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USS Marlin, lost..... then found 231 days later

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  • #46
    Originally posted by Ken_NJ View Post
    Sorry never got back to you guys. Here is what I tried. Soldered the original antennae onto the receiver. Tested, same problem, loss of signal about 75 feet. Tried coiling the antennae around a dowel. Still LOS. Resoldered the receiver antennae connection. Still LOS. Opened the transmitter to check the antennae, it connects to a machine screw which connects to an L bracket, I loosened and tightened the nuts. Still LOS.

    I had two receivers with this transmitter which was reserved for using with subs. The first receiver did this same thing, LOS about 50-70 feet. I checked with Tony at RC South and Hitec, they both said no parts are available.
    I was using the second receiver in the Marlin. I bought this off of eBay, NIB, at 72 Mhz. I sent it tony Tony years ago to have him tune it for 75Mhz and been using it ever since. Now this one crapped out.

    Any ideas what now?

    The radio is on 75.730 CH77 and is a Hitec Laser 6. Both receivers are dual conversion. Will any of Bob's single conversion receivers work if I can get the same frequency? Pressure is on me. If I don't get this resolved its not worth going to Groton as I won't have a working sub.
    A single conversion crystal that is FM and on that channel will work just fine, Ken.

    The only variable is the receiver and crystal as far as single or dual conversion goes. If the detector circuit of the receiver (the input, or 'front-end') is single or dual conversion, then you need a single or dual conversion crystal -- even though both types will state the specific frequency/channel (let's say, ch-77) on the crystal. The transmitter, as long as it's FM, does not give a whit how the receiver processes the signal, just as long as the intelligence sent from the transmitter (the pulse train, which is encoded as variations of frequency) matches the decoder logic of the receiver.

    Dual conversion receiver must use a dual conversion crystal, single conversion receiver must use a single conversion crystal. Transmitter don't care!

    One fly in the ointment -- the transmitter encoder logic must match that of the receiver decoder logic. Today it's either PCM or PPM. Make sure your receiver and transmitter share the same encryption type.

    Snatch up a new receiver from Bob -- all he sells now are FM types, and they come with crystal installed. Tell him what channel your transmitters on, maybe he can find a receiver already on ch-77 for you.

    If Bob can't get it to you right away I can rip a receiver out of an inactive boat and loan that to you. Finding one on ch-77 will be a problem though. Is your transmitter Futaba crystal compatible?

    Hope I did not throw too much **** at you at once, Ken. Keep posting, pal. We'll work this out.

    We'll get you back into the water. No excuses!

    Last edited by He Who Shall Not Be Named; 08-19-2019, 02:40 PM.
    "... well, that takes care of Jorgenson's theory!"


    • #47
      Thanks David,

      Looks like I'm partly in luck. The Xmitter is PPM and both receivers Bob sells are PPM. I'm limited by the SD diameter which is 2-3/8 or 60mm so either one should fit even with the plugs coming out the end. The regular one is 48mm without the case and the mini one is 40mm without the case. Just need to find out if he has CH77. Will post in his Product forum.


      • #48
        Bob doesn't have CH77. I did find a transmitter crystal on CH65 on Amazon.
        Last edited by Ken_NJ; 08-19-2019, 04:25 PM.