Technology & Updates
The Radio Delta AM knowledge desk: transmitters, antennas, audio processing, RF monitoring, propagation tests and real listener reports — explained so others can learn, rebuild and experiment.
Shortwave radio technology as a practical workbench
This page is our shortwave radio technology workbench. It is not just a list of old equipment, but the place where we explain how Radio Delta AM works: why a frequency behaves differently by season, how a transmitter becomes a usable AM signal, how audio processing affects intelligibility, and how listener reports help us improve the station.
Shortwave is not a fixed cable. It is a changing radio path through the ionosphere. That is why we combine workshop experience, transmitter measurements, KiwiSDR recordings, local monitoring and reception reports from real listeners. The goal is not only to reach farther, but to understand what really works on air.
Radio Delta Knowledge Desk
These are the technical themes we are building into deeper articles and practical updates. The aim is simple: explain the craft behind shortwave broadcasting in a way that helps other people test, learn and build.
Frequency & band tests
A shortwave frequency is never “good” or “bad” by itself. It depends on season, time, distance, solar conditions and noise.
- Why 49 metres works well on summer evenings
- Why 75 metres becomes stronger in winter darkness
- How skip zones and listener activity affect real choices
From RF power to useful coverage
The antenna decides how transmitter power becomes field strength. Height, angle, ground system and band choice matter.
- Inverted-V behaviour on 49m and 75m
- Verticals, radials and low-angle radiation
- Why local coverage and DX are not always the same goal
Carrier, modulation and reliability
AM is simple to receive, but not simple to transmit well. A stable carrier and clean modulation are essential.
- Tube transmitters, solid-state stages and RF monitoring
- Positive and negative modulation peaks
- Why reliability matters more than maximum power
Processing for shortwave AM
Shortwave audio must survive fading, noise and narrow bandwidth. Processing is about clarity, not just loudness.
- Orban and software processing experiments
- Speech intelligibility and music density
- How the waterfall, receiver AGC and ears all tell a story
KiwiSDR, local checks and recordings
We do not judge a transmission from the studio alone. We listen remotely and compare recordings in real conditions.
- Remote receivers across Europe
- Comparing signal, noise and fading over time
- Using recordings to verify real-world improvements
Reception reports as measurements
SINPO reports are not just nice messages. They help us understand coverage, distance, noise and listener experience.
- Reports become map pins and technical feedback
- Distance, time, frequency and antenna data matter
- The Listener Map becomes part of the measurement system
Current working model
The detailed broadcast times belong on the Program Schedule page. Technically, the current working model is simple: 49 metres in summer, 75 metres in winter, and 25 metres for special DX broadcasts. The summer focus is 6190 kHz, with 6170 kHz as a reserve. In winter, 3985 kHz remains the classic evening band. 6040 kHz is mainly a winter daytime option, and 12085 kHz is kept for special DX tests.
The important question is not only which frequency is active, but why it works at that moment. That is what we want to document here: the technical reasoning, the test results, and the lessons that others can use.
Looking for times and frequencies? The current on-air planning is listed on the Program Schedule page.
View Program ScheduleHow we test a shortwave broadcast
A good test is more than turning on a transmitter. We compare several signals and sources before drawing conclusions.
Choose the band
We select a frequency based on season, time, expected coverage area, known QRM and earlier listener reports.
Monitor locally
We check carrier stability, modulation, audio level, RF behaviour and how the signal sounds on normal receivers.
Check remotely
KiwiSDR and off-air recordings show how the signal behaves away from the transmitter site and across Europe.
Compare reports
SINPO, distance, antenna type, receiver and time help us compare real reception instead of guessing from theory.
Technical Spotlights
Radio Delta engineering history — classic transmitters, audio processing and the experiments that shaped the station.
R&S SK050 with the Orban 9200
“A robust HF transmitter from the Radio Delta collection — preserved close to its original broadcast character.”
The SK050 was one of the practical transmission workhorses from the earlier Radio Delta years. With wide HF coverage from 1.5 to 24 MHz and a reputation for stability, it shows how classic broadcast equipment can still produce serious shortwave coverage.
Breakaway software audio processing
“Software audio processing showed how much clarity and presence could be shaped before the transmitter.”
Breakaway was an important experiment in the Radio Delta audio chain. It showed how software processing could create a loud, clear and detailed AM sound, while still keeping the signal listenable on real shortwave receivers.
Telefunken S2525/3 on air
“A great shortwave transmitter with very nice audio quality.”
The Telefunken S2525/3 was used often on the 48 metre band. Its stable design, synthesized coverage and strong audio performance made it a practical and reliable transmitter for real weekend broadcasting.
R&S SK080 refurbished
“A beautiful vintage AM transmitter brought back to life by Radio Delta engineers.”
The R&S SK080 is classic broadcast engineering: heavy, analogue and full of character. With its internal modulator and tube-based design, it connects Radio Delta’s present experiments to the golden age of AM broadcasting.
Technical archive: older transmitter, antenna and audio processing posts remain part of the Radio Delta technical history. New deeper updates will be collected under Technology & Updates.
Explore Technology & UpdatesBuild along: videos & experiments
Real checks and real on-air results — so others can learn, rebuild and test along.
Transmitter / RF build & checks
Practical steps, measurements and what to watch for: audio-to-RF, modulation, monitoring and reliability.
On-air testing & monitoring
Real on-air runs, practical checks, and what we learn from listener feedback and remote reception.
Help improve the signal. Send a reception report with SINPO, receiver, antenna, location and frequency. Your report becomes a Radio Delta Hero pin and helps us measure real propagation.
Send a reception report