[Elecraft] First pass... sidetone output tests

[George, W5YR]

Tom, while my brief examination of the audio on #489 is limited to
measuring speaker output only, perhaps the data will be of interest.

Equipment used:

K2 #489

Goldstar 9020 20-MHz dual-trace scope

Beckman 2020 True RMS DMM and Radio Shack 22-168 DMM

Procedure:

1. The scope and 10X probe were calibrated against the internal scope
calibrator signal to 500 millivolts per centimeter. A resistive load
measuring 4.03 ohms was connected to the Speaker jack and voltage
measurements taken across that load.

2. With ST L set at 050, I measured a peak-to-peak 702 Hz tone signal of
240 millivolts. This corresponds to 84.8 millivolts rms. The BI DMM read 80
millivolts rms while the RS DMM read 83.1 millivolts. While the waveform
was a true "eyeball" sinewave, the BI meter reads true rms while the RS
meter does not.

3. With ST-L set at 255, the scope signal computed to be 424.2 millivolts
rms. I did not make DMM measurements since the first test produced similar
readings.

My K2 does have the AF filter installed but it was not used for these
measurements. The sidetone waveform mod has been installed. In general
usage, I do not consider the K2 to be deficient on audio except on very
weak or marginal signals. On any signal that is S5 or above, the audio
level is adequate.

Tom, I note that your sidetone level was set for 052 which might account
for the somewhat higher readings you observed.

Incidently, I have to set CAL ST P at 0.69 in order to get the 702 Hz tone.
The sidetone pitch is about 10 Hz high if I set it at 0.70. C22 has been
adjusted to place the MCU clock at 4000.000 MHz per my Icom 756 PRO which
is calibrated to within less than two-Hz error against WWV. 

I calibrated C22 at the fourth harmonic of 16 MHz using One-Hz resolution
on the PRO and measuring the beatnote both by scope and by HP 400 AC VTVM
to find minimum AC for the zero-beat state. Final adjustment had the
oscillator at less than one Hz beatnote against the PRO. Even after all
that, ST P still has to be set at 0.69 to produce a 702 Hz sidetone pitch.
Any ideas?

I have recently completed a 95 dB attenuator for the PRO to provide a
sufficiently low output signal to run tests with the K2. The PRO has a
minimum r-f output level of 1.55 watts which is reduced by 95 dB to produce
about an S5 signal on the K2. So, until I can find something like an HP 606
signal generator, I will have to make do with the PRO.

73/72, George    
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489      Icom IC-765 #2349     Icom IC-756 PRO  #2121


Tom Hammond N�SS wrote:
> 
> Hi folks:
> 
> OK... haing recovered from a near heart attack when I lost sidetone
> temporarily, I have the following measurements to offer.
> 
> My first tests were on the SIDETONE since I didn't have to provide an audio
> signal external from the K2.
> 
> SIDETONE TEST RESULTS
> 
>    1. Used three (3) 12 Ohms resistors in parallel to give 4 Ohm
>       load at the 2-pin SPKR plug on the RF board.
> 
>    2. Set ST L (050) to produce 0.4V p-p @ RP7-8.
>       On my (Field Test) K2, this generally produces
>       a very usable sidetone level in the speaker.
> 
>    3. Voltages read at:
>                 O'scope    RMS DMM      Comment
>        RP7-8   0.40V p-p (88.5mV RMS)
>        RP3-4   0.22V p-p (81.7mV RMS)
>        RP3-6   0.20V p-p (71.5mV RMS)
>        U10B-7  0.20V p-p (74.0mV RMS)
>        U9-8    0.29V p-p (106.7mV RMS)   BYPASS of U9
>        U9-6    0.30V p-p (107.0mV RMS)   AF OUT of U9
>        Spkr    0.26V p-p (92.0mV RMS)    @ 4 Ohms load
>                                    Note: I get 1.4V p-p (743 mV RMS)
>                                          across the 4 Ohm SPKR output
>                                          load when ST L = 255
> 
> Test conditions:
> 
>    K2 #0008
>    U8-4 (KIO2) mod installed
>    Sidetone sine wave mod installed
>    KAF2 NOT installed (Control Board KAF2 connector pins
>      jumpered 1-to-1 and 2-to-2).
> 
> Equipment used:
>    Tektronix 2236 Scope 10X probe
>    Fluke 187 True RMS multimeter
> 
> Now, to break out the sig gen and do some RF voltage checks.
> 
> More later. I'd be REALLY interested to see if others obtain similar results.
> 
> 73,
> 
> Tom  N0SS