[time-nuts] Re: Eloran long test from now to August or September.

[jeanmichel.friedt at femto-st.fr]

This is indeed the approach I promoted in 
https://www.youtube.com/watch?v=rqa8VqSj7m8&t=9246s
but on a dedicated channel since the timing accuracy improvement over the sampling
period is determined by the signal to noise ratio during the peak fitting.
Thank you for the insight indeed.

--
JM Friedt, FEMTO-ST Time & Frequency, 26 rue de l'Epitaphe, 25000 Besancon, France

September 27, 2023 5:16 PM, "Lester Veenstra" <m0ycm at veenstras.com> wrote:

> Agree very old and multi used idea. 
> For the clever ones in DSP, penetrate a time coherent spread spectrum that can be inband but under
> the noise floor of the collection bandwidth. Correlate on receive in the same sample environment as
> you are doing science.
> 
> Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)
> lester at veenstras.com
> 
> 452 Stable Ln
> Keyser WV 26726 USA
> 
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> -----Original Message-----
> From: Jim Lux via time-nuts [time-nuts at lists.febo.com] 
> Sent: Tuesday, September 26, 2023 3:33 PM
> To: jeanmichel.friedt at femto-st.fr; time-nuts at lists.febo.com
> Cc: Jim Lux
> Subject: [time-nuts] Re: Eloran long test from now to August or September.
> 
> Exactly.. That does work, although it requires opening up your RTL-SDR (and on V3, in HF receiver
> mode, the RF input is directly coupled to the Q input, without going through the front end
> downconverter.). It didn’t work well.
> And ultimately, I was trying to figure out something that would work at Ku band, so I could
> “calibrate out” the delay through the LNB, the coax, and the RTL-SDR. 
> The basic technique has been around since the 1960s. Bracewell used it at Stanford, and a similar
> scheme was used for the Jansky VLA in New Mexico.
> 
> On Tue, 26 Sep 2023 19:24:21 +0000, jeanmichel.friedt at femto-st.fr wrote:
> 
>> I did it with 4 RTL-SDRs, and I’ll scrounge up the measurements. My first attempt was just to
>> couple the 1pps from a GPS module into the inputs - that’s not easily detectable (I was hoping that
>> the fast edges would be sufficiently broadband to be detectable in the sampled data stream -
>> nope..)
> 
> See attached: I capacitively inject the 1-PPS on the RTL2832 input (either I or Q), not
> the R820(T2) radiofrequency frontend. This allows for timestamping on the rising edge
> of GPS 1-PPS the datastream fetched by the ADCs of the RTL-SDR.
> 
> Best, JM
> 
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