I updated and greatly expanded my October 2020 whitepaper “Amateur DSN Lessons Learned (so far…).” The new version is available at: Amateur_DSN_Prutchi_2023. It is meant to supplement my presentation at the 2023 Hackaday Superconference.
My talk on Amateur DSN at Hackaday Supercon has been scheduled for Sunday, November 5 from 11am to 11:40am. See you there!
I’m excited to announce that I’ll be presenting “Receiving Microwave Signals from Deep-Space Probes: Amateur DSN and the Ultimate DX” at the 2023 Hackaday Superconference (Nov 3 – 5, 2023).
I got fed up with my prior hosting service, which was always slow, their servers were massively overloaded, and I could never get a straight answer from support.
The new hosting provides really fast service, so I plan to post new content after completing the website migrations.
For a detailed writeup in pdf format please CLICK HERE
I’ve been planning some experiments with single-photon and ultra-low light levels. For these experiments I want the collection area to be large and for the detector to have very broad spectral response, so my preference is to use a photomultiplier tube (PMT) instead of a “silicon photomultiplier” avalanche single-photon detector.
I found a brand new EMI 9816B PMT on eBay® which meets my requirements. The 9816B is a 51 mm (2”) diameter end-window photomultiplier, with an S20 infrared-sensitive photocathode, and 14 BeCu dynodes of linear focused design. This tube features a very high gain of 25×106 A/lm under nominal conditions (2,200V) with a quantum efficiency of 21% at the peak response wavelength.
Integration time, and ultimately resolution and sensitivity for detecting single-photons or ultra-weak light levels are dependent on the noise floor (dark counts) which is a function of temperature. Cooling the PMT dramatically reduces its dark current and counts.
I bought a surplus thermoelectrically-cooled housing by Products for Research (Model TE-182) which is made for 2” end-window PMTs. I could not find a surplus base for the EMI 9816B 14-dynode PMT, so I decided to buy a surplus base for a different tube and modify it for the 9816B.
Clearing the inside of the base was a very messy affair. This is because the dynode voltage divider chain is partially potted in silicone, and the rest of the base is filled with expanding thermal-isolation foam. Part of the base is made of plastic, so the use of harsh chemical solvents or heat to remove the silicone rubber and expanding foam were not possible. I thus had to use a scalpel and dental picks to remove all this insulation and be able to disassemble the tube socket.
I built a new divider on a piece of phenolic breadboard . The base is wired for high voltage (-2,300V) applied to the cathode (through a 33k? resistor). The dynode_1-to-dynode_14 divider is built with 330k? resistors. As suggested by EMI, the cathode-to-focus (and dynode_1) is set at a fixed 300V difference using two 150V Zener diodes in series.
Results from a characterization run are shown in the following table. The room-temperature dark current agrees with the specified value. A very dramatic drop in dark current and dark count rate can be observed when the PMT is cooled.
For a detailed writeup in pdf format please CLICK HERE
I have kept on making space in my lab for new projects, and came across 3 new-old-stock Marx generator modules that were made for the Fexitron and Febetron flash X-ray sources and electron accelerators. The Fexitron and Febetron devices were made in the 1970s by the Field Emission Corporation, a division of HP, which is now L-3 Pulse Sciences.
Each module contains two complete 30 kV Marx stages. In the Febetron/Fexitron pulsers, modules were stacked to form Marx generators of up to 2.3MV output. The spark gap distance is adjustable. These modules are designed for use under 20-70 psi air or nitrogen.
My intention was to build a 180 kV fast Marx with these, so I had reverse-engineered the schematic for these modules. I’m putting it here in case that someone is interested.
The following are interesting links related to Fexitron/Febetron units:
- The Hofstra Group used to carry them. They probably can still repair them.
- Picture of a 1200 MW flash x-ray tube made for the Fexitron. Beam volume was 3.5 cc (600 kV, 2000 amps, 0.2 µs).
- Febetron information from RPI.
- Field Emission Corp patent: Fexitron Febetron Marx Generator Patent US3783289
After some time of not looking at S-band, today I used the 1.5m dish to receive some S-band spacecraft. My receptions for today: Wind, Chandra, SOHO, and Queqiao.
Sanity check after moving the X-Band system from the 1.2m offset dish to the 3.5m dish. OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) spacecraft comes in strongly two days before its first sampling attempt of asteroid Bennu.
New one to me: received the fast-moving Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter while locked to Madrid DSN using the 1.2m offset dish antenna.
I’ve been working on my system for receiving signals from deep-space spacecraft since the summer of 2019 when KC2TDS and I built an X-band circular polarization feed and downconverter that we tested at MUD 2019.
My first true-DSN X-band reception happened in May 2020. I was able to receive and track Bepi-Colombo, which at that time was 15.2 million km away from Earth. The signal was received with the feed built by KC2TDS mounted on a 1.2m f/d=0.6 offset dish steered by a Yaesu G-5500 az/el rotator. I used a Kuhne LNA-8000B low-noise amplifier connected directly to the probe, and the amplified signal was sent to the N2QG downconverter (LO=8GHz) mounted on the boom. Downconverted signals (400 – 450 MHz) were received using an AOR AR-5000. The radio’s IF was sampled by an SDR-14 and displayed with SpectraVue. Tracking of the probe was with PstRotator’s DSN feature.
Figure 1 – Block diagram of N2QG’s X-band Amateur DSN station in June 2020.
I purchased a squeezed-tube depolarizer and super Kumar scalar ring from M0EYT (from uhf-satcom.com). 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. I mounted this feed on my 3.5m dish and was able to receive Mars Express, MRO, and OSIRIS-ReX.
Despite carefully tweaking the feed, I’ve been unable to get the system mounted on the 3.5m dish to yield the signal levels that I’m expecting. I suspect surface accuracy is the culprit because the 3.5m dish behaves well at 1296 MHz, but the g/t is just not there at 8.45 GHz. I can receive Bepi-Colombo on the 1.2m dish with around 12 dB compared to 16dB on the 3.5m dish. However, M0EYT receives it at around 30dB on his 2.4m prime dish. In July I worked on decreasing the SNR of the downconverter, which improved signals some, but definitely not as much as I would have liked to receive from a 3.5m dish.
Towards the end of that month I returned the X-band feed and downconverter to the 1.2m offset dish because I needed the 3.5m dish to participate in the EME SSTV Moon Landing Party hosted by PI9CAM at Dwingeloo Radio-Observatory in the Netherlands.
Juno remains out of my reach, so I’m considering next steps to improve my system. I thought that this would be a good point in time to summarize my experience so far, and discuss out loud plans for the future in case that it helps someone else who is just getting started in Amateur DSN. CLICK HERE for my whitepaper “Amateur DSN Lessons Learned (so far…).”