SSB Radio

While SSB is by many regarded as out of fashion, it still represent a good way of talking to other yachts while out on the open sea (VHF has a short range). Not to mention all the weather and safety transmissions that can be received. Adding to this is all the broadcasts you can listen to while being far out from any DAB or FM transmissions. With enough persistence and will power it's also possible to send and receive (short) emails. As with all radio communications the antenna is an essential part ! Ham radio just add to this.

Ham radio, also known as amateur radio, can be a valuable tool for yacht owners and sailors looking to stay connected while out at sea. Ham radio enables sailors to communicate with other boats, shore stations, and even other countries using a network of radio frequencies. This can be especially useful in areas where traditional forms of communication, such as cell phones or satellite phones, may not be available or reliable.

Ham radio can also be a source of entertainment and information for sailors on long journeys. With access to a variety of frequencies, sailors can listen to music, news, and weather reports from around the world. Additionally, ham radio operators can participate in various contests and events that allow them to connect with other operators and hone their skills.

While operating a ham radio requires a license and some technical knowledge, it can be a rewarding and fulfilling hobby for yacht owners and sailors. With the ability to connect with others and stay informed while out at sea, ham radio can be an important part of any sailor's toolkit.

Installing email software

Installing email software on Raspberry Pi is possible, winlink is not fully supported for Raspberry Pi. While RPis are popular for rig control not all software development have shifted to Raspberry and it's associated set of Linux operating systems. I have installed the latest Pat software which is a client offered for RPi, including VARA for Pat and RPi. There are a some good instructional videos available, but I like text instructions with cut & paste commands that I can just paste. My github repo for amateur/ham radio have instructions and some helper files, some in the yacht-computer repo. My radio is a Xiegu G90 which I also have written some scripts for, like setting the dual frequency MF/HF maritime working channels. I also include some script to request data from the SignalK server, like location and time. Both needed for the RPi connected to the radio.

Backstay antenna - installation and testing

Testing the raw backstay

First one need to measure the impedance for the various frequencies. The Z is a complex impedance with resistive and capacitive/inductive components, but only the magnitude (length, a real number in ohms) is used hereafter. A lot of magic is hidden behind the scenes, like the fact that if imaginary part is positive there is a net inductance, while a negative is an indication of a net capacitance.

A SARK-100 antenna analyzer from China is used to measure the antenna (manual). As with all end fed antennas it show high impedance for large parts of the band. The backstay is a type of random wire antenna. For this antenna the reactive part is over the frequency range mostly inductive.

Secondly, how should this match the antenna tuner, most tuners struggle with this high impedance. A transformer (unbalanced to unbalance - or an autotransformer) could bring the impedance down within the tuner's range. A 1:9 transformer would bring 450 Ω to 50 Ω, while still keep the lowest valleys within the tuner's range.

Tesing the unbalanced to unbalanced transformer

A small unbalanced to unbalanced transformer is a autotransformer with a common ground connection. The signal is fed into a part of the coil while the antenna is connected at the top of the coil. The impedance change is a function of difference in the numbers of windings.

The impedance transformer, Unbalanced to Unbalanced (unun) shows some impdence variance over the MF/HF band. Using a 450 Ω resistor as a dummy antenna load the impedance at the input should be found to be around 50 Ω, the plot show acceptable variance below 20 MHz, with good fit at 8 MHz.

Without information about the torioid material it's not easy to predict the behavior at 25W power either. A DIY is probably a better solution, where all parts are well defined and documented.

To make things simpler I have adopted the G90's built in antenna tuner. While the tuner should be at the base of antenna and not at the coax at the radio it works well for short (10m) good coax (LM240). Testing have shown ok SWR seen at the radio, G90 has built i SWR measurement. While this is not 100% correct as the coax is also now part of the antenna. HF range seems ok when running digital modes, mostly email/winlink.

Testing the backstay and transformer together.

Installing the 9:1 unbalanced to unbalanced transformer provide a solution ready to be connected to the ATU-100 antenna tuner.

The antenna seen from the low impedance side of the the transformer is a nice fit for the antenna tuner. The ATU-100 can tackle 15-800 Ω impedance (it can choose inductance from 0.05 μH to 8.53 μH or capacitance from 10 pF to 1869 pF). Even without the tuner the SWR is not prohibitive high. However, an SWR above 5 is not regarded as a good fit. However, the whole band from 1.6 to 30 MHz is within the range of the ATU-100's capabilities.

The Xiegu G90's antenna tuner is also an alternative, which have performed well. The short coax from the G90 to unun does not interfere too much.

The antenna ground is AC grounded using 5 x 100 nF 3 kV capacitors, which effectively DC isolate the negative from the hull. Isolation is important with a metal (Aluminium) hull.

High voltage cable spaced using garden hose and strips. Isolator high enough not to be reached when holding onto backstay («your wife want curly hair?» someone once remarked).

The Q900 radio have a built in antenna tuner. This how it looks as seen from the radio. The 10 meter LMR 240 cable is part of the tuned antenna. Only 10 meter at relatively low frequencies should still be ok. At the end of the cable is a 1:9 unun and a high voltage cable go up to the backstay. The high voltage cable is also part of the antenna.

The SWR seems to be under control at 40, 20 and 15 meters. At 160 meters it tunes but the tuner is unable to get it below 4.5 . Any random antenna which a backstay is cannot be optimal for anything, but it can be useful for many frequencies. At 50 MHz I think the ferrite core take the better part of the 20 W pushed into it.

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