Not a ham radio antenna, but it is a radio antenna...

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KI7HSB, May 17, 2020.

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  1. KI7HSB

    KI7HSB Ham Member QRZ Page

    Hopefully, one of you guys and gals knows how these things operate. This attached photo is the receiver module for the remote control accessory to the winch that is mounted onto my car transport trailer. The little green wire that hangs down off of the device is the antenna. This sort of receiver is common on garage door openers.

    To cut to the chase, my question is, how critical is the length of that sort of antenna to reception performance? It operates on 4.897Mhz

    Read further only if you want to know the back story and why I would ask such an off-beat question...

    The trailer often goes months or years between uses and I don't want the winch system left out in the weather all that time. Also, due to space limitations, the trailer's long term parking spot is away from my house so it's a potential theft item. Historically, I remove the winch system after use and keep it in my shop or storage where it gets moved around, bits and pieces get lost and the battery gets used for something else or goes dead for not being on a tender. Whenever I need the trailer, its a huge pain to get it serviceable again.

    To remedy that headache, I am modifying the trailer to have the entire winch system enclosed in a secure weather tight steel trailer tongue box along with a solar powered battery tender. For security, reliability, weather protection and a clean design, I wanted to mount everything inside the box, but what about that antenna? Inside a steel box, it's not going to be receiving a strong signal from the remote control fob.

    Solution? Extend the antenna wire so that it can be routed through a grommet to an external location where it can receive a strong signal. But what will that do to reception? Its not coax, it is the antenna, so I'm assuming that its tuned to some degree, but how sensitive are these types of short range low power setups?

    I'd rather not because it a risk of getting whacked, but an alternative could be to go ahead and mount this one component on the back wall of the box, but laying flat against a steel plate, wouldn't that deteriorate the reception?

    Attached Files:

  2. KI8DJ

    KI8DJ Ham Member QRZ Page

    I would assume a lot longer wire
    would be much more gain full. 1/4 wave at that frequency would be about 45 feet. That being said radio signals would like swamp the receiver on the unit. It might be short for a reason.
    KI7HSB likes this.
  3. KI7HSB

    KI7HSB Ham Member QRZ Page

    I had theorized that as a possibility... But with no experience to back that up, I can't really judge how much trash it would pick up. My vision of a new antenna is no bigger than the original, just located outside the steel enclosure, plus whatever length needed to get back to the controller.

    I'm wondering if I couldn't replace the antenna at the unit with a length of LM-195 coax and run that out to an external antenna the same length as the as-built unit....
  4. KI8DJ

    KI8DJ Ham Member QRZ Page

    Probably but the losses in the coax might facilitate a slightly longer wire. Would you be making a dipole? This might require the old try it and see.
  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    My cars and airplanes are stored in a great big (RF shielded) metal box called an aircraft hangar. Needless to say, my garage door operators, and the wireless operator that opens the big hangar door must have outside antennas. Both of these remotes operate on 433.92MHz, as does your remote-controlled winch ( I have no idea where you got 4.897MHz?).

    The hangar door installer realized that an outside antenna was needed to get any usable range. Here is what they did. The 433MHz receiver is in the box, inside the hangar building.
    See the RG-59A/U and type F coax connector?

    This is the whip that the Hangar door installer mounted on the outside of the hangar door at the other end of about 5ft of RG-59A/U. They are not hams or RF experts, so they left the whip parallel (and very close to) the sheet metal. Being a ham, I knew to bend the whip away from the door so that it forms a "sloper" for 433MHz ;)

    Now I can open the hangar door from inside the airplane while taxiing to the hangar from a distance of about 1/8 of a mile...

    I built a 433MHz radio-remote-controlled system that operates my drive-through swing gate and both garage doors:

    The 433MHz transmitters and receivers for that project came from EBay. They look like this:

    I solved the outdoor antenna for the super-regen 433MHz receiver problem by mounting the receiver and its "433MHz dipole" outside high on the hangar wall. The receiver is housed inside a piece of PVC water pipe that also supports the dipole antenna. You can see the receiver and dipole in this picture above the motion light:

    Yes, Jeeves, I modeled the 433Mhz dipole in EzNec to optimize how far it should be from the vertical metal surface....:) I have the cheap EBay transmitters in all my cars and golf cart, and can open the swing gate and/or the garage doors from about 1/8 of a mi away, even with the broken off antenna on the transmitter shown in the picture above...

    Hope this gives you some ideas....
    Last edited: May 17, 2020
    KI7HSB likes this.
  6. K8JD

    K8JD Ham Member QRZ Page

    ACTUAL Frequency ?
    Was that freq actualy 4... MHz or 4 thousand MHz ? a big diff in antenna requiremenets.
    If that freq (4.897) is stamped on the xtal it is probably multiplied many times to the actual operating freq. hance that short wire antenna.
    KI7HSB likes this.
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    Legally, you can only sell radio remotes that operate in certain license-free bands that are set-aside for that use. 315MHz and 433.92MHz are the most likely frequencies used in the OP's remote winch. Most hams do not realize that 433.92MHz is in the ham band...

    I bought a Chicom 12V DC winch that came with an RF remote I never used because the winch is hard-wired. It came with a 433.92 MHz key-fob and a super-regen receiver similar to ones I pictured... I still have the remote controller here is someone needs one...

    I occasionally tune my RSP sdr RX to 433.92MHz to listen there. You would be amazed at the number of transmissions that happen there within a one minute window. Lots or remote thermometers, weather stations, etc use 433.92 to telemeter their data on...
    KI7HSB likes this.
  8. K7JEM

    K7JEM Ham Member QRZ Page

    The 4.897 MHz crystal is a reference used by many of the wireless chips that operate on 315MHz or sometimes on 433 MHz. Measure the antenna length, it is likely a QW piece of wire, so it may be around 6" or around 9" in length, that may tell the band that it is on. You probably could solder on a coax to where the antenna attaches to the board, and run it to some externally mounted antenna, even many feet away from actual receiver.
    KI7HSB likes this.
  9. WA7ARK

    WA7ARK Ham Member QRZ Page

    Or you could receive the transmitted signal like I do with the SDR receiver...
    KI7HSB likes this.
  10. KI7HSB

    KI7HSB Ham Member QRZ Page

    I really don't know for sure... There is no mention whatsoever of the operating frequency in any of the documentation that came with it. All I have to go on is the number 4.897 stamped on what appears to be a crystal on the RF board....

    Attached Files:

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