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AM QRP

Discussion in 'Amplitude Modulation' started by AC0OB, Oct 15, 2019.

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  1. AC0OB

    AC0OB Subscriber QRZ Page

    If anyone is interested in QRP operations for AM, David Cripe NM0S has developed a 5 Watt AM transmitter kit.

    http://www.4sqrp.com/n-75.php

    It uses a Class E final with a Class G modulator.


    Pheel
     
    W8KHK likes this.
  2. N2DTS

    N2DTS Ham Member QRZ Page

    Ordered, thanks for letting us know.
     
    W8KHK likes this.
  3. N2DTS

    N2DTS Ham Member QRZ Page

    How to open up the response a little?
    U2 looks to limit the bandwidth...c35 and c37?
     
  4. AC0OB

    AC0OB Subscriber QRZ Page

    I had that question as well.

    At first glance it appears to be a second order lowpass filter and I'll try to find out what the current audio passband is and what R and C values it would take to open it up a bit if it is too restricted.


    Pheel
     
  5. K5UJ

    K5UJ Ham Member QRZ Page

    Calling all sadists: wide tx bandwidth and 5 watts....be sure to operate it on 160 m. Make 20 minute transmissions.
     
    WD4IGX, K0UO, AC0OB and 4 others like this.
  6. AC0OB

    AC0OB Subscriber QRZ Page

    With the current values, the audio passband is about 3.0 kHz with a LF rolloff at 300 Hz.

    For a 5kHz audio passband, C37 = 0.0068 and C35 needs to be 680 pF; LF rolloff is now about 100 Hz.


    Pheel
     
    W8KHK likes this.
  7. AC0OB

    AC0OB Subscriber QRZ Page

    Currently it is an 80 meter rig only.

    "Transmit frequency 3.605 MHz to 3.995 MHz."


    Pheel
     
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  8. N2DTS

    N2DTS Ham Member QRZ Page

    100 to maybe 4000 Hz would be better, you can use a D104 or other means to make the audio punchy but its better if it goes above 3000 I think.

    I tend to not make old buzzard transmissions when running 25 watts or less, but I seem to be heard quite well by lots of people even running 2 watts carrier out of some small SDR radios.

    Also, if you are going to be wide, its better to do it at low power.
    I also tend to run the modulation heavy when doing qrp.

    And...some people run low power rigs into amplifiers....
     
    Last edited: Oct 16, 2019
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  9. W8KHK

    W8KHK Ham Member QRZ Page

    I just ordered one. Should be a fun kit to build. Great for that long old buzzard transmission during QSB!
     
    AC0OB likes this.
  10. K4KYV

    K4KYV Subscriber QRZ Page

    The weaker they are, the longer they talk.
     
    K0UO, AC0OB and W8KHK like this.

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