Stefan's Radio Blog

AM Modulator

In Europe a lot of AM transmitters for medium wave have been switched off. When you want to listen to an old AM receiver a small AM modulator can help to fill the gap as your private radio station. Here is a first idea for such a small Transmitter:

As RF source a 12 Mhz crystal and a CMOS IC HCF4060 is used. It provides a very stable square wave signal of 750 khz that is used as carrier signal.

The two transistors BC546 and BF245C are used to modulate the carrier with an incoming audio signal. Finally a small LC circuit provides some basic harmonics suppression. With 30cm wire as antenna it should be possible to receive the signal over a distance of about 1 meter.

Working on HAM Radio Apps

Even though my year started with a business trip I found some time to work on my HAM radio apps. Last year I was busy with some other hobby so these apps were a little bit left behind.

APRS Windows Phone has got a fix of the faulty beacon counter. After some intensive testing during my business trip its now released in version I am currently working on a sound modem to support beaconing over a radio transmitter. So far I have got the modulator and NRZI working, next steps are to implement HDLC and AX.25 framing.

HF Propagation has problems with data provided by N0NBH now in a slightly modified format. The current parser sometimes can not digest the data properly. That prevents to display the complete data set. The parser is fixed now and I am working on the display part: Windows 8 is not any longer actively supported, for Windows 10 I want to introduce something like a "Gadget View".

APRS for Windows Phone - published

For Christmas I have published a new version of my APRS app for Windows phone. It comes with only a few changes and no major new features:

  • fixed reported speed
  • fixed wrong colors for some APRS symbols
  • added manual mode for position reporting
  • removed dynamic advertising and replaced it with a link to my blog
In the next version, planned for January 2017 I want to fix an newly introduced bug with the beacon counter and some other potential problems caused by my latest changes. Further down the road I want to support Bluetooth and a sound modem, so that APRS tracking can be used without connection to the internet. Please see also my roadmap for the app here.

60m band in Switzerland

I found this today on the USKA's news page: Beginning with 1st of Januar the 60m band will available for HAM radio operators ins Switzerland. Allowed power is 15 Watts EIRP.

This is the IARU band plan for region 1:

5351.5 - 5354.0 khz
CW, Narrow band modes, digimodes
5354.0 - 5366.0 khz
All modes, USB recommended for voice operations
5366.0 - 5366.5 khz
Weak signal narrow band modes

Before Mars

Prequel to National Geographic channel's "MARS": Two young girls are moving into a new town. In the attic of their  house they find an old HAM radio transceiver. With the help of an old man they can finally make a contact with the ISS. The 30 minutes video can be found here on YouTube.

If you want to contact the ISS yourself start with listening. The AMSAT-UK provides a short guide to the beginner on their website, more information is available on the ISS fan club website. National Geographic created also a Guide To HAM Radio.