[aprssig] Kenwood D700 TNC Transmit Equalization ScrewedUp! (Repost)
bruninga at usna.edu
Mon Apr 25 18:51:29 CDT 2005
This debate is as old as packet radio. Some insist on
discriminator connection, some insist the other way.
And it is trivial to add some emphasis back into a digi
to compormise between the two schools of thought.
Just a simple capacitor of the right value between the
receiver and the input to the TNC will do the trick.
>>> scott at opentrac.org 4/25/05 7:17:57 PM >>>
Am I the only one who sees this as a significant design flaw? From
"More important, if the low tone coming out of the speaker is stronger
the high tone, many TNCs based on the TAPR TNC-2 design, including the
popular MFJ-1270 series, will have great difficulty demodulating
The demodulator chip in these TNCs, the XR-2211, is particularly
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
that these units can decode, and that means signals that do not have a
twist favoring the low tone."
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
about? I thought 6 dB/octave preemphasis had been the standard for as
as 1200 baud packet's been around.
On the other hand, maybe it's good for Kenwood's brand lock-in... after
they'll decode each other just fine. TNC-2 won't cut it? Gotta buy
yourself a new D700...
----- 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
> >>> 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.
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