[OZAPRS] Re: 40m Traffic & TX DELAY

Ray Wells vk2tv at exemail.com.au
Sun Apr 5 08:34:16 EST 2009

Here's a tad more info on txtail.

FYI, this site has the original description of the KISS protocol by Mike 
Chepponis and Phil Karn


If the name Phil Karn sounds familiar to some old hands, he's the guy 
that ported "The Net" from Unix to DOS, and many of us came to know it 
as JNOS. This was circa 1990, maybe a bit earlier. I was certainly 
playing NOS in 1992.

I guess this Feb 2000 mailing list extract sums up txtail.


On Tue, 1 Feb 2000, Jens David wrote:
> John Ackermann wrote:
> > Not all hardware implementations need it, but there are at least some systems
> > where dropping the PTT immediately results in the tail end of the packet
> > (including the CRC and closing flag) to be chopped off.
> In fact per definition the txtail starts after the closing flag has been sent.
> Usually it´s the modem which causes some delay on the signal. Consider for
> example the scrambler or the FIR filter on a G3RUH-compatible modem.
So .. ok .. txtail is important. Couldn't we use some fixed (or computed)
value which couldn't be mis-configured ?
(driver/baudrate/anything dependant)


For those who are relatively new to packet, the G3RUH modem (circa 1988 
and still current) is an advanced design 9k6 modem that utilised the 
expansion header in TNC2 compatible TNCs. Hey, this was in the days of a 
very fast computer being a 486DX66, with 32M RAM so "smart" software 
(sound card) modems weren't an option.

If you want to know more about these modems, Google for G3RUH or James 

FIR filter - Finite Impulse Response filter.

Ray vk2tv

David and Justine Olsen wrote:
> MixW has a Tx tail setting, currently 0
> Do you have any recommendations for my soundcard setup with respect to 
> TxTail.
> David
> On 5 Apr 2009, at 06:01, Ray Wells wrote:
>> In my early days of running HF for the BBS I experienced some 
>> variable results that I attributed to TXD being marginal. Setting TXD 
>> to 450mS ironed out that problem and it remains the value I use with 
>> The Kenwood TS430, a Tracker Lynx and a couple of Codans.
>> There is another setting which, although largely deprecated, can 
>> prove useful on HF, and that's TXTAIL, the purpose of which is to 
>> hold the TX up to ensure the data has cleared the radio. It's like 
>> TXD in reverse.
>> It's certainly still available as an option with KISS TNC's in Linux 
>> kernel ax25, and my Baycom USCC> 4, four port internal card has it as 
>> well.
>> Ray vk2tv
>> Tony Hunt wrote:
>>> David. I dont know what others are running but I run 480mS .. I 
>>> messed about
>>> with TXDelay on 30m a while back with Tiny Trackers and found that 
>>> figures
>>> closer to 500mS seemed more reliable. I remember some earlier TNC2 
>>> firmware
>>> for VHF that came out with default Txdelays of 300mS . Surely its 
>>> going to
>>> be higher as a rule on HF !!
>>> I wonder what everyone is running as a rule?
>>> Of course it all depends on different radios your running etc etc.. 
>>> It also
>>> depends on different receivers that others are running and software and
>>> squelches etc. Those latter things are all out of your control..
>>> I picked some frames up from you on 40m early this morning around 
>>> the grey
>>> line at 0413 local. The same with ZL4TZE-4 at the same time. So Ive 
>>> got 8
>>> stations on the heard list so far.
>>> Tony Hunt  VK5AH
>>> ----- Original Message -----
>>>> Date: Sat, 4 Apr 2009 14:14:08 +1000
>>>> From: David and Justine Olsen <davejust at bigpond.net.au>
>>>> Subject: Re: [OZAPRS] 40m Traffic & TX DELAY
>>>> To: Australian APRS Users <ozaprs at aprs.net.au>
>>>> Message-ID: <5DF92CC8-3A97-461B-97F8-2B9C3E37F8F3 at bigpond.net.au>
>>>> Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
>>>> I have a very short packet, but my Tx delay is 300mS
>>>> David
>>> _______________________________________________
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>>> Ozaprs at aprs.net.au
>>> http://aprs.net.au/mailman/listinfo/ozaprs
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