[Elecraft] Re: Think more of you would like this mod
Wayne Burdick
[email protected]
Mon Aug 11 15:48:01 2003
This mod will dramatically increase the assertion (fall) time of the /mute
signal at the JFET gates. Another way to achieve the same effect is to insert a
largish resistor (try 100 k) in series with pin 17 on the MCU. This would add
only 150 microseconds to the /mute fall and rise times. In previous designs
using JFET muting, this has reduced a leading-edge click during keying with a
hand key and/or long keying lines. I didn't think this was necessary on the K2,
given its different receiver gain distribution, and haven't tried it yet.
The mod recommended here, however, would increase the mute assertion time by
some 15 ms. This might result in some J310s not getting fully cutoff in time to
prevent TX-mode artifacts that are under firmware control. So, if you make this
mod and notice problems with muting behavior, I'd advise replacing the J310s
with J309s, which have a much lower pinchoff voltage (Vgs) and will get cutoff
much more quickly.
If some variantion on this theme proves to work well for a lot of K2 owners,
we'll write an application note and post it on our web site.
73,
Wayne
N6KR
[email protected] wrote:
I am surprised more of you are not putting in this mod....
OLD R17
+------+
/MUTE------+--| 3.3M |----(Q7 Source)
| +------+
|
+--- (Q6, Q7 Gates)
|
-----
C23 0.01 uF
-----
|
|
(earth)
NEW R17
+------+
/MUTE------+--| 1.5M |----(Q7 Source)
| +------+
|
+---+
| | new resistor
| | 1.5M
| |
+---+
|
|
+--- (Q6, Q7 Gates)
|
-----
C23 0.01 uF
-----
|
|
(earth)
>REMEMBER, THIS IS NOT AN AUTHORIZED MOD!
>73,
>Lyle KK7P