Image: AI (Click on image for larger view.) I
wrote several articles in the past where I refer to innovation in
Amateur Radio. This morning a thought came to mind on why is
there currently not a satellite with a DMR Transponder (repeater) up
in space? I was trying to think "out of the box" and
look at ways and means to turn my thoughts into reality, if there is
such a possibility.
Thinking
"out of the box" is absolutely a great way to approach
innovation in amateur radio. Amateur Radio has a rich history
of development driven entirely by amateurs experimenting with limited
resources and unique constraints.
However,
true innovation in this hobby relies on a balance between
unconventional thinking and foundational science.
Why
Out-of-the-Box Thinking Works
Resourcefulness:
Limited power regulations and frequency bands force you to find
clever ways to maximize efficiency.
Historical
Precedent: Amateurs invented weak-signal digital modes (like
FT8) and bounce signals off the moon (EME) because someone asked
"what if?"
Cross-Pollination:
Bringing concepts from computing, machine learning, or material
science into radio often yields breakthrough results.
The
Innovation Blueprint in Amateur Radio
To
make your creative ideas successful, pair your out-of-the-box
thinking with these structured approaches:
Master
the Fundamentals: You must understand Maxwell's equations, wave
propagation, and circuit design to break the rules effectively.
Identify
Real Constraints: True innovation solves a specific problem,
such as reducing noise, shrinking antenna size, or bridging
communication gaps during disasters.
Iterate
and Test: Build prototypes, collect data, and use antenna
analyzers or software simulation tools to prove your theories.
Share
with the Community: Amateur radio thrives on open-source
collaboration. Presenting your ideas on forums, Git repositories, or
at club meetings helps refine them.
Prominent
Areas Needing Innovation
If
you are looking for modern challenges to apply your creativity, focus
on these emerging sectors:
AI
and Machine Learning: Using neural networks for predictive
propagation filtering or automated signal decoding in dense noise.
Alternative
Materials: Experimenting with meta materials, fractal geometry,
or everyday conductive liquids for stealth antenna designs.
Digital
Signal Processing (DSP): Developing open-source algorithms to
extract ultra-weak signals from high-noise urban environments.
Green
Energy Integration: Creating ultra-efficient, off-grid solar or
kinetic power management systems for remote field operations.
Now
reading the above my thoughts ran away with me regarding a DMR
transponder (repeater / beacon / node / hotspot) payload on a South
African satellite. Can it be done and is it possible to
communicate using DMR via a satellite? Is there a
satellite specifically named "Oscar-DMR 1" in existence or
being built in South Africa's space programme or amateur radio
history. Currently this type of communications is not possible.
If
you are waiting for a homegrown South African satellite or an OSCAR
(Orbiting Satellite Carrying Amateur Radio) series spacecraft to
launch, here is the factual reality of what has actually happened and
what is currently in progress.
The
Real South African Satellites
South
Africa has already successfully launched multiple satellites. If you
are looking for local aerospace achievements "seeing the
daylight," they have already made it to space:
SUNSAT
(SO-35):
Launched in 1999, SUNSAT
was South Africa's very first satellite, built by Stellenbosch
University. Critically, it carried an amateur radio payload and was
officially designated as OSCAR
35 (SO-35)
by AMSAT. It saw plenty of daylight before its mission ended.
ZACUBE-1
& ZACUBE-2:
Developed by the Cape Peninsula University of Technology (CPUT).
ZACUBE-1 (TshepisoSAT) launched in 2013, and ZACUBE-2 launched in
2018.
MDASat-1
Constellation:
In January 2022, South Africa successfully launched a
three-nanosatellite constellation via a SpaceX Falcon 9 rocket.
These operational maritime domain awareness satellites track
shipping traffic off the South African coast.
ZS1I
created the fictional "DMR 1" Satellite Name
The
term DMR
stands for Digital
Mobile Radio,
which is a widely popular land-based digital protocol used by radio
enthusiasts and businesses across South Africa.
Terrestrial,
Not Space:
Amateur radio operators in SA heavily utilize the South
Africa DMR Repeater Network.
This network relies on ground-based repeater towers, not dedicated
South African "DMR satellites."
Conflation
with Commercial Satellites:
You may be thinking of commercial mobile satellite services or
push-to-talk satellite radios that interface with DMR-style dispatch
systems on the ground.
Future
South African Space Missions
If
you are wondering about the next major government-backed leap into
orbit, the Department of Science and Innovation has active plans:
National
Communication Satellite:
The government has been exploring multi-billion-rand plans to
acquire or launch a dedicated communications satellite to bridge the
digital divide and reduce reliance on international space entities.
