Hmmm, interesting.
Was this with E4000 tuners, or R820T tuners?
Was this with E4000 tuners, or R820T tuners?
What was your exact test setup, tuned-frequency, etc?
on Sep 25, 2013, Juha Vierinen <[email protected]> wrote:
Hi guys,Based on my very limited understanding on electronics, osclilators and other such things, I would expect oscillator effects to cancel out when looking at the relative phase of two channels. I would expect the phase jitter on the relative phase to be dominated by what happens in the ADC and the digital down conversion. That is why I am running the two dongles off the same clock.I have some measurements of the relative IQ signal (z_1/z_2) at 100 kHz, 10 Hz, and 1 Hz sample rates. I did a power spectrum estimate using a Hanning window to look at relative phase noise. I didn't do any incoherent averaging on any of these, so there is some statistical noise. I only see some "imperfections" in the 10 Hz and 1 Hz spectrum. However, I see these kinds of effects in 100 times more expensive receivers too. For my purposes, the relative phase behaviour of the two channels is good enough.I have attached the spectra. I have also attached the 1 Hz IQ signal, which shows a small systematic wiggle, but very little phase difference between the two channels.The samples also are aligned over two hours of sampling, which means that there cannot really be a very large amount of clock drift between the two systems.Sure, the thing has it's faults. But with $16, you really can't beat the price.juha
On Wed, Sep 25, 2013 at 1:21 AM, Marcus D. Leech <[email protected]> wrote:
On 09/25/2013 12:04 AM, Jared Clements wrote:
I'll get to that tomorrow night.
Hi Marcus,
Interesting discussion. I was wondering how well synchronized clocking might work. Was hoping it would work better than it sounds. Could you quantify the level of phase noise you're seeing, like with a power spectral density plot? Just for curiosity's sake?
I know of a recently updated OOT module that should have the blocks you need ;-)
I was hoping to build a correlating interferometer by modifying several of these dongles to run off the same clock. I may need to rethink the plan.
Jared
I just ran a simulation of what I was observing (just because the lab is downstairs, and I'm upstairs).
Looks like the best it does is about -40dB/c 75kHz from the carrier. That's bluddy awful.
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