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I'm getting into a new hobby: amateur radio astronomy. From what I understand you need an dish with d > 1m to pick up hydrogen line emission well. I'd be inte
by FredPret 3y ago
I'm getting into a new hobby: amateur radio astronomy.
From what I understand you need an dish with d > 1m to pick up hydrogen line emission well.
I'd be interested to know if I can just build a wide wire helix like this instead of investing in a big dish. It'd have to look nice and be weather-proof to be wife-approved though.
- petschge 3y agoTo get sensitivity you actually need collection area.
- FredPret 3y agoFair point. I’m trying all kinds of backflips to avoid buying a huge dish
- strangattractor 3y agoI 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] [1] https://www.vla.nrao.edu/ https://www.vla.nrao.edu/ [2] https://www.crowdsupply.com/krakenrf/krakensdr https://www.crowdsupply.com/krakenrf/krakensdr
- FredPret 3y agoThat 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.
- bgnn 3y agoI 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.
- strangattractor 3y agoThere 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;)
- bgnn 3y agoOne 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.
- tejtm 3y agocan 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
- strangattractor 3y agoAnother 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. [1] https://digitaldisplay.com/network-clock/master-clock/gps-vs-ntp-master-clock/#:~:text=GPS%20accuracy%20is%20~%201%20microsecond,less%20latency%20compared%20to%20NTP.&text=clear%20sky%2C%20and%20after%20satellites,second%20to%20the%20slave%20clocks https://digitaldisplay.com/network-clock/master-clock/gps-vs.... [2]https://destevez.net/2022/03/timing-sdr-recordings-with-gps/ https://destevez.net/2022/03/timing-sdr-recordings-with-gps/
- 3y ago
- sciurus 3y agoSeen https://www.crowdsupply.com/krakenrf/discovery-dish https://www.crowdsupply.com/krakenrf/discovery-dish ?
- tejtm 3y agopeople will throw them away or pay you to take them away