Re: Spurs/Harmonics fixes for v4 based on v5 board design?

Bill Cromwell <wrcromwell@...>

Hi Jerry,

The work-around I saw was using a notch filter to reduce the carrier a specified or known amount. The idea being the carrier is reduced going into the SA but the harmonics are not. Obviously close-in spurs are attenuated too. So it's not good for measuring those unless they are really gross. Nothing is done to the ADC.

The trick is to assure we reduce the carrier without reducing any other part of the spectrum. A good spectrum analyzer with a tracking generator could do that. It would be needed each time the 'trick' was used and adjusted. We might be able to do that but it seems like more of a headache than it's worth. I would have trouble trusting the notch.


Bill KU8H

On 1/21/19 11:33 AM, Jerry Gaffke via Groups.Io wrote:
If anybody can remember more about this 40dB dynamic range get around, I'd be very curious.
Can't imagine how you would set up an 8bit ADC to get around the dynamic range problem.
Seems the only path is to somehow filter out the strong signal(s).
Would be interesting to tear apart an RF Explorer.
I'd half expect to find a DVB-T dongle buried in there somewhere.
An RTL SDR plus upconverter and step attenuator can be a very useful "toy".
Even if it only has a 40dB dynamic range.
Verifying that spurs and harmonics from a uBitx are at least 40dB down
is about good enough for a 10W rig.  Much better than just hoping.
Educational too.
On Mon, Jan 21, 2019 at 08:17 AM, Bill Cromwell wrote:
I read something in an ARRL publication about getting around that 40
dB dynamic range problem. Maybe by W7ZOI or W1FB. But it almost
wants a spectrum analyzer to set it up. So it's a circular solution.
Circular means chasing your own tail :) If you have a spectrum
analyzer to set it up why do you need the toy analyzer?
It might be doable without a second SA.
bark less - wag more

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