Optoinsulated PTT interface for digital modes (PSK - RTTY - AFSK)
An interface of only 1.5 centimeter X 1.5 centimeter, a square that contain 5 components, it allows you to switch intransmission the radio equipment in order to operate the digital modes.
In the old equipment transceivers to go in transmission, we must close the PTT switch to ground, be it for the front or rear microphones normal dedicated to a line input for digital modulations(PSK, RTTY, OLIVIA, MFSK, ROS, JT65, ecc).
This circuit makes it usable for QSOs in digital equipment such as Kenwood TS-2000, , TS-950, TS-940, TS-870, TS-450, TS-430; ICOM-706; YAESU FT-1000D that despite having CAT control of the frequency and settings need to automatically switch in the TX / RX of a "switch" that when the PC starts to modulate sends in the transmission equipment, and when the PC has finished modulate the message, makes wipe the radio reception. The switching time is obviously very fast, in the order of tens of microseconds.
When you ask the software for encoding and decoding of digital modulations to convey the message, it must inform the radio transmission to go and do it through the serial port, sending a high logic level the 7th leg RTS, the optocoupler at this point closes electrically PTT radio to ground, and the radio transmits, when the software has finished the message has to say on the radio to return to receive, then, again via the serial port, sends a low logic level pin 7, the optocoupler reopens electrically PTT from the crowd and then the radio will return to receive.
Another advantage is that the interface separates galvanically radio, computer, avoiding interference will from the computer to the radio and transient parasites from radios to computers.
The cost to implement the interface is less than 2 €, virtually the optocoupler 0.45, 0.20 for the LED, the resistance 0.10 to 0.15 oer the diode, the base to be engraved for the pcb is easily recoverable from some scrap size or more with a breadboard, however, a size so small even is sold, if we consider the price per sqm say that would cost about 0:30.
And 'possible to even realize it cost 0.00, the optocoupler you can safely recycle by switching power supplies for PCs, digital terrestrial, mobile and various alri home devices, in particular the 4N25 is virtually everywhere, probably in all appliances that surround us in house there will be a dozen. Same thing goes for the LED, the diode and the resistance that is even easier to find them on broken or malfunctioning devices.