[RTTY] FSK Keying on an Icom 7800 Problem

[Jim W7RY]

I use darlington output opto isolators. They have always worked. Keeps 
things isolated too. The 4N25 works well with a 1.2K or 1.5K LED 
dropping resistor. LOTS of circuits on the interwebs for FSK and PTT 
circuits from com ports.


73
Jim W7RY



On 2/1/2014 8:09 AM, Jim Hargrave wrote:
> Dennis,
>
> I have had good success with a 2N5306 darlington transistor. I use a 3.3k
> base resistor to insure full saturation.
>
> Check the voltage on the FSK line on both radios. You could have a 
> problem with
> the one that does not work,
>
> I assume you have tried them on the same computer/adapter. If not, 
> switch them
> around and see if it helps isolate the problem.
>
> Another option is to install a pull-up resistor on the radio side to 
> insure good
>  transition between Mark/Space This will allso assist in a slight 
> increase in
> collector current that will reduce the internal resistance.
>
> Jim w5ifp at gvtc.com
> On 2/1/2014 7:43 AM, Dennis wrote:
>> I have two Icom 7800s that I want to use on FSK RTTY.  I have tried 
>> several different
>> keying interfaces on each, i.e. simple transistor, FET transistor, 
>> several different
>> Opto-isolator chips; on one of the 7800s, they all work, and on the 
>> other 7800,
>> none of them work.  The only thing that all the interfaces have in 
>> common is that
>> they are all "passive"; none of them require any external power.
>>
>> For the 7800 that won't key, grounding the FSK lead does get the tone to
>> change, so they actually circuitry of the 7800 seems to be okay; the 
>> problem
>> seems to be that none of the keying interfaces pulls the 7800 FSK 
>> lead close
>> enough to ground to get the FSK keying to work.
>>
>> Can someone point me to a circuit that brings the Icom FSK lead close 
>> enough to
>> ground to key the circuit?  A no-power circuit is preferred, but I 
>> can also
>> do a powered circuit if that is the only way to do it.  I also 
>> haven't investigated
>> using a reed relay or similar, as I'm not sure it is fast enough to 
>> keep up with
>> the keying signal.
>>
>> Dennis W1UE
>>
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>
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