[Elecraft] VCO voltages for 160m band??

[W3FPR - Don Wilhelm]

Bob and all,

There is a difference in which frequencies will produce the lowest/highest 
VCO voltage if the K60XV is installed.  Without the K60XV, the lowest 
reading is usually 7 mHz, but after the K60XV installation, 1800 kHz and 
4000 kHz become the more critical points.  With the K60XV added, it is good 
practice to check all the band ends to be certain they are within range.

Your observations about the AGC Threshold are correct - there is some 
variation for the proper threshold voltage from K2 to K2 (but normally not 
as wide as you report).  However, be certain you are doing the AGC On/Off 
check on a quiet band because even an S-1 noise level will alter your 
adjustments from the norm.  For my own - if I had a high noise level, I 
would want the AGC Threshold set so no AGC action occurs because of the 
noise - even if it results in 'strange' value settings.  Bottom line, your 
abnormal settings could be due to conditions present at your QTH.

73,
Don W3FPR

----- Original Message ----- 

>
> I needed to open up my K2 serial no. 4168 to tinker with the AGC threshold
> setting so took the time to measure what the VCO voltages at R30 were on 
> 160m.
> The results are:
>                        1800kHz  = 1.68V
>                        2000kHz  = 3.83V
>
> On my particular K2 on initial testing the lowest reading VCO voltage
> reading came out on 7000kHz rather than 3500kHz so made that the reference 
> setting
> at 1.50V. This shifted up 3500KHz to 2.40V and 4000kHz to 6.85V. All 
> still
> within the stated goal posts.
>
> As a side issue the optimum AGC threshold seemed to be at 3.70V rather 
> than
> the initial 3.80V on this K2. Another item noticed during testing was that
> even  with the S LO and S HI correctly adjusted for the new threshold the 
> signal
> level  required for S9 reduced with lower threshold settings. On this K2 
> with
> the  preamp off the settings for S9 came out as follows:
>
> AGC threshold V.    uV PD for S9.
> 3.80V                        63uV  (-71dBm)
> 3.70V                        40uV  (-75dBm)
> 3.60V                        25uV  (-79dBm)
>
> With the new setting of 3.70V the audible low level band noise  from AGC 
> on
> to AGC off is just reached the point of no change. This compares  with the
> initial AGC threshold setting of 3.80v, where there was  a small increase 
> in noise
> when the AGC was switched off.
>