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LED Matrix

Homemade > RTTY Decoder


Home-bulit year 1985

LED-Matrix-Tuningdisplay for RTTY

From Wilhelm Peter Schneider, DL6GW, Braunschweig
As described in the Journal ‘RTTY’, Edition 4/83

Introductory views to tuning mechanisms of teleprinter converters in the amateur radio from the year 1983.

It is already interesting to examine RTTY literature on tuning components for teletype converter. Here there is the most different variant of circuits, which occurred to technically experienced radio amateurs to this complex.

Before we get to the individual variations, first determine the following applies: a high-quality teletype converter can be compared only with a powerful tuning unit for optimal working conditions. It is rare that will not help transmit-receive operation of the teletype converter retuned to the received RTTY station needs. AFSK transmitter and receiver and are often constant only after a long burn-in frequency.

In the meantime it always applies to hold the teletype converter with the help of the tuning display by optimal trimming in its most favourable work area. A tuning display must already small modifications of the optimal tuning display and thus to the operator the possibility for the correction to the tuning open.
Each radio amateur with RTTY experience knows that the oscilloscopes tuning display with electron beam tube is to be arranged in the efficiency at the point of the scale of all RTTY tuning circuits.
Why with this clarity are different tuners built again and again?
This is in a sense of the word a genuine matter of price. Who does not need to look on the change, has anyway with the problems of the teletype converter tuning no problems. One carries it evenly, as they are offered together with a commercial teleprinter converter. Only who with small background and much self initiative would like to force for making its RTTY hobby, which also over the tuning display its thoughts to make will have itself.
A comfort: The experiences and discussions with other OM, which develop inevitably when building a RTTY system, are unpayable and full wealth. The success experience of the first RTTY QSOs with the built system remains unforgettable.

Which RTTY helps for co-ordinating the RF-receiver and the teleprinter converter are usual with radio amateurs?

  • tuning display using an oscilloscope
  • tuning display using LED-Matrix
  • tuning display using two lines of LED
  • tuning display using two LED
  • tuning display using two turning reel instrument

To the oscilloscope tuning display to are sufficient referred, it is also with distance the concerning the highest price circuit. Sometimes there is favourable gel geneses, an older oscilloscope to acquire however. If one has luck, the price is to a built oscilloscope tuning unit under that and the oscilloscope offers at the same time the possibility, to make electronic measurements at RTTY mechanisms.

Tuning mechanism with light emitting diodes - matrix

Over the tuning display, structured with a light emitting diode matrix, is to be reported in this work. It is well suitable for the tuning of a RTTY slave station, although the fine structures received Mark- and of space tones, which are overlaid by parasitic oscillations mostly on short wave, are not due to the bigger diode raster to detect .

Perfect alignment and tuning RF receiver and teleprinter converter with such a tuning unit ensured. Naturally one detects with a oscilloscope display, which operates with an electron beam tube, already in former times, when the received teleprinter station runs out out of the most favourable alignment of the own converter. The tuning of the RTTY slave station on a received RTTY station is naturally more difficult, if the tuning unit supplies few information for co-ordinating. A two-line LED display, how they is used e.g. also in the broadcast, is more difficult to handle and offers fewer upper view than an LED matrix. The recognition of - RTTY - signals is not pedantic. tuning units with only 2 light emitting diodes or 2 turning reeling instruments can be regarded in each case as rough behalf for the tuning of teleprinter stations (receiver + converters).

Operational principle of the LED matrix tuning display

In Fig. 1 is represented the operational principle as block diagram. From the Mark and space oscillations (1275 cycles per second and 1445 cycles per second or 2125 cycles per second) with the envelope detectors (3 diodes and a following RC element for the Mark and space signal, switched into series) the amplitude processes or envelope of the two oscillations are won and up-modulated with the help of controlled switches (HEF 4016) 150 cycles per second of square wave pulses.

The generator G produces the 150 cycle per second of square wave pulse, with which the CMOS switches connect the envelopes through to the outputs C and D in the circuit in the rhythm of the 150-Hz-cycle. The following bandpass filters let only with the envelope of the Mark and space oscillations modulated 150 cycles per second sinus oscillations through. They correspond in the envelopes the Mark and space sinus oscillations coming from the teleprinter converter.

These two amplitude-modulated 150 cycle per second oscillations reject the following diode display as X and Y signal. It was represented in fig. 1 only as matrix. The frequency transformation of the teleprinter frequency waves on 150 cycles per second was executed, because the UAA170-component, which heads for the diode matrix, operates at 150 cycles per second better than at e.g. 2125 cycles per second.

Figures of the Mark and space AF oscillations become with lower frequencies more sharply. The 3 input diodes for each channel increase the operating threshold of the tuning display and prevent that small parasitic oscillations illuminate the diode matrix.

Operational data (more "data" do I have not in my mind)

Power : +/-12 V
Power Input : approx. ca. 75-100mA

Functional block diagram of the tuning display and pictures of the circuit


Front view

Assembled module, component side

Detail view of the LED-wiring,
(Copper lacquer wire)



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