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[aprssig] Kenwood D700 TNC Transmit Equalization ScrewedUp! (Repost)

Scott Miller scott at opentrac.org
Mon Apr 25 23:17:57 UTC 2005


Am I the only one who sees this as a significant design flaw?  From John
Ackermann's site:

"More important, if the low tone coming out of the speaker is stronger than
the high tone, many TNCs based on the TAPR TNC-2 design, including the very
popular MFJ-1270 series, will have great difficulty demodulating packets.
The demodulator chip in these TNCs, the XR-2211, is particularly unhappy if
it sees a low tone that is louder than the high tone. Because XR-2211
demodulators are so common, it's very important that we transmit signals
that these units can decode, and that means signals that do not have a a
twist favoring the low tone."
http://www.febo.com/packet/layer-one/transmit.html

There are a LOT of digis out there that are going to be at a real
disadvantage because of this.  How many of them can realistically be
expected to adjust their deemphasis?

Has anyone brought this to Kenwood's attention?  How did these even come
about?  I thought 6 dB/octave preemphasis had been the standard for as long
as 1200 baud packet's been around.

On the other hand, maybe it's good for Kenwood's brand lock-in... after all,
they'll decode each other just fine.  TNC-2 won't cut it?  Gotta buy
yourself a new D700...

Scott, N1VG
http://n1vg.net/opentracker


----- Original Message ----- 
From: "Robert Bruninga" <bruninga at usna.edu>
To: <wa8lmf2 at aol.com>; <aprssig at lists.tapr.org>
Sent: Monday, April 25, 2005 10:54 AM
Subject: Re: [aprssig] Kenwood D700 TNC Transmit Equalization ScrewedUp!
(Repost)


> >>> wa8lmf2 at aol.com 4/25/05 5:05:22 AM >>>
> >In the course of capturing signals..., I was shocked to
> >discover that the Kenwood D700 transmits 1200 baud "flat"
> >with no pre-emphasis...
>
> Yes, the TNC is used at both 9600 and 1200 baud and
> the 9600 baud has to be flat to work well.  Apparently
> 1200 baud is also transmitted and received flat.  This is why
> it is important to make sure in all digipeaters that there is no
> audio roll-off any worse than the usual de-emphasis. or even
> better, that the TNC is connected to the discriminator...
>
> A good compromise is to set about 3 dB of de-emphasis
> at the digis to account for both types of users.
>
> Bob





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