Re: YAM/Tekk help

["Mike Murphree" <mike@xxxxxxxxx>]

Jim Meehan said:
> I'm trying to get two Linux systems talking to each other over 9600 bps
> packet.
> Here's my setup:
>
> System 1:
> Pentium 133 MHz running RedHat 8
> Kenwood TM-D700A /w integrated 9600 bps TNC
> AX25 HW addr: W6XE-12
> IP addr 10.0.0.1
>
>
> System 2:
> Soekris single-board computer running custom Linux mini-distro
> Kernel version 2.4.20
> YAM 9600 bps modem
> Tekk KS-900L radio
> AX25 HW addr: W6XE-14
> IP addr 10.0.0.2

Hi Jim,

I sold a KS-900L sometime ago, I can't remember if it was to you.
I did find the manuals eventually.

>
> Problem 1:
>
> If I ping from either side, that machine sends out ARP requests endlessly.
> If I do "ifconfig" on the other side, I can see the RX packet counter
> incrementing, and in "listen" I can see the ARP requests being received.
> But no ARP reply is ever sent.  If I create a static ARP entries on both
> sides,
> then the machines can find each other, and I can ping in both directions.
> I guess it's not really such a problem to add static ARP entries on both
> sides,
> since there won't be any stations other than these two.  Would be nice to
> know why ARP isn't working though.

Do you have some problem with your DCD detection?  If the receiving end
thinks that DCD is always active, it won't transmit.

> Problem 2:
>
> The link is not reliable.  Right now, I've got the txdelay set to 300 ms
> on
> both sides, and I'm still getting 3 or 4 percent packet loss with 64 byte
> pings.  If I increase that to 192 byte pings (which is a more realistic
> size
> for real world data transfer) that goes up to ~ 12 percent packet loss.
> This
> isn't really acceptable, especially since the two systems are just one
> room
> away from each other at the moment.

The Tekk radio only needs maybe 70 ms for txdelay, but your D700A could be
much longer.

>
> It looks like packets sent by the TM-D700A are received reliably by the
> YAM/Tekk side, but packets going the other direction are prone to bit
> errors.
> Since there are really no adjustments to make on the TM-D700A, I suspect
> that
> something needs to be adjusted on the YAM/Tekk combo.  There's one
> adjustment
> on the YAM, for TX gain, and I've tried to adjust that for best
> reliability.
> There are also a ton of trimmers and adjustments inside the Tekk, and I
> suspect
> it needs to be realigned.  There are pretty detailed tune-up instructions
> for
> the Tekk radio here:
>
> http://www.guerrilla.net/reference/tekk/ks960_techman.html

A KS-900L should almost work out of the box without messing with anything
inside.  The KS-960 was a lot harder.  Make sure your deviation level does
not exceed 3.5 kHz maximum.  It's unlikely that you needed to do anything
beyond netting the crystal and possibly retuning the front end if you
moved the frequency a lot.

> But I don't own the equipment necessary to make all the adjustments.
>
> Anyone in the SF bay area who has access to that gear who'd be willing to
> help me tune up the Tekk radio?  Any other suggestions on how to get the
> YAM/Tekk combo tuned up and working more reliably?

Just a quick check of the deviation with another open squelch FM receiver
is that when you are transmitting 9600 bps FSK, the noise should actually
decrease during transmit.

I also agree with the comment that the TNCs in the Kenwood radios are crap
for this application.  They were not designed for this kind of use.

73
Mike W4LNA



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