Cutting-edge diy projects

Prutchi.com

Cutting-edge diy projects

The Cable is Eating my Lunch!

Posted on by Posted in Amateur Radio N2QG, David, Earth-Moon-Earth

1296 MHz EME RF power to feed N2QG (c) 2020 David Prutchi PhD

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.

N2QG 1296 MHz power amplifier (c) 2020 David Prutchi, PhD

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.

1296 MHz EME cable loss N2QG (c) 2020 David Prutchi PhD

 

 

Using Geosynchronous Satellites as Fiduciary Points for Aiming Dish

Posted on by Posted in Amateur DSN, Amateur Radio N2QG, David, Earth-Moon-Earth

Chaparral Corotor II feedhorn for aiming EME/DSN dish at N2QG (c) 2020 David Prutchi, PhD

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.

Polarization-selection element in the Chaparral Corotor II (c)2020 N2QG David Prutchi PhD

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.

 

Chaparral Corotor II polarization controller (c)2020 N2QG David Prutchi PhD

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.

Taking Orders for Canadian Geese Microwaved On-The-Fly ;)

Posted on by Posted in Amateur Radio N2QG, David, Earth-Moon-Earth

N2QG 1296MHz 600W power amplifier (c) N2QG David Prutchi Ph.D.

This weekend I was able to combine the power of two 320W pallets using ring hybrid couplers (rat races) for an output of around 600W.  The strength of my own CW echoes improved dramatically.  The setup above still needs cleanup, and I may end up placing it at the base of the antenna to reduce cable losses.  On the meantime however, my system is ready for CW QSOs.

A number of stations calling CQ this afternoon at 1296.020. (c)2020 N2QG David Prutchi PhD

Conditions were good today, and there were quite a few stations calling CQ off the Moon.  Unfortunately, I realized how rusty my code has become, and cheating by using decoding software does not help at these signal levels, so I decided to hold off on answering until I get my code back up to speed.

JT65-C decode by N2QG

I also started playing with JT65.  I can decode straight from both the IC-9700 and the AOR AR5000/SDR14.  Next weekend I’ll build a circuit so that the computer can trigger the PA sequencer to be able to TX JT65C.

 

Scalar Ring for the 1296 MHz Septum Feed

Posted on by Posted in Amateur Radio N2QG, David, Earth-Moon-Earth

This weekend I exchanged the LNA isolation relay by a transmit-type relay with N connectors, and replaced a short cable and N-to-SMA adapters by just two N adapters.  This gave me one extra dB of Sun vs. cold sky.  I then swept the position of the feed very carefully, but the best I could get was 9 dB of Sun noise.

KC2TDS (Jason) and I calculated the F/D of the dish to be around 0.45, which would mean that the septum feed would be OK as-is, but the dish’s manufacturer specs state its F/D at 0.37, although with inconsistent measurements.  I decided to try a scalar ring to change the feed’s beam pattern in case that would be the reason for my low Sun measurements.

I cut out an 18″ diameter x 3″ deep “Fat Daddio” cake pan to allow the feed to protrude through the center.  I reinforced the two sides of the orifice with frames cut of the waterjet.  Two brackets hold the scalar ring firmly against the feed.

I am limited by the geometry of the struts, but was nevertheless able to gain 2 dB of Sun noise vs. cold sky (for a total of 11 dB) with this arrangement!  ON0EME now comes in at  approximately 5 dB above my noise floor, making for easy copy.

I also wired the TX port all the way to the nearby shed where the PA will reside, but didn’t get to wire the RX/TX relays, so trying to transmit and receive echoes off the Moon will have to wait until next weekend.

 

Sun Noise vs Cold Sky, and ON0EME copy with N2QG’s 12 ft dish

 

12 ft dish at N2QG with 1296 MHz septum feed and scalar ring.

 

First 1296 MHz Signals Received Off the Moon with 12 ft Dish

Posted on by Posted in Amateur Radio N2QG, David, Earth-Moon-Earth

After two weeks of battling with my receiver setup, I finally found the problem: The output stage of my home-brewed GPS-disciplined 10MHz reference was clipping on one side, which caused the AOR AR5000 to misbehave.  My reception cleaned up as soon as I connected the rubidium reference instead of the GPS-locked source.

The feed is not optimized because I’m receiving only 8dB of Sun noise above cold sky, but this was nevertheless good enough to receive and clearly copy by ear the ON0EME beacon bouncing off the Moon.

Next: Optimize the feed and connect the power amplifier to start transmitting my own signals towards the Moon.

ARISS SSTV Event Received with IC9700

Posted on by Posted in Amateur Radio N2QG, David

RS0ISS transmitted PD120 SSTV postcards December 28 2019 – January 1 2020 in memory of cosmonaut Alexei Leonov. I received the signals at 145.800 MHz using my new IC9700 rig and a M2 2MCP8A antenna.  I did not use Doppler compensation, which accounts for some of the wobbliness.  I used Nova for Windows to track the ISS.

Air Force Major General Alexei Leonov (1934 – 2019) was a Soviet and Russian cosmonaut, who in March 1965 became the first human to conduct a spacewalk.  In July 1975, Leonov commanded the Soyuz capsule in the Soyuz–Apollo mission.

Click here for larger image.

1296 MHz Septum Feed Installed on 12 ft. Dish

Posted on by Posted in Amateur Radio N2QG, David, Radio Astronomy

1296 MHz septum feed for EME mounted on 12 ft dish. (c) 2019 N2QG David Prutchi, Ph.D.

I took advantage of the mild weather and holiday off time to install the 1296 MHz septum feed on the 12 ft dish.

Conditions are horrible right now for EME (the Moon is right next to the Sun), but I’m anyway still working on the power amplifier to make CW QSOs.  So far all I have been able to do is to optimize the feed’s position using Sun noise.  -3dB beamwidth is around 4 degrees, which is what I expected from this 3.5 m dish at 1.2 GHz.

The plastic box on the feed houses the RX isolation relay, LNA, filter, and cable driver.  The feed is mounted using a modified RF Hamdesign CLX05 bracket, which connects to the struts via a universal-mounting bracket designed by KC2TDS:

A C/Ku Polarotor Feed is mounted 7 degrees from prime focus to aid in calibrating the antenna’s rotor controller against geostationary-orbit satellites.  Here is the antenna pointing at the horizon, waiting for the next moonrise:

 

Visit to Satellogic’s Satellite Assembly Facility in Uruguay

Posted on by Posted in Amateur DSN, David, Travel
Visit to Satellogic's satellite assembly facility (c)2019 David Prutchi PhD www.prutchi.com

Left to right: Pedro Arzuaga, Assembled ÑuSat satellite, Jason Meyers, David Prutchi, and Julio Arzuaga at Satellogic’s assembly facility in Uruguay

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.

ÑuSat satellite of the Aleph-1 series designed and operated by Satellogic
Artist conception by Dererk – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=56277284

 

 

N2QG/KC2TDS X-Band Amateur DSN Project

Posted on by Posted in Amateur DSN, Amateur Radio N2QG, David

Jason Meyers (KC2TDS) and I have been working on a circular polarization feed and downconverter to mount on the 12′ dish for X-band (8.4 – 8.45 GHz) amateur DSN reception (receiving signals from planetary probes using Deep Space Network frequencies).

The feedhorn is based on the dimensions of the one constructed by Michal SQ5KTM:

We used McMaster-Carr materials for our version of the feedhorn:

Jason KC2TDS carefully handcrafted the squeezed-tube depolarizer and built the feed:

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!

We measured the feed’s gain, circularity ratio, and beamwidth at Microwave Update 2019:

Results were as follows:

Gain – 13.2 dB with a linearly polarized signal normal to polarizer inserts

Circularity: -2.5 dB with horn rotated 90 degrees

-3 dB Beamwidth: 33 degrees

S11: -18.5 dB at 8.45 GHz

We plan to place a Kuhne Electronic KU LNA (model 8000 B, 8000 to 8450 MHz, 28 db Gain,
0.8 dB NF @ 18 °C) right at the feed.

Measurements taken at Microwave Update 2019 showed a 0.9 dB NF and 29.5 dB gain at 8.45 GHz for our unit.

The LNA will feed the 400 – 450 MHz IF downconverter that we built:

We also tested the downconverter at Microwave Update 2019 and found that it has a measured noise figure of 4.58 dB and a gain of 24.4 dB.

Next step is to mount the setup on the dish and start experimenting with real DSN signals.

We’ll provide more details and updates as we continue working on this project.