A SPARTAN MARINE RADIO RECEIVER
(1984)
Really freezing cold weather and there Martin stood very Spartan in the middle of winter barefoot next to his sailing yacht!
Really freezing cold weather and there Martin stood barefoot next to his sailing yacht in the middle of winter
Once Martin had had a good office job with a suit, tie, and polished shoes. But one day he stopped coming to the office and went to live very Spartan on a second-hand sailing yacht. Stress and an indecent boss, it had been enough. No shoes anymore, very Spartan on bare feet, he didn't want to waste money on unnecessary shoes! He only had a pair of flip-flops for when he had to go to town or a store!
Martin wanted to buy a radio to receive weather and marine warnings by the coastal stations. But the commercial radios are way too expensive, consume too much power and are so big. And a company had to install that and the entire backstay had to be replaced, that had to become an antenna. Could I not make such a radio and less expensive? And simple and not too big? Just for weather reports and navigation messages for shipping. And maybe something for direction finding of radio beacons.
This would have been a very suitable marine radio for Martin, but it was too expensive...
Very Spartan in the middle of winter on bare feet!
We went on board, no shoes allowed, barefoot!
Everything perfectly organised. Very sober, simple and solid and super clean! No television, no heating. Only an oil lamp and a gas lamp. No VHF marine radio, just flares. Martin didn't want to travel the world. Only the Netherlands, Denmark, the North Sea, that's enough. I looked at our ice cold stiff, numb red toes on the ice cold deck. Very Spartan and very extreme to go barefoot in the winter cold! Suddenly I understood what Martin wanted, a Spartan marine radio, very simple, without comfort and challenging to operate! And I was the only one who could make him such a Spartan shipping radio!
The idea of making the frequency scale. A simple, well-arranged table!
The biggest problem is an easy tuning mechanism!
When I got home I quickly forgot the Spartan cold. I was already thinking of a super and expensive crystal filter and a frequency stabilizer for the VFO and a frequency counter with an impressive power-hungry display. Completely wrong! It had to be very Spartan.
How am I going to tune that Spartan shipping radio and how do I make a simple frequency readout? A tuning capacitor is mechanically very difficult and is large. I found a simple solution! A 10 turn potentiometer with a knob with 1000 divisions and varicap diodes, that's what it had to be! With a simple table that converts frequencies to values from 0 to 1000 that you then have to set. An excellent Spartan solution for tuning and frequency readout. Steps of 100 kHz are sufficient to find the coast station. No, no comfort, but simple and challenging!
The Spartan marine radio receiver!
Fine tuning, 10 turn for tuning, volume control and a few switches.
And on the left a shielded ferrite antenna for the direction finding of radio beacons! Extremely simple and easy!
Simple direct conversion receiver!
How should the rest of the receiver be??? Leave everything out... Of course that comes at the expense of comfort and performance.
So no complex superhet single sideband receiver, but a simple direct conversion radio. Then you also hear the unwanted sideband, but that is practically never a problem. Usually nothing can be heard there or at most a few weaker signals. But in your everyday life you often have disturbing background noises during a conversation, don't you? And yet you can follow that conversation just fine! Double sideband, with a negative mindset that's a huge compromise, but in practice it's no problem at all and... it's so much easier!
No automatic volume control, just a simple button as a volume control works fine in practice. And Martin only uses it in harbours, so a small loudspeaker and low audio power is sufficient. At sea you have so much noise that you have to use closed headphones which attenuate the sounds of the lapping water. That is also the case with a "real" marine radio receiver!
No high-frequency stability PLL, every now and then tweak the tuning a little with the fine-tuning! Everything very Spartan!
The diagram
The diagram explained in more detail.
The FET at the antenna input ensures a high input impedance. A short antenna wire of 50cm to 1 meter directly at the antenna input is therefore sufficient to receive the coast stations. At the entrance you will also see a tuned circuit for the preselection. This is a huge improvement for a simple receiver and very simple. The diodes 1n4148 protect the FET against excessive peak voltages. The 27 pF capacitor at the gate of the FET is a drawing error, it must be a 60 pF trimmer.
