Yaesu FL-2100B SWR in standby

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

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  1. N8VIL

    N8VIL Ham Member QRZ Page

    I did answer answer the question. From the amplifier to the dummy load is perfect on all bands. 50 ohm load. I am measuring pass through SWR and I don't have the amplifier plugged in to the power outlet. If you are asking what the SWR is on the amplifiers SWR meter, I am not even paying attention to that.

    "Now you have me confused. The problem is while in standby (pass through) measured SWR going from the exciter to the amplifier is high on the higher bands (20-15-10) with the amplifier output connected to a 50 ohm dummyload. Out of the amplifier I also have a SWR meter between the amplifier and dummy load measuring SWR just to make sure that the dummy load was showing a perfect match to the amplifier output connector. My goal is to get the SWR as low as possible while in standby (pass through) between the exciter and amplifier.
    I hope to have time here soon to try the capacitor in the circuit to see if that makes a difference"
  2. G3YRO

    G3YRO Ham Member QRZ Page

    Surely the question is very simple!

    You said you have one SWR Meter between your Transmitter and the Amplifier, and another SWR Meter between the Amplifier and the Dummy Load.

    So here the question again . . . . When the Amp is in Standby, what does the SWR Meter between the Amp and the Dummy Load read? (compared to the other one)

    You have never answered this!
  3. N8VIL

    N8VIL Ham Member QRZ Page

    Here is a picture of what I mean. Somehow we have a disconnect on this. Hopefully this clarifies things. Like they say "a picture is worth a thousand words"

  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    VIL, I understood first time you posted about this -- thought you were pretty clear, but then English is my first language.

    Did you try the 33 pF cap yet...
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Oh, oops, I see you answered this.

    Lou's suggestion was great and obviously based on experience with the amp. I suggested maybe a 'trimmer' cap would work, so you could check input SWR on 'bypass' vs. frequency and adjust the cap to whatever nulled it on a band you favor.

    Since this is a low-Z point in the system, the voltage should never be very high and a pretty small variable cap should work.
  6. WN2C

    WN2C Ham Member QRZ Page

    There is something wrong in that picture... second SWR meter bad? 2.8:1 input and 1:1 output just don't jive.
  7. G3YRO

    G3YRO Ham Member QRZ Page

    OK . . . now you have cleared up that you are saying your Output VSWR is 1:1 when the Amplifier is in Standby. (this wasn't clear before)

    The point is that your results don't make any sense!

    If the amplifier is in Standby, there is no electronics between the input and the output. (it's effectively the same piece of coax, but with a join)

    So the VSWR should be THE SAME on either side of the amplifier.

    Eg, If the VSWR is 2:1 on the input, it should be 2:1 on the output.

    The fact that it ISN'T means you have something strange going on. (ie you can't trust your readings)

    For a start, see what happens to all the readings with different lengths of coax on either side of the amplifier . . . I bet you get different results.
  8. AC8AC

    AC8AC Ham Member QRZ Page

    yes that will change it G3YRO if if you get reduce the reaction happening within the amplifier jumper length will be less critical
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Of course they do jive...they're at very different points along a line that does not have constant impedance.
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    No, that's not true.

    We're dealing with a transmission line inside the amp which is not constant impedance. SWR at each end of that line, even though only a foot or two long, can be very, very different when measured with an SWR50 bridge.

    For example, if you use a source into a 100 Ohm transmission line terminated in a 50 Ohm load...the SWR50 at the source and the SWR50 at the termination can be wildly different. Even though it's the same line.

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