground rod. I have 10 x 8 foot earth rods spaced about 4 feet apart all connected by the same half inch multi-stranded tin. Each item on the shack desk is earthed to the ATU, ie Radios, amps etc etc.
When I TX on HF, on 80m as an example, with just 25watts output power on SSB, it kills ADSL - the router is in the house 100foot away from the shack. I It kills DSL both wired DSL and wireless DSL - it all stops until about a minute after I stop TXing then it comes back on again.
Also, a few weeks ago a neighbour told me her television set was turning off and on when I was transmitting operating on 80m SSB with about 400watts.
A local amateur told me as my antenna system is balanced, and a good earthing system he thought it must be being caused by RF being introduced into the mains system. I wasnt sure, but I am no expert so I plugged in a dummy load into the ATU instead of the doublet and transmitted - wired DSL and wireless DSL is fine - it only crashes when the doublet is plugged in.
The local amateur still thinks it is mains born interference and tells me I should invest in some mains filtering.
In the UK our mains is 240v.
So couple of questions.
1) Does this sound like mains born interference, and if so can anyone point me to a filter that I can put in line in the shack. One I have found is listed on Ebay, take a look at:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=120483658596&ru=http%3A%2F%2Fshop.ebay.co.uk%3A80%2F%3F_from%3DR40%26_trksid%3Dp4712.m38.l1313%26_nkw%3D120483658596%26_sacat%3DSee-All-Categories%26_fvi%3D1&_rdc=1
Or ebay.co.uk item number: 120483658596
The local amateur tells me I need to get a filter which filters the Neutral, Earth and Live wire in the mains system.
Will it filter it both ways, ie will it kill any mains born interference that I may receive into the radio?
Even if the DSL problem is not mains bound - is it still worth adding a filter just to be sure and to do 'best practise'
Any other filters other than the one listed above?
I saw someone on the net suggesting to use a 'line conditioner' by APC similar to the ones that can be seen here:
http://cgi.ebay.co.uk/APC-UPS-Line-R-Power-Conditioner-Reg-1200VA-LE1200I_W0QQitemZ140357297060QQcmdZViewItemQQptZUK_Computing_PowerSupplies_EH?hash=item20adf263a4
Or go to ebay.co.uk and type in item number: 140357297060
But these APC Line conditioners do not appear to me to have any RFI filtering ?
Anyway, enough words from me
Hope you can help
Thanks, and 73 Simon - UK
|
| |
|
RE: MAINS FILTER REQUIRED ? & RFI problems pls help !
|
Reply
|
|
by W5CPT on November 4, 2009
|
Mail this to a friend!
|
Given that there was no problem when you transmitted into the Dummy Load I would guess that your RF is not getting into the house via the power wiring. Filters will not solve your problem. I would think that your antenna is entirely too low. I think you are getting near-field radiation in the house. Is there any way to orient the antenna so no part of it is over or near the house? I will assume that you can not get it any higher as if you could have you would have.
Borrow or build a vertical with one or two radials and try to locate it as far as you can from the house and test that set-up.
Clint - W5CPT
|
| |
|
RE: MAINS FILTER REQUIRED ? & RFI problems pls help !
|
Reply
|
|
by W8JI on November 4, 2009
|
Mail this to a friend!
|
The problem is almost always in the telco lines for the ADSL, not the mains.
ADSL runsup to 1 MHz or so, so the modems have a pretty good response up to HF. I had one ADSL modem here that would wipe out with 100 watts with a 160 antenna 500 feet away!
The problem with ADSL is if you build a good low-pass filter it will almost always slow the ADSL down or prevent it from working. I guess I could have gotten a 3.4 MHz lowpass with a notch at 3.5 to work, but I damn sure couldn't get 160 out of it.
