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Thread: ALC cable to linear?

  1. #21
    K7KBN's Avatar
    Join Date
    Jul 2008
    Bremerton WA USA


    Bird (Model 43) wattmeters are highly touted as the best, but they're not particularly accurate (±5% of full scale), and that drops to ±8% FS if you add the "Peak" circuit. The Bird 43 IS rugged - it'll take bumps that would put other meters out of the game. It has to be recalibrated every six months for use in the Navy - both the meter and the slug TOGETHER, as one unit.
    Pat K7KBN
    Semper ubi sub ubi.

  2. #22


    I ran across this information today about AL811:
    ALC Adjustment and Operation
    Never use ALC as a primary power control. The ALC control is another way to reduce the transceiver's output power. Unless connected to the radio, ALC has no effect.
    1. Leave the ALC disconnected and tune the amplifier to the desired output level, not to exceed maximum plate or grid currents, or maximum output power.

    2. Connect the ALC line with the ALC adjust fully clockwise (facing the back of the amplifier).

    3. Transmit with amplifier operating and adjust the ALC until the grid meter or output power starts to drop. Stop at the point when the meter starts to drop.

    4. The ALC is now adjusted for the desired power limit.
    Increasing the transceiver’s power control beyond this set point should not increase meter readings on the amplifier. This will verify the ALC is controlling the transceiver. We do not recommend depending on simple basic ALC systems for operating power control. It is only a safety measure.

    My MFJ891 wattmeter arrived today. The zero on both needles were off, so I had to adjust them both down to zero. I really like the big dial on this meter as did my poor eyesight. I Hooked everything together with my homemade dummy load and slowly followed my amp directions to tune this up on the 40 meter band. By the time I got this maxed out, I notice that the oil in my dummy load would bubble and boil if I held the key down more than a few seconds (manual recommended 5 seconds max and 15 seconds idle). According to the new meter I was getting about 750 watts out PEP, which I thought was a little high for the AL811, but I backed my FT847 drive down to where it was maxing out at about 300 watts so I could put my antenna tuner & antenna in the mix, but I had a patch cable go bad, so I will have to wait till I repair it or get a new one before going any further.

  3. #23


    This should be about my last update to this thread. I ended up having a make up a new coax patch cable, but I now got the FT847 transceiver to AL811 linear to MFJ891 wattmeter to MFJ969 tuner to 40-6m Windom antenna connected together. The FT847 output is set at about 10 o'clock (roughly about 30-35 watts) to give me 300 keyed down CW watts out of the linear. However after connecting the ALC cable I made up I noticed the peak had dropped several watts and that was with the ALC control on the back of the amp wide open, so I disconnect that from the back of the amp. I may need to go back and readjust my amp again. ???? Last night I heard a guy from Italy calling CQ at about at 5-7 signal strength on my FT847 meter just above the noise on 40 meters SSB so I flipped the amp on prepared to give this outfit a test. Just before I transmitted to him his signal faded almost out, but I answered anyway. To my surprise he came back to me. His signal came back up for a few minutes and said I was a 5-8 to him in Italy. Usually I have to repeat my call several times to understood at that distance, but he understood me right off. So it appears that my new setup is giving me the signal strength to reach out to the stations that I used to be able to hear, but I was not always strong enough for them to hear me or hear me clearly. I am happy that this is giving me the results I was hoping for before busting into my toy funds. My early Christmas present to myself.

  4. #24

    Join Date
    Dec 2008
    Elgin, Illinois


    Hello Mitch,

    I'm glad you've got your RF Amplifier Up and in use without having too many problems. Basing your FT-847 at 30 to 35 W, you're getting +9 to +10 dB of signal gain on the RF Amplifier's Output in this configuration. I suspect you'll be burning up the airwaves with your set up.


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