After the FET comes a low-pass filter. This attenuates shortwave signals. Otherwise you will hear interfering signals caused by shortwave broadcast stations mixing with harmonics from the VFO. Tuning is done with the 10k 10 turn potentiometer in combination with the varicap diodes BB212. This is much simpler than a mechanically difficult to mount tuning capacitor, but less stable. But I think positively, the advantages far outweigh the disadvantages!
The IC SO41P is the mixer and at the same time also the VFO. Of course you would use a NE612 nowadays instead of a SO41P. It is specially made for this purpose. The HF signals are mixed to audio frequencies. The VFO is tuned to the receiving frequency. And then there are two low-pass filters that also amplify about 20 dB. Finally, an LM358 as audio amplifier for the loudspeaker.
Then there is also a second receiver with SO41P. This one is for the longwave radio navigation beacons between 280 kHz and 434 kHz. With a ferrite antenna as a direction finding antenna. You have to tune this with a variable mica capacitor for maximum signal. As an oscillator coil, such a small yellow intermediate frequency transformer is used from an old transistor radio.
And there is another switch as a tone control to attenuate the low tones a bit. Then the sound is better when using headphones.
The current consumption is only 20 to 30 mA. That is 30x less than a "real" receiver!!!
Two printed circuit boards with a shielding can around the VFO in a standard aluminum box.
All very simple, what a difference with a real professional receiver!!!
A real Spartan shipping receiver, very simple, small and with very little power consumption!
I did it, the Spartan receiver had cost me little money. Admittedly, I had quite a few parts in the junk box like that expensive 10 turn potentiometer with knob. A standard aluminum case. A reasonably nice cabinet is important. And making holes in aluminum is very easy. Text with a pen and cover with transparent foil. Making printed circuit boards was still the most work. But very nice. I was proud of myself! A real Spartan marine radio receiver, very simple, small and with very little power consumption!
It was nice to walk a few hours barefoot on the ice where I sailed during the summer!
But... never try that when it is colder than -3C to -4C (26F)!
That Spartan marine radio receiver and Martin, it was love at first sight!
That Spartan marine radio receiver and Martin, it was love at first sight! A wire of less than 1 meter and... many coast stations were received, also the more remote English ones. The sound quality was great! Martin had a Nautical Almanac! This enabled us to find broadcast times and frequencies of weather reports. And on 2182 kHz it was a huge bustle of all kinds of announcements. The frequency stability was not so good, but thanks to the fine tuning this was easy to correct. Martin had a lot of trouble tuning in to SSB stations, everyone has to learn that first. No problems with signals on the unwanted sideband. The tuning was easy with the table, despite the large 100 kHz steps. Interpolating was not difficult, Martin was quite intelligent.
The lighthouse of Vlieland with the radio navigation beacon "VL".
We did some direction finding of beacons with the ferrite antenna. The beacon "VL" on the lighthouse of the island of Vlieland and another beacon. We found our position in the harbor within 3 nautical miles. Great when it's foggy. And you can also measure the direction of 1 beacon, which is why Martin found the beacon on Vlieland so important. Measure the distance you have sailed from when the beacon is 45 degrees forward until it is transverse to you. The distance you have traveled is the distance to the beacon. And of course you also know the direction. Unbelievable so many beacons we could receive. Also weaker, more distant beacons. Using the Nautical Almanac we were able to determine the frequencies and positions of the longwave beacons. And I still listened to Morse code messages for shipping. Faded glory, Morse code was hardly used and was abolished 15 years later.
Martin used the receiver for many hours every day. He knew all the broadcast times and frequencies of the coastal stations. Tuning into SSB stations had become routine. On a few occasions he has used bearings on radio beacons during fog. And he also listened to amateur radio chats at 80 meters. Crazy people who have a special language with Q abbreviations and say "best 73" while it isn't 1973 anymore. Are radio amateurs crazy people? I got the receiver back 25 years later, when there were other means of communication such as a smartphone and navtex radio. But it still works fine now, 35 years after it was made!
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