Lets talk lichtsprecher....

[fieldgear]

Thanks Pierre

I do have this book, so will go have another look at the details!

best,.>Rob

[Funksammler]

Bringing the Lichtsprechers back to life

I was planning to test my Lichtsprechers for a while now, as I am hoping to recreate the historic Lichtsprech link from Omaha Beach for the oncoming 70 year commemorations. Some queries from fieldgear, who is also hoping to restore his sets to working condition prompted me to dust off the old equipment, build some power supplies and see if I could get them to work.

The Lichtsprech Geraet needs two power source, a 2,4 Volt supply to supply the filament current for the valves and power the lamp in the optical head (on earlier versions a 4.8 Volt battery was used in addition to power the lamp, but both my optical heads are fitted with 2,4 Volt lamps). I am using an original 2,4NC28 battery and a russian equivalent to power the two sets:

<a href="http://s672.photobucket.com/user/Funksammler/media/DSC06185_zpsf1aa70ed.jpg.html" target="_blank"><img src="http://i672.photobucket.com/albums/vv86/Funksammler/DSC06185_zpsf1aa70ed.jpg" border="0" alt=" photo DSC06185_zpsf1aa70ed.jpg"/></a>

The anode battery has to supply +50, +60 and -1.5 Volts. This was simply made by clicking 7 9-Volt cells together, an extra wire was connected between the 6th and 7th cells, this gives 54 and 63 Volt which is close enough to operate the set. A 1.5 Volt C-type cell was soldered to the negative terminal to provide the - 1.5 Volt. A bit of tape to hold the batteries together and a contact strip completed the Anode battery:

<a href="http://s672.photobucket.com/user/Funksammler/media/DSC06184_zps9bd99ed5.jpg.html" target="_blank"><img src="http://i672.photobucket.com/albums/vv86/Funksammler/DSC06184_zps9bd99ed5.jpg" border="0" alt=" photo DSC06184_zps9bd99ed5.jpg"/></a>

Initial tests of the first set were slightly disappointing, the amplifier was dead as there was no noise coming from the headset although I could get the prism unit in the optical head to vibrate when speaking the microphone. The problem was traced to a faulty valve and a broken soldering connection on one of the valve sockets. After fixing this a noise could be heard through the headset. Here is the amplifier in operation, showing the 2,4 Volt supply voltage on the instrument:

<a href="http://s672.photobucket.com/user/Funksammler/media/DSC06174_zpsbcbe2a14.jpg.html" target="_blank"><img src="http://i672.photobucket.com/albums/vv86/Funksammler/DSC06174_zpsbcbe2a14.jpg" border="0" alt=" photo DSC06174_zpsbcbe2a14.jpg"/></a>

The testing of the second set revealed no major problems, so now it was time to connect the optical heads to see if we could hear the light! As soon as I turned on the set I could hear a clear buzzing sound. My optical head was pointing at a tube light and moving my hand before the receiver lense reduced the buzzing. Switching the light on and off could clearly be heard in the headset, result!

After testing the second set with similar results it was time to set up the sets oposting eachouter and see if they would communicate. Here is set nr 1 ready to go:

<a href="http://s672.photobucket.com/user/Funksammler/media/DSC06173_zps2bce65cd.jpg.html" target="_blank"><img src="http://i672.photobucket.com/albums/vv86/Funksammler/DSC06173_zps2bce65cd.jpg" border="0" alt=" photo DSC06173_zps2bce65cd.jpg"/></a>

After a bit of tinkering I managed to get them to work! The alignment of the optical heads proved very critical, even at this very short distance. The modution control (a small adjustment know on the bottom of the optical head) needs to be tweaked before proper light modulation occurs, When speaking loudly into the microphone, a clear "rattling" noise can be heard in the optical head. The rattling means the modulator is a bit too loose causing distortion of the signal, so a sligth adjustment will tune it properly. Here is the Lichtspecher lighting up:

<a href="http://s672.photobucket.com/user/Funksammler/media/DSC06176_zps7092591c.jpg.html" target="_blank"><img src="http://i672.photobucket.com/albums/vv86/Funksammler/DSC06176_zps7092591c.jpg" border="0" alt=" photo DSC06176_zps7092591c.jpg"/></a>

