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Re: Kenwood TH-D7



on 2/8/00 08:57, Luis Martins at luis.martins@ruido-visual.pt wrote:

> Since you happen to know the TH-D7 so well, I believe you can answer
> this
> questions.
> I've been talking to some local ham in Lisbon and they seem to be having
> trouble
> connecting on 9k6 DX packet clusters and BBSs with th TH-D7, some of
> them say
> that it's because of the KISS mode which is not fully implemented !?
> Others say it's because the internal TNC is not TNC2 compatible and you
> can't use
> any packet program with it.

I know the answer to this Luis, but you won't like it!

The TH-D7A has a synthesizer inside that is used to tune the radio.  This
synthesizer has a finite lock time.  In other words, it takes a certain
amount of time for the VCO to change frequency and lock in on that
frequency.

When you transmit, the VCO in the synthesizer is operating at one frequency.
When you stop transmitting and switch to receive, the VCO is operating at
another frequency.  There is a certain amount of time that is required for
this switch to occur.  This time is controlled by the loop bandwidth of the
PLL.  This loop bandwidth can be changed so as to speed up the locking of
the VCO, but then other bad things happen to your audio and so forth.

9600 baud packet happens very fast.  It is so fast that the TH-D7A cannot
keep up with it.  By the time the radio has locked in on its receive
frequency the other station has already sent its acknowledgement but you
didn't hear it.  This is why your friends are having trouble.  Some TH-D7A
owners report that the lock time is on the order of 250 mS!  For 1200 baud
packet this is OK, for 9600 it is NOT.

This same problem occurs with most of the FM single band mobile rigs out
there.  That is why most people doing 9600 baud packet use rigs with 2 VFOs,
crystal rigs, or all mode rigs which do things differently internally as
well.  Some users have reported that the TH-D7A works fine for them on 9600
baud packet.  I suppose it depends on the network.  If the station you are
connecting to allows enough delay before transmitting it will work.
However, no you have slowed down everything and your data efficiency is not
as good.

I have verified this with my TH-D7A and compared it to my 9600 baud modem on
my FT-847.  I have a 9k6 BBS about 1/2 mile from my house.  I connect just
fine and blazingly fast with the FT-847.  With the TH-D7A, I can connect,
but it is very very difficult to use the BBS and I get easily disconnected.

Bottom line: The TH-D7A just really does not work well for 9k6 packet.
Sorry folks!

73,

Jon
KE9NA
--------------------------------------------------------------------------
The Second Amendment is NOT about duck hunting!


Jon Ogden

jono@enteract.com
www.qsl.net/ke9na

"A life lived in fear is a life half lived."

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