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Thread: 500W PEP on ALS-600

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  1. #1

    Question 500W PEP on ALS-600

    I have space restrictions at my QTH to install inverted V antennas, etc, so I am using a folded terminated dipole broadband antenna rated for 500 watts PEP on SSB. Before I purchase an Ameritron ALS-600 which produces 600 watts PEP output, is there a way to limit the power output to 500 watts without distorting my signal. That is, am I incorrect in understanding from the ALS-600 online manual that one shouldn't use the ALC Control to limit output because it "pumps" the signal causing distortion on AM (SSB?) transmissions. No such distortion is noted in constant amplitude FM and RTTY modes.

    Sidenotes: (1) I considered the ALS-500, which produces 500 watts output, but the 80 amp 13.8VDC requirement is a bit much--plus 12 volt transistors are noisier than 50v transistor systems.
    (2) I would consider buying the Elecraft 500 watt linear, but my transceiver cannot be limited to 30-40 watts to drive it. (My transciever will put out only 100 watts or 50 watts.)

  2. #2

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    It's not "noisy," it just doesn't have the better IMD performance that the 50V FETs offer. I'd go for the ALS-600 also, it's more sensible.

    You can easily limit your transceiver to lower power if you wish; several ways to do this which will work on "all modes," depending exactly what that transceiver is. What is it?

    One fail-safe way of course is to build more padding into the amp itself, by adding 3 dB more loss to what's there now. Not difficult to do at all. Another way with a lot of the old tube and hybrid rigs is to add a source of adjustable negative bias to the ALC input port. Thousand have done this with a simple 9V battery and a 1 Meg pot connected as a voltage divider.
    What if soy milk is just regular milk introducing itself in Spanish?

  3. #3

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    My transceiver is an Alinco DX-SR8.

    Would adding a negative bias to the ALC input be similar to adjusting the ALC control on the front of the linear?

  4. #4

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    Quote Originally Posted by WB5PKK View Post
    My transceiver is an Alinco DX-SR8.

    Would adding a negative bias to the ALC input be similar to adjusting the ALC control on the front of the linear?
    It might be. Try it, assuming you have it all connected (that is, rig and amp ALC connection is made).

    The ALC control on an amp does absolutely nothing unless the ALC control line is connected to the transmitter.
    What if soy milk is just regular milk introducing itself in Spanish?

  5. #5
    Join Date
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    I would doubt the antenna has any way of knowing you're over 500 watts but they maybe telling you that the rating for their antenna is questionable and you should avoid using higher power. There is a dissipation resistor on the TTFD antenna and that's what will be limiting your operations. As noted above, it's not that good of an antenna. It'll work and you'll make contacts just don't heat up the resistor to the point where it self-destructs.
    The ALC action on the ALS-600 is good and 50 watts in should get you just about exactly what you want for a 500 watt level on voice peaks. This depends on the band you're on. I usually wouldn't sweat a few extra watts unless you're a contest station running all the time. The other alternative is to replace the resistor on the antenna with a higher powered one of the same value.
    Look around for another antenna and see if you like it better in A/B comparisons. You may be surprised at what will work.
    Have fun
    73
    Gary

  6. #6

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    Just run it in RTTY position, which merely limits the current from the PS, or adjust your TX input power as others said.
    [B][COLOR=#008000]vy 73,

    Casey, TI2/NA7U
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