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Junior 1 von Stampfl


Heinz Stampfl (HB9KOC), who is well-known because of his hand-made precision Morse keys,  has also a heart for radio listeners. For some time now, Heinz has been tinkering with several receiver concepts, which he also shows on his web site. It is his aim to be able to offer these projects as assembly kits in the future.  But unfortunately, this is not as easy as it sounds. On the one hand, enough kits have to be produced for the project to be profitable, and on the other enough buyers have to be found as well. These days, when everything can be bought as "plug and play" such a projects bears a big financial risk.

Despite these risks, Heinz Stampfl now would like to offer a small kit: the Junior 1.

Description of the Junior 1 kit (by Heinz Stampfl)

The Junior1 one is a double conversion shortwave receiver, which can easily and quickly be assembled.  No alignments, no measuring equipment or special knowledge of high frequency technology are necessary. Junior 1 is meant to be a small project for the young and for the young-at-heart listeners, who are interested in radio technology.
The main part of the radio is an AM/FM-IC from the former DDR (East Germany), the A4100D, which was especially developed for battery-powered devices.  According to the data sheet, the A4100D has a particularly good signal/noise ratio for AM and FM and only requires little external wiring.
The tried and tested NE612 is used for the front end mixer and for the oscillator.  It is possible to connect a low-resistance dipole with a coil. Tests, which were run during the early evening hours, surprisingly showed no overloads when using a G5RV.  If you want to use the Junior 1 as a portable, 1.5m of Litz wire should be enough for the high-resistance antenna connector.
For cost-reasons, the 1. IF-filter comes as a ceramic resonator. Because of its high bandwidth, it does nothing for the near-selection of the radio and so no effort was spared for the 2. IF-filter. The conversion oscillator (10.245 MHz) is a monolithic and adjustment-free component. If you are fond of experiments, you can design you own favorite frequency range by altering the input circuit and the oscillator stage. A LED is used as a field strength indicator.  You can connect a A-meter with a suitable series resistor.
In the original design, the input circuit and the oscillator are mainly for the 49m/41m band. A local oscillator makes SSB-reception in the 40m ham radio band possible. But let me make clear: Due to the high 1. IF-frequency and the varactor diode of the LO, SSB reception is a little adventuresome and nothing for experienced DXers.  But nonetheless, it is certainly exciting for someone who has never listened to ham radio operators.  
Power consumption and the supply voltage range is from 7.5V to 16V at approx. 70mA. A LM380 with a 4 Ohm loudspeaker makes for good reception.
In conclusion, the Junior 1 has a deliberately simple concept, but still is an effective receiver, which shows good audio, high selectivity, high sensitivity and at the same time good signal processing.
The case is made of blue anodized aluminum. The labeling is etched with laser. 



Heinz Stampfl was friendly enough and put a Junior 1 at my disposal for testing purposes.  The radio came assembled, though, because I did not have the time for putting it together.

As can be seen in the picture, the receiver has the serial number 001. It is the first radio which comes out in the open.

I had the Junior 1 on my table for over a month and used it at every opportunity.  I mainly used external antennas for the Junior 1. To make this possible, I added a BNC-connector. To test the potential of the kit, I wanted to avoid interferences in my house. On the front of the radio, you can plug in a piece of wire as an antenna with a banana plug. There is also a connector for grounding the radio. To avoid overloads, I used a switchable attenuator and because the Junior 1 is not made for highly effective antennas, I used a 10 - 20dB attenuation.  Interestingly, there were no overloads. There were hardly any "ghost stations" to be heard and only during the early evening hours and very weak at that. Because the radio is a simple do-it-yourself project, the Junior 1 needs a little warm-up time because the oscillator drifts a little. You can power the receiver with either a 9V battery or an external power supply with 7.5V to 16V.

Because the frequency is not shown, tuning is a little unusual. Starting with the rotary knob all the way to the left,  you have to turn it five times to reach the 40m ham radio band. Then you switch to SSB and scan slowly and carefully through the band with the big tuning knob until you hear a station.  After that fine tuning is done with the left -0+ knobs until you hear the station clearly. With a little practice and patience, it works rather well. The low noise and the bright and intelligible audio are surprising.  Selectivity is good enough to receive SSB signals in the 40m band.  If you tune further down, you will come to the 41m broadcast band.  Then you select AM again and can listen to programs.  Comparisons with other radios showed rather high sensitivity.  Very weak stations on a clear frequency could be listened to well and intelligibly. It is clear that the Junior 1 is no DX machine, but for such a small radio, reception is rather good.


Heinz Stampfl dared to start an interesting do-it-yourself project. For young beginners, who are interested in building a radio themselves, the Junior 1 is the ideal kit.  But also for experienced listeners, the kit is certainly interesting.  For assembling the radio, you need interest and some experience with a soldering iron. It remains to be hoped that the Junior 1 will become a success. Perhaps then a kit will appear on the market, which Heinz will proudly present on his web page.

The Junior 1 kit is now available at "Stampfl Morsetasten" and costs CHF 72.-

Beginning in 2015, the Junior 1 will be available in the shop of the "Funkamateur" magazine.

The assembly instructions can be downloaded here.

posted November 22, 2014



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