This weekend’s detection: STEREO-A received on X-band using 1.2m offset dish:
I received a squeezed-tube depolarizer and super Kumar scalar ring from Paul M0EYT (from uhf-satcom.com). Jason KC2TDS terminated it with a waterjet-cut copper disk and added a probe which he carefully tuned with the VNA to get <20dB return loss in the 8.4 to 8.45GHz DSN band.
My plans for this weekend are to take down the 23cm EME feed from the 3.5m dish and test this feed after taking some measurements with the horn that Jason KC2TDS built based on Michal SQ5KTM’s design.
IMPORTANT UPDATE 1 June 2020: Please see http://www.prutchi.com/2020/06/01/probe-location-for-squeezed-tube-x-band-dsn-feed/ for the correct probe orientation!
I finally got around to building a 3.5-turn helical feed for the 1.2m offset dish to receive S-Band satellite and DSN signals. VSWR is quite OK (1.5:1 to 1.6:1) within the Near-Earth and Deep-Space S-band (2.2 to 2.3 GHz):
Click here for high-resolution version of the image.
DSP-F21 is a satellite of the US Air Force’s Defense Support Program (DSP) which operates the Satellite Early Warning System. The TLEs for this satellite (USA-159) are distributed by SpaceTrack. The satellite was launched in 2001 and is still used for missile launch detection. The satellite emits a constant carrier at 2237.5 MHz which sometimes becomes active with data during Early Warning and LEO SIGINT operations.
My favorite microwave receiver is the AOR AR5000. I have it locked to either my 10 MHz rubidium or GPS references. The 10.7 MHz IF output goes to an RFspace SDR-14 which I display using SpectraVue.
The SDR-14 does not come with a provision for feeding an external reference, but I know I had seen something about this a long time ago. I Googled it, and found out that Dave Powis, G4HUP, the originator of the mod had become SK. His web page is no longer active, but found it using WayBackMachine.
I successfully modified my SDR-14 and am feeding it 66.666,666 MHz from a Leo Bodnar Mini Precision GPS Reference Clock.
Click here for my writeup of the mod with pictures, as well as Dave’s original posting.
The CoVid-19 quarantine has given me the opportunity to revisit neglected home projects, so I decided to add another Az/El dish to my antenna garden. The main purpose of this new dish will be to serve as a low-gain testbead before moving an experiment to the 3.5 m dish.
My first experiment for the new dish will be on S-band DSN, especially to “learn the ropes” about tracking non-terrestrial-orbiting probes before I try it on the high-gain dish.
The S-band DSN frequencies are as follows:
The downlinks require the receiver to operate between 2200 and 2300 MHz.
My dish’s Az/El are controlled using a Green Heron RT-21azel that Jeff kindly modified to accept input directly from the US Digital T7 RS232 absolute inclinometer on the dish’s mount. As such, I always have certainty about the dish’s elevation. However, I don’t have any absolute reference for azimuth, so my preference is to rely on the location of geostationary satellites for calibration.
To do so, I have a Chaparral Corotor II with C/Ku LNBs mounted 7 degrees to the side of the main feed. An issue occurred however when I had to mount a 18″ diameter scalar ring on the 1296 MHz septum feed to improve illumination of the dish, thus blocking the Chaparral’s aperture. Cutting a hole on the scalar ring solved the problem. This did not reduce the efficiency of the scalar ring (I still have 11dB of Sun noise over cold sky on the 3.5m dish). Jason (KC2TDS) will cut a second hole on the other side of the feed for the DSN X-band feedhorn that he built.
Of course, this arrangement invalidates the Chaparral’s scalar ring, but the signals from the satellites are strong enough on both C and Ku to be received at my QTH without the need for optimizing the feed pattern.
Now, to be able to receive linearly-polarized satellites along the full geosynchronous arc (the Clarke Belt), the skew angle needs to be adjustable. This is why I use a Corotor – because the polarization angle can be finely controlled through a servo motor on the Corotor II (the blue box in the back part of the feed) that rotates the polarization-selection element inside the Corotor’s feed.
The servo in the Corotor II works just like a regular hobby servo, which allows me to control it from the shack using a simple PWM servo tester.
My experience using the BIG-RAS rotator has been excellent since I got the Green Heron Controller (instead of the SPID Controller). I set it to ignore pulses when it’s not being commanded to move, and haven’t needed any resetting whatsoever after high winds. I have a few of the geosynchronous satellites as presets on PSTRotor, and always end up spot-on when checking positioning accuracy.
Satellogic is an Argentinian company founded in 2010 specialized in Earth-observation satellites. Satellogic began launching their Aleph-1 constellation of ÑuSat satellites in May 2016, and as of September 2019, have launched 5 satellites in that series (Fresco, Batata, MilaneSat, Ada, and Maryam). We were invited to visit their satellite assembly facility in Zonamerica, near Montevideo, Uruguay.
Each ÑuSat weighs some 70 kgs (154 lbs) and are launched as secondary payloads on Chinese Long March 6 rockets. Once in orbit, these devices travel at 25,000 kph (15,500 mph) and take about 90 minutes to encircle Earth. With the on-board telescope, these satellites yield images with one-meter-per-pixel resolution, which is impressive given the small size and reduced cost of the satellites.
The assembly facility, led by Eng. Fabricio Borsellino, is a truly remarkable example of how a high-tech manufacturing site should be run. In a very short time Fabricio has managed to hire excellent personnel to conduct all of the activities required for the delicate process of assembling a satellite, and has been able to instate a culture of personal responsibility, ethics, and quality throughout the organization that will undoubtedly pay off as Satellogic’s demands for higher throughput grows.
Satellogic’s plan in the coming years is to maintain a constellation of 300 satellites. Each satellite has a mission lifespan of around 3 years, so the assembly facility in Uruguay is gearing up to manufacture 100 satellites per year for ongoing maintenance and renewal of the constellation.