Announcement

Collapse

Forum rules and expectations

Hello, and welcome to the forums at the Nautilus Drydocks, formerly Sub-driver.com!

We welcome anyone with a passion for submarines and a desire to learn and share knowledge about this fascinating hobby. Use of these forums indicates your intention to abide by our code of conduct:


1. No spam. All automated messages, advertisements, and links to competitor websites will be deleted immediately.

2. Please post in relevant sub-forums only. Messages posted in the wrong topic area will be removed and placed in the correct sub-forum by moderators.

3. Respect other users. No flaming or abusing fellow forum members. Users who continue to post inflammatory, abusive comments will be deleted from the forum after or without a warning.

4. No threats or harassment of other users will be tolerated. Any instance of threatening or harassing behavior is grounds for deletion from the forums.

5. No profanity or pornography is allowed. Posts containing adult material will be deleted.

6. No re-posting of copyrighted materials or other illegal content is allowed. Any posts containing illegal content or copyrighted materials will be deleted.
See more
See less

Sub Antennas

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • 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.

    Comment


    • #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

      Comment


      • #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, 07:14 AM.
        "... well, that takes care of Jorgenson's theory!"

        Comment


        • #5
          I install a thru hull tube or it could be a pressure tap nipple in the WTC bulkhead. Then run the antenna wire out the fitting and into a "dry" tube made from a long piece of tygon with a plug in the far end and slipped onto the nipple. Now there is no cutting of the factory antenna, it stays out of the water and can be run thru out the wet area of the sub.

          Comment


          • #6
            Mate, you've got too much antenna. For 27 Megs you need 14.6 inches. Cut some wire off that sucker and see what the result is. Not too much difference between running it out side, inside, wound around a plastic rod etc etc. 40 Megs also works well and is readily available in Europe (that place that you are about to become estranged from).

            Comment


            • #7
              Yes the ideal length for a 27meg antenna is 14.6" in theory-read this exchange(particular posts #7 & #8...it says a lot and confuses more. This is why they say never cut the factory antenna, contact the factory and get the proper length and best case buy a replacement (type/ gage /and insulation matters) if the antenna we are talking about is a factory antenna-its right unless the rec. has been tuned to another length.
              RC Car Radio Equipment - Antennas: How long for 27 mhz? - What is the standard antenna length(s) for 27 mhz? My brother tore up his antenna and we

              Comment


              • #8
                Originally posted by mikew8760 View Post
                At present my antenna is about 2 feet of single wire strung around the inside of the water tight compartment..
                If that wire is not the factory length, the key word here is ABOUT 2 feet...the lengths of an ant. is critical as to tenths of an inch including any thru hull studs (no about)

                Comment


                • #9
                  Originally posted by Bob Gato View Post

                  If that wire is not the factory length, the key word here is ABOUT 2 feet...the lengths of an ant. is critical as to tenths of an inch including any thru hull studs (no about)
                  Not been my experience with fractional antennas. Close to optimum harmonic length is close enough. Now, full-wave antennas, the UHF stuff (microwave), yes, length is critical.

                  David
                  "... well, that takes care of Jorgenson's theory!"

                  Comment


                  • #10
                    I stand corrected on that...You have to admit that there is a big difference between 14.6" and about 2' or factory 40"...who's right-I'd still call the manufacturer..the difference between 24" and 14.6 is the difference between fully operational and a range check

                    Comment


                    • #11
                      Please allow me to interject some thoughts here. I have multi years of experience designing antennas in the HF and VHF range. For our purposes there are two kinds of antennas - resonant and non-resonant/active types. To be honest I don't know which type RC manufacturers use although from the suggested lengths I suspect it's the non-resonant/active type. Regardless of which type it actually is the "calculated" or empirical lengths are determined in a free air environment and not underwater. When you surround the antenna in a medium with a totally different dielectric constant like water rather than air, all calculations go out the window. It's probably best to try different lengths until you find one that works for you in the water you're sailing in. Best of luck.

                      Dan
                      Born in Detroit - where the weak are killed and eaten.

                      Comment


                      • #12
                        Originally posted by roedj View Post
                        Please allow me to interject some thoughts here. I have multi years of experience designing antennas in the HF and VHF range. For our purposes there are two kinds of antennas - resonant and non-resonant/active types. To be honest I don't know which type RC manufacturers use although from the suggested lengths I suspect it's the non-resonant/active type. Regardless of which type it actually is the "calculated" or empirical lengths are determined in a free air environment and not underwater. When you surround the antenna in a medium with a totally different dielectric constant like water rather than air, all calculations go out the window. It's probably best to try different lengths until you find one that works for you in the water you're sailing in. Best of luck.

                        Dan
                        Good, informative stuff, Dan. I had no idea.

                        David
                        "... well, that takes care of Jorgenson's theory!"

                        Comment


                        • #13
                          In the old days of CB radio-an SWR meter was commonly used-since the MHZ range is the same (27), could one be dusted off and rigged to answer that question?

                          Comment


                          • #14
                            On the antenna issue, specifically what systems may soon become illegal to use in the USA:

                            27, 72, and the 75mHz bands may soon be sold by the FCC to non-r/c users. Today, without the great lobbying support of the AMA -- who's members have almost to the man gone to 2.4gHz -- we (the r/c submarine community) are at risk of loosing those bands in an instant, making all our r/c equipment obsolete and against the law to transmit on.

                            Our representative government no longer represents the common citizen, the legislature only listens and works to the benefit of organizations and businesses with the juice to hire lobbyist -- lobbyist that insure Congressmen get enough freebee rides and 'deals' to insure they bend to the wants of those who hire the lobbying firms.

                            Look to the day when 2.4gHz WILL be the only game in town that is readily available.

                            Secure from Rant!

                            David
                            "... well, that takes care of Jorgenson's theory!"

                            Comment


                            • #15
                              I'm not so sure Dave. Those lower frequencies are of limited use, as they lack the bandwidth for much of todays requirements.

                              Here in the UK we have one of the most generous allocations of radio frequencies for hobby use in the World. 40mhz and 35mhz largely took over from 27mhz back in the 1980's, yet 27mhz is still legal and in use by some. Then we have 458mhz and 868mhz which work underwater, 868mhz a bit more limited. More choice than we ever had, as 458 and 868mhz radios weren't widely available until the last few years.
                              DIVE IN! Go on, go on, go on, go on, GO ON! http://www.diveintomodelsubmarines.co.uk

                              Comment

                              Working...
                              X