Gates M-5693 Modulation Monitor

Discussion in 'Amplitude Modulation' started by W2WDX, Jul 11, 2018.

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  1. W7TFO

    W7TFO Platinum Subscriber Platinum Subscriber QRZ Page

    Why make things more complex/difficult?

    A Bud box with a 2" dia coil of 50-60 turns tappable. Run the coil across the feed point to ground. I/O just passes thru.

    Run the tap to a BNC or UHF connector for yer MM. The old tube rigs liked the industry standard of 10V RF under load. Adjust to set carrier level centered.

  2. W2WDX

    W2WDX Subscriber QRZ Page

    @W7TFO Dennis, should the tap be at any particular place? I have a dip meter BTW. Or should I just tap for highest voltage at the MM? I have a bunch of tappable 2" airdux coil. The reason being, like a tank, should I tap for each band? I have a gazillion of Centralab switches, and it would be easy to build a switch in for each band going to the RF connector to the MM. Does it matter? I would assume there is one tap on BC transmitters since they are at only one frequency.
    Last edited: Jul 12, 2018
  3. N1BCG

    N1BCG Ham Member QRZ Page

    It’s an auto-transformer. You tap it for the voltage division you need.
  4. W2WDX

    W2WDX Subscriber QRZ Page

    Ah, of course. I was off in resonant circuit realm for no good reason. So I'll have to find a happy median point for the voltage tap for the range of outpoot power for the different transmitters (exciters). A tap that keeps them all in range of the input (carrier) adjustment on the MM. I get it. Or could still use a switch for different transmitters, keeping the input voltage to the MM the same regardless of which radio (tap) I select. Am I correct?

    I have different transmitters some; 50w input, 100w input, etc.

    Does not frequency play some role as well tho?
    Last edited: Jul 13, 2018
  5. W7TFO

    W7TFO Platinum Subscriber Platinum Subscriber QRZ Page

    A secret...use a baby roller...set for enuf carrier per band...that meter just wants E...Voila!

  6. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page


  7. N2DTS

    N2DTS Ham Member QRZ Page

    Why not just a resistive voltage divider like later mod monitors used?

  8. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    The RF Front End of his monitor already has a voltage divider.

    All he has to do is get enough PU coil turns to get about 5-7 volts rms RF across the PU coil load resistor.


    Attached Files:

  9. W2WDX

    W2WDX Subscriber QRZ Page

    I think I am going with a simple roller inductor across the transmitter(s) output. I do not operate 160m, and I have several big rollers and an instrument case that they can fit in. It should have enough inductance for 80m and above, and might even be usable up to QRO (if I ever get there).

    As far as XT2, I'll get some of those Millen 4 plug coil holders (like the Gates original) and roll my own.

    I'll keep ya'll posted.
  10. N2DTS

    N2DTS Ham Member QRZ Page

    I do not understand why an inductor is needed rather then a resistor, or a variable capacitor.
    Its said the capacitor will induce deadly phase shift, but does not an inductor do the same?
    I never noticed any problems with a variable cap as a pickup.

    I would worry an inductor across a feedline would interact at points (in bad ways) as you adjust it and move around bands and adjust the antenna tuna.
    It may be fine for broadcast work on a fixed frequency and power level, but maybe not with wide changes in frequency, feedline impedance, various reactances, and so on....

    I would think a non reactive way of doing it would be much better, like a resistor network or something...

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