Re: Re: Discriminator tap question

As I said,
the resistor is protecting the scanner from external damage due to loading down 
and capacitive isolation.    The cap is to isolate DC getting into other 
external devices or external voltages getting in and upsetting the discriminator 
bias.

If you are happy to have no protection then a bit of wire to the socket is all 
that is needed from the discriminator tap point.

Since I experiment with data decoders inc 2 and 3 level data slices on 
prototyping boards I prefer to protect my scanner at all costs while on the work 
bench as a data source.

Cheers,
OldOne.


On 07 Mar 2013 20:07, Bigjed wrote:
> OK.A bit of a conflict here then.Question:Would I get away with using nothing at all?Just a wire from the tapping point to a phono socket mounted at the rear of the radio.No danger of headphones being plugged into that.I intend to use the socket for the purpose of decoding pager signals and the like and want a nice clean signal.
>
> Gerry.
>
> --- In [email protected], OldOne <oldone45@...> wrote:
>>
>>
>>
>>     I normally use a 1K resistor as an isolator incase some one plugs a 32 ohm
>> earpiece into the socket and almost shorts the discriminator point to ground.
>>
>> Also do not use a 0.01 uf cap as DC blocking if you want a clean data waveform
>> out as it will phase distort the low frequency squarewaves output for data
>> decoding.   If you must block the DC use a least a 1.0 uf  50v monolithic cap
>> when feeding into a 10k load of the sound card input.
>>
>>
>>
>> On 06 Mar 2013 08:57, Bigjed wrote:
>>
>> --- In [email protected], Don <stb55@> wrote:
>>>>
>>>> Usually it is advisable to use a small value ceramic cap like 0.01 uf to
>>>> block DC - no resistor needed - that would drop the signal some.
>>>>
>>>> Doesn't hurt to use coax like RG-174 but not really needed. Depends on
>>>> how much you want to put into a project labor wise. Also I always think
>>>> about resale value - like putting holes for switches on a front panel.
>>>>
>>>>
>>>> Thanx Don.I've seen a couple of conflicting articles re this.Some recommend the resistor with coax,some just a wire from the tapping point straight to a phono socket on the rear of the radio.I've not seen the ceramic cap mentioned yet tho'.is that just connected in series,like the resistor would be?
>>>>>


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