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 https://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 His web page is no longer active, but found it using WayBackMachine.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.
The highlight of my weekend was a JT65C EME QSO with Andrey 4X1AJ in Israel! That’s my personal longest EME DX. My 1296 MHz PA output was 600W, out of which I’m putting 400W at the feed of the 3.5 dish. In Andrey’s words, I was “booming” on his side (-17dB).
Very pleased with my current setup! THX Andrey for the QSO! 73
Before I package my 600W 1296MHz Power Amplifier into a single enclosure to be placed closer to the antenna, I thought it would be a good idea to take some pictures and draw a block diagram in case anyone wants to build something similar.
My original idea was to build a 600W PA using W6PQL boards. However, things have become very busy at work, so realistically building the PA would have taken a very long time. As a compromise, I decided to buy a 300W pallet and its companion controller from VHFDesign, not really knowing how that would go.
I was very pleasantly surprised by the VHFDesign unit. I purchased it directly from their website using PayPal. The unit arrived quite quickly from Ukraine. The instructions are clear, so once I got around to it, installation went easily. Their 2-cascade LNA has also been a pleasure to use, but I’ll leave that review for a future post.
After working at 300W for a while, I decided it was time for an upgrade, so I purchased a second unit with the intention of combining their outputs using ring hybrid couplers. The final block diagram is shown in this figure. The splayed-out view of the modules is shown in the following figure:
With an output of 326W for each VHFDesign pallet, each (suitable for CW and SSB), The PA produces a combined output of 600W. IMPORTANT NOTE: See my post about phase equalization! I’ll optimize cabling and phase matching once I assemble everything into a single enclosure. For now, it all works nicely splayed-out indoors.
Today was a nice, sunny day, with temperatures in the 40s, so I decided to measure the power drop along the coax from my 1296MHz power amp to the feed. The PA is at the closest indoors site to the dish.
I am measuring 520W going into the 35 feet or so of LMR900-DB that takes the signal to a junction box mounted at the antenna mast. There, I measure 420W remaining, which go into 27 feet of LMR600-UF to the feed (mast + rotor loop + cable to reach feed on 12 ft dish). After that much cable, barely 320W are left to go into the septum feed.
The numbers check out with the expected cable attenuation, so I understand that I’m simply experiencing normal cable loss. However, loosing 200W to heat the ground bothers me, so I’m looking for ways of increasing the power that reaches the septum feed. I’m first considering ways of keeping the amp indoors, but I’m afraid that I’ll ultimately have to put it all at the mast and use a hanging cable loop straight to the feed to minimize losses.
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.