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Posts posted by Steve714

  1. Hi, Thanks for that. I'll quickly write out a few details in addition to the components used so that there is some context for anyone who might be interested in this area of work. I've also attached a more representative graph of  Taurus A . This method can be used to perform drift scans on thermal sources (Sun and Moon) and supernova remnants such as Cassiopeia A, Cygnus A and Taurus A. Virgo A is probably a challenge too far as the flux density is around an order of magnitude lower than that of Taurus A.



    1.9m diameter prime focus mesh (3mm) dish f/d=0.35 coupled to an EQ6 mount.


    Two circuits were used. The first received signals from the dish and the second with identical components was connected to a 50 ohm matched load termination and acted as a reference.

    Circuit 1:- A WR229 waveguide to coaxial adapter (3.3-4.9GHz) with feedhorn and scalar ring was positioned so that the dish focal point was 0.7cm inside the feedhorn. The first low noise amplifier (Mini Circuits ZX60-63GLN+, Gain 28dB, Noise Figure 0.8dB) was connected directly to the WR229 output. A semi-flexible 50 ohm coaxial cable with sma connectors, positioned along the dish strut, connected the output to a second LNA (Avantek AWT6032, Gain 20dB). The outputs of both LNAs had attached dc blocking components.  A 3m length of high quality, heavy duty cable then delivered the signal to the receiver housing where it connected to a narrow bandpass filter (K&L X5FVSP-3316.5/E67, 3.27-3.37GHz) and then to the Limesdr Channel 1 receiver input.

    Circuit 2: The reference circuit with identical coaxial lines and components to the active Circuit 1 was terminated with a 50 ohm matched load. This circuit was placed on a tripod approximately 3m from the dish and connected to Channel 2 of the LimeSDR receiver.

    The receiver communicated with a high spec PC via a 15m USB3 (56bps) cable with inline amplification.

    Of critical importance to the sensitivity of this system were the noise figures of the first LNAs in each circuit which should be as low as possible and the bandwidth of the receiver which should be as high as possible. The noise specs of the second LNAs are not critical.

    The open source software employed for data capture was the excellent SDR_Angel with the Radio Astronomy plugin. Data analysis and presentation was performed using a program written in R.

    Reference data was subtracted from Sample (Dish) data to provide results relatively free from the effects of drift in the receiver output due to temperature fluctuations. (NB this must be performed after the two datasets have been converted to linear format; the result can then be transformed back to a log format).


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  2. Great 21cm work! Also from Sussex (East), I thought some measurements at ~3.3GHz on usual suspects (thermal (Moon)and supernova remnant(Taurus A)) might be of interest. This drift scan was made using a 1.9m diameter dish and LimeSDR receiver.  The moon was 1.4 degrees lower in the sky than the dish elevation which was set for Taurus A. Happy to provide details of system (LNAs, filters, software etc).



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  3. Has anyone experience of using Spectrum Lab above 2GHz. I would like to use SL with a LimeSDR which is capable of 3.5GHz but seem to have a problem persuading SL to cooperate. I have successfully changed the max frequency in the interpreter command window with cfg.SpecFreqMax but any attempt to increase over 2GHz is ignored.  

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