Here is the link to the modification of the PK-232 for 170 shift and to narrow
the filters.
http://www.qsl.net/k0bx/align.htm
Joe K0BX
Stop the insanity!
Please do not add me to any distribution lists (Joke, Stories or Junk) without
my permission.
________________________________
From: "Joe Subich, W4TV" <lists@subich.com>
To: rtty@contesting.com
Sent: Thu, June 9, 2011 11:03:17 AM
Subject: Re: [RTTY] Shift 170 -vs- 200
> I believe part of the reason is that the TNC manufacturers were
> really selling the TNCs for HF Packet (200 Hz shift), with RTTY/Amtor
> (170 Hz shift) tagging along just to pad the specs sheet.
That's probably true ... all of the 200 Hz TNCs included HF (and VHF)
packet.
> What probably hurt more than 200 Hz shift was the fact that the TNCs
> had such broad filters (needing to pass 300 baud HF Packet data
> rate).
That's probably true as well ... but the 200 Hz transmission certainly
did not help with the ability to be heard due to the tuning issues.
> Garry NI6T had modified the PK-232 to narrow the filters down. I
> forget now, but I recall vaguely that the filters use bi-quad
> topology with opamps, resistors and capacitors.
The modification is still floating around the net ... as I recall it
was something like four resistors. When the PK-232 was modified for
the narrow filters and the PLL tuned for 170 Hz shift it wasn't a bad
HF modem but still doesn't hold up to even the "Standard RTTY" profile
in MMTTY much less some of the better software (e.g., cocoaModem<G>).
However, a good 400 Hz IF filter and 90 dB DR receiver can do a lot
with even moderately good decoders. Proper filtering and AGC can take
a lot of the strain off the decoder although flutter, multi-path and
selective fading will still take their toll.
73,
... Joe, W4TV
testing.com/mailman/listinfo/rtty
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