[RTTY] Question

[Joe Subich, W4TV]

On 5/17/2014 5:48 PM, Kok Chen wrote:
 > Allow me to add just one thing to David's sound [sic] advice: place
 > that attenuator as close to the transceiver's line input as you can,

To which, let me add, *always* use the transceiver's *line* input.
A microphone input designed for a dynamic mic (Yaesu, Kenwood, TenTec)
expects less than 10 mV of signal and typically has a 20 dB gain preamp
*before* the mic gain control.  It is very easy to drive that preamp
into clipping which will create garbage before there is any chance to
do anything about it.

If you must use a mic input, a 40 dB attenuator may be more appropriate
as the sound card output can be on the order of 1.0 to 1.5V RMS.  A 20 
dB attenuator may be appropriate for a transceiver designed for use
with an electret mic (Icom, Kenwood) which is generally abut 150 mV.

73,

    ... Joe, W4TV


On 5/17/2014 5:48 PM, Kok Chen wrote:
> Ah, I see David G3YYD has beaten me to the draw on most of it :-) :-)
>
> He also wrote:
>
>> Many rigs which have too large a AFSK input signal will produce 2nd harmonic
>> output that will cause QRM to other amateurs. This is totally avoidable by
>> attenuating the sound card output by about 20dB, a 10K series resistor and a
>> 1K resistor to ground will do this for you.
>
> Allow me to add just one thing to David's sound [sic] advice: place that attenuator as close to the transceiver's line input as you can, and not at the sound card end. This way, when the cabling is long, the noise that is picked up is also attenuated before reaching the transmitter.
>
> (This is like the sage advice when traveling by airline -- instead of just wearing a pair of headphones to remove the engine noise, use foam earplugs, and over that, a pair of headphones.  You then crank the volume of the headphones high enough so you can hear the music through the ear plugs.  This way, you will hear the music, but the engine noise is now much lower.  David's 20 dB voltage divider serves the function of the foam earplugs.)
>
> 73
> Chen, W7AY
>
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