I have a similar interest. One way to avoid the large antennas is to have multiple separated small antennas - like the VLA [1] - using an SDR receiver like Kraken [2]
That is so cool. I’d call mine the Very Small Array.
I was always under the impression that it’s super hard to pull off interferometery due to precise positioning and timing requirements, but looks like the Kraken multi-antenna you linked has that figured out in a simple way.
I never done sth like this but you can lock the clocks of each of the samplers I guess. Simplest solution might be using a single source clock and distributing it to each board with equal length of cables. You can calibrate the lenght of the cable precisely if you have access to a pulse generator and a scope. Though, alternative would be shifting the sample times in post-processing the data by searching for a high correlation. I believe both are used in practice.
There are other SDR receivers that have external clock inputs. The Kraken does that for you because it is a single unit. Of course there is likely a limit to how long the coax to the antennas can be. Just a guess - for an amateur rig I would think 30 to 60 ft antenna separation would be impressive resolution. Certainly better than buying a 60 ft dish;)
One can always use clock repraters or a reclocking with a new PLL in the middle if the cable length gets too long and caused ISI (inter-symbol-interference). I don't think 30 ft requires this. At 60ft you might need it though it depends on the clock frequency. If the syncronization is done with low frequency clock (10 - 25 MHz or so) you don't need any of that. 60ft cable won't have too strong of an attenuation at those frequencies. GHz rate clock would be a problem.
can we not now use fiberoptic cables to provide a common timestamp signal well above the shannon limit of the emmission lines that would need to be reassembled
Another interesting possibility is to use GPS for a clock. [1] Apparently 1 microsecond accuracy. Maybe useful if you want to make the distance really far. Someone has an article [2] Would be cool if you could pool the resources of multiple amateur rigs over a great distance in ad hoc antenna arrays.
Short answer is: no. The long answer is: Speed of light on glass is not so different than electromagnetic signal speed in copper, approximately 0.66C. Considering clock sources output electrical signals, using a coax cable instead of fibre optic has several advantages: simpler signal chain means lower delay, and avoiding highly noisy optical-electrical conversion means less jitter.
Fun fact: RF signals in air travel faster than light in glass fibre (0.8C instead of 0.66C).