Yaesu FL-2100B SWR in standby

Discussion in 'Amateur Radio Amplifiers' started by N8VIL, Jan 10, 2016.

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  1. G1XRJ

    G1XRJ Ham Member QRZ Page

    33pf from relay to GND almost cured problem (still slightly high top end of 28MHZ)
    Added further 15pf and perfect all the way through.
    Thanks for the advice.
    Steve
     
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  2. 9BC357

    9BC357 QRZ Member

    Hello, I'd like to correct a few things in this topic if I may.

    The input "jumper" is NEVER switched out.
    Its going from the input SO239 to the relay and connected to 2 PINS.

    Running the 33pf from this "jumper" to GROUND will always be in circuit during RX and TX.

    The only way to have it switched out during TX is to connect it to the "jumper" and to the INPUT OF THE TUBES.
    The input of the tubes is grounded on RX and is not grounded on TX.
    The method mentioned in this topic is wrong I'm sorry to say.

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    N8VIL likes this.
  3. W1QJ

    W1QJ Ham Member QRZ Page

    Indeed, obviously, Yeasu used quite an unconventional relay switching system as is seen in the schematic. No other amplifier I am aware of uses this scheme of switching. Perhaps this is why they had stability issues with this amp. Definitely unconventional. In light of the fact, the proper position for the capacitor is as shown in the "right" photo.
     
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  4. N8VIL

    N8VIL Ham Member QRZ Page

    This is they way I did mine and all works well.
     
    9BC357 likes this.
  5. G3YRO

    G3YRO Ham Member QRZ Page

    People should note that the wiring in the FL2100Z is different in several respects, espacially when it comes to the antenna switching and bias circuits!

    However, the wiring in the FL2100, FL2100B and FL2000B is all the same.

    Roger G3YRO
     
  6. WA7PRC

    WA7PRC Ham Member QRZ Page

    Mainly, WARC bands and a halfwave tripler for cutoff bias.
    I show that in the schematics I redrew using Visio, "printed" to PDF, and uploaded to my website. Text & lines are SHARP (every hard copy is 1st generation), and text is searchable. File sizes are tiny, too. :)
     
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  7. G1XRJ

    G1XRJ Ham Member QRZ Page

    Just caught back up on this thread.
    I see the correction regarding the cap position, and understand how this allows the cap only to be grounded during RX, but not TX?
    Can you clarify? Since the cap effects the input SWR, what is the purpose of it being switched out during TX.?

    Do you mean RX (TX in standby, so the radio see in the amp input circuit ) ..TX (TX in operation, so radio see antenna SWR )?
     
  8. W1QJ

    W1QJ Ham Member QRZ Page

    The relay in the RX position has a reactance on higher bands and the radio sees a bit if an swr because of that. To smooth out that swr the radio sees in rx bypass mode the capacitor nulls the inductive reactance and the radio sees a flat swr. You only want this in the RX mode and not in xmit mode since it's not needed or wanted in xmit. So the cap has to be strategically placed so it's in on rx and out on tx.
     
  9. 9BC357

    9BC357 QRZ Member

    Good enough for the girls I know.



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  10. KM3F

    KM3F Ham Member QRZ Page

    A lot of gyration in this thread.
    The input to the amplifier has enough reactance that gets greater as the frequency goes up .
    This is to be expected.
    Amplifier off, unplugged and opened up.
    Use an antenna analyzer looking into the amplifier to see the mismatch with a flat load on the output.
    Use a trimmer cap connected to the proper point in the circuit, that will handle the a RF, and trim it to lowest SWR on the highest band.
    This cancels out the inductive reactance.
    On the lower bands the trimmer or cap has less effect so does not up set the match on the lower bands.
    I have been using this trick for years on anything that has a match issue from SS amp to 50 ohm dummy loads making them good all the way to the 450 band.
    It even works on an old Heath Kit Cantenna dummy load making it good on 6 meters.
    All that is happening is the cancellation of inductive reactance in the local part of the circuit due to lead lengths.
    Some circuits benefit from replacing poor wiring with small coax cable keeping leads and shield ground short as possible.
    Replacing some open single leads in some Tuners can make them even good on 6 meters to use on utility antennas just to get on that band with an existing antenna..
    Good luck.
    .
     

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