Wiring a radio - Anyone using MGL V series COMs?

Discussion in 'Instruments / Avionics / Electrical System' started by Battson, Sep 11, 2012.

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  1. Sep 11, 2012 #1

    Battson

    Battson

    Battson

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    Hey - is anyone here using this brand of COM unit?
    I have some questions about PTT wiring, and what is required to get a clean signal:

    Studying the harness wiring diagram, I notice the pilot and co-pilot PPT circuit runs in parallel between the second Mic terminals and plug locations 18 & 19, and the wire shielding (earth). This raised a question for me:
    Does the MGL V6 simply require voltage at the PPT terminal locations, to “switch” the PTT on and transmit the modulated signal when the button is depressed? Or does a modulated signal from the second Mic terminal actually flow through the PPT switch and into the MGL unit for subsequent transmission?

    I have already wired my PPT switches (integral to the joysticks), and fear I may be forced to “break into” the wiring harness (in which case I would try and make it myself). Else I might need to tear my joysticks down again, to revise the PTT earth wiring, also not ideal. But if it's just a question of voltage to switch, then the signal will hopefully be clean enough with my current configuration.

    View attachment V6 diagram.xls (4 place) - June 25, 2012.pdf

    I also asked the guys at MGL about this, eagerly awaiting a reply...
     
  2. Sep 11, 2012 #2

    clanon

    clanon

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    Not familiar with any of this (not sure what you ask) in my view of drawing all you do on pilot ptt and or pass ptt is GND(anytime you give gnd to PTT1 and or PTT2 you are transmitting)
    From 18 ~ 23 only audio signals...
    The last wires are 2 pairs of RS-232 data (digital)(16 and3 ; 2 and 15)
    And power on number 1 pin or wire...
    Hope it helps
     
  3. Sep 11, 2012 #3

    Battson

    Battson

    Battson

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    The guts of my questions is:

    How the the PTT circuit interact with the COM unit?
    Does it mearly switch COM on by closing the circuit to earth (providing voltage to the plug)?
    OR does it actually open up another LF modulated terminal of the Mic jack to transmit through, and thus need a much cleaner signal (earth) connection?
     
  4. Sep 11, 2012 #4

    djschwartz

    djschwartz

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    I'm not familiar with this particular radio but looking at the wiring diagram it seems similar to other radios I've installed.

    The ground is common to all circuits. Grounding the PTT input makes the radio transmit. So yes, the common ground carries the return signals for everything. Shielded wire should be used for the audio and the shield provides the ground return. The shields of each wire set should only be connected to each other at the radio end. For the PTT a pair of unshielded wires should be run to each PTT switch. The ground wires of each should be connected to the shields of the audio wires at the radio end. It should be acceptable to "daisy chain" the grounds of the PTT sets from one switch to the other. Do not daisy chain any of the wires to the audio jacks.

    You may already know this but DO NOT rely on the airframe to provide the ground return from the buttons and jacks to the radio. This will cause you severe ground loop noise pickup. Also, the jacks themselves need to be isolated from ground. You can buy special plastic shoulder washers from Aircraft Spruce or others for this purpose. They are cheap.
     
  5. Sep 11, 2012 #5

    Battson

    Battson

    Battson

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    Thanks DJ, can you tell me - in the wiring diagram - the earth wires are shown connected to square boxes at the jacks, what does that represent? It seems to be an earth connection to something, but as you say, the jacks aren't earthed to the frame or to the shielding. So I presume that is a seperate earth wire, which is also shielded (at earth potential)....???

    I ran a common earth wire from my PPT switches, to get a clean cable run. I also earthed this to my starpoint earth (where the radio will earth) rather than at the radio directly. I realise that's not ideal, but I dont expect earth loops either. Thoughts?

    I also shared this common earth with other control switches on my joystick (per the stick grip's wiring instructions for PTT). I should have given this more thought, but I feel like if Ray Allen Company recommended it be wired that way, it should be alright... they sell a lot of stick grips...
    But I am worried about it.
     
  6. Sep 12, 2012 #6

    djschwartz

    djschwartz

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    The square boxes represent the "ring" or the body of the jack. One of the solder terminals of the jack is connected to this part. And no, there isn't a separate ground wire. The shield is the ground connection.

    The common ground connection for the PTT's shouldn't be a problem but running it to anything other than the radio is not a good idea. You are setting yourself up for ground loop audio noise. It may be OK but you won't know until you can operate the aircraft.

    Bad assumption. They are showing the easiest, and most favorable for them, installation; not necessarily the best. Again, it may be OK but you won't know til you operate the aircraft and then you might have to re-do it if you have noise problems.

    Dave
     
  7. Sep 13, 2012 #7

    Battson

    Battson

    Battson

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    That is exactly what I am worried about now. It was a case of not knowing what I didn't know.

    I wonder what the odds are of it being noisy... It's only shared with the trim and other radio functions. So the trim might interupt the PTT, but that's not the end of the world. You dont trim and TX very often.

    It's noise at the starpoint earth that worries me more. To clean that problem up is a lot more work.... I have a provision for it, but it's fiddly work.
     
  8. Oct 2, 2012 #8

    Battson

    Battson

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    Re: Where to find radio jacks?

    Hey - does anyone know where to buy jacks (is it 6.5mm and 5.25mm) for aircraft headsets?
     
  9. Oct 3, 2012 #9

    djschwartz

    djschwartz

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    Re: Where to find radio jacks?

    The 1/4 inch jack for the headphones is the same as used for audio gear and can be purchased anywhere that sells that stuff, Radio Shack, Fry's, Digi-Key, etc. The 3/16 jack for the mic is less common. Aircraft Spruce sells both:

    PANEL JACKS from Aircraft Spruce

    If they're going in a metal panel or structure remember to buy the insulated flat washers and insulated shoulder washers for each jack as well

    Dave
     
  10. Oct 3, 2012 #10

    Battson

    Battson

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    Thanks Dave - you've been really helpful!
     

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