GHG high pass filter

[nihilcat]

I've noticed that there are two dials below the handwheel on the GHG compensator.

http://www.ubootwaffe.pl/images/phocagallery/okrety/u995/U-995_070.jpg


What was their use? Could the high pass filter be adjusted with them?

As far as I understand the higher the frequency, the better the accuracy, but also range gets worse. I believe that such adjustments had to be possible as with fixed filter one wouldn't hear the higher frequencies without a proper amplification.

My leading theory is that one of these knobs adjusts the cutout frequency, while the second one adjusts the volume gain, but I haven't found any sources that would confirm that.

Any help in figuring this out will be greatly appreciated! :Kaleun_Salute:

[nihilcat]

I've made some progress by looking at the photo over and over again :Kaleun_Wink:

There are 4 scales at the central indicator. The most outward scale (the white one) is the relative bearing spanning from 0 to 360 degrees.

Initially I assummed that the 3 innermost scales were somehow used to convert relative bearing to true bearing, but that turns out to be completely wrong, if you will take a closer look at their ranges:

- yellow 400 - 860
- white 800 - 1750
- green 1600 - 3500

Their total range covers values from 400 to 3500, so now I'm pretty sure that these are the sound frequencies! I believe that there must be two pointers here - one pointing the angle and second indicating the cutout frequency.

There are still some questions left:

1. Where is the second pointer? Is that this thin line at the center of the big pointer? There doesn't seem to be any other possibilities.

2. How to choose a specific value with a single pointer, considering that the numbers are spanning through three scales - yellow, white and the green one? Do you somehow switch between three modes? My theory is that the small dial on the left is a three state switch between three ranges and the second small dial is used to choose a specific value, by rotating the pointer.

3. Where to set the volume gain, if there are no dials left? Is that device on the left an amplifier?

http://www.ubootwaffe.pl/images/phocagallery/okrety/u995/U-995_072.jpg

[Legion1183]

Nihilcat I did find these that may be able to help you I am sorry if it is not in Polish I found this in English it follows from what I can translate of the German version Nilex posted on Kickstarter. It follows a lot of the ideas but has in my opinion easier to follow pictures.

http://www.cdvandt.org/GHG1996.pdf

[nihilcat]

Nihilcat I did find these that may be able to help you I am sorry if it is not in Polish I found this in English it follows from what I can translate of the German version Nilex posted on Kickstarter. It follows a lot of the ideas but has in my opinion easier to follow pictures.

http://www.cdvandt.org/GHG1996.pdf

Thank you. I've seen that pdf before, but somehow missed some of the important parts back then. It seems to confirm the NileX13 translation and the final conclusions, so we are good :up:

To sum things up for the next generations :03: GHG compensator could operate in three frequency ranges:

- Yellow, 1 kHz center frequency, high pass filter cutoff range of 400 - 860 Hz.
- White, 3 kHz center frequency, high pass filter cutoff range of 800 - 1750 Hz.
- Green, 6 kHz center frequency, high pass filter cutoff range of 1600 - 3500 Hz.

Dials:

- Left dial sets the frequency range - yellow, white or green.
- Right dial sets the direction.
- Central dial sets the high pass filter cutoff frequency and its value is repeated by the big pointer at the center.

It's still unclear, if there is a second pointer that would indicate the direction. Probably not :hmmm:

Symbols above the left dial cast some doubt on my interpretation of its function as they doesn't seem to be related. That seems to be the only possibility though and it's confirmed by one external site (https://www.u-historia.com/uhistoria/tecnico/visitaguiada/salaradio/salaradio.htm).

Many thanks to NileX13 for helping me to figure this out :Kaleun_Cheers: