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Thread: 70cm Interference

  1. #1

    Default 70cm Interference

    Apologies if you get fed up with these type of questions: Since Christmas, my 433.92MHz remote key fob will not operate my car doors near my house. If I drive half a mile away, then it works perfectly, so no issue with car or fob. Tuning my IC-R5 to 433.92MHz at my house, I get a noisy AM signal with a faint "blip" every 5 seconds. The "noise" sounds like mains hum. BTW - I have not had any RF gadgets for Christmas! The interference disappears after a hundred yards or so, so I am wondering if a neighbour has a new toy, or could it be a local 70cm repeater that is picking up and repeating this? In which case I would expect the local radio amateurs would be a bit miffed. I have resigned myself to standing right next to the car to unlock it these days. I would appreciate any input - thanks for reading!

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    Quote Originally Posted by Crinkmeister View Post
    Apologies if you get fed up with these type of questions: Since Christmas, my 433.92MHz remote key fob will not operate my car doors near my house. If I drive half a mile away, then it works perfectly, so no issue with car or fob. Tuning my IC-R5 to 433.92MHz at my house, I get a noisy AM signal with a faint "blip" every 5 seconds. The "noise" sounds like mains hum. BTW - I have not had any RF gadgets for Christmas! The interference disappears after a hundred yards or so, so I am wondering if a neighbour has a new toy, or could it be a local 70cm repeater that is picking up and repeating this? In which case I would expect the local radio amateurs would be a bit miffed. I have resigned myself to standing right next to the car to unlock it these days. I would appreciate any input - thanks for reading!
    All things considered since I don't know whether you're located in the United States or United Kingdom having the said Interference on 433.920 MHz RF Channel, most of the Key FOBs are manufactured and programmed on this frequency but I found another device computer related that is manufactured in Australia and programmed for the same frequency and it might be the Interference source that could be generating enough signal 25 milliwatts RF Output to cause problems. Here's the website http://rfmodules.com.au/RMX232-433.920P This device would be connected to a person's computer system using an RS-232 application.

    Heaven knows who has it in your neighborhood as almost everyone has a computer so you will be required to build a small 4 element Yagi beam antenna http://www.jerryclement.ca/MachineSh...rks/i-ZX22KLG/ and connect it to your ICOM IC-R5 Receiver input connector using RG-58C/U 50 OHM Flexible coaxial cable between the receiver and the UHF Yagi beam antenna and start Direction Finding where the strongest unwanted signal is coming from. I would believe that the IC-R5 has a "S" meter built in and either RF anttenuators or a RF receive control to reduce the signal level as you get closest to your Interferring source signal. I also feel the IC-R5 is capable of using a +12 VDC Power Source for Portable or Mobile applications which will be needed to find the source of this signal.

    There's one other issue you should keep in mind, I don't know whether this Interferring signal unit is Legal or Not considering the RF Output Level in milliwatts. You will be required to Contact the F.C.C. in the United States, OFCOM in the United Kingdom or the equivalent office in any other country around the world for their advice on such a product and an Export Control Number Assignment for the product. This one thing may be your best "Smoking Gun" issue in itself as everything manufactured has to have an Export Control Number Assignment Classification (ECCN), no matter which country it comes from. If and when you are able to find the actual unit be sure to carry a Pen & Paper to copy all the information on the unit, Model Number, Serial Number and anything else provided.

    Remember that you are not an official of the government so use the utmost Diplomacy when dealing with a neighbor or business person to gain their respect. You are there to identify the Interference signal and then try to go about to help correct the problem whatever it is. This will not be an overnight success story as you will need to verify the manufacture, find the ECCN, the Engineering Test and Certification information and possibly working with your Government Communication Department about the Legality of the product. If it is something that is home made or homebrew, then contact the Government Communications Department of your country, provide a Name, Street Address, City, State, Zip Code and what you have discovered the offending Transmitting Unit. Document everything.

    Dan
    WA9WVX

  3. #3

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    Thanks for replying Dan. I should have said that I am in Paignton Devon, UK. I had considered knocking up a small Yagi to do direction finding. I will obviously not be the only person with this issue although my wife's car uses a different frequency and so is not affected. I think 433.92MHz is a VAG favourite and probably other European car manufacturers too.

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    Super Moderator 5B4AJB's Avatar
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    Part of 70cm is shared with unlicensed "low power" devices in the UK.
    I use one myself, but it only transmits when you push the button, maybe the device in question needs attention...

    [edit] a small loop on a handheld should be enough to DF the offender...

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    Once in a while, when a USN ship is doing radar and Combat Systems testing nearby at the Naval Shipyard about five miles from me, I get the same thing, and so do a lot of my former co-workers (I'm retired) and my neighbors. I don't know if you have any RN radar installations in your area in Devon, but that might be the cause. The Isle of Wight might be a bit too far away, but maybe a passing vessel on the right frequency ... ?
    73
    Pat K7KBN
    Semper ubi sub ubi.

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    Quote Originally Posted by Crinkmeister View Post
    Thanks for replying Dan. I should have said that I am in Paignton Devon, UK. I had considered knocking up a small Yagi to do direction finding. I will obviously not be the only person with this issue although my wife's car uses a different frequency and so is not affected. I think 433.92MHz is a VAG favourite and probably other European car manufacturers too.
    As I recall the European Auto Manufactures use 315 MHz still in the UHF Band. This 433.920 MHz frequency used worldwide from want I've researched on the Internet. I just thought that the Australian Unit had a bit higher RF Output Power being 25 milliwatts rather than most Key FOBs using microwatts of RF Output Power. So in your case OFCOM is your Government Communications Department to discuss any issues you find.

    Dan
    WA9WVX

  7. #7

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    Here is an option:
    buy one of these: http://www.ebay.com/itm/331294812276...%3AMEBIDX%3AIT

    Then build a 3 to 4 element 70cm handheld yagi, simple wood dowel and solid copper wires...

    Stand outside and point the yagi in various directions until it comes in close to the problematic frequency and start walking towards it. If it is too far, start driving towards it, drive a few hundred feet and point it again, keep driving in the direction it is coming from. Point it at power transformers up on poles, neighbor houses, telephone or internet boxes, and as you get closer it should be easier to find out exactly what it is.

    Where it ends up will probably be a bit of a surprise.
    Last edited by screwballl; Wed 4th Feb 2015 at 18:36. Reason: spelling
    de K4ISR

    KM4FMK.com

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    Quote Originally Posted by screwballl View Post
    Here is an option:
    buy one of these: http://www.ebay.com/itm/331294812276...%3AMEBIDX%3AIT

    Then build a 3 to 4 element 70cm handheld yagi, simple wood dowel and solid copper wires...

    Stand outside and point the yagi in various directions until it comes in close to the problematic frequency and start walking towards it. If it is too far, start driving towards it, drive a few hundred feet and point it again, keep driving in the direction it is coming from. Point it at power transformers up on poles, neighbor houses, telephone or internet boxes, and as you get closer it should be easier to find out exactly what it is.

    Where it ends up will probably be a bit of a surprise.
    Interesting little 500 MHz Frequency Counter although they don't supply any electrical specifications as to the signal level required to detect any RF level a.k.a. Input Sensitivity in milli-Volts. I went out to the internet and requested what the average sensitivity of a Frequency Counter is at 500 MHz and found that the minimum is 5 milli-Volts. Basing this information against Crinkmiester's ICOM IC-5 General Coverage Receiver which is specified at less than 5 micro-Volts, a Frequency Counter with a 3 to 5 element UHF Yagi antenna is deaf compared to the IC-5 receiver and the IC-R5 receiver is capable of mobile applications with a "S" meter for strongest signal strength. What may look like an ideal piece of test equipment for use around the ham shack may not measure up for using out in the field for tracking interference or the intensity level. Here's a website explaining General Frequency Counter requirements:

    http://www.item-bioenergy.com/rfi/so...eqcounter.html

    Dan
    WA9WVX

  9. #9

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    Hi to the OP.

    There are a lot of devices which use 433.920MHz, most of which would be sporadic in their use of the rf link. One type of device which tends to use it more or less continuously is the popular type of wireless weather station or temperature monitor. Sadly, since in the UK these are type approved and if used within their approval there's not a lot the authorities will do about it.

    I would suspect that someone near you got a weather station for Xmas and is making the most of their present.

    Regards
    Jason G7RUX

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