Selction issues - looking to build a sweep marker generator

for 262 KKz, 455 Khz, possible 600 Khz and 10.7 Mhz and possibly other's.

Someone was successfull using abother technolofy at changing the frequency at 8 x per second for <= 455 Khz and generating a marker that's 1 ms long.  This is done, primarily so the AGC doesn't mess with the signal.  The marker would use the scope blanking input.  I guess, if I wanted to venture into more unknown territory, I could use a display and make the unit self-contained.

I guess, I would want to select the center frequency and the width but also have a variable marker.

It's Odd that none of the chips seems to have the ability to generate a marker at a specific frequency when sweeping.

With an 8 Hz updating that's not much processing power.

So, lets just say that for starters, there is a 0 to 1 (+-1) Volt signal might be better for the X axis and a to-be determined signal for the Y-axis.

Later, a Log amp might be added and a integral display making the unit self-contained.

Does anyone have an idea what part to select and what, if any output filter is required.

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  • 0
    •  Analog Employees 
    on Sep 16, 2011 3:23 AM

    Hmmm, this sounds like an amateur radio project -- I recognize some of the IFs as being used in my Boatanchor collection.

    (My HQ-170 used a third IF of 60 kHz. )

    There was a scalar network analyzer design in QEX (www.arrl.org) using the AD8302 and one of our DDS ICs a few years ago.

    This article probably contains all the information you need. I wouldn't worry about exact frequency values for your readout; the DDS ICs

    have more than enough resolution to get with a few (milli)Hz of the exact frequency you want. You can round off the value for the display

    to the nearest kHz, which should still give you 455.000 kHz.

    I have not done this myself but if you digitize the output of the detector (AD8302 or other ADI log amp) and keep the sample and associated frequency value in a buffer than after each sweep you'd find the maximum value (and thus center frequency) and the two values that 0.707 of the maximum value and you'd have the center frequency and -3 B points to add to the display via software before you update the display. In other words, crunch all the number during the blanking interval and you'll have them available for the new display update.

    When we first started doing log amps, it turned out that filter delay through 455 kHz filters wasn't insignificant, so you're on the

    right track with a slow sweep signal. (A couple of us built an FM IF strip at 455 kHz using the AD608 but unfortunately Murata

    discontinued the discriminator we used so we had to drop the application from the data sheet.)

    Although the AD9850 is used in a lot of amateur radio projects, you might want to look at the AD9913, which is much newer.

    Regards,

    Bob

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  • 0
    •  Analog Employees 
    on Sep 16, 2011 3:23 AM

    Hmmm, this sounds like an amateur radio project -- I recognize some of the IFs as being used in my Boatanchor collection.

    (My HQ-170 used a third IF of 60 kHz. )

    There was a scalar network analyzer design in QEX (www.arrl.org) using the AD8302 and one of our DDS ICs a few years ago.

    This article probably contains all the information you need. I wouldn't worry about exact frequency values for your readout; the DDS ICs

    have more than enough resolution to get with a few (milli)Hz of the exact frequency you want. You can round off the value for the display

    to the nearest kHz, which should still give you 455.000 kHz.

    I have not done this myself but if you digitize the output of the detector (AD8302 or other ADI log amp) and keep the sample and associated frequency value in a buffer than after each sweep you'd find the maximum value (and thus center frequency) and the two values that 0.707 of the maximum value and you'd have the center frequency and -3 B points to add to the display via software before you update the display. In other words, crunch all the number during the blanking interval and you'll have them available for the new display update.

    When we first started doing log amps, it turned out that filter delay through 455 kHz filters wasn't insignificant, so you're on the

    right track with a slow sweep signal. (A couple of us built an FM IF strip at 455 kHz using the AD608 but unfortunately Murata

    discontinued the discriminator we used so we had to drop the application from the data sheet.)

    Although the AD9850 is used in a lot of amateur radio projects, you might want to look at the AD9913, which is much newer.

    Regards,

    Bob

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