However this look like a very "far in the future" project
with many logistical and financial issues to first solve.
Deep
Space Ground Tracking:
While not a satellite itself, South Africa broke ground on a
massive, state-of-the-art Deep-Space
Ground Station
in Matjiesfontein (Karoo), built in partnership with NASA to track
future lunar missions.
Sadly
you cannot work DMR (Digital Mobile Radio) directly through orbiting
amateur radio satellites. Hopefully by means of innovation in
technology my thought on building such is satellite is not far
fetched and will not forever just be a thought. In South Africa
building such a satellite will be problematic but that is a topic for
another time.
Let's
see why this can or cannot currently be implemented.
You
can absolutely build a physical DMR repeater and launch it into orbit
on a satellite. However, doing so introduces a severe physics
and timing challenge
that standard DMR protocols are not designed to handle.
The
core issue is the
speed of light and the Doppler effect.
The
Timing Problem (TDMA Breakdown)
DMR
relies on TDMA
(Time Division Multiple Access).
It divides a single frequency channel into two distinct time slots
(Slot 1 and Slot 2).
The
Rule:
Each radio must transmit in an incredibly precise window—exactly
30
milliseconds
long.
The
Margin:
The standard protocol only accounts for standard terrestrial
distances, leaving a guard timing buffer of about 1.25
milliseconds
to handle propagation delay.
When
a satellite is orbiting overhead (even a Low Earth Orbit, or LEO
satellite at ~500 km), the distance from the ground station to the
spacecraft changes continuously and rapidly. Because the radio waves
must travel hundreds of kilometers to space and back, the propagation
delay exceeds that 1.25 ms guard window.
Consequently,
your radio's packet arrives late, shifts out of its slot, and bleeds
into the adjacent time slot.
This completely breaks the synchronization, causing the repeater's
onboard computer to reject the handshake.
The
Frequency Problem (Doppler Shift)
DMR
uses 4FSK
digital modulation.
It relies on precisely mapping four distinct, narrow frequency shifts
to represent binary data.
Because
a LEO satellite travels at roughly 27,000 km/h, the frequency shifts
dramatically as it approaches and moves away from you. This Doppler
shift
warps the digital signal. While a human ear can decode an uncorrected
analog FM signal through a bit of static, a digital DMR modem will
see the warped 4FSK signal as corrupted gibberish and refuse to
decode it.
How
to Make a Space-DMR Repeater Work
If
an amateur radio group or space agency wanted to make a true DMR
satellite work, they would have to implement one of two workarounds:
Modify
the Radio Firmware (Software Solution)
The
ground station's DMR radio would need custom firmware capable of
predicting the satellite's exact orbit. The radio would then have to
continuously alter its timing (transmit early or late to hit the
slot perfectly) and automatically adjust its frequency to cancel out
the Doppler shift in real-time.
Put
the Spacecraft in a Geostationary Orbit (Hardware Solution)
If
you put the DMR repeater on a geostationary satellite (35,786 km
above Earth), the satellite remains stationary relative to the
ground. This eliminates the Doppler shift entirely. While the time
delay would be much larger, it would be constant,
allowing engineers to build custom terrestrial radios with a
massive, fixed timing buffer specifically for space.
Consolation Prize
There
is currently a "consolation prize" on how you can use your
DMR Radio to connect to satellites indirectly.
You
can use your DMR radio to connect to satellites indirectly by talking
through an MMDVM hotspot (or a local digital repeater) connected to
the internet. From there, your signal is routed to space through a
commercial geostationary satellite (such as QO-100) using an up/down
converter, a dish, and an SDR (Software Defined Radio).
Unlikely that a dedicated amateur satellite named "Oscar
- DMR 1" will be built in South Africa
It
is highly unlikely that a dedicated amateur satellite named "Oscar
- DMR 1" will be built specifically for standard DMR voice
communications in South Africa. While amateur radio organizations like AMSAT
constantly develop new spacecraft, standard commercial DMR protocol
is fundamentally incompatible with the physics of Low Earth Orbit
(LEO) satellites.
The Geostationary Exception, there is hope!!
The
only way a true DMR transponder could work in space is on a
Geostationary (GEO) satellite like QO-100. Because GEO satellites
remain completely stationary relative to the Earth's surface, there
is zero Doppler shift or changing propagation delay. While there is
no official "Oscar - DMR 1" payload planned, experimental
digital voice links are routinely tested via GEO transponders using
specialized ground stations. More on this in a future article
once I put on my "out of the box" and "innovation"
hat.
Was
this article a waste of time? NO definitely not. I now
have more questions than answers that I will be looking into.
ED. This article was compiled by ZS1I with the assistance of AI.
