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About Steve714

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  1. Have been looking for a receiver to upgrade from the SDR (FC Pro+) that I have been using so far for work in the 1-10GHz frequency range. I've seen that many people have recommended the old ICOM (7000, 7100, 8500, 9000) and AOR receivers that date back to the 1980's but which can still be purchased secondhand. However, it seems that these have generally been run long and hot and require substantial repair/refitting to bring them back into spec. Are there any receivers operating up to 2GHz that are more current or still in production which anyone would recommend?
  2. Robin, Thanks for that. The receiver does have AGC but the signal strength is relatively low so this shouldn't be a issue. Have seen 18dB increase in signal strength with no problem pointing at the sun. Having said that, I think that the SDR receiver is causing problems (eg image signals) and that I need to upgrade to a spectrum analyser (and a larger diameter dish). I would be grateful for any suggestions. Thanks, Steve
  3. My recent foray into meridian drift scanning has produced traces which are inverted compared with what I would intuitively expected ie a dip in magnitude of the received (noisy) signal rather than a peak. This drop is recorded at exactly the expected time of the radio source transit and the transit time is precisely what is predicted (Radio-Eyes). This is repeatable for varying starting times and has been recorded for both Cass A and Cyg A. I am using a dish antenna at 3.4GHz. Would be grateful for any insight into this from more experienced practitioners.
  4. Thanks for your replies. I was hoping to find an off-the-shelf solution rather than getting involved in Smith charts and circuit building again. To be more specific about the circuit problem, I have a standard commercial LNB, an in-line amplifier, a power inserter and dc block which are all 75 ohm F-type and a Funcube pro which is 50 ohm SMA. The impedance mismatch at present is 1.5:1 which will result in 20% of the power being reflected at the junction between the two impedances. An impedance matching transformer would reduce this to around 10%. I guess the only other option would be to buy a 75 ohm SDR but so far I've been unable to source one.
  5. Another basic newcomer question. It seems that the detector end of amateur radio telescope equipment eg LNA, LNB, filters etc are almost exclusively 75 ohm input impedance while receivers / analysers are almost exclusively 50 ohm impedance. How is this mismatch managed in the rf circuit avoiding relatively high insertion loss and more importantly reflections resulting in degradation of the source signal?
  6. I am thinking of setting up a basic RT and am limited to a dish diameter of around 1.9m (mesh, 2.8mm holes). I think this means that I'm going to be working at X- and/or C-band frequencies since the beam width will be too large for L-band work. Both C- and X-bands have potential problems though since gain is likely to be low for C and the dish quality requirement at 10GHz of being accurate to 1/10 wavelength might be in question. If anyone has any comments on this I'd be very grateful. My second issue is regarding signal conditioning. I was planning to use an SDR (eg Funcube pro +) at the spectrum end of the circuit. Does this require the signal to be downconverted using an LNB? If so, is it necessary to have the LNB positioned on the dish with an appropriate feed or is it better to have a matched feed with an amplifier on the dish and the LNB or similar further downstream? Any comments or recommendations to pieces of kit here would be great.
  7. As a newcomer to radio astronomy, I am wondering about which type of mount to purchase. I notice that most people use AZ/EL mounts with their dishes as opposed to EQ mounts which are favoured in optical astronomy. Is payload weight the reason for this? I note that AZ/EL mounts are more problematic for use when tracking because of field rotation and tracking motion. Are there methods for correcting for these?
  8. I have an interest in both photoastronomy and radio astronomy and would like to purchase a mount that would allow me to do both if possible. From my limited reading on this subject, it would seem that a good EQ mount is a must for photoastronomy. I note that Primalucelab use the NEQ6 Skyscan EQ mount for their Spider230 2.3m dish antenna RT but would, if possible, like to avoid the additional counterbalance system they have and couple the dish directly to the mount. I wonder if it is feasible to do this? The advantage would be that the mount counterbalance would actively balance the dish antenna but of course the dish direction would not be correct and I think that there could well be problems with Goto and tracking. Is there any way around this? Any advice would be very welcome.
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