My recent efforts in optimizing the SG504 head has led to this concept which addresses a lack of accurate freq. display and amplitude compensation using digital controls.
These functions can be 'built in' to an upgraded leveling head (Li Ion battery powered, rechargeable).
Concept statement subject to refinement.
In using the SG504, one of the areas I think could make the unit more useful is a reasonably accurate frequency counter display. Perhaps to 1Khz via a uC comparator triggered pulse counting.
I've come up with a concept 'head' which adds a battery operated low power microcontroller to do the job via a small 8 x 2 LCD display (58mm x 32mm) mounted in the head. LCD display triggers by detection of a FRQ sweep or flashes the static FRQ one sec in every 5 secs to conserve power.
Now this approach will allow anyone to also 'flatten' the head output relative to the ref. 6Mhz level to potentially within 0.01dB steps via a 0.31dB range of adjustment ((5 bit) DAC output). This requires an additional schottky detector coupled @ the head output.
The process works by activating the cal. mode (pushbutton) while in the 6Mhz range. The controller then locks the amplitude ref. . Then the user switches to the Low range and starts to sweep, slowly, then the high range, repeat sweep. The controller monitors the frequencies and determines amplitude offset points to 'map' the head amplitude flat. Once the frequency stops changing for a few secs the head comes out of cal mode and applies frequency mapped corrections (every 3.2 Mhz step) via it's (5 bit) DAC output. No PWM.
It 'corrects' the head amplitude by modifying the DC level amplitude signal to the SG504.
In terms of operation, I see it working like this.
The user sets the amplitude and selects the 6Mhz SG504 ref. The controller detects the 6Mhz ref and grabs the ref. amplitude. Then it can properly apply all the stored corrections to the current amplitude level.
Thus when changing amplitude the user would need to activate the 6Mhz ref, set the amplitude and switch back to the frequency of interest for precision leveling.(Perhaps using 12 or 14 bit oversampling)
The system can permit an RS232 to USB serial link to a PC to output live frequency and ref. amplitude data.
I might look at a 10Mhz ref input as a feature for syncing to a common source, which can then provide direct means to cal the SG504 6Mhz frq ref. with just the head alone.
Idk whether this seems worthwhile to the forum, but it's an idea that is interesting to me and seems economically viable and adds usefulness to the instrument without having to 'hack' the instrument itself.