Ford:
The relative performance of hardware vs. software modems has little to do
wtih the sound card, unless it is being overdriven and is distorting or it
has a very poor A to D converter (ADC). The relative performance has
everything to do with how the signals are processed.
Older "multimode" controllers utilized the classic bandpass
filter/limiter/discriminator/lowpass filter approach. This can and should
work well, but, to minimize parts count, the units were really
two-mode---VHF packet, and everything else. The "everything else" mode
included RTTY, AMTOR, HF Packet, WEFAX, etc; the filter and discriminator
bandwidths were set for the widest modes, and were suboptimal for RTTY. I
know this was the case for the PK232, and I presume it to be true for other
controllers of that era.Performance can be stunningly improved.
"Soundcard" modems utilize the card's ADC to digitize incoming audio; the
soundcard does no filtering. What happens after digitizing depends upon the
software chosen. For example, K6STI's RITTY used a matched-filter receive
algorithm that was inherently superior to what could be done with
limiter/discriminator receivers, even if properly implemented, which, as I
said, they were not. I have not yet gotten into the bowels of MMTTY, so I do
not know what algorithm it uses. But I intend to run MMTTY in tandem with my
modified PK232 to see how good it is. I already know that my modified 232,
which is superior to a stock 232, is inferior to RITTY,especially in
weak-signal and polar flutter environments. Unfortunately, it was a bear to
use RITTY in a Windows environment, although I understand some guys are
doing it successfully, and I'd like to know how to use it with WL.
You say your KAM "actually keys true FSK," but that is not correct. The KAM,
and all other "FSK" sources, provide logic-level outputs that do not
directly manipulate the frequency generator in your radio, but which select
dividers in the radio that provide tones to modulate your SSB transmitter
downstream from your microphone preamps. IOW, you are merely generating AFSK
with logic levels, and most certainly do not eliminate your audio stages.
What it does free you from is the necessity to worry about microphone gain
and the status of your compressor.
73,
Garry, NI6T
> -----Original Message-----
> From: writelog-admin@contesting.com
> [mailto:writelog-admin@contesting.com]On Behalf Of Ford Peterson
> Sent: Friday, October 11, 2002 03:25
> To: Dean Gramling
> Cc: writelog@contesting.com
> Subject: Re: [WriteLog] WL with KAM XL
>
>
>
> From: "Dean Gramling"
>
> > I realize that MMTTY is a much better way to do rtty during the contests
> but...
>
> Dean:
>
> I use an older KAM Plus unit. I find that if the KAM is properly
> integrated
> in the software, I get much better results than using a sound
> card. Why? I
> can only speculate but here is my opinion...
>
> The KAM's audio filtering is much better than any sound card. Better
> dynamic range for one thing. I can actually copy one of two stations
> occupying nearly the same frequency within the passband of my rig. Also,
> the rig actually keys true FSK. It's hard to believe but eliminating all
> the audio circuits in the transmitter does reduce distortion, and
> I think it
> shows up in better print on the other end.
>
> I've been looking at the new KAM to replace my aging KAM Plus. I'll be
> interested to know if you get this resolved. Perhaps the fix is to send
> your unit to WL and do all of us a great service. Service? Did somebody
> say service? Too bad Kantronics isn't on his reflector...
>
> Ford-N0FP
> ford@cmgate.com
>
>
>
>
>
>
>
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