Now that Solar Cycle 25 is upon us, I wanted to get active on the HF bands. My primary bands of interest are 40 and 20 meters, so I wanted to build a multi-band antenna for these frequencies. After some research, and wanting only one antenna connection for my Kenwood TS-2000 radio, I settled on a fan/parallel dipole antenna. It's very simple to build, and really hard to beat the performance of resonant dipoles.

Choke Balun

A balun is required when you are interfacing a BALanced device, such as a dipole antenna, to an UNbalanced device, such as a coaxial cable. Coaxial cables are unbalanced because from an RF perspective, there are actually 3 conductors in a coax cable: the center conductor, the inside of the shield, and the outside of the shield. The outside of the shield acts like another ground wire, and can bring RF energy and noise down into the shack.

This antenna and balun/choke design came from the 2008 ARRL Handbook for Radio Amateurs. I always encourage amateur radio operators to have ...

Read More →

After my talk at Pacificon a few months ago, several people reached out to me about setting up a radiosonde receiving station at their house. They specifically had questions about the antenna and LNA, and after answering the same question a few times I decided to do a post about this topic.

Building a 1/4 wave ground plane antenna is very easy to do. The overall design is simple, with a vertical element surrounded by a ground plane consisting of two or four wires bent down. Here are the dimensions for the VHF/UHF amateur radio bands (from the ARRL Handbook), but these dimensions can be scaled to any frequency.

There are many online calculators that will give you the approximate dimensions for the elements, but I usually use M0KUD's calculator. Whenever you are making antennas, always cut your elements a bit longer (maybe 20%) than the calculation says, then trim them during tuning.

Use any type of wire for the elements. I use standard 14-gauge solid copper wire because it's easy to get from the hardware store, it's ...

Read More →

David WB6TOU, Martin W6MRR, and myself gave a presentation at the Pacificon, which is the annual ARRL Pacific Division ham radio conference held in San Ramon in the fall. Our presentation was titled "Picoballooning in the Bay Area: High Altitude Balloons, Picoballoons, and Radiosondes." Download the slides here.

We also used this opportunity to launch the new SF-HAB website, which is a collection of how-tos, resources, and blog posts about our ballooning activities.

The first third of the presentation was David talking about balloon mechanics, including how to prestrech, fill, measure, and release SBS-13 and cheap Aliexpress picoballoons. David launched two SBS-13 picoballoons from the Central Valley in winter 2021, one of which went 2.5 times around the world.

The second third was Martin talking about picoballoon electronics. He discussed using APRS and WSPR for publishing telemetryon the internet. Martin designed and built a custom tracker for all of the picoballoon launches we have done from the Berkeley Marina.

The last third of the presentation was yours truly talking about radiosondes. I gave a brief overview of their purpose ...

Read More →

I've been spending a lot of time recently listening to WSPR beacons. The recent picoballoons that I have launched all used WSPR for to transmit their location and altitude. WSPR is a great for solar-powered picoballoons because the transmit power is on the order of 10 dBm (10 milliwatts), which is extremely low.

One night, I was just passively watching the WSPR decodes while doing other things on my shack computer. Every once in a while, I would notice a WSPR beacon that was outside of the 200 Hz WSPR band, and therefore wasn't decoded by WSJT-X. I thought this was interesting, who was transmitting out of the band? The transmissions seemed to always be on the high side.

This waterfall plot shows the 200 Hz WSPR decoding band as 1400 to 1600 Hz, denoted by the green bar at the top. You can see the signal marked with the red arrow is just above this band. This signal is also tilted slightly to the left, indicating that as the transmitter heated up, the frequency decreases by a few Hertz ...

Read More →

After my very successful SOTA activation of San Pedro Mountain the previous weekend, and the San Francisco Radio Club Angel Island expedition at the same time, the club decided to do another SOTA activation on Saturday November 14th. Antonis AA6PP, Jeff KK6JJZ, Rick K6TOR, David KN6HFV, and myself went up to the top of Mt. Davidson and activated the peak under the club's callsign W6PW.

It was a beautiful day, very clear after the rains the previous evening. We had a total of five stations. Antonis AA6PP and Jeff KK6JJZ ran the HF voice stations, trading off on 40, 20, and 15 meters during our activation. Rick K6TOR ran HF CW, and Dave KN6HFV ran the UHF station on 445.525 MHz with his HT and an Elk Antennas 5-element log periodic antenna.

Here is Antonis AA6PP running one of the HF SSB stations with an Elecraft KX2 transciever, AX1 multi-band whip antenna, powered from a Bioenno 4.5 Ah LiFePO4 battery. Notice the antenna counterpoise on the ground, stretched out in front of him.

I was using the same ...

Read More →

Summits on the Air (SOTA) combines two of my favorite pastimes, amateur radio and hiking. The objective is to climb to a nearby peak, then contact as many people as you can on the radio. While most SOTA peak activations are on HF, my only portable gear at the moment is a few HTs.

On Saturday Nov 7th, I activated San Pedro Mountain, which is 1058 ft tall. It's located in Harry A. Barbier Memorial Park in the hills above San Rafael, next to China Camp State Park.

I took the Knight Dr route, from Tom AI6CU, hiking along the Ridge Fire Road. The hike up took about 45 minutes, and some sections of the trail were very steep. I arrived on top about 12:30pm, ate a quick sandwich, and cooled off.

The radio equipment I was using was a 3-element Arrow II yagi antenna, and my trusty Icom IC-T7H handheld transceiver. RF output was about 1 watt, and the gain of the antenna was about 5 dB. Unfortunately, I only had a metal broomstick to hold the yagi ...

Read More →