[Elecraft] S-Meter Calibration

George, W5YR [email protected]
Mon Feb 11 13:26:11 2002


Although the Kachina 505 DSP radio has a few drawbacks, one of its sterling
qualities is an S-meter that operates just as Bob describes: from a
calibration table. It can read out in S units, dbm or microvolts.

I have been pleased to see that the Icom 756 PRO S-meter follows very
closely with the Kachina meter when doing A/B tests. A brief comparison
with a K2 showed that the K2 usually reads "in the ballpark" although it
offers much less resolution due to the LED display. 

Another convenient feature of the Kachina is output power controllable to
within 0.1 db of the indicated value. I use this feature as an attenuator
test generator to evaluate and calibrate wattmeters. For example, the
wattmeter in my MFJ 989C is right on at 10 watts up to 100 watts, to within
a pointer width, but has increasing error below 10 watts. The QRP level of
5 watts actually is indicated at 7.5 - 8 watts on the meter scale.

I know none of this applies to the Elecraft products, but I just wanted Bob
to know that at least one commercial radio has realized his goal. I suspect
that many if not most high-end military receivers have as well, but at
multiple kilobuck prices.

72/73/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771
Icom IC-756PRO #02121  Kachina #91900556  IC-765 #02437

All outgoing email virus-checked by Norton Anti-Virus 2002


"Bob Lewis (AA4PB)" wrote:
> 
> > In theory, I like the idea of calibrating the S-meter to show S-9 at
> 50 uV.
> 
> One problem is that unless you've done some very careful receiver
> design, the reading would only be accurate at one meter reading (S-9)
> and on the band that the calibration was done. Using firmware, it
> might be possible to provide a calibration table that would compensate
> for different receiver gains on different bands and for the
> differences at different signal levels including whether or not the
> preamp was switched on. Unfortunately not many of us would have the
> test equipment available to do an accurate calibration of the system.