EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: josephny on October 22, 2015, 08:38:59 pm
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Can someone explain why the following happens:
I generator a 400mhz carrier FM modulated with a 1Khz tone and feed it into the DSA715 SA
I see the signal displayed.
I turn on DEMODULATE, plug in a headset and I hear the tone go on and then off and repeater (a pulse).
I then tuned the SA to a local FM broadcast, did the same thing and heard the broadcast station in the same way (1/2 second on, 1/2 second off).
I played with "demod time" but it didn't get rid of the on/off pattern.
What am I doing wrong?
Thank you!
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You're doing nothing wrong, the spectrum analyzer is "sweeping" a single frequency. Even if the frequency isn't changing it is effectively restarting the sweep each time at an interval determined by the "demod time".
Moral of the story - a spectrum analyzer isn't a standard receiver.
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You're doing nothing wrong, the spectrum analyzer is "sweeping" a single frequency. Even if the frequency isn't changing it is effectively restarting the sweep each time at an interval determined by the "demod time".
Moral of the story - a spectrum analyzer isn't a standard receiver.
Unless it is an old analog HP,which will happily act as a receiver.
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I see!
So even at zero span, it's restarting it's measurement at the interval that "demod time" is set to.
Thank you so much!
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You're doing nothing wrong, the spectrum analyzer is "sweeping" a single frequency. Even if the frequency isn't changing it is effectively restarting the sweep each time at an interval determined by the "demod time".
Moral of the story - a spectrum analyzer isn't a standard receiver.
Unless it is an old analog HP,which will happily act as a receiver.
What models would constitute an old analog HP (where is the demarcation in their models between old and new?)
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Any of the HP 8590 series will give you excellent audio either AM or FM. Just make sure it has option 102, which is the AM/FM demodulator board. No matter what the scan you will hear a constant good signal on AM or FM, and you can do Zero Scan as well with the same results.
I had a new DSA815 and sent it back for that exact reason. Also the Rigol front end sensitivity was not anywhere near as good as the HP 8595E that I purchased to replace it. You can purchase one of the 8590 series HP SA's for about the same price, or less than the DSA815.
Hope this helps..............