[Elecraft] Sigmoidal keying mod, whoop solved

[Vic Rosenthal]

Indy wrote:

> The solution to the "whoop" for my radio, serial # 700, was simple,
> and thanks to Gary (as usual).
> 
> The construction manual at that time says, "Set the VCO voltage as
> high as possible as long as no reading is over 7.5 volts."  I managed
> to obtain 7.4 volts at 4.0 mhz, the rest follows.  I had 6.25 volts
> on 7.3 mhz.
> 
> Gary advised setting the VCO voltage on 4.000 mhz to 6.0 volts which
> i did.  That led to the voltage on 7.300 being 4.9 volts.  He said
> that above 5.5 volts it seemed that the voltage did not have time to
> drop to zero before keying began, hence the brief frequency change.

I had the same problem and the same fix worked.  It occurred to me that 
some operators may not be sure whether or not they have a chirp (it can 
be hard to detect for some people).  Here is how to listen for it:

Use another receiver which can be set to a bandwidth wide enough to 
allow you to hear both sides of zero beat.  Transmit with your K2 into a 
dummy load at low power, and turn down the RF gain control of the other 
receiver so that you won't be distracted by AGC action.

Transmit dits with the K2.  Listen first on one side of zero beat and 
then the other.  The signals should sound exactly the same.  If there is 
a frequency change associated with keying (chirp), the pitch change will 
be reversed on either side of zero beat.  Most people have no trouble 
hearing the difference.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco