[RTTY] FSK Keying on an Icom 7800 Problem

[Joe Subich, W4TV]

2N3904 and a 1.5K base resistor is plenty.

73,

    ... Joe, W4TV


On 2/1/2014 11:46 AM, Jim W7RY wrote:
> 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
>>>
>>> _______________________________________________
>>> RTTY mailing list
>>> RTTY at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/rtty
>>>
>>
>> _______________________________________________
>> RTTY mailing list
>> RTTY at contesting.com
>> http://lists.contesting.com/mailman/listinfo/rtty
>>
>>
>
> _______________________________________________
> RTTY mailing list
> RTTY at contesting.com
> http://lists.contesting.com/mailman/listinfo/rtty
>