Author Archives: David Prutchi
My Current X-Band DSN Setup
Probe Location for Squeezed-Tube X-Band DSN Feed
Feeds with squeezed-tube depolarizers are popular among amateur DSN enthusiasts because of their straightforward, no-tune construction. Luis Cupido CT1DMK published a design that is often followed, and has been used successfully by Paul Marsh M0EYT, Micha? Zawada SQ5KTM and other hams interested in DSN.
Signals from planetary probes are weak, so as many variables as possible need to be eliminated when first setting up and debugging an X-band system. One of them is the polarization of the antenna. I found myself in that situation, and after some experimentation plus helpful answers from hams on the Amateur-DSN groups.io board, I’m now certain that I have the probe correctly oriented for DSN DXing.
As shown in the figure, an LHCP feed is needed to receive the RHCP signals transmitted by the vast majority of DSN spacecraft (when operating nominally). This is because when the feed is mounted on a parabolic antenna, the feed’s LHCP signal becomes RHCP after being reflected by the dish. The exception to this is for Cassegrain or Gregorian dishes, where a a secondary reflector is used to direct the energy into the parabolic reflector from a feed antenna located away from the primary focal point. In this case, the RHCP signal becomes LHCP at the secondary reflector, and then back to RHCP again when reflected by the dish.
STEREO-A Received on X-Band from a Distance of 173.8 Million km
This weekend’s detection: STEREO-A received on X-band using 1.2m offset dish:
My First True-DSN X-Band DX: Bepi-Colombo at 15.2 Million km from Earth
Today I was able to receive my first true-DSN X-band DX from Bepi-Colombo at a distance of 15.2 million km (around 9.5 million miles) away from Earth!
The squeezed-tube feed was made by Jason Meyers KC2TDS based on a design by Micha? Zawada SQ5KTM :
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!
The signal was received with the feed mounted on a 1.2m f/d=0.6 offset dish steered by a Yaesu G-5500 az/el rotator:
There is a Kuhne LNA-8000B low-noise amplifier connected directly to the probe, and the amplified signal is sent to the downconverter (LO=8GHz) mounted on the boom.
Downconverted signals (400 – 450 MHz) are received using an AOR AR-5000. The radio’s IF is sampled by a SDR-14 and displayed with SpectraVue.
Tracking of the probe is with PstRotator’s new DSN feature which downloads ephemeris data straight from NASA JPL’s Horizons:
Super-Kumar DSN X-Band Feed Ready for Testing this Memorial Day Weekend
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!
DSN S-Band Helical Feed for 1.2m F/d=0.6 Offset Dish
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):
This feed works much better than the PCB LPA with which I started my experiments. Here is USA159 (DSP-21):
First light on S-band with low-gain (1.2m) offset dish
I have the aiming of the 1.2m offset dish calibrated, so it’s ready for receiving on DSN bands. I started by placing a WA5VJB wideband log-periodic array at the focal point followed by a Minicircuits LNA. I placed the filter/cable driver in the mast box to send the S-band signal via 100 ft of LMR400 to the shack.
With the Az/El under the command of NOVA for Windows, I set it to track DSP-F21 (USA-159). The satellite transmits using circular polarization, so I know that I’m wasting at least half of the signal by receiving with linear polarization, but this is the feed that I have on hand for this antenna. Nevertheless, the received signal is very clearly seen against the low noise floor:
Next: Mount the DSN x-band horn/lna/downconverter on the 1.2m dish and start to practice tracking of non-Earth-orbiting probes.
Decontaminating N95 Masks at Home to Extend their Use During CoVid-19 Pandemic
Remember that book that I wrote on UV Photography? Well, I ended up collecting/building a number of UV lamps, and some of them emit UV-C. I set them up as a makeshift decontamination rack for our N95 masks.
The effectiveness of using germicidal (UV-C) light to decontaminate N95 masks to extend their useful time is well established. In fact, use of Ultraviolet Germicidal Irradiation (UVGI) has been recommended as an emergency measure by the CDC. The limiting factor is that UV-C degrades polymers, so it will eventually cause failure to the mask’s structural integrity (Lindsley et al, 2015).
Our protocol at home, based on my understanding of CDC’s guidelines and the intensity of my lights is to use masks for up to 8 hours (of actual use time when outside of the house grocery shopping or running essential errands) and then expose them for 15 minutes per side to UVGI before reuse.
The link to my DIY Long/Med/Short UV lamp is available here. Or in whitepaper format here.
IMPORTANT NOTE: This post should not be construed as advice on the decontamination of PPE. Please refer to official information on this matter from the CDC.
WARNING: Midrange and short-wave ultraviolet radiation can cause permanent eye and skin damage. Do not look directly at midrange or short-wave UV radiation, even for brief periods. Take appropriate precautions with pets and other living organisms that might suffer injury or damage due to UV exposure at these wavelengths.
Defense Support Program (DSP) F21 2237.5 MHz Carrier as it Orbits
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.