Wavetek Signal Generator Type 2407

 This equipment provides coverage from 10KHz to 550MHz via step up and step down push buttons or direct key entry.

It was relatively cheap to buy (under £200 in 2002 when it was 11 years old) considering the build quality and performance.

 The complete user manual can be seen here

 Below is a key to the controls. It's quite user friendly but it needed a handbook to let me know most of the functions. When the power is turned on (button 1) the generator runs through a self test routine which gets more worrying as the equipment ages. I've had two problems so far. One, immediately after buying it and turning it on for the first time, which turned out to be a short-circuit protection diode and the second quite recently which was again the loss of an internal power rail. This was easily fixed although the self test gave a strange fault report which I imagine was because the guys writing the test firmware must have imagined the power supplies would never fail?

The two most frequently used functions are setting the frequency and setting its level.

Direct entry via the keypad "3" is the most useful way of doing either but the up and down arrows "4" can make incremental changes, for example to determine the tuning peak of a circuit.

For example: pressing Freq, 465 then KHz will set the generator to 465KHz. Pressing Lvl, 5 then uV will set the output to 5 microVolts. Once this has been done you can set the output to CW "Mod Off", AM, or FM setting the modulation depth as required. The button marked "5" switches the output on or off and "Rate" sets the modulation to either 400Hz or 1KHz.

All perfectly logical. Also, there's a menu feature which lets you set global parameters such as the display brightness.

A store feature lets you keep routinely used output settings.

 

 Although synthesised generators are jolly stable and accurate they are not always as useful as an old fashioned analogue equipment when aligning a radio.

In the case where one needs to tune a generator to a radio for example an analogue type is just twiddled until a signal appears but a synthesised type often is tricky to use. I've often listened for clicking noises which is the generator locking to its frequency and increasing or decreasing the settings until the clicking gets louder and louder. Once you're hearing fairly loud clicks you can increase the frequency resolution until the clicking changes to a signal, a bit messy.

When I was testing my DST100 receiver the Wavetech broke down. It took me a little time to discover the fact because the receiver has a few intermittent faults. When AM was selected the received signal kept cutting out for brief moments before re-appearing almost instantly, but connecting the generator to an oscilloscope showed it was the Wavetech not the receiver. RF output was OK but switching on modulation resulted in an intermittent RF signal. The manual points to modulation problems being in a specific area, that of the AM/DIV module so that's where I started. After removing two dozen screws the top cover can be detached revealing at the side of the unit the view below.

 

 

 
 The AM/DIV module has two circuit boards mounted in an aluminium sleeve which can be removed after unplugging various RF plumbing, including one at the rear of the unit connecting to a power amplifier module. At each end of the sleeve you need to remove the end plates by taking out their four fixing screws plus unscrewing the nuts securing the RF plugs.

 

Below, pictures of the circuit board carrying a lot of the final RF circuitry. Modulation is carried out using a mathematical process controlled by one of the units two microprocessors, but as with all the circuit boards in the signal generator local power supplies are fitted in order to provide accurate voltages. The top view does have a clue to the fault I'm investigating but the underside view reveals clearly what's happening.

 

 
 Here's the fault: three dry joints at the pins of a power regulator transistor. Although the designers included a hole for fitting a heatsink, this wasn't fitted so after replacing the solder I fitted a small brass bush which should help keep the transistor temperature down a little.

 

 Back in business after the Wavetech had gone successfully through its diagnostic tests.

 

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