Test Equipment and Tools
Test equipment and tools
It was extremely important for Station L to be able to make on-site repairs to equipment. It would have been totally impractical, especially during the radio station's war years, to have to send equipment to some repair facility. It was also required of the more technical characters on site to build some equipment. Their first radio transmitter was built on-site. Although this was a fairly simple crystal controlled, CW only, oscillator, buffer/frequency multiplier, final rf stage line-up transmitter, it was well built and very functional. I saw (in the early 1970's) the copy version that T McMenemy had built (during the early 1960's) for his personal use and it was a high quality transmitter. So, Station L had some basic test equipment and construction tools. I will provide a list of items here which they used up to and until about 1975 when the station was dismantled and the "L" team went underground due to political bickering and ill-conceived political and organizational interference throughout Europe. Not much of the test equipment found its way back to South Africa, however, some things did, so I will add these to the small repair section that was located in the radio room as well as in the generator room. Don't expect anything fancy.
BC-221 (SCR-211)
The BC-221 is a frequency meter that can be used for many purposes, including the frequency measurement of a transmitter or the frequency to which a receiver is tuned. When packed with all its ancillary components (calibration book, Bristo wrenches, instruction book, set of spare tubes and carry bag), it is known as the SCR-211. One also requires a headset and set of batteries before the BC-221 can be used. A compartment in the bottom houses the batteries; 6 V at 0.9 A and 130 V at 13 mA are required. The complete set weighs ~31 lbs. A built-in crystal oscillator is used as frequency standard.
The radio station at Luven used several BC-221 frequency meters. They were used to check transmitter frequency, also as a modulation monitor, and receivers were set to the exact required frequency by zero-beating on the BC-221 oscillator output. They were also used to align receivers as they could be used as a signal generator where the output was either set to the receiver IF or to an alignment frequency (typically at a low and then a high frequency within a particular waveband range of the receiver). As the correct batteries were nearly impossible to acquire in Switzerland during WW2, the station operators built a stand-alone power supply which fed the BC-221 meters. The LT and HT from this supply were coupled to the battery sockets; all were accessible via the rear compartment.
At a later stage I will add some photos of the actual installation and add a point from which the manuals can be retrieved. Although quite simple in design and having only a 3-tube circuit, these BC-221's and their LM variants were extremely useful, functional and reliable. In fact, it would be very hard to be without one.
BC-221 curcuit.jpg
Figure 5. AVO Model 8 MkIII, complete with manual, probes and leather carry case.
AvoMeter MKIII
The Station L operators used a Universal AvoMeter Model 8 MKIII multimeter that was manufactured in September 1965 (Figure 4). From the notes I have, the Avo was a very useful and popular all-rounder at the station. The MKIII features automatic overload protection, which protects the meter movement against excessive current and damage. They also had a 1964 military model of the universal AVO Model 8 MkIII (Figure 5), this has a metal rear casing. This meter is complete with probes, manual and leather case.
Figure 6. Wavemeter W.1117.
Wavemeter W.1117
Wavemeter W.1117 (Figure 6) covers the frequency range 125 kc/s to 20 Mc/s. The Luven radio station did not have many test instruments especially in the stations' early years. From my notes, it appeared that this wavemeter was carried off in November 1939 from the University of Bern to Luvis, which became Luven later on. At that stage it was quite new, as the W.1117 was manufactured in 1938. According to its manual, wavemeter W.1117 was designed primarily to tune master-oscillator controlled aircraft transmitters on the ground, and could also be used on aircraft carriers and in W/T vehicles. Below 8 Mc/s, it can indicate a difference on +- 2 kc/s, and above that resolution was a bit less, but still of the highest order available for this kind of instrument. It utilizes batteries for power, the L.T. supply is derived from a 2 volt, 7 Ah accumulator, the HT supply from a 120-volt dry battery and the bias voltage from a 4 - 5 volt dry battery. The batteries are accessed through a hinged door at the back of the wavemeter. The Luven unit is shown in Figure 6, it will need a clean-up, but is complete and original.
Figure 7. Triplett 1621 tube tester.
Triplett 1621 tube tester
This tube tester (Fig. 7) was manufactured in 1940. A fold-out booklet (Fig. 8) contains settings for different tube types.
Figure 8. Triplett settings for different tubes are tabled in a neat fold-out booklet attached to its front.