[RTTY] FSK interface circuit troubles

[Bill, W6WRT]

Hi Alfred:  I suspect your problem there is with the transistor. Not
that it is bad necessarily, but mis-wired. Transistors come in a
variety of pin configurations and it is real easy to get it wrong. I
wish I was there and we could get it sorted out pretty quick. Try to
find a transistor you can be sure of the pin configuration and it
should work. This circuit is dead simple and should be a cinch. keep
at it. :-)

73, Bill W6WRT


------------ ORIGINAL MESSAGE ------------


On Tue, 9 Dec 2008 22:16:29 -0500, "Alfred Frugoli" <ke1fo at arrl.net>
wrote:

>Hello folks,
>
>I'm trying to build up the interface listed at the bottom of
>http://www.aa5au.com/rttyinterface.html#PNP_Transistor_FSK_Circuit using a
>PNP transistor.  I'm using generic PNP transistors from Radio Shack (the
>package says they're 2n3906 but there are a mix of various numbers in the
>package) and a 1k resistor.
>
>I'm building up the circuit for use with Software FSK in Writelog (using
>RTTYwrite not MMTTY).  I originally built the NPN circuit at the top of the
>page and got inverted keying.  Then I built up the PNP circuit and all was
>well.  I then went to build up a 2nd identical interface, and it did not
>work.  I took apart the case of the first interface to make sure they were
>wired identically.  I put it in line without the case to make sure it
>worked, and it did not.  Since that point I have not been able to build a
>working interface, and the original that did work, no longer does.
>
>I have tested the RTTY port on the rig, and all is well there - when I
>ground the center pin it shifts tones.  I've tested the Serial port, and I
>get either +9v or -9vdc between pin 3 and signal ground depening on the
>state of the serial port.  I've tried a different USB/Serial converter, and
>no joy there, so I'm assuming I've done something wrong in the circuit.
>I've tested my transistors prior to inserting them in the circuit and they
>seem to be good both before being in the circuit and after not working (i.e.
>nothing is zapping them when they get connected to the rig and serial
>port).  I've "reversed" the transistor (i.e. swapping emitter and collector
>leads just in case the transistor is miswired/mislabeled).  I've tried
>connecting the base back to the "ground" connection of the RTTY port on the
>rig rather than to pin 5 of the serial port (signal ground).
>
>Everything I've tried has resulted in the rig not shifting tones.  The
>USB/Serial converter has an LED to show activity, and when I send I can see
>activity on the prort, but the rig just stays on a single tone and does not
>shift at all.
>
>I don't know what else to try, except maybe a lower value resistor, but that
>doesn't seem to make sense since the circuit worked once.
>
>Thoughts?
>
>73 de Al, KE1FO
>
>-----
>Visit my amateur radio contesting blog at ke1fo.wordpress.com.
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