I had to change to a 2wire 2701HG-B Gateway. Then all the problems vanished. I can run any power on any antenna and it doesn't care. I can run 1500 watts beaming right into the building and it stays synced. It never drops the connection.
http://www.2wire.com/?p=106
Filtering the mains is a waste of time. Look at what I have:
http://www.w8ji.com/rfi_rf_grounding.htm
It will give you some perspective of how to settle things down.
|
| |
|
RE: MAINS FILTER REQUIRED ? & RFI problems pls help !
|
Reply
|
|
by KQ6Q on November 4, 2009
|
Mail this to a friend!
|
If your mains distributioin and telephon wires are above ground strung on poles, your long horizontal antenna is perfectly situated to couple your RF into both power and phone lines.
Solution, as mentioned by an earlier responder - VERTICAL Antenna(s) as far as possible from overhead wires. If you could move to a subdivision with underground utilities and no overhead wires, your overhead doublet would be a delight. As it is, it's your problem!
|
| |
|
RE: MAINS FILTER REQUIRED ? & RFI problems pls help !
|
Reply
|
|
by WA3SKN on November 5, 2009
|
Mail this to a friend!
|
Your RF is getting into the lines, probably both telco and power, and they are most probably above ground. Above ground wires act as antennas and pick up the signals. Power transformers on the poles won't pass more than about 400 Khz, keeping things local. The telco lines are balanced, and the ADSL modem is just being overloaded (fundamental overload). Most telcos have filters available if you contact them. Snap-on ferrites just before the modems (wrap the telco wire several times on the ferrite) will probably cure the ADSL problem. The neighbor's TV problem will be a little more complicated. Not sure whether the RF is getting to the TV via the antenna or the power line, or by direct radiation... and we need to know that to determine the type filtering or shielding needed. Does she still have the problem if you drop power to 100 watts? How close is the TV antenna and set to your antenna?
-Mike.
|
| |
|
RE: MAINS FILTER REQUIRED ? & RFI problems pls help !
|
Reply
|
|
by W8JI on November 5, 2009
|
Mail this to a friend!
|
I hate to bust the polarization bubble, but really long conductors over lossy earth are vertically polarization sensitive. You may reduce levels with a vertical, and you may increase them.
This really all goes back to how the modem works. ADSL is a series of modulated carriers from just above audio up to around 1 MHz.
If your modem is like most ADSL modems I tried here you can throw beads and filters at it all day and it won't help. I made custom filters, I have buried shielded telco cables, and I have a very clean RF layout and low bands would wipe out my ADSL.
After working on it a few weeks the telco company sent me a 2Wire brand modem and with no traps, filters or anything else it all cleaned right up.
Tom
|
| |
|
RE: MAINS FILTER REQUIRED ? & RFI problems pls help !
|
Reply
|
|
by G8JNJ on November 5, 2009
|
Mail this to a friend!
|
Hi Simon,
I think there was some discussion about 80m and ADSL on uk.radio.amateur a few weeks ago.
I've also had a few problems with ADSL in the past but am now able to operate OK.
The trick seems to be to use individual ferrite chokes on each of the cables going into the ADSL router, especially the phone line and DC power leads. Put them as close to the router as possible.
Like most digital services it either works or it doesn't - not much in between the two. So you can't easily tell how much of a problem you have got.
To be successful, you need to be able to monitor the ADSL router S/N ratio whilst transmitting at different power levels. The ADSL router will have this information hidden away somewhere, but you should be able to find it.
Transmit a CW carrier and increase the power until the S/N degrades to say 6dB.
Stop transmitting and add some ferrite rings.
Transmit again, wind up the power until you get the same S/N as before and see how much of an improvement you have achieved.
Fiddle with the number of turns and placement until you can no longer achieve better results.
Initially you may not be able to run 400W, but you will be able to operate at progressively higher power levels as you gradually sort it out.
The TV problem can probably be fixed by separate ferrite rings on each of the connecting cables.
Don't underestimate how much ferrite you need to use on the LF bands. One clip-on bead will make no difference.
See
http://audiosystemsgroup.com/RFI-Ham.pdf
And
http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
Good Luck,
Martin - G8JNJ
www.g8jnj.webs.com
|
| |
|
RE: MAINS FILTER REQUIRED ? & RFI problems pls help !
|
Reply
|
|
by W8JI on November 5, 2009
|
Mail this to a friend!
|
ADSL uses phase modulated carriers. I think about 256 of them spread between upper audio and 1 MHz. Each carries a portion of the information so the overall speed is fast if the whole bandwidth is good.
If we go throwing ferrite beads on the line it forms a simple very low Q two-pole filter with almost no shunt C. The rolloff is not that good, and if you attenuate 2 MHz even just 6 dB it will attenuate the upper carriers nearly the same amount. I could not filter 160 and 80 out of the modems I had without severely attenuating the upper carriers. While that didn't aways stop all the modems from syncing, it slowed it way down.
Now it might be workable if someone is pretty close to the digital interface, but I'm 20,000 feet away from mine. By the time I got 80m and 160m out of mine the speed was down around 350 kbps from the unfiltered 1494 kbps and sync was unreliable.
I would not only check the S/N ratio in the modem, I'd check the speed.
My 2wire 2701HG-B Gateway doesn't need any filter at all, and none of the Bell South filters did a thing on the other modems they tried.
I have:
Downstream Rate: 1494 kbps
Upstream Rate: 253 kbps
Channel: Interleaved
Current Noise Margin: 15.8 dB (Downstream) 15.7 dB (Upstream)
Current Attenuation: 60.6 dB (Downstream) 32.3 dB (Upstream)
Current Output Power: 15.7 dBm (Downstream) -0.3 dBm (Upstream)
and it stays the same if I transmit or not with the 2wire 2701HG-B Gateway. Best modem I've ever seen for RFI and lightning immunity.
Tom
|
| |
|
RE: MAINS FILTER REQUIRED ? & RFI problems pls help !
|
Reply
|
|
by N5LRZ on November 5, 2009
|
Mail this to a friend!
|
Re IVJ...
Rules and regulations governing Ameteur Radio differ from country to country. You might want to check into your rules and regs governing Amateur Radio to verify your level of responsibility.
BUT that aside, from your description it sounds like your neighbors TV Receiver is experiencing some kind of Front End Overload from your signal that is causing her 'off/on' circuit to trigger.
Your signals are acting like a TV Romote Control.
I do not know if you are per your rules and regs responsible and to what degree that responsiblity extends. So check with your rules and regs for your little corner of the globe.
|
| |
|
RE: MAINS FILTER REQUIRED ? & RFI problems pls help !
|
Reply
|
|
by G8JNJ on November 6, 2009
|
Mail this to a friend!
|
Hi All,
Sorry I should have clarified a point in my last post.
The ferrite is used as a choking balun on the phone line pair to remove the unwanted common mode component, whilst preserving the wanted, but much lower level differential mode ADSL signal. It is not placed on each individual core of the line pair.
Look here for a similar type of filter, although this one has been optimised for AM BC band rejection.
http://www.ky-filters.com/rfchoke.htm
Various factors contribute to line imbalance in UK telephone systems. One of the main ones the addition of a 'bell' capacitor and third 'anti-tinkle' wire which is connected to one of the line pair when it enters the BT line termination box at the premises. All the internal wiring has this wire present, which results in a major unbalance of the line pair at RF frequencies.
BT sells a 'line accelerator' iPlate module which fits in place of the termination box faceplate. This incorporates a choke in series with the third wire and a choking balun on the signal pair.
http://www.shop.bt.com/products/bt-iplate---bt-broadband-accelerator-58LT.html?q=iplate
You can often improve things by disconnecting the third wire.
http://www.kitz.co.uk/adsl/socket.htm
However I’ve found that it is more effective to wind the ADSL cable through a suitable ring core at the point it enters the ADSL router. You can add another one on the phone line pair where it enters the premises if you want to do an even better job. This also helps reduce ADSL hash on RX.
Incidentally, even if you don’t have an EMC problem, adding ferrite chokes can improve ADSL S/N and therefore line speed.
Hope this helps.
Martin – G8JNJ
www.g8jnj.webs.com
|
| |
|
Email Subscription
You are not subscribed to this topic.
Subscribe!
My Subscriptions
Subscriptions Help
Check our help page for help using
Forum, or send questions, comments, or suggestions to the
Forum Manager.
|
|
|
