[RTTY] any way

[David G3YYD]

With sound card decoders then the limit on dynamic range is the receiver
distortion. If the receiver is at 2.4KHz bandwidth then it will be a
combination of harmonic distortion and Intermodulation products within the
IF and AF stages. These can be minimised by using receiver IF filter set for
no narrower than 350Hz. 

Narrower than 350Hz increases group delay distortion that causes Inter
Symbol Interference (ISI). This is where the energy of the previous bit of
the RTTY character is spread in time so it causes interference to the
following bit at the sample point - the receiver can be too narrow.

The dynamic range of a reasonable $25 or more expensive) sound card is
nominally about 90dB. However because of decimation within 2Tone the dynamic
range is a lot more. Do avoid the very cheap $5 cards as I have tested one
of them and they are poor performers.
73 David G3YYD

-----Original Message-----
From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of Joe Subich,
W4TV
Sent: 19 July 2015 17:38
To: rtty at contesting.com
Subject: Re: [RTTY] any way


 > DONT LIKE SOUND CARD NO FILTERS. OR IS THERE SOME FILTTERS YOU  > CAN
BULDING -TO RUN OUT OF REC. TO SOUND CARD..

You don't need filters with sound card RTTY as long as you turn off the
receiver AGC and adjust the RF Gain to prevent strong adjacent signals from
overloading the receiver and/or sound card.

A decent sound card has a dynamic range of around 90 dB - which means
signals up to S9+20 dB should be fine if the receiver can handle them.  The
attenuator in the typical receiver should be good for another 10 dB if
needed before resorting to the RF (or
IF) gain control.

This doesn't mean that a quality 400 or 500 Hz (CW filter) will not help
sound card RTTY with most rigs - it will certainly mean less need to adjust
the attenuator or RF/IF gain.  However, the sound card RTTY software (MMTTY,
2Tone, etc.) does the MARK/SPACE filtering in the digital domain which means
the IF filter primarily protects the IF, product detector and AGC system
against overload from strong adjacent signals.

73,

    ... Joe, W4TV


On 2015-07-19 12:38 PM, wa4jjy at comcast.net wrote:
> WAS ON RTTY WAY BACK IN 64.HAVE BEEN OF AND ON BUT DONT LIKE SOUND CARD NO
FILTERS.
> OR IS THERE SOME FILTTERS YOU CAN BULDING -TO RUN OUT OF REC. TO SOUND
CARD..
>
> IS THERE ANY WAY TO RUN ANY OF THE OLD TU -LIKE HAL ST-6-----PK232--- 2232
ON SOUNDCARD..
> TNX
> EDDIE
> WA4JJY
> _______________________________________________
> RTTY mailing list
> RTTY at contesting.com
> http://lists.contesting.com/mailman/listinfo/rtty
>
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