[Elecraft] K3 TX delay

[Igor Sokolov]

Don,
I will try to explain.
Forget about QSK all together.
Apart from linear amp, there are other external relays like stack control 
relays, T/R relays when you want to use different antennas for TX/RX etc.
PTT signal can either be controlled by the logger (CW, VOICE Keyer, DIGI 
modes) or by PTT footswitch. In both cases PTT signal goes into PTT IN of 
K3.
About 6ms later you get sort of PTT OUT on the KEY OUT connector. This KEY 
OUT signal controls linear, T/R antenna relays, stack relays etc. Then 8ms 
later you get RF out of the K3. These 8ms is not enough for all the external 
relays to settle.
PTT delay of 20 ms should be more or less OK (although I would not mind it 
to be extended to 30ms) but then CW generated by  a logger gets choppy.
I can overcome the problem of non adjustable TX delay of K3 by configuring 
my logger to start sending say 30 ms after PTT was asserted. I can even 
connect PTT footswitch to the computer, but that will only work for CW 
sending from the keyboard, computer voice keyer and digi signals generated 
by the computer. If I send from the K3 internal keyer or use k3 mike I am in 
danger to hot switch some of the external relays.
Therefore instead of being able to extend TX delay inside K3 I will probably 
have to build some sort of circit which will take low level from KEY OUT and 
form some sort of positive or negative impulse of a required length (say 30 
ms) to apply to INH input of K3. I was hoping to build it inside the DB-15 
cabinet since KEY OUT and INH pins are available on the ACC connector. But 
there is no any 12 v or 5v pins available on that connector. So it makes 
life more complicated.
If you can suggest different approach. which does not involve building 
external sequencer, I would really appreciate it.

73, Igor UA9CDC


>I fail to understand why anyone who is using PTT switching would want to 
>set the TX DLY parameter to  greater than the default of 8 ms.  Use PTT and 
>a footswitch if you are using a slow amp relay.
>
> If your amplifier uses a slow relay, then you really cannot use QSK, so 
> just use PTT and a footpedal instead - things will work out much better. 
> There are QSK mods available for amplifiers that use slow relays.  Some 
> mods are relatively inexpensive (the owner does the work), while other can 
> cost upwards of $400 (purchase a commercial version).
>
> 73,
> Don W3FPR
>
> On 2/16/2012 11:05 PM, Igor Sokolov wrote:
>>> But I am finishing my 300w HF amplifier kit and will be using a dc
>>> open-frame relay for TR switching of RF.  I guess I can time it using
>>> my dual trace scope and set K3 TX DLY accordingly (amp will be keyed
>>> with KEYOUT).  I do not use CW very much on HF so QSK with 300w is
>>> not necessary (or probably possible).
>> Even if you use PTT CW and set TX delay for 20 ms you will get choppy CW
>>
>>> There is one thing I do not see being addressed in this
>>> discussion.  Maybe more important than clipping of CW characters is
>>> avoiding QRO "Hot Switching" of RF.  Calculate the RF voltage for
>>> several thousand ohms impedance (open circuit) that will result if
>>> the amp is pumping out "globs" of RF before being connected to a good
>>> load.  The relay contacts will definitely get burned big time.  And
>>> maybe your output devices will have a short live-span.
>>>
>>>
>>> 73, Ed - KL7UW, WD2XSH/45
>> The entire topic stems from the fact that I wanted to avoid hot switching 
>> of
>> the external relays (linear amp, stack switching etc). To acheave that I
>> have tried to increase TX delay and got choppy CW. So without external
>> sequencer there is a choise between the two - 'hot switching' or 'choppy
>> cw'.
>>
>> 73. Igor UA9CDC
>>
>>
>>> ======================================
>>> BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
>>> EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-?
>>> DUBUS Magazine USA Rep dubususa at gmail.com
>>> "Kits made by KL7UW" http://www.kl7uw.com/kits.htm
>>> ======================================
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:Elecraft at mailman.qth.net
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>