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    D9 Engel Submarine

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    DAVE J
    AMS member

    Posts : 27
    Join date : 2010-11-13

    D9 Engel Submarine

    Post  DAVE J on Sun Feb 15, 2015 7:01 pm

    Sailing today the model went out of range after 30feet from the bank (on the surface) on dry land 100% ok. Last year the same problem arose and i thought it was because the aerial was in the pressure hull. Since then I have brought the aerial through the pressure hull deck and laid it under the the free flood deck.Has anyone had problems similiar?
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    salmon
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    Re: D9 Engel Submarine

    Post  salmon on Mon Feb 16, 2015 9:07 am

    I had the same problem. I had the aerial going outside the wtc.
    What fixed it was a different receiver (and that one I left the aerial inside the wtc).


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    DAVE J
    AMS member

    Posts : 27
    Join date : 2010-11-13

    D9 Engel Submarine

    Post  DAVE J on Mon Feb 16, 2015 6:57 pm

    Thank's for the reply,
    At present the TX is a Futaba FF7 and the Rx is a Futaba R147F, the BEC comes from one of the two ESC in the system, I will change the Rx to another make and see if makes a differance. Does your D9 use Bec or is the Rx supply from another source?
    I was wondering if I was getting interference from my Bec system. With the range being good out of the water and motors running without any load no interference was obvious. The only difference when in the water was the power being used to drive the motors, and then the limited range cuts the power. Within 6foot of the Tx all the controls work correctly in the water. Out of the water I have full range. I will now change the Tx
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    david f
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    Re: D9 Engel Submarine

    Post  david f on Wed Feb 18, 2015 10:09 am

    I have often had similar problems - although I have never had the aerial outside the wtc (never seems like a good idea.)

    I have gone for dual conversion receivers (Futaba mostly.) Really cheap receivers give problems!

    I have had the BEC  intermittently cutting out on Mtronik ESCs and so I sometimes use standalone becs based on the LM2940 chip. This link gives more info:

    http://www.theassociationofmodelsubmariners.com/t594-mtronik-speed-controllers-with-separate-bec

    David

    DAVE J
    AMS member

    Posts : 27
    Join date : 2010-11-13

    D9 Engel Submarine

    Post  DAVE J on Wed Feb 18, 2015 7:13 pm

    First thoughts about the aerial fed along inside the wtc alongside the numerous power cables coud have been causing the range problems and taking the aerial through a gland in the perspex cover into the free flood space (with the aerial end sealed) may have improved the problem. I have now taken the futaba rx out and replaced it with a schulze delta-840 receiver which has a micro processor system (This is the receiver which Norbert Bruggen advised to use when I had problems sailing the smaller compact ALFA submarine)  I have now tried this in the test tank and with a range check with the tx aerial down at + 20 yards the model will submerge and surface ok. Although this is not on the lake it looks promising.
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    Hermann
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    Re: D9 Engel Submarine

    Post  Hermann on Wed Feb 18, 2015 9:38 pm

    Hello everyone,

    please let me give also some remarks concerning receiving aerials in submarine models.

    In principle and independent of the model category routing of the receiving aerial has a major influence of the receiving quality and with bad routing the usable control range may be reduced dramatically ( just like on the transmitter side when the transmitter antenna is not expanded and only a stub).

    But which kind of routing is poor an which is most useful? To receive the control signal the receiver needs a signal voltage at its input, this signal voltage develops between the aerial wire as one pole and the residual wiring such as supply cable, servo cables, speed controller cable etc. ; that residual wiring serves as a "counterweight" to the aerial, as the second pole. A voltage means always a difference between the electrical potentials of two poles, in this case the voltage occurs between the aerial wire and the "counterweight" given by the residual wiring. To pick up as much radio frequency energy of the signal from the electromagnetic field as possible, aerial wire and counterweigth should be layed out as far as possible apart from each other. They shall not be routed together(or even worse, in the same bundle). You can explain this circumstance by yourself when you remember that the measurement unit for the electric field strength is defined as Volt per metre (V/m), so if you have a certain field strength at the location of your model you will get more voltage if you increase the distance between aerial and counterweight (well, when submerged the voltages will be very low, in the range of microvolts). Of course separating aerial wire from the other cabling may be problematic in some cases, especially for small models, but in general it is useful and recommended to follow that rule.

    It is not necessary to route the aerial inside the pressure hull, the aerial may be also in the flooded aria. If your pressure hull (or WTC) contains additional conductive structures (e.g. thread rods of a technics rack) it is important to keep the aerial on distance to these elements and put it outside.

    Of course it is also important to have an effective suppression of interference generated by sources within the model (e.g. brush type motors or switchmode voltage regulators for power supply). For good signal reception a good signal to noise ratio is essential. That means if the field strength of the signal is low (due to attenuation in water) the noise level must be consequently also low and even lower to maintain a sufficient good signal to noise ratio.

    When arranged outside the pressure hull in water it is not necessary to isolate the aerial wire towards the ambient water (but it is also not a disadvantage) because the electrical field component of the electromagnetic waves is exposed to the conductivity of the water.

    Concerning the transition of the radio waves from air to water there are multiple effects that cause a reduction of reception quality. For the first you will have a certain amount of reflection of radio waves at the border layer between the two media air and water (as known from the reflection of light at the water surface). In addition the electrical field component suffers a reduction by the relative high dielectric behaviour of water (relative dielectric coefficient of water is 80!) because the water molecules are in fact small dipoles. So the electric component is reduced very much. On the opposite the magnetic component remains nearly the same.

    You can see from these considerations that we must cope with very small field strengths when submerged , therefore we have nothing to waste of our receiver sensitivity. And therefore it is recommended to route the aerial outside of the pressure hull (or WTC) and as far apart from it as possible. This is even more important when you have metallic structures inside your hull (WTC).

    I think our AMS member John Robinson who is a radio specialist will confirm these considerations.

    Kind regards
    Klaus-Dieter (Hermann)
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    nigele(ADMIN)2
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    Re: D9 Engel Submarine

    Post  nigele(ADMIN)2 on Wed Feb 18, 2015 10:32 pm

    Yes I agree with Hermann 100%, Talking about John her raised a very interesting point in a conversation I had with him some time ago,this concerned the tuned length of the Arial underwater, I happen to mention that I had often found that a shorter Arial seem to work better and give less trouble with interference than the standard length,and John said that that was quite likely to be the case as the wave length underwater is not the same as on the surface he said that there is a formula for working this out.

    DAVE J
    AMS member

    Posts : 27
    Join date : 2010-11-13

    D9 Engel Submarine

    Post  DAVE J on Sun Feb 22, 2015 8:00 pm

    Sailed with new rx today, no problems with the range, only the trim to sort out now.

    D.

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