[UK-CONTEST] 80M CC G3SJJ

[Ian White GM3SEK]

Clive GM3POI wrote:
>I gather the situation with the Inrad mod is it is not as good as the 
>W8JI mod. An 1000mp still has close in clicks after the mod but is 
>better than the stock MP and can be installed fairly easily.

I did the W8JI mod with the two IF board trimpots brought out onto a bit 
of Veroboard, just to have a twiddle and see what happened... and was 
glad I did.

As W8JI points out, there are small differences from one rig to the 
next, which seem to have a big effect on the keyclick levels. The fixed 
component values in the Inrad mod are OK for most rigs, but the clicks 
can often be improved even further by using slightly different values on 
the IF board - hence the trimpots.

On the other hand, the capacitor under the RF board doesn't seem as 
critical, so you can simply solder that one in and forget it.



Responding to Clive POI's previous message, I did an 'In Practice' about 
the causes of key-clicks a couple of years ago. The most important 
source of the clicks is not the total rise and fall time of the keying 
envelope, but the sharpness of the CORNERS at the beginning and end of 
the rise or fall.

The keying envelope of a dot or dash is roughly a rectangle, so it has 
four corners. All four of them need to be smoothed off to avoid clicks.

The classic RC-shaped envelope is actually quite poor. It only softens 
two of those corners, while still leaving extremely sharp transitions at 
the moments of key-down and key-up. In other words, it only does half 
the job.

The unmodified FT-1000 has bad clicks at both key-down and key-up, and 
on my rig at last, the worst were at key-up.

The ideal rise and fall is kind of S-shaped. It changes slowly at the 
start, speeds up in the middle, and then slows down again for the final 
corner. That gives the best balance between clearly formed characters 
and low levels of clicks.


But having said all that, the worst clicks of all are probably due to 
people trying to use full QSK with an amplifier that can't keep up. 
Those clicks are caused by the amplifier relays hot-switching the RF. If 
the owners ever looked at the relays in the dark, they could probably 
watch themselves transmitting Spark.



-- 

73 from Ian GM3SEK