Colour convention for the wires on AM antennas?

Discussion in 'Tuners' started by steveUK, Mar 2, 2017.

  1. steveUK

    steveUK Active Member

    Messages:
    237
    Location:
    Midlands, UK.
    Without going into detail here, I'm attempting to replace a missing AM antenna (back of set mounted, swivelable type) with one from another set, albeit the same make. The receiver in need of the antenna has the original wires still hanging out the back of it where the antenna was cut/removed. The replacement antenna has the same colour wires, but confusingly, plus a white wire too. I just looked at an old spare receiver chassis that I have (not the same brand) and it too uses similar colour wires. It got me wondering if there is a colour convention associated with the wiring for these rear mounted AM antennas?
     
  2. rcs16

    rcs16 Super Member

    Messages:
    2,862
    Location:
    Baldwin, Ontario, Canada
    I was wonder when you were going to get to this point. I do not know if there is a convention or not. I would have to check all the schematics.
    Refresh my memory you are attempting to replace the AM bar antenna on a what Pioneer model? with one from a what model?
    I said to you before you are trying to match up the antenna inductance portion of the i/p tuned circuit with the var caps on the tuner pcb. If they do not resonate in the AM freq band of interest, track with the LO, it will not work very well, it at all, since it is out of tune. Someone mentioned that there is some adjustment but is it enough.
    iirc it is was a sx-1250 ? and it was unique (different part number) from most of the other ones, which sort of tells me it is not the same inductance because the var cap in the SX-1250 is unique.
    You have to ask yourself, why they did not use the same AM bar antenna, as all the other models?
    It is a long shot.
    Now that I look at some of the schematics and the one I have in my had from a SX-1050, Pioneer has standardized on the wire colours.
    1) blue wire is the pick up coil going to the AM i/p jack,
    2) red wire goes to the var cap , input tuned ckt
    3) yellow is the i/p to the rf amp for the IAM IC, such a HA1138 in the SX-1250 case
    4) black is the common ground

    Are you sure you are not mixing up white with yellow? as I do not see any white wire in the schematics for a sx-1250
    It might be possible to alter the inductance to bring it into range, that requires some experimenting by determining what the tuning range is for combination that you have, for that you need some instruments and knowledge.
     
    Last edited: Mar 2, 2017
  3. steveUK

    steveUK Active Member

    Messages:
    237
    Location:
    Midlands, UK.
    Thanks RCS16. A Pioneer SX-1250 receiver is missing it rear mounted, hinged ferrite rod antenna. However the wiring associated with this missing antenna is still in place hanging out of the back of the set, colours red, blue, yellow and black. The blue wire is internally connected to the external AM aerial terminal and the other three go to the tuner PCB – not sure exactly where circuit-wise as it would take some serious PCB tracing. Luckily I have a ‘replacement’ antenna in the form of a similar unit taken from a Pioneer SX-535 receiver. Interestingly, It has the same coloured wires plus a white wire. If it were not for this extra wire I would simply join up the wires by colour matching them and if it works, maybe perform some realignment tweaks to better match it to the SX-1250. So, can someone can tell me how to join up the two sets of wires please?! (remembering that the replacement antenna has an 'extra' wire coloured white). Thanks!
     
  4. rcs16

    rcs16 Super Member

    Messages:
    2,862
    Location:
    Baldwin, Ontario, Canada
    Right, like I said the wires out of the 1250 match the schematics.
    I looked at a sx-535 schematic, it has no wire colours in the schematic, great. But it only shows 3 wires from the AM bar antenna to the pcb. the schematic show 3 coils.
    So what does the white wire do?
    Ohm out the antenna coils, what wires match what coils?
    I suspect the white wire is another coil common (ground) and should tie to the black wire, which connects to pcb terminal 28.
     
  5. vwestlife

    vwestlife Active Member

    Messages:
    340
    Easiest thing to do is simply try different wiring schemes to see what results in the best reception.
     
  6. steveUK

    steveUK Active Member

    Messages:
    237
    Location:
    Midlands, UK.
    Easy? there's 24 ways of interconnecting four wires to another four wires - and that's without the complication of an extra white wire with nowhere to go..
     
  7. steveUK

    steveUK Active Member

    Messages:
    237
    Location:
    Midlands, UK.
    To my knowledge, the 1250 schematics mention no colours, so what 'match' are you referring to?

    I've checked the resistance of the wires on the 535 antenna as follows:

    Yellow to white: 0.3 ohms
    Blue to black: 0.3 ohms
    Black to red: 1.4 ohms
     
  8. rcs16

    rcs16 Super Member

    Messages:
    2,862
    Location:
    Baldwin, Ontario, Canada
    I got a chuckle out of that comment, oh boy :dunno:

    You have to look carefully, it is only shown in one spot.
    The colours are shown in the big schematic for internals of the T2 symbol (AM Bar Antenna,ATB-051), which is shown below the RF FE on the left side.
    So based on your measurements, black is the common and so is the white wire, so short them together, connect to the black wire, which should connect to terminal 25(E) on AWE-068(AM/FM tuner Ass'y)
    The blue wire goes to the AM antenna jack on the back panel.
    The red wire goes to terminal C on AWB-023
    The yellow wire goes to terminal 28 on AWE-068(AM Antenna)

    These should match what was wired on your existing unit since you said that the wires were cut at the back panel strain relief.

    Good Luck Steve I hope it works, let me know how it goes

    Cheers
    Rick
     
  9. steveUK

    steveUK Active Member

    Messages:
    237
    Location:
    Midlands, UK.
    Thanks Rick.

    I connected it up colour for colour and with the white wire shorted to the black (not sure if that is exactly how you described things as I haven't yet checked where the 'cut' wires hanging out of the set go). In that configuration, no joy, silence, worse than without anything connected. Not expecting it to make any difference I disconnected the white wire and it burst into live. Well not quite, there was a general lack of gain, the signal strength meter doesn't register even on the 'strongest' stations, so I’ve gone through the service manual AM set up procedure albeit using real live radio stations rather than a sig gen. I used stations at 693 at the lower end and 1458 at the top (manual says 600 and 1400). There were improvements but the signal meter still does not move even on the strongest station and 693 is very noisy - a kind of background hum/buzz. I tried hooking up a length of wire to the external antenna terminal (blue wire) and it made little, if any difference. However when I touched this length of wire (or my hand) to the yellow wire the volume came up appreciably albeit with an equal increase in noise, and the signal strength meter showed a strong deflection. I've gone through the setting up procedure a few times so I know that that is optimum, but clearly something is still not right. BTW, strangely, rotating the rod antenna does not seem to make much difference at all, if any. Normally I would expect there to be a clear null point and a somewhat less obvious maximum signal point at right angles to that (depending on the direction of the station obviously). That suggests to me that the ferrite core of the antenna isn't really doing much, the set is just picking up signals from all these wires floating around?! Maybe I need to check the destinations of the wires hanging out of the set and be sure that I am connecting things up as you suggest, because at the moment that is not a certainty, I just thought that the colours would have corresponded..
     
  10. rcs16

    rcs16 Super Member

    Messages:
    2,862
    Location:
    Baldwin, Ontario, Canada
    I am puzzled that removing the white wire from the black(ground) makes it works better, go figure :idea: Might change the tuning of the circuit, bring it closer to resonance in the AM band.
    Placing your fingers on the wires must de-tune the circuit which does make sense. Touching it would I think add capacity to the tuned ckt, lower the resonant freq.
    When I look at the sx-780, they have placed a inductors in the uH range in series with the var caps, it subtracts from the inductance of the coil in the ferrite antenna.
    It would help a lot to be able to measure the cap of the var cap and the coils in the ferrite bar ant. so that we can figure calculate what freq these ckts are tuned to or resonating at.
    Another option is to wind your own ferrite or rip it apart to re-wind it to what it should be.

    Another thing I thought of for the wiring, try connecting the black and maybe the white to the ground terminal on the back, it needs to be connect up as well some how.

    In the sx-780, they have a 100uH in series with the blue wire, it is placed between the AM antenna jack and the blue wire of the AM bar antenna. Something to try is to use a var inductor in that range.
    They also have a 2.2uH in series with the red AM bar antenna lead which goes to one of the var cap gangs.
    I will attach the schematic for you to look at, to see what I am talking about. It will not let me upload the file it is too big. PM me with your email addr and I will send it to you that way.
    You can also get the schematic from hifiengine of course.
     
    Last edited: Mar 3, 2017
  11. steveUK

    steveUK Active Member

    Messages:
    237
    Location:
    Midlands, UK.
    Rick,
    I've checked the connections that you mention above, and they are indeed the correct connections for the existing wires that still remain hanging from the set after someone cut off the antenna at the back. My set matches those connections/colours. However, connecting the 535 antenna to those wires 'colour for colour' (and with the black and white wires joined) does not work as I explain in my previous post. It would appear that the wire colours do not match - that or it's a question of figuring out what to do with the extra white wire.
     
  12. steveUK

    steveUK Active Member

    Messages:
    237
    Location:
    Midlands, UK.
    Update. Cracked it! I realised that to do any good I really needed to get some info wrt the colours of the new antenna - where they should connect to circuit-wise. After much searching I found a photo on the internet of an SX-535 with cover removed - see photo. Although not mega clear, I could see that the red wire went to the tuner, the yellow wire went to a resistor on the tuner pcb, the black and white wires were joined (as such I supposed, connected to chassis) that left the blue wire which although not in view, it identified that it was going to the AM aerial socket, unseen behind the rear panel. Comparing that with circuitry for both sets I got my answer - the yellow and red wires were used for opposite purposes in the two sets. So I connected the antenna to my set colour for colour except for the red and yellow wires swapped ie red to yellow. The receiver now shows a deflection on the signal strength meter and rotating the antenna brings the signal to maxima and minima - it didn't before. Also, connecting an external wire aerial to the AM terminal now 'blows the speakers up'. It just lashed up at the moment but I will renew wires etc in due course. But saying that, I'm still looking for the pukka SX-1250 antenna that has a refined ball joint assembly that gives rotatable, 180 degree, side to side movement capability. The one I have presently just swings up and down - bad luck if where you've got the receiver the antenna is in line with the signal!
    [​IMG]
     
  13. rcs16

    rcs16 Super Member

    Messages:
    2,862
    Location:
    Baldwin, Ontario, Canada
    That is exactly what I was going to respond and suggest, but you beat me to it, look at the way it is wired on a sx-535.
    Also I was going to say this thread would be better served in the Pioneer section as there would be many more folks to read and help us out.
    None the less, you succeeded. Good stuff.

    Cheers
    Rick
     
  14. steveUK

    steveUK Active Member

    Messages:
    237
    Location:
    Midlands, UK.
    Thanks Rick, and thanks to all who responded with input.
     

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