I was testing my Morse Code transmitter last night by sending a CQ on 7.102 MHz using various transmit powers ranging from 5 to 10 watts QRP, up to 100 watts full power, using an ICOM 718 and a home-brewed antenna. It appears that 4 stations (one in the Pacific and 3 on the other side of the world—in the US) heard my signal, as reported in the Reverse Beacon Network (an automated system that receives and logs Morse code transmissions).
While this is probably the farthest distance to date that my signal was able to reach, this is just one-way communication. Probably as I improve my antenna, I’d also be able to hear the faint signals coming from the other side of the world.
I’ve built a simple HF (40-meter band) wire antenna with some scrap wires, a length of RG8 cable, PVC pipe as insulator, and some way of securing and making it waterproof. This antenna is intended for receiving (RX only) so I could listen to local voice and Morse code net calls using a Software-Defined Radio (SDR).
The antenna is a dipole with 10 meters of conductor on each side. One conductor is soldered directly to the coax’s outer conductor (braid), while the other conductor is soldered to the coax’s center conductor. I did not use a balun for this antenna, but you may try to use one. Each end of the conductors terminate with a PVC insulator. If you plan on transmiting with a wire antenna, you will need to adjust the length of each conductor for best SWR. I will be using this antenna for receiving signals in the 40-meter band while I wait for a proper HF radio equipped with a transmitter.
I have built an ultra-compact DIY iambic Morse code keyer for a dual-paddle key based on the work of PA3HCM. The keyer uses an Arduino Uno and a few components such as a potentiometer for adjusting the words per minute (WPM), a small speaker, some resistors, and LED indicators. I housed the circuitry in a neat enclosure and added some terminals (for signal line-out and an auxiliary connection for a second key). I then attached a dual-paddle key onto the enclosure, making the keyer and key setup a very portable trainer for code practice.
To watch the keyer in action, click version 1 and version 2. 73, DU1AU (Philippines).
NOAA satellites transmit weather images in APT format at 137 MHz which may be received using just a VHF antenna, a software-defined radio (SDR), and a decoder such as Wxtoimg running on a laptop.
Here’s my first weather satellite image decoded on December 3, 2020, as NOAA 18 passes over the Philippines.
I repurposed my old dash camera (Polaroid N302) as a planetary camera.
The lens was removed and replaced with a webcam-to-telescope adapter and then mounted on to a 4 in diameter, 900 mm focal length Sky-Watcher 100ED telescope on a tracking mount.
A 2X Barlow was used to further magnify the image (this video shows 1800 mm effective focal length). Jupiter’s could bands are visible in this video (1080P).
Venus showing a crescent phase, imaged using a Sky-Watcher 4 in f/9 refractor with 2x Barlow and a Canon 1100D in video mode (700 individual image frames stacked using SIRIL).
I’ve recently finished building a satellite traker based on SATNOGS satellite tracker.
The automated tracker uses an Arduino to control a pair of stepper motors that move two cross-yagi antennas (VHF and UHF). The Arduino receives satellite’s azimuth and elevation info using the tracking software Gpredict. Hamlib is then used to establish a link between the computer and Arduino through USB connection via EasyComm III protocol.
The tracker was built with parts taken from a drill such as gears and bearings, along with a pair of worm drive from a photocopying machine. The total costs of the project is less than 100 USD, antennas included. The tracker uses two A4988 stepper motor driver, and two geared stepper motors. A weatherproof metal ammo box is used as a case, and rubber seals (particularly in the azimuth and elevation shafts) prevent water from entering.
Initial tests showed good tracking accuracy, allowing reliable full-duplex communications with any passing amateur radio or weather satellite.
I have finished building and testing a DIY Terminal Node Controller (TNC). With DIY TNC, it is possible for any radio to encode and decode signals in the Automatic Packet Reporting System (APRS) format. This TNC is based on the home-brewed TNC project by VK3DAN.
The TNC requires a smart phone running APRSdroid connected via bluetooth. It taps directly to a radio through dedicated audio line-in and line-out ports (or microphone in and speaker out). The PTT is automatically activated as a packet is transmitted. I’ve tested this TNC to work with the International Space Station’s (ISS) digipeater at 145.825 MHz, digipath: ARISS.
PSAT2 transmits SSTV images at 435.360 MHz (UHF) which may be received using just a DIY Moxon-Yagi satellite antenna, a UHF radio, and a decoder such as Robot 36 running on a smartphone (Android).
Here are some images decoded on May 1 and May 5, 2020, as PSAT2 passes over the Philippines.
SSTV transmission in PSAT2 is only active in daytime. Doppler effect compensation is necessary to properly receive the transmission. Tune your radio from 435.370 MHz down to 435.350 MHz from start to end of the pass. You may decode up to two SSTV images per pass.
This page contains information on how to build a DIY satellite antenna. Two versions of the plan is provided: original and modified.
Moxon-Yagi Version 1: Original Moxon-Yagi Measurements This version of the plan shows the general measurements for a Moxon-Yagi as designed by Ly3LP. Please note that since the performance of the antenna depends on the specific materials used, you may need to make slight adjustments on the measurements in order to tune the antenna to a specific frequency in VHF and UHF.
Moxon-Yagi Version 2: Modified Moxon-Yagi Measurements This version of the plan shows the measurements of the antenna we used during the testing of Diwata 2 (PO-101) satellite, incorporating slight variation in the measurements such as changes in spacing and length of the elements, as it is optimized to work best for PO-101. This antenna also works with any other UHF-VHF satellite.
For details, please read full article below:
A satellite antenna can be made from 3 mm copper or aluminum elements, PVC boom, and some parts you may already have at home. To download the original Moxon-Yagi measurements (highest-resolution), click here.
1. All measurements are in millimeters (mm). 2. Use 3 mm copper or aluminum elements. 3. Adjust the critical gaps for lowest SWR (adjust the 14 mm and 22 mm gaps as needed). 4. Only the VHF elements (Moxon part) are connected to the feedline. The UHF element (325 mm) closest to the feedpoint is the UHF driven element. It is not connected to the feedline, but resonates only when the proper gap is achieved. 5. The feedline connects directly to the radio (no diplexer/duplexer needed). 6. Use translucent plastic insulator from an RG8 cable for the 14 mm Moxon gap 7. Use non-metallic boom (wood or orange PVC pipe). 8. The feedpoint gap is 10 mm. 9. The antenna works with any dual-band UHF-VHF radios
Here’s another version with slightly different dimensions, tuned to have lowest SWR specifically at our local satellite Diwata 2 (PO-101) frequency 145.9 MHz downlink and 437.5 MHz uplink (you may change the UHF and VHF frequencies by adjusting the critical gaps as described above). This antenna has been tested to work also with other satellites such as AO-91, AO-92, SO-50, IO-86, ISS, and PSAT2. Here’s the plan for this antenna, again, with slight variations in measurements as it is optimized for PO-101.
I’ve recently added a PTT switch on the boom, for one-hand operation. Watch the video below to see how the antenna is used in an actual satellite QSO!
Also, the Moxon elements may now be folded, making this antenna far easier to transport. Shown below are 2 versions, one using 3 mm elements, and another using 6 mm elements. The fully-collapsible antenna assembles and disassembles in just a few minutes!
For inquiries, email me at du1au@nightskyinfocus.com. To learn more about satellite communications, click here.
