[GreenKeys] RTTY Journal help

[Harold Hallikainen]

Have a look at
https://pdf.datasheetcatalog.com/datasheet/exar/XR2206v103.pdf#page=9 .

The XR2206 is an interesting chip! It starts with a triangle wave
generator. The frequency is determined by a capacitor and resistor. The
timing resistor is switched between two external resistors by the logic
level on pin 9. There is a sine shaper that converts the triangle wave to
a sine wave. There is an analog multiplier (balanced modulator) where the
sine or triangle wave is multiplied by an external voltage. It is a
balanced modulator in that the output phase flips as the modulating signal
passes through its midpoint. There is also an open collector square wave
output.

In the 1970s and 1980s, I used the XR2206 in several products. I used it
as an AFSK generator using Bell 202 tones. I used it as a linear FM
modulator to generate subcarriers for broadcast studio to transmitter
links (110 kHz) and FM broadcast (67 or 92 kHz). I used it as a frequency
converter where the multiplier is used as a balanced mixer to convert a
subcarrier frequency (one of those listed above) to 455 kHz where it went
through an IF amplifier with ceramic filters, then an FM demodulator based
on a ceramic discriminator. The oscillator function in the XR2206 was the
local oscillator for this frequency conversion. These are all used in
https://bh.hallikainen.org/uploads/HfDrc190.pdf .

Harold


On Fri, October 4, 2024 8:37 am, Ken LoCasale wrote:
> Gang,
>
> I am trying to read an article from the RTTY Journal Dec. 1978, AFSK
> Generator about p.16, (attached). The generator uses an EXAR 2206 chip.
> On the hand drawn schematic, I cannot read the pinouts, especially the
> lower part of the chip around C3. Can't read the numbers or if there are
> connections or pass throughs. On the schematic some obvious crossovers
> are dotted for connections, some obvious connections are not dotted. 
> Right around C3 is the issue. Is anyone familiar with this circuit or
> have a better copy?
>
> 73,
>
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