ClearSkyRF

Tag: antennas

  • Antennas in Various Stages of Operation on Our Site

    As of January 2026, we have several antenna setups that are in various stages of operation or repair on our site. Here’s an overview.

    The start of the Giga Loop

    A full-wave 630m loop at varying heights ranging from 10 to 100ft off the ground. In practice, the feedpoint impedance is way off from the simulations, but that’s okay. As of Spring 2025, it is partially dismantled for construction work on the property, but even with half the wire coiled up, it still picks up stations from across the world.

    It starts off here and circles a part of the property:

    Perhaps because of the capacitive loading and its proximity to ground, it resonates much lower than  I anticipated/simulated, and the feedpoint impedance is miles off from where it should be.

    We use the learnings from this experiment to build our Giga Loop, which will cover over 15 acres.

    A fan diapole

    This antenna hung about 75 feet over a canyon on our property. The feedline was balanced at the 600-ohm line. This antenna is currently down, mostly because the feedline was not practical due to the distance to the shack — it constantly got tangled up. I will need to either build a remote tuner or maybe find a source of 450-ohm ladder line at a reasonable price, as I might need about a quarter mile.

    I love the simplicity of a fan dipole, also strung over the canyon. This is fed by a current balun and RG-6 Cable TV coax at 75 ohms, because it is cheap for long runs and has no significant loss at HF for resonant antenna use.

    Vertical Antennas

    I’m not exactly a “vertical enthusiast” (they’re noisy), but this contraption is quite useful for transmitting. It has four radiating elements and eight elevated radials. Fed with one 75-ohms coax for all 6 bands.

    Another dual bander: vertical for 80, inverted L for 160. All wire. Strung over a canyon with six radials going east-west and the “L” going north-south. The radiation pattern is almost omnidirectional.

    Sometimes, temporary antennas stay up a little longer than planned. Almost a year ago, I planted a few 2x4s into the ground as a makeshift “mast” to get something in the air for 6m, 2m, 20m, and 40m. All are fed with RG-6, as I had a couple of 500ft spools lying around.

    The 2-meter antenna is a monopole with radials bent to match the 75-ohm impedance of the cable. The physical insulator is a spark plug. The 6-meter antenna on the right is a vertical dipole. No balun was used, even though it is a balanced antenna. It was supposed to be up for a day, and I was out of balun materials. 

    These two inverted Vs share a 4×2 “mast” (pole? stick? contraption? eyesore!) Both coaxials are RG-6. Balun is 1:1. 

  • A Back-to-Basics WSPR Beacon Setup (It Reached Tasmania!)


    For me, Amateur Radio is about designing and building equipment, experimenting, and learning. I have done so for/on almost every amateur frequency, from 630m to X-band. Rag chews or contesting do not speak to me much. My antennas are mostly omnidirectional, simple, and resonant, including a full-wavelength loop on 472 kHz. However, reality forces me to settle for a 630m loop that is just a fraction of a wavelength above ground.

    I’ve been working on this back-to-basics WSPR beacon since June, 2025.

    If you pick up my WSPR beacon on 80m, this is what the signal came from: a homebrew built-from-first-principles design. The oscillator is a 74HC00 NAND gate. The NTSC color burst crystal was modified with a Sharpie to oscillate on 3570.1 kHz. 

    A second NAND gate is used to gate the oscillator signal, producing CW. I sign off my WSPR transmissions with my callsign in CW.

    The microcontroller is an ATTiny88 in some Arduino form factor. I never developed an interest in object-oriented programming, so I usually wipe the bootloader and write my own code in assembler or sometimes a higher-level language.

    Time comes from a DS3121 RTC. Drift is deep sub-second per day, but it needs occasional tuning to keep the drift under a second.

    WSPR modulation is created by driving a low-pass-filtered PWM signal into a reverse-biased red LED, which is used as a varactor in the crystal circuit. A few pF is enough to pull the crystal over the ~4.5Hz range dictated by the WSPR protocol.

    The PA is a 74AC240 with two times 4 drivers driven differentially. I measured the differential output impedance to be about 17 ohms, so I use a 5:1 balanced-to-balanced impedance transformer (a balbal?), giving about 90 ohms to the antenna port. LPF is a 5th-order differential Butterworth LC filter. I know I should not have used an SMA connector, but I was originally not planning on a differential drive.

    Power is a single Li-Ion cell, with no power conversion. This causes about 20Hz of drift over the supply range. The 2Ah cell powers the beacon through the night. 

    The transmission line to the antenna is about 30m / 100ft of Cat-5 network cable.

    The antenna is an inverted V with the apex at 30ft / 10m, but unfortunately, 100mW will not boil off any clouds. 

    One night of operation on one battery charge yields the following. I’m rather pleased with that for 100mW of power into an inverted V at one-eighth of a wavelength high.

    It was even spotted in Tasmania — with 100 mW, on 80m! On a couple of occasions, it got to Alaska, which I thought was pretty good, but Exceter in Tasmania is 12,839km. Almost 130,000 km per watt, with an NVIS antenna made from garbage wire (24 Ga CCA, so aluminum).

    If you pick up my WSPR beacon on 20m, the story is somewhat different. This is a more “traditional” approach, using an Si5351A CMOS clock generator programmed around the 20m WSPR frequencies on both sides of 14.097100 MHz.

    The rest is mostly the same; the LVDS 3.3V p-p signal is boosted to 5V with a 74HC gate, and the PA is a 74AC240, here driven at 6V.

    When loaded between 15 and 20 ohms differentially, Pout is around 300mW, and PA dissipation is about a Watt before the output filter. The transmission line (CAT-5) is over 20 ohms resistively alone. The ERP is about 100mW into a resonant inverted V about 7 meters up. 20m is an easy band, so down under and “up over” at VY0ERC showed up within hours.

  • Creative Antenna Experiments Series: A Cavity Filter for 70cm Wavelength

    Our mission at ClearSkyRF is to provide a low-threshold experimental environment that unleashes new forms of creativity and scientific insight.

    Using what’s at hand and making the most of your surroundings is critical to gaining quick insights without the high price tag associated with formal experimentation.

    In this series, I share documentation from my past experiments — hopefully to spark ideas and conversations.

    First up, here’s a cavity filter for 70cm wavelength: