100W vs. 250W of output power, will anyone ever notice the difference?

Discussion in 'Amateur Radio Amplifiers' started by 4L4AGU, Dec 2, 2011.

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  1. 4L4AGU

    4L4AGU Ham Member QRZ Page

    This question might be already discussed, but all what I found belongs to larger power differencies.

    Shortly, my transceiver outputs 100W.

    I've assembled simple amplifier using MRF141G, which outputs 250W.

    Since currently it has no ALC, output filters, etc, I've operated it only couple of times, and got mixed results from other hams (from "no change" to "20db difference").

    So the question is, how it will work in real life? does it worth to finish this amplifier at all? (adding ALC, finding apropriate case, output filters, etc.) ?
  2. N5CEY

    N5CEY Ham Member QRZ Page

    Just my humble opinion,
    First, going from 100 watts to 250 watts gives you about 1/2 an s-unit of improvement. In reality, most people could not tell the difference.
    Second, operating without ALC and Output filters, I gaurantee that you are putting out harmonics and other trash well above your country's limits. You need to tame that thing or not use it.
    Third, you are probably going to overdrive and kill it if your not very careful.
    Good luck.
  3. G4LNA

    G4LNA Ham Member QRZ Page

    20db difference would indicate to me that their S meter needs calibrating. As N5CEY has said it would be very difficult to notice, anyway I suspect the 20db could well be taken up with QSB between reports.

    Just to add, be careful that the amp isn't clipping and making it sound like a 20db increase, I've just noticed that you have no affective control over the amp, put an oscilloscope on it and check what's happening.
  4. W0LPQ

    W0LPQ Ham Member QRZ Page

    An increase from 100W to 250W is NOT 20dB. That I guarantee. No one will ever notice the difference. As has been said ... look at the output with a scope to make sure something else is not coming out.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I think it will make 3.9794 dB difference if the 250W is clean and makes it through the filter you should be using.:eek:

    That could be "anything" on an "S" meter, from just about nothing to maybe an S unit or so, depending on the receiver.

    Should make a difference if you're right in the noise.
  6. W8JI

    W8JI Ham Member QRZ Page

    We mostly pretend S units are 6 dB.

    Very few S meters are 6 dB per S unit. On the low end of the scale, where the AGC is just starting to tip in, most S units are a dB or so, more or even less. Most meters are not even attempted to be 6 dB. Collins was around 3-4 dB, and Drake targeted 5 dB, although both vary with position on the scales and the band.

    It has really only been with modern solid state that there is any hope of meeting a standard.

    Also, so far as copy, when a signal is near noise or QRM levels, just a few dB can make an amazing difference. When our signals are 20 dB out of noise, a few dB makes no difference. When a signal is just a few dB out of noise or less, a couple dB can sound huge.

    73 Tom
  7. AG6K

    AG6K Guest

     which is 4db or 2/3 of one S-unit.
    • Rich, ag6k
  8. KD8DEY

    KD8DEY Ham Member QRZ Page

    I doubt if anybody on the air will notice any difference BUT I bet your electric company will love you.
  9. 4L4AGU

    4L4AGU Ham Member QRZ Page

    The 250W was the clean output, I can boost it to 300W, and this is when the clipping starts. Yes I know that operating without the filters is not good, so I've used it total for couple of minutes, not more, and not using now.
  10. W8GP

    W8GP Ham Member QRZ Page

    Power difference

    Would you notice the difference between 1000 watts and 2500 watts?
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