kevin's website

amateur radio

Why amateur radio is cool

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

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

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

Resources

Some websites with good resources:

Some great content on youtube (mainly sdr stuff):

SDR

rtl-sdr

rtl-sdr comes from a digital TV chip that was hacked and now we have cheap sdrs

the rtl-sdr dongles can do hf with some work arounds:

SDR software

GNU-Radio

GPS

very cool concept for an open source off-grid mesh network using relatively inexpensive GPS radio microcontrollers using the LoRa protocol

meshtastic.org

VHF/UHF

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.

an example of a radio with some no-licence bands pre programmed in
an example of a radio with some no-licence bands pre programmed in

Modes

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

SSTV

SSTV stands for slow scan television.

SSTV on Wikipedia

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

FT-8

what is ft8?

APRS

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.

antennae

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.

Yagi-Uda

Yagi-Uda on Wikipedia
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

turnstile antenna design for 137MHz

Turnstile antenna on Wikipedia
Turnstile antenna on Wikipedia

V Dipole

V Dipole for 137MHz NOAA sattelites

QFH

QFH stands for quadrifilar helicoidal antenna

online calculator 3d printable bracket for 137MHz on thingiverse

Components

connectors

cable

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