Carrier Current AM interference

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Carrier Current AM interference

i have a two fold problem with my carrier current am. it so far does not appear to interfering with any electronics outside my household but it is interfering with two peices of equipment in here.


1) i have a baseband NTSC security camera system that the AM is putting RF interference patterns across the cameras


2) it jams out 850 khz on my TFT EAS 930 AM Receiver.


it does not appear to intefere with other radios just the card in the EAS 930. probably poor design on the Rx Card.


i think i need 3 fold solution. i need a low pass filter for am broadcast in addition to an 850khz reject filter on the Tx and a 1630 reject filter on the Rx deck.

the Tx filters would need to handle up to 5 watts average power.


i need some basic designs for said filters.


since carrier current is largely not used anymore there is not any info on the web (that i can locate) for such designs.



Try one of those LINE NOISE

Try one of those LINE NOISE filters used for expensive high end preamp power amp component systems.  Plug the receiver into that and see if it kills the RF from coming into the receiver with interference issues.


Let us know the results.

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i want to be 0db down at 1635 and -3db down at 1670

for the low pass filter and as much as practical on 850khz and 1630khz reject filters.

been there done that. i think the only solution is the one i have proposed. i am essentially within my blanketing interference contour that every broadcast station generates.


i am hoping Neil will chime in with something

Part 15 Engineer

Hindsight is 2020

I'm not a democrat or a republican, i'm a common sense moderate progressive


please don't forget to register and vote

On the face of it, it sounds

On the face of it, it sounds like harmonic interference, especially if you can find out if the interference is happening at a multiples of the carrier frequency, like twice and 3X, 5X etc.

Rectification between metal surfaces in the home that are touching can make local harmonics, and ground loops can amplify switching power supply noise at different frequencies, look into that possibility if the interference is non-harmonic with the carrier.

If you're using a commercial transmitter like LPB, Radio Systems or even one of the Geek designed units like THE FOX, harmonics from it should be really low when tuned well. If the matching to the line is really bad, high SWR, then harmonics can leak out.

Carrier systems tend to be wide bandwidth and low Q factor, a benefit if you're broadcasting hifi audio, but with the higher power, and wider bandwidth of the system, spurs can get through too, compared to 100 mw systems with the big  hi-Q matching coil.

I'd check all of those things first, then if you know your transmitter really needs a filter, try a PI filter, there are calculators you can use to find the values for your frequency. The AARL might have one on their webpage.

If you can list details about what you're using, like what your transmitter and tuner are, and how you're coupled to the line, that would be helpful.

i am neutral loaded

using The Fox @ about 2-2.5W into an lpb TCU-30 coupler using an isolated 2ft ground rod and #10 stranded wire going to the rod from the coupler. the fox is pretty clean i think it is more or less proximity overload. it does not affect the camera system 150ft away in the garage so it is local. and it is only those two items in very close proximity to the transmitter and nothing else even in close proximity, my all band can be tuned to 850 and be right next to Tx wth no issue.

everything is rack mounted and professional balanced gear.

here are some older pics of the station

all the loose wiring has bean cleaned up and put into raceways and the AC wiring more uniform.

i have yet to update the pictures to the new stuff but the layout isd basically the same just cleaned up the wiring.

the AM Tx and couplers are plugged directly each into seperate outlets. they do not go through the line conditioners and they are not both on the same outlet


Part 15 Engineer

Hindsight is 2020

I'm not a democrat or a republican, i'm a common sense moderate progressive


please don't forget to register and vote

one down i think,,,

it appears the Rx deck on the EAS 930 might be bad, think i have some spare


i was reading the BCD wrong and had it tuned to the wrong frequency all this time!!!


had it tuned to 18500 khz which beside being out of the AM BCB is out of that decks rx range. i reset it to the proper 850 and in 850 comes clear as a bell!!!!

so i had it 1 MHz = 8, 100khz= 5, 10khz= 0 instead of 1m= 0, 100k= 8, and 10k= 5


now it just leaves the issue with my NTSC baseband surveillance camera system and DVR.

Part 15 Engineer

Hindsight is 2020

I'm not a democrat or a republican, i'm a common sense moderate progressive


please don't forget to register and vote

I'd toss a ferrite core on

I'd toss a ferrite core on the camera's line.


Most likely your problems are being caused by the camera and receiver being overloaded by the strong RF signal and, if so, a filter will not help.  You seem to have no other indications that there is a problem with the transmitter.

Lots of things can happen when a strong RF signal is present on the AC house wiring as Nate mentioned above and which does not mean the transmitter is producing spurs or harmonics directly.

For your camera, you might try to keep the RF out of it by wrapping it in foil and/or using clamp on ferrite chokes around the coax and power leads.



i have checked with

spec-an, various receivers, and apliances. it isn't interfering with anything but the cameras locally here. so it must just be local overload into the cameras.


i looked into why my eas stopped relaying weather alerts as well and some how the WX receiver input got shut out of the scan sequence.

bet my eas will now start relaying weather alerts now that i fixed that settings issue.


i am slowly hammering out my issues here

Part 15 Engineer

Hindsight is 2020

I'm not a democrat or a republican, i'm a common sense moderate progressive


please don't forget to register and vote

You would need ferrites on

You would need ferrites on all cables running to the camera , power cable , ethernet cable, etc. and they would need to be the low frequency kind used by amateur radio operators.

After you get the ferrites on if it still is a problem then you may have high frequency harmonics that are making it past the ferrites.  At that point you would be doing the low pass filter like you said but you may have to make one. 

here is how to make your low pass filters

After you that and there is still a problem you may have to either reduce your transmitter power or move the camera away from the antenna. 

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