[RTTY] RTTY spectrum analysis article

[Joe Subich, W4TV]

> Then how do you keep strong signals in the passband of the (now
> wider) rig filter away from the AGC in the rig?

400 Hz is nearly the minimum bandwidth necessary for proper decoding
(minimum intersymbol interference).  Narrower filters work by cutting
adjacent signals more than the desired signal but they impose a much
higher group delay than a filter that is "flat" across the necessary
350 to 370 Hz bandwidth.

73,

    ... Joe, W4TV


On 1/10/2013 9:44 AM, Al Kozakiewicz wrote:
> Then how do you keep strong signals in the passband of the (now wider) rig filter away from the AGC in the rig?  Attenuating a strong signal now in the passband also attenuates the weak adjacent ones I'm trying to work, no?
>
> Ignorance is a powerful sedative, so perhaps I don't know what I'm missing, but the 250hz RTTY filter in my Icom radios turned me from a 150 QSO/contest frustrated S&Per into a 1200 QSO/contest participant that enjoys the time spent in the chair!
>
> Al
> AB2ZY
>
> ________________________________________
> From: Jeff Blaine [keepwalking188 at yahoo.com]
> Sent: Thursday, January 10, 2013 9:34 AM
> To: Al Kozakiewicz; RTTY Mailing List
> Subject: Re: [RTTY] RTTY spectrum analysis article
>
> The best place for RTTY rx filtering is in the demod, not the rig.  narrow
> crystal filter and it's group delay gives more problems than it solves.
>
> The solution is to run a filter wide enough to let you quickly tune (400-500
> hz?), but not so razor sharp that the rig rather than the demod is doing the
> selectivity filtering.
>
> 73/jeff/ac0c
> www.ac0c.com
> alpha-charlie-zero-charlie
>
> -----Original Message-----
> From: Al Kozakiewicz
> Sent: Thursday, January 10, 2013 8:30 AM
> To: RTTY Mailing List
> Subject: Re: [RTTY] RTTY spectrum analysis article
>
>> No, this doesn't necessarily mean you should give
>> up "true" FSK keying. There are things you can do about it, and some
>> people are people taking responsibility and doing these things--please read
>> the
>> article!
>
> That was depressing.  Transmit filters are only enabled on the Icom radios I
> have on SSB, so there is no apparent option for improvement that I can see
> for without switching to AFSK which, in turn, makes the radios just about
> useless for contesting as there is no practical way to use the RTTY Rx
> filters without also transmitting FSK.
>
> Unless I missed it in the article, I see no way to improve things short of
> buying a new radio with a design that does not currently exist!
>
> Al
> AB2ZY
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