[OZAPRS] Re: 40m Traffic & TX DELAY

Ray Wells vk2tv at exemail.com.au
Sun Apr 5 09:15:14 EST 2009


Peter Mallett wrote:
> 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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>>>   
>>
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>
> Hi Ray & All,
>
>                    I have always used 500ms for TXDELAY and 100ms for 
> TXTAIL on HF and found it to work very well.
>
> If one has trouble with the station at the other end not hearing you 
> all the time, try extending the TXTAIL a bit as that usually helps.
>
> The TXDELAY should of course, take in all factors, rig power up of 
> transmitter, switching time from RX to TX and the most important 
> things like, allowing for a receiving station who may have a 
> commercial rig with squelch built in.
>
> There are many factors on HF, propagation being the "unknown" factor.
>
> Regards ..... Peter
>
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Hi Peter,

TXD is usually considered to be a transmitter-dependent setting but you 
touched on an overlooked factor, rx response time. TXD needs to be 
sufficiently long to enable the slowest rx to respond. This may be mute 
delay as Peter has said, or it may be the tx to rx turn-around time.

I once had a crystal-locked commercial base station on packet, that had 
electronic tx/rx changeover, which you would expect to be blindingly 
fast compared with relays. The changeover was fast but the tx settling 
time was pathetic. That rig needed 450mS and a long(ish) txtail as well.

Ray vk2tv
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