By Ian Walker ZL1BFB
In the early 1960s the Radio Inspectors tested not only for radio interference but also when applications for radio transmitter licenses were received, including CB sets.
This photo was taken at the Regional Engineers Building in Federal St (Reid House) on the first floor where tests were carried out. This room was used for testing all appliances, etc. for type approval to the BS800 interference specifications and the NZ Radio Regulations.
The photo shows the tool shadow rack on the wall designed and painted by myself and mounted on the wall above the test bench where transmitters and tools, etc. were tested for interference.
No prizes for guessing the identity of the fine young, clean shaven and well groomed person in the photo. I am testing a CB set for type approval at the time of issuing a licence.
Starting from the left of the photo we have the shadow board, arranged by myself so that the tools required were easily accessible. These had previously been located in desk drawers or on shelves in a clutter.*
On the far left is the paint brush used to clean the working components or graphite from within the equipment to be tested. A lot of interference could be caused by tracking within the appliance from soft carbon brush material. Many of the electrical tools or pieces of equipment that came in for testing had been given a hard life and found to be electrically noisy, so cleaning out the residue of the soft carbon brushes was a priority.
The Skill battery drill was used on the many screws or sets that were holding appliances together and had the advantage of not having to rely on mains power other than for charging. Allan keys were also used to open appliances. To the left of the scissors is a second chuck for the drill and above this is the socket set and drive adapters for the battery drill.
On the top shelf is an AM/FM modulation meter, and to the right of this the two-tone audio generator which was applied to hand microphones. Next is the 50 watt dummy antenna load, mainly used on MF radio equipment; this had an output terminal for the counter, etc.
For testing the accuracy of frequency measurement we used the Marconi digital frequency counter. This incorporated a down converter that would extend the counter range to 10 GHz. Again to the right is the 12 volt regulated power supply which was coupled to the CB set being measured. This was set at 13.5 volts and could handle up to 7 amps. It was purpose built by the NZPO Radio Workshop in Galatos St.
Like all the best radio workshops, we couldn’t be without the AVO-8 volt/ohm meter.
Below the counter is the 3 watt / 10 watt Marconi dummy load with direct readout of the power of the set under test. The CB set under test is being tested into this and the readout can been seen (on the original photo) as 26.499770 Hz, although the watt meter reading is hard to read. Also on the main bench is a hand-held CB which was waiting to go through the same process.
At the bottom far left is our oscilloscope, used for harmonic checks and distortion on signals, etc. generated by appliances when operated from the mains. The equipment was also able to be used in the field on a battery supply (although not often).
The RI 2 measured frequencies from 35 MHz to 220 MHz with three RF amplifiers into one common IF amplifier unit. There was a mains isolation head which acted as the artificial antenna pick up.
This was normally used in the office for measurements of electrical noise from appliances using the mains. The measurements were at +/- 3dB at the frequency after calibration, whereas the frequency of the RI 1 was for LF (beacon band) to 30 MHz, and had to be recalibrated after each frequency shift. It was accurate to also +/- 3dB. Both measurement receivers could be used in the field by using lead acid batteries and power supplies. Both units had similar types of artificial antenna pick up for measurement in this case. When used in field testing they used calibrated antennas. All equipment at the office was operated on isolation for the protection of staff.
In order to prevent damage to any equipment being tested or the testing equipment itself, the bench top was covered with a padded insulating material. From memory this was the same as that used for appliance testing – a ¼ inch, rubber, non static sheet.
* No comment! – Ann Walker ZL1TRH (Ian’s XYL)