[RTTY] FSK interface circuit troubles

[Robert Chudek - K0RC]

Al,

A USB to Serial converter is a hit-or-mis proposition. Many of them do not 
provide enough current on the control signals to drive a transistor. If you 
have a 'real' COM port to make the connection, give this a try with your 
circuit. It will probably work just fine. If your computer has a LPT port, 
this is a good alternative for PTT and FSK keying. It is the same circuit, 
just wired to different pins on the dB25 connector.

73 de Bob - KØRC in MN


----- Original Message ----- 
From: "Bill, W6WRT" <dezrat1242 at yahoo.com>
To: <ke1fo at arrl.net>
Cc: <rtty at contesting.com>
Sent: Tuesday, December 09, 2008 10:23 PM
Subject: Re: [RTTY] FSK interface circuit troubles


> 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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>>RTTY at contesting.com
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