I also decided to test the field telephone line functionality of the Lichtsprechgereat by rigging up two FF33's to one of the unit. By switching to field telephone mode, an extra amplifier stage is switched on. Somewhere in the circuit some feedback is created as on high volume a loud beeping noise occurs, which dissapears when the volume is dialled back somewhat. I have not figured out yet where the feedback oscillation between the transmitter and receiver circuits occurs, probably through the anode supply voltage. In any case, the field telephone link works, allowing me to speak from either FF33 to the opposing Lichtsprecher. Here is set 2 with field telephones connected:

<a href="http://s672.photobucket.com/user/Funksammler/media/DSC06177_zpsedf510cd.jpg.html" target="_blank"><img src="http://i672.photobucket.com/albums/vv86/Funksammler/DSC06177_zpsedf510cd.jpg" border="0" alt=" photo DSC06177_zpsedf510cd.jpg"/></a>

If the set is operated in field telephone mode, the reception and transmission signals are coupled in the telephone circuit, this means that the signal transmitted from set 1 to set 2 is coupled back into the transmitter circuit of set 2 through the telephone amplification circuit and re-transmitter back to set 1. So when speaking in the microphone of set 1, you can hear your own voice in the headphones of set 1.

Testing the two sets in such close proximity makes it possible to operate the microphone of one set and hear the result in the second set. Using your own voice makes it difficult though to judge the quality of the signal so I will have to do some more experiments over a greater distance when the weather allows me to play outside!

regards,

Funksammler

[Val]

Love it! When will there be an Omaha link?

[fieldgear]

Hi All

Firstly a huge thanks to Funksammler for the assistance with my project to get my 2 units working. Unfortunately I cant announce success yet, but there have been several steps forward.

Both my amplifiers have been tested & found to be working. Here is the test regime as per the info provided by Funksammler. (I used a digital auto ranging multimeter for this.) I'm posting this pretty much in its entirety so the data is preserved for everyone:




"Disconnect the cable to the optical head; connect the batteries and insert the headphone. Connect the - terminal of your multimeter to the Lb/E terminal of the telephone connection (earth), set your mulitmeter to the first range over 60 Volt. Wear the headphones for this little test. Switch the amplifier to Sendeempfang.

1) measure the left most contact of the 6-pin plug, this will read 40-60 volt (you are measuring over capacitor 10 on the schematic which doesn't conduct the DC voltage apart from a bit of leakage)

2) measure the second contact of the 6-pin plug, this will read 2,4 volt. If the amplifier is switched to empfaeng, this voltage will disappear (what you are measuring is the supply voltage to the lamp in the optical head)

3) measure the third contact of the 6-pin plug, this will read 30-50 Volts (what you are measuring is the suppressor grid supply voltage to the valve in the optical head, this runs via resistor 28 in the schematic and capacitor 31; the measured voltage will depend a bit on the leak resistance of the capacitor, the higher the voltage measured, the better the capacitor....)

4) measure the fourth contact of the 6-pin plug, this will read about 2-2.2 Volt (what you are measuring is the filament voltage to the valve in the optical head)

5) measure the fifth contact of the 6-pin plug, this will read -1.5 volt (what you are measuring the negative grid bias voltage)

6) measure the sixth (rightmost) contact in the 6-pin plug, this will read about 60 Volt. When touching this terminal you should hear a clear crackling noise in your headphones (what you are measuring is the anode voltage supply to the valve in the optical head, this is connected via capacitor 35 to the input of the audio amplifier. The capacitor stops the DC voltage going through, but any audio signal should pass - hence the crackling noise when this terminal is touched).

If you get the crackling in your headset when doing measurement 6), the amplifier is working OK."




My units matched the voltages pretty much perfectly at both the socket on the amplifier & at the end of the connecting lead.

However, after reconnecting to the optic head, there was no response.

Following on from here, a test was devised for the light sensitive units. (A simple resistance test.) Both mine were found to be open circuit & hence "dead".

Today, I have obtained 2 light dependant resistors (20M ohm dark) & fitted these to my optics. Both units now "see" the 50Hz buzz from flouro tube lights. It is quite distinct & disappears / reappears as the lens is covered or not. Unfortunately the LDR is slightly too big to fit into the hole in the ceramic. but it does fit nicely over the hole with the wires "press fitted" to the original mount. This keeps the mount original.

