94
Item nr.
Measuring instrument for adjusting army transmitters in the field
| Production | USA, 1943. |
|---|---|
| Bands | 125-20,000 kHz. |
| Tubes | 77 6A7 76. |
| Cabinet | Steel. Size 24x36x22 cm. |
| Power | Originally: Batteries 250 and 12V Now: AC230V. |
| Documents | Calibration table. |
To enable high precision operation, the LM13 has a crystal oscillator that runs on 125 kHz with a precision of about 1 in 100,000 and a temperature drift of 1 per million per degree. The variable oscillator is calibrated against this crystal at every multiple of 125 kHz. Before measuring a certain frequency, first the oscillator is calibrated at the nearest reference point. Reading out the meter is a pain in the butt because the dial is not marked in frequencies, but with numbers from 1 to 5000. A little booklet that goes with the unit gives the correspondence between numbers and frequencies.
Besides LM13, the unit is known under type number SCR-211. The meter unit alone, which can be taken out of the black battery and carrying case, has type number BC-221 (where BC stands for Basic Component). The black case was used during the forties. In the fifties the units were still in use, but then the outer cases were of olive color. (Source: George F. Miller.)
| Obtained | 6/1998 from person in Rijswijk. |
|---|---|
| Condition | 8. |
| Disposed | Sold 10/2013. |
After the Second World War, a lot of army devices became obsolete and were bought by radio amateurs. Because they did not use the equipment in the battle fields but at their home QTH, they often fitted the apparatus with main power supplies. Like the Knight, the unit had to be adapted for European use. The power supply was thrown out and replaced by a modern one for 230V AC. It is still a very useful instrument and the picture shows me using it for frequency measurements on a EAK6450.