Re: Waterfall display slightly offset from actual signal strength display
Neil Smith G4DBN
Hi Ron, how wide are the FFT bins you are using? On the DUO at max zoom on the main waterfall, with a bin size of 11.7 Hz, the peak is around 6Hz off. On the IF windows at 2.9 Hz bins, it is around 1.5 Hz off. The reason is just that the peak for my 10.00000000MHz signal is "somewhere" in a bin that happens to be from (perhaps) 10000000 Hz to 10000011.7 Hz instead of 9999994.65 to 10000005.35 Hz, when it would appear to peak at 10.000000 exactly.
IF window, showing peak at about 1.5 Hz HF of the 10.000600 Hz
point (I'm using CW offset of 600 Hz). Sometimes, you'll find the
peak is in the middle of a bin, but on average it will be around
6Hz off from the true frequency simply because that's how the
maths work. (or "how the math works" for those who use the
singular shortened form of "mathematics").
You should be able to calculate the bin edges and make any necessary adjustments. However, if you really want to know the exact frequency, and your radio is locked to a precision 10 MHz reference, you can use Spectrum Lab on a long integration FFT (262144 bins perhaps) to check your PC sourd card clock calibration against a precise tone generated from your reference, then use Speclab to look at the actual frequency:
That is monitoring drift of an OCXO at 1kHz offset and 512k bins
in Speclab. The DUO shows it at 1006 Hz offset approximately.
On 23/05/2021 13:09, Ron Hunsicker via groups.io wrote:
Srinivas: I see something similar with my S3.