438
Item nr.


Gerard GolfRekker Micro transmitter

Little gem to keep old radios running.


Data for Gerard GolfRekker
ProductionThe Netherlands, 2016.
Price was ca. €35.
BandsMW.
Semi-
conductors
5 ICs: CD4053B (modulator), CD4060B (crystal oscillator plus binary divisor), CD4046 (Oscillator), CD40103 (programmable divisor), LM358 (audio amp), 4 diodes (rectifier), P229B (radio IC).
CabinetWood. Size 22x15x4cm.
PowerAC 230V @ 2W.

The Design

A lot of AM stations close down, and this little machine will provide AM radio signals in your house to keep your old tube sets glowing.

The device is based on the PLL transmitter, the Ottozender. Reneke provided construction kits including a power supply. I scrapped an Addex AD87 radio to include an FM receiver in the box. The device now receives ultra short waves (as selected by the Addex dial) and transmits the sound on medium waves (as selected by the Ottozender's dipswitch). So, basically it makes waves longer (for all who don't care about amplitude or frequency modulation), hence I call it a Wave Stretcher, or GolfRekker in Dutch.

Operation: The jack on the edge is for the antenna, and the next two are input jacks to connect line audio. Then comes the modulation depth control and a switch to connect or disconnect the FM radio as a source. The red light shines when the set is connected to the mains (and works). You can open the box and tune the FM radio and listen to the program with the built-in monitor speaker.


Obtained2/2016 from Home construction.
Condition8.
Value (est.)10€.
Sound samplePLAY SOUND   Most of my radios sound better from an Ottozender that from a "real" transmitter (if you can find one). I'm satisfied with the quality of modulation, but there is a lot of side noise like hum and static. Nana Mouskouri was reproduced from MP3, transmitted with the GolfRekker and received on a Grundig 2100.

This Object

The package of Reneke contains a PCB for the Ottozender, all the parts (except a few that are not really necessary) and even a transformer. After soldering the board, I tested to see if the Addex makes a suitable signal source, which it does.

I also measured the supply current of the Addex (20mA) to compute the dropping resistor necessary to supply it from the Ottozender board. This turned out to be 510 Ohms, which I had in store, and I mounted it and also included a 1000uF elco on the low end. Then I could fix the Ottoboard, Addexboard, speaker, switch, antenna, dropping resistor, and smoothing cap in the cardboard box in which the parts were sent to me.

Cardboard is not the most firm and suitable material, so, after the cardbox had proved its size to be suitable, I bought a small wood box and mounted everything in it. Also, for 1 euro I found a nice television speaker to serve as a better monitor.

I set the transmitter to 675kHz to replace the ceased Radio Maria on my dials, and it works very well with a 2m antenna. Together with my other Ottozender, I can set it up for stereo broadcasts. To receive it, you'll need two almost similar radio's, tuned to 675kHz and 828kHz. Unfortunately, the Ottozenders are very sensitive to line hum.

In May 2018 I increased the gain of the AM amplifier by decreasing R6. This 22k resistor is part of the negative feedback circuit of the LM358 and with a 4k3 bypass, the feedback is reduced so the gain increases.


Part of Gerard's Radio Corner.
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