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Sub Antennas

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  • Sub Antennas

    Here in the UK most of the RC models/modellers now use 2.4GHz, but fortunately I have several 27MHz kits. These are leftovers from my aeromodelling days, but I expected this frequency to be OK for model subs. However, on my Kriegsmarine Type VIIC I have found the range, even on the surface, to be only about 15 feet. So, my question is, what is the best arrangement for the receiver antenna? At present my antenna is about 2 feet of single wire strung around the inside of the water tight compartment. I wonder if it would be better for it to be outside the WTC, i.e. in clear water?
    Any suggestions and advice would be most welcome; perhaps I might add that I've looked around the internet and it seems this topic is never mentioned.

  • #2
    I cannot speak to 27MHz specifically, but I have found little difference between running my 75MHz in the tube or out of the tube. The biggest benefit I have seen is reducing noise in my system (make sure capacitors are installed on the motors and use ferrite rings on noisy channels. Consider also the older systems may not have the best filtering of signals or the older AM radios were prone to interference. I have a old 27MHz system I am about to send off for tuning to a receiver, so hopefully I can speak from a more educated experience in the near future.
    Peace,
    Tom
    If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

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    • #3
      Hello Mike,

      I'm in the UK. I'll add a little to Tom's advice. Most of us use 40mhz, but 27mhz equipment should work just fine. Later sets were only available in the higher frequency once that band became available in the 1980's, many of those sets benefited from digital signal processing which tends to remove glitches in the signal by filtering them out before they get to the servo, very worthwhile on subs.

      Nowadays there is only a small amount of 40mhz equipment available as a result of the switch to 2.4ghz. Some modellers have found the 458mhz and 868mhz equipment works well enough for them underwater, with the lower frequency giving the best range. This equipment can be purchased new, and so can benefit from the many advances in R/C technology.

      You're not specific about that 15 feet range. If you mean depth, that's good going, if you mean from the bankside, then that's poor range. Generally the deeper you go, the shallower you can dive and maintain a signal, however the most limiting factor is generally your ability to see what the model is doing rather than the radio signal.

      Placing the aerial in the wet should improve things, but only by a small amount. You must add a blob of slow cure epoxy or similar waterproof glue/mastic to the end of the aerial to prevent water drawing through the cable under capillary reaction.

      As most manufacturers discontinued multi-channel 27mhz sets once 40mhz became legal, I would guess your sets are over thirty years old. Some electronic parts age e.g. electrolytic capacitors, so your set(s) may not be firing on all cylinders and need a bit of a tune-up. Maybe do a good old fashioned range check in air.

      Also make sure you're operating in fresh water, if the water is salty or brackish, your range will either be diminished or non-existent unless you run an aerial to the surface. The mineral content in the water shorts out the signal.
      DIVE IN! Go on, go on, go on, go on, GO ON! http://www.diveintomodelsubmarines.co.uk

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      • #4
        Originally posted by mikew8760 View Post
        Here in the UK most of the RC models/modellers now use 2.4GHz, but fortunately I have several 27MHz kits. These are leftovers from my aeromodelling days, but I expected this frequency to be OK for model subs. However, on my Kriegsmarine Type VIIC I have found the range, even on the surface, to be only about 15 feet. So, my question is, what is the best arrangement for the receiver antenna? At present my antenna is about 2 feet of single wire strung around the inside of the water tight compartment. I wonder if it would be better for it to be outside the WTC, i.e. in clear water?
        Any suggestions and advice would be most welcome; perhaps I might add that I've looked around the internet and it seems this topic is never mentioned.
        When employing the antenna in the water it's a good practice to isolate the antenna itself from the interior of the dry space. Connect it through a threaded stud that runs throught the after bulkhead of the water tight bulkhead. Like so:




        The antenna elements are arranged as, short length of antenna between receiver and antenna stud - antenna stud - long length of antenna in the wet





        David
        Last edited by He Who Shall Not Be Named; 01-03-2019, 08:14 AM.
        "... well, that takes care of Jorgenson's theory!"

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