SG 504 leveling head gets a surprise upgrade.


 

Hi All:
I did some more work on improving the SG-504 leveling head performance. This improvement happened by accident due to a poor solder joint on one caused me to dig deeper into the impedance matching arena.
I determined that a 0.15dB loss (4Vpp) at the SG504 operating frequencies from 250Mhz thru 1050 Mhz is relatively consistent, from small impedance matching losses in the head as it is in the signal line.
Usually I compensate the hi range using stub tuning via PCB parasitic capacitance to improve the accuracy at the high end (800 to 1050MHz)to around .05dB. This compensation had much less effect on the low range being freq. dependent.
With some impedance matching adjustments on the output of the head it now achieves a sub 0.1dB accuracy across the whole range, indeed usually sub .05dB!
The caveat is with the 6MHz test signal you will see a 6.15dB level outputted @ 4Vpp due to minimal test frequency losses.

Since the SG 504 operational frequencies of interest (250Mhz thru 1050Mhz) are now calibrated to usually reach 0.05dB accuracy @ 4Vpp, I feel the
head is improved with no added costs. Had to add one extra SMT resistor to compensate for small resistive and frequency related losses in the signal path.

So the most recent purchaser, a gentleman from the UK, has the 1st of the new generation in precision leveling heads on its way to him.

I employ a 12Ghz Sensor Head, Boonton 4210 RF microwattmeter to achieve the precision dB measurements.

If you are interested in purchasing my improved SG504 Leveling Head please contact me OFF-LIST at @Protofabtt.

cheers,
Ancel

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