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About RobB

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  • Interests
    Amateur Radio, Astronomy, Physics, C++/C# development
  • Location
    South Devon
  1. I use a hot air gun and solder paste for my smd components.
  2. Wow !! - I'm still waiting for some clear nights to get my first DSO after 20 years away from the hobby. I hope it is half as good as yours!
  3. RobB


    I was watching this AstroBackyard tutorial last night (trying to soak up as much info before I begin my baby steps in astrophotography). Trevor, at one point, goes into removing halos. https://youtu.be/5GgruZ-1zQ0. I think just after halfway.
  4. I would have thought a local Astronomical Society would take them, assuming they have the storage facilities?
  5. Currently away from home and haven't applied any flats to the image. The processed image above was not from the FITS files but from the jpg. I need to install a FITS application but as I'm connecting my laptop via my mobile I'll wait until late tonight when I get home. Maybe the lines will go away. Not too worried myself but it would be good if they could investigate the issue. I'm using the course as a v.small taster of doing a longer AstroPhysics course. i.e. can I find the time to study. Maybe the PGDip Astronomy from York.
  6. Hopefully I'll be able to take one with my own telescope this weekend although South Devon isn't particularly known for clear skies.
  7. My first image in about 20 years! Taken with the Open University 14" SCT (COAST) on Tenerife last night. A single 120sec frame, BVR filter. A little bit fiddling of light levels by me (total novice here). I'm running thru the short FREE 8 week course "Astronomy with an online telescope"
  8. Hi Leon Also a Radio Ham and also looking to get into Radio Astronomy. Rob
  9. Some of the GPS Disciplined Oven controlled crystal oscillators I've seen so far need the unit turned on for hours, if not a day, to fully stabilise.
  10. The standard for VLBI is Hydrogen Maser. GPS is then used to timestamp the data streams. Rubidium can be used below 1GHz as the errors due to ionosphere path delays are greater than any timing errors due to the Rubidium, and can also be used as a backup. Not sure about a GPS disciplined Rubidium oscillator. Hydrogen Maser drift: < 10 to the power -15 Hz per day Rubidium drift: 10 to the power -13 Hz per day [how can you superscript here?] And if your beam happens to encompass a pulsar you can use that...it will be a lot more accurate! Unfortunately our dishes won't be big enough p.s. Trying not to sound like a know-it-all....I've just read this in section 9.5.3 of "Interferometry and Synthesis in Radio Astronomy"
  11. It's a bit long but have a look at this YouTube video - GPS Disciplined Crystal Oscillator. The way GPS works is based on very accurate clocks so you can 'measure' the distance from yourself to a number of satellites. Trigonometry does the rest. To do this the GPS satellites transmit a very accurate timebase/clock. As a side effect the receiver (the one with you) can provide a very accurate 1 second 'tick', the rubidium or crystal (or even cesium) oscillator fills in between each tick. So the oscillator gets a very small correction every second removing thermal drift and aging errors.
  12. Coto - I think the H142-One receiver has a GPS device to stop any frequency drift from the internal local oscillator. i.e. when you looking at 1420MHz it really is 1420MHz your looking at and not drifted to 1420.10MHz once it's warmed up. The clock defines the sampling rate of the SDR. The 'disciplined' part of 'gps disciplined' removes long term drift effects of temperature etc on the local oscillator, while the local oscillator handles the short term stability. And the discipline part needs to done in a way that doesn't cause phase noise (i.e. correcting frequency in sharp jumps). For radio interferometry it will do the same job, i.e. the frequency drift is reduced to almost zero. However, as you guessed, it does another role and therefore needs to be a lot more accurate and reproducible. Very accurate timestamp so when we recombine the signals at the computer the signal coming from the same direction we're interested in are constructively summed (need to delay one data stream in software to match the other due to path difference) whereas signals from other directions are not. I'm still trying to work out the accuracy required (% of wavelength time.. for 21cm this is 0.7ns) to give a small enough phase error for an acceptable result. Also, is the timestamp from GPS accurate enough (the 1pps output, is it at the same time at both sites)? Also need to accurately plot where the two aerials are in relation to each other to a fraction of a wavelength. Not so easy for us amateurs if not within a few hundred meters. Military GPS receiver or averaging civilian gps position over an extended time? Anybody a surveyor here who can tell me it's easy? GPS is of course derived from atomic clocks (in each satellite and at the ground base station).
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