(more follows above)

[fieldgear]

Following on from below, the next test is to make sure the optic alignment is ok & the 2 units look directly at each other. Short ranges are a bit tricky in that the beam is not big. Small adjustments could make a big difference. The fact that they "see the light" so to speak & I can clearly hear the 50Hz buzz, makes me optimistic.

A quick attempt today has not been successful, but at the end of a working day, there are other demands...

Hopefully by the weekend I can announce success. I will also take a few pics then & post these also.

Best,>>Rob

[Funksammler]

Great to hear that you can now pick up the light! The semiconductor materials used in the 1930's by the Germans unfortunately do not last very well. Originally the Lichtsprechers were supplied with four spare light cells, indicating that even at the time they were not seen as 100% reliable. The cells in my equipment were replaced by modern LDR's (Light Dependent Resistors) in the 1980's, even at that time the original cells had already perished. Fortunately replacing them with a modern example is a simple and cheap option. Based on the Lichtsprecher schematics and the materials used originally, the LDR's need to have quite a high resistance, hence the recommendation to go for a type with a dark resistance of 20 Mega-Ohm. As Fieldgear shows they can easily be fitted to the Lichtsprecher's optical unit.

The other components used in the electronics by Zeiss seem to be of exceptional quality. Both in my own units and those of Fieldgear the capacitors all seem to have survived. I believe there must be more Lichtsprechers out there with the potential to work again!

The next step will be to get the two units aligned. The easiest way to do this is to set up the optical heads in a darkened room with a wall behind them. This way you can see the lightbeam projected on the wall and it is easy to guide it to the receiver lens of the opposing optical head. You will clearly hear the noise level change when the lightcell picks up the beam. After repeating the process on the other end the Lichtsprechers are aligned. You can verify the optics by peering through the viewfinder, the red dot should be centred on the viewfinder lense of the opposing unit.

Now it will be time to adjust the modulation. The viewfinder will show a green grid in the bottom, turn the modulator adjustment so that the grid just starts to light up. Speaking into the microphone should be clearly visible on the grid as a variation of brightness. Loud noises in the microphone result in a clattering noise in the optical head. This is the electromechanical mechanism vibrating. With your receiver and amplifier now working, you should be able to hear the voice in the opposing set.

Good luck with the tests!

As far as my own experiments are concerned, I aim to do the recreation near Omaha beach on the 6th of June. I am going to seek official permission to use the Colleville church tower, as that has an unobstructed view to WN62. I am planning to run a field telephone line from the church to WN63, which will be pretty close to the original setup used in 1944.

Regards,

Funksammler

[Val]

About LiSpr and Omaha...

LA6NCA, in the end of your page there are several images unaccessable, including the Omaha ones. Could you please check this? Thank you.

http://www.laud.no/ww2/lispr/

[Funksammler]

Here are some pictures of the fortifications on WN 62 on Omaha Beach. The first picture gives an overview of the the rearside facilities. I am standing on an underground passage towards the sleeping quarters for the crew (to my left) with a trench leading towards two Tobruk stands (to the right) and a small concrete construction in the back which is now largely filled in with soil:

<a href="http://s672.photobucket.com/user/Funksammler/media/DSC01978_zpsbed14130.jpg.html" target="_blank"><img src="http://i672.photobucket.com/albums/vv86/Funksammler/DSC01978_zpsbed14130.jpg" border="0" alt=" photo DSC01978_zpsbed14130.jpg"/></a>

This concrete construction was a bit of a mystery, until I came across a German account of the history of WN62 which mentioned the use of a Lichtsprechgeraet to communicate with the inland command post (WN 63). Suddenly everything clicked into place, the mysterious little pillbox was in fact a protective stand for the Lichtsprechgeraet:

<a href="http://s672.photobucket.com/user/Funksammler/media/DSC01979_zps50603dde.jpg.html" target="_blank"><img src="http://i672.photobucket.com/albums/vv86/Funksammler/DSC01979_zps50603dde.jpg" border="0" alt=" photo DSC01979_zps50603dde.jpg"/></a>

You can see the Colliville church spire in the background, WN 63 is located just in front a little bit lower down. Due to the trees it will not be possible to link to WN 63 directly, but I should be able to get a clear connection to the church tower

Here is a picture of the rear of the Lichtsprechgeraet pillbox. It has a small slit just large enough for the optical head of the Lichtsprecher to peek through.

