Amplifier ALC Theory questions and help

Discussion in 'Amateur Radio Amplifiers' started by N2RDQ, Jun 29, 2018.

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  1. AC0OB

    AC0OB Subscriber QRZ Page

    Collins never did anything simplistically. :D I worked for RockwellCollins.

  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Well, I worked for AT&T Bell Labs. And there, usually "simple" was the correct answer.

    The 30S-1 had an advanced ALC circuit which compared input to output signals: Complex, but it actually worked. Unfortunately, although it did work, it was frequency dependent and had to be adjusted per band. I sold my 30S-1 to a JA ham 25 years ago, but it did have some innovative circuitry. It also had design problems including exhausting the heat from the PA to its rear, so you couldn't push it up against a wall.

  3. G3YRO

    G3YRO Ham Member QRZ Page

    Ah but Frank . . . you're forgetting that everything made in the USA is always MUCH better LOL!

    (They're great at AC Mains frequencies . . . but I would certainly never use a 1N400X as an RF detector!)

    Roger G3YRO
  4. AC0OB

    AC0OB Subscriber QRZ Page

    For the two diodes of MIC brand I used, they were manf. in India, whereas the NTE125 diode (NXP) was manf. in Eindhoven, the Netherlands (formerly Philips).

    Are there better RF detector diodes out there? Of course. For signal detection and for use in lower RF voltage circuits, today I would use one of the low Vf Germanium diodes, a Schottky silicon diode such as the 1N5711, or a GaS diode.

    GSR never posted his circuit nor did he say he used my simplified Dentron ALC circuit with the 1N4007, nor did he report his values of negative DC voltages across the load.

    Last edited: Jul 6, 2018
  5. G0GSR

    G0GSR Ham Member QRZ Page

    Phil, I used a simple half wave rectifier circuit containing only a diode and load resistor. Any further complication is unnecessary to compare the AC performance of diodes.
    The input was from my signal generator, 50R source impedance 20v p/p.
    Charging a capacitor from the output would have destroyed the beautiful charge storage response of a slow diode.
    You can infer the DC component from the AC waveform. Would have been boring to post a picture of a straight line.
  6. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Somebody had to sweep the floors!

    Perhaps you could post video of "Generating a fairly smooth voltage" considering that ALC modulation may be a problem in some current radios. Frank proved his point!
  7. AC0OB

    AC0OB Subscriber QRZ Page

    AXN: "Perhaps you could post video of "Generating a fairly smooth voltage" considering that ALC modulation may be a problem in some current radios. Frank proved his point!"

    The measured resulting DC voltage of ~ - 4.8 volts has a ripple voltage of 35 millivolts P-P at 3.75 MHz.
    15 millivolts of that 35 mV ripple contains a broad, "forced commutation" spike due to the diodes reverse recovery characteristics.

    My scope doesn't have the output features that Frank's has, but Frank is still in denial.:D

    This circuit does work for its intended purpose and is a functional circuit for the ALC generation task of the day.

    As far as modern transceivers, most filter the ALC voltages anyway, so I doubt the low ripple voltage would get through. But as was noted before, be careful to limit the ALC from these older Linears because they can easily exceed
    - 4V.

    So AXN, construct the test circuit and then tell us if you see any carrier modulation due to the ALC.


  8. K9AXN

    K9AXN Premium Subscriber QRZ Page

    While you were sweeping the floors at Collins did you have any thoughts of moving on to more complex endeavors like kitchen help or advanced shoe polishing?

    The list has gone way off the tracks --- have a nice day ---- weather 's great here, going to saddle up for some hang gliding at Whitewater tomorrow --- going to be some magnificent thermals.

    Cheers your pal Jim
  9. AC0OB

    AC0OB Subscriber QRZ Page

    Nah. Just played Physicist my whole time there and developed Weather Radar, SDR transceivers, TCAS, Synthetic Vision, Nuclear Hardening of Mil. Avionics System, HF transmitters and Antennas, etc.

    Just the mundane stuff, Jim. :D

    So are you a Railroad Engineer 'cause you seem to off track quite a bit?o_O

    Stay safe this weekend, put on your SPF75, and

    Your friend,

    Last edited: Jul 6, 2018
  10. AC0OB

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