kevin's website

amateur radio

I am currently in the process of acquiring my amateur radio licence but I have still had a chance to play around a bit. On of my biggest interests is software defined radio which can be super powerful and makes it very easy (and cheap) to visualise the RF spectrum over really wide bandwidths.

Why amateur radio is cool

Here is a collection of cool stuff that you can do with amateur radio.

This excellent talk by Gerard de Jong goes over a lot of cool stuff you can do with sdr and amateur radio.

Here are some of my favorites (not all of these are from the above video):

You can also use a raspberry pi to transmit radio signals. Here are a few projects that allow you to do that.


Some websites with good resources:

Some great content on youtube (mainly sdr stuff):



The rtl-sdr comes from a digital TV chip that was "hacked" to receive a much wider range of signals than originally intended and now we have really cheap (receive only) sdrs

The rtl-sdr dongles can do hf with some work arounds, but are most comfortable in the range of 500 kHz - 1766 MHz, Depending on what sdr software you use it can sample up to 24MHz but is most stable at 2.4MHz:

the rtl-sdr-blog radio has a great datasheet

SDR software

Here are some SDR softwares. Personally, I User SDR++ and GQRX.


I have not dedicated the time to learn gnu-radio but it seems like an extremely powerful toolkit for processing of RF signal (and signals in general).

GPS is a very cool concept for an open source off-grid mesh network, powered by LoRa-WAN, that uses relatively inexpensive microcontrollers.


I have a baofeng uv5-r for VHF/UHF

A lot of satellites and even the ISS use VHF/UHF

Security Companies

In south africa a lot of radios targeted at security companies use the 464 and 446MHz UHF bands at 0.5 watts to avoid the need for a licence.


you can use the sigid wiki to help identify a signal and aid in decoding it.


SSTV stands for slow scan television.

SSTV on Wikipedia

The ISS sometimes transmits an image over sstv that you can receive and decode.


what is ft8?


APRS stands for automatic packet reporting system.

see APRS on Wikipedia.

Curious Electron article

aprs on the Baofeng uv5-r

In order to use aprs on the baofeng you need the appropriate cable and some software

The cable: BTECH APRS-K1 Cable

The software: aprs droid

Aprs required a TNC (Terminal Node Controller) in order to decode the signals.

TNC and AX.25 resources

The aprs droid app is able to process the audio and decode aprs packets.

I have yet to try this out in real life as I do not have the appropriate cable. There are some resources on making your own cable:

Here is also a really cool mobile aprs digital repeater built into a pelican case.


to make any of these antennae you can just search "$ANTENNANAME calculator". there are many different calculators that can assist in working out the measurements for the antennae.


The Yagi-Uda antenna has a bit of a thomas edison/nikola tesla telephone thing going on, it seems that Uda was largely responsible for it's creation but He worked under Yagi and thus the Yagi-Uda antenna was born. It is most commonly just referred to as a Yagi.

Yagi-Uda on Wikipedia

The only decent calculator I could find was the changpuak yagi-uda calculator based on the Rothammel / DL6WU design as well as the changpuak yagi-uda calculator based on a constant spacing of 0.2 λ

It seems that the yagi-uda antenna is fairly complex and requires a good bit of fine tuning and adjustment with iterative analysis.

The designs available online are therefore a lot more like "recipes" and there can be differences between 2 yagi-uda designs for the same frequency. Here is some history about the DL6WU design.

Cross Dipole

4 dipole antennae angled at 30° arranged in a square across from each other.

A cross dipole is omnidirectional.

qsl: designing a cross dipole for vhf and noaa sattelite receiving

Planar Disk

planar disk antenna build guide pdf


turnstile antenna design for 137MHz

Turnstile antenna on Wikipedia

V Dipole

V Dipole for 137MHz NOAA sattelites


QFH stands for quadrifilar helicoidal antenna

online calculator 3d printable bracket for 137MHz on thingiverse




different types of coax are rated for different losses at different frequencies.

you can use online calculators (like this old one or this one by times microwave systems) to see what you need for your frequency and length.

different kinds of coax for different purposes