<a href="http://s672.photobucket.com/user/Funksammler/media/DSC01980_zpsfa89969b.jpg.html" target="_blank"><img src="http://i672.photobucket.com/albums/vv86/Funksammler/DSC01980_zpsfa89969b.jpg" border="0" alt=" photo DSC01980_zpsfa89969b.jpg"/></a>

German accounts tell that the microphone of the Lichtsprechgeraet near WN 63 was connected to the speaker of an old grammophone, the operators in WN 62 could so secretly enjoy listening to some music in their time off!

The accounts also tell that in the afternoon on D-day, when ordered to retreat, two crewmembers actually packed up the Lichtsprechgereat and took it with them. During their circuitous and dangerous escape, they decided to dump the equipment somewhere in the bushes behind the beach, where they may well lay undiscovered to this day!

regards,

Funksammler

[Val]

I am going to seek official permission to use the Colleville church tower, as that has an unobstructed view to WN62.

Is this the church you are referring?

http://en.wikipedia.org/wiki/File:L&#39;...Colleville.jpg

[Val]

Here is also LiSpr mentioned at WN62

http://www.jewishvirtuallibrary.org/...ww2/omaha.html

Funksammler, do you have an info/picture - where at WN63 LiSpr was
originally located?

[fieldgear]

Hi Funksammler & all.

I wish I could be there for this re-enactment!

Last night I managed to slip out to further test my gear. I seem to still have an issue somewhere.

To recap, both units "see" the 50Hz from tubes & emit a strong buzz when the tube is lit. Both heads show the grid ok however the light output from head B has become a little weak. At a range of only 2 metres it is good enough to illuminate the LDR in head A. I will get to the bottom of this in the next day or so.

With both sets properly aligned with each other, Set B is turned to Sendeempfang. As soon as Set A is turned to Sendeempfang, Set B goes quiet. When done in reverse, Set A does not react. (Issue1)

There is no voice either way. (Issue2) I have tested both mics with a FF33 phone. With clip leads, I connected the earpice to the terminals & the mic to the mic terminals. Using my cellphone as a music source, on pressing the mic button, the music can be heard in the earpiece.

Having confirmed the mics are OK, back to the Lispr. Reconnecting to the amplifier & speaking into the mic, there is no visible change to the grid.

Also, when the mic switch is depressed, the electromagent can be heard moving. I cannot say I have ever heard it "clatter" In my case both heads "click" when the mic switch is depressed, but not clatter. (Issue3) Is it the electromagnet or what drives it?

Best,.>Rob

[Funksammler]

It was placed on top of the roof of WN63. They built a shelter on top of WN63 to protect the equipment from the elements.

The unit on WN63 was operated by Obergefreiter Bernhard Lehmkuhl while Obergefreiter Luetzen was responsible for communications on WN62 with Oberschuetze Bruno Plota as his deputy. During the morning of d-day, Luetzen was wounded in his shoulder and his hand, but he initially agreed to stay at his post. Early in the afternoon he and some other wounded were allowed to retreat and the responsibility for the Lichtsprechgeraet was handed over to Plota. Plota was ordered to withdraw about 15:00 and it was him who dismantled the Lichtsprecher and carried it down the hill before discarding it.

Regards,

Funksammler

[Val]

Fieldgear, are the cables from the amplf. unit to the head OK? Test them with multimeter, bend them...

2. Test the modulator RV 2 P 800

[Funksammler]

Rob,

What type of microphone are you using? Can you test the left bottom valve (nr 6in the schematic)?

The weakening light is either a fading power supply or a dirty contact, or the lightbulb itself. There is just the transmit switch between the 2,4 Volt supply and the bulb. Also check the earth contacts of the cables between the amp and optical units....

Regards,

Funksammler

[Val]

Funksammler, what kind of Blinktaster was used with the LiSpr?