Using aa Yaesu 757 antenna tuner with a newer radio?

Discussion in 'General Technical Questions and Answers' started by N3FH, Sep 5, 2019.

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  1. N3FH

    N3FH Premium Subscriber QRZ Page

    I have a Yaesu FC-757AT that I want to use with a newer radio. The manual verifies that this can be done and explains how. When used with an FT-757GX, power is supplied through a special control cable that plugs into a 9-pin Molex connector on the tuner. To use another radio, 13.8v must be supplied to the same Molex connector from a dc power supply. The problem is that there is no pinout diagram of any kind in any of the manuals.
    Can anyone tell me which of the pins in that connector are for 13.8+ and - ?
    (The manuals indicate an optional cable for that purpose, Cable B, mpn# T9015099, but since I did not buy the tuner new, I do not have that cable and no pinout for it is provided.)
  2. K8JD

    K8JD Ham Member QRZ Page

    Would be nice if you could see a black wire to ground on the connector , inside the tuner, and a red wire from the connector , to an obvious power distribution point. But it probably is not going to be that easy. :eek:
  3. WA4SIX

    WA4SIX Ham Member QRZ Page

    Download the service manual for the 757. THat should have a pinout diagram.

    K6LPM likes this.
  4. K6LPM

    K6LPM Ham Member QRZ Page

    I dont have the info in hand right at this moment but thought I would chime in with my own two cents about my experience with this tuner. If you dont locate the info you desire, let me know and I will dig it up later when I have a better opportunity to wade thru my boxes of paperwork.
    Anyways the molex that you are seeking the pinout (if I recall correctly) purpose and function is not actually to provide source power for the tuner. This interface purpose is to provide automatic band switching from the transciever to the tuner. This is a very common and nearly universal way in which Yaesu provided band switching interoperability between many of their transceivers and line of optional accessories.
    It isnt very complicated as it simply is a different voltage is assigned to a matrix of each pin to denote what band range the radio is currently operating. This usually will switch a bank of relays/drivers/switches , ect..... within the matching Yaesu accessory.
    I believe many aftermarket devices capitalized on the convienence of using this "interface" to utilize or facilitate "reading" of the band "data" range that the transceiver was operational.
    Getting back to the usefulness of the Yaesu FC757 auto tuner accessory on a non Yaesu transceiver without the same interface. You would have to provide a way to convert from whatever band switching data scheme your non Yaesu radio employs, (if in fact the radio offers any type of operational status type of external controls...
    OR SIMPLY.....
    operate the bandswitching of the FC tuner manually. When you change bands on your transciever, you simply switch to the correct band on the tuner.
    Once you are on the correct band you transmit a carrier into the tuner and you manually push the auto tune button on tuner and done, or optionally manually tune the inductive and capacitive loads of the tuner with the rocker buttons on the tuner.
    That is all good and understood? Right?
    Well yeah, you probably know all that but your obstacle is that the Tuner still requires power in the form of 12v dc at probably at least 500mA
    I believe that the tuner has a separate power source 12v input.
    I know I had used such tuner with my Icom 735.
    If you still cant locate info I will look it up for you later when I return home.

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