[TenTec] omni v short dits

[Jim Brown]

On Sun, 25 Jul 2004 00:04:55 +0000, ac5e at comcast.net wrote:

>Well, after ten years or so memory gets tricky but the paddles plugged 
>into a mini stereo phone jack on the right side of the rig, facing the back. 
>Said jack going to the internal keyer, if my memory serves. The 
>straight/bug key jack should be an RCA jack on the same row of jacks 
>as the relay jack close to the bottom of the rig. 
>
>One Field Day we had a guy bring a bug with a phone plug and an 
>adapter who tried to use his bug in a manner unacceptable to the V. 
>I don't remember what problem it caused but I do remember being 
>roused from a sound sleep to find a proper adapter and plug it into 
>the straight key jack. Which solved that problem but poor baby couldn't 
>adjust the keyer speed from the Omni's front panel any more. 

Memory is, indeed, flaky. Perhaps your experience on Field Day was with an 
Omni VI or VI Plus. The Omni V does not have an internal keyer, and has only 
a single keying input -- an RCA connector mounted to the Control Board that 
keys the base of a 2N5087.  Actually, there are two RCA jacks in parallel -- 
one is labeled CW Key, the other is labeled RTTY key. All the connectors on 
this board have a pin 1 problem (that is, their shells go to the circuit board, 
not to the chassis)!  A wild guess is that RF in the Field Day shack (and with 
the radio that has this problem at home) might have been exciting it with the 
bug but not with whatever keyer was being used with the rig. The difference 
could be how that keyer was powered, the length of the leads, the wiring 
interconnecting them, etc. 

W4BQF noted:

>Reason it's puzzeling is in test I've done this week, I found the Omni 6 has
>a 12ms delay from the keying input signal's transition to the leading edge
>of the RF output waveform. The Omni 6 Plus has an 18ms delay. The Orion
>has a varying delay from 18ms to 25ms that changes with each generated
>character.

If you study the manuals and/or QST reviews for any modern transceiver that 
does QSK, you will find that the ALL delay the keying by some interval 
between 10 ms and 20 ms from the actual key press, whether the key press 
is generated by a straight key, bug, external keyer, or internal keyer. The 
firsts time I saw this circuit was on the first Ten Tec radio I bought in 1980, an 
Omni A. I'm sure that a study of earlier Ten Tec radios will show a similar 
circuit. The reason is simple -- the delay gives the antenna switching relay 
time to pull in before the transmitter transmits, so that the relay is not "hot-
switching."  

When operating normally, this delay should NOT shorten the CW characters 
-- it should simply delay them.  In some radios (some Icom's, for example), 
the QSK circuit is not nearly so elegant, and some of these radios are well 
known to shorten dits badly at moderate to high speeds. 

Over the years, the designers of radios have increased the keying delay. I 
suspect, but do not know, that the increased delay time was needed to 
address tolerances, wear, or design issues in the switching relays. It may 
also enhance interface options with external power amps. 

Jim Brown  K9YC