Samwell and Hutton CT501 Wobbulator

Samwell and Hutton CT501

The CT501 is a ruggedized version of the 78m Wobbulator. It is built into a solid metal case which is air transportable. The front of the cabinet is fastened with a number of knurled thumb screws which clamp it securely to the rubber seals that surround the mating surfaces of the case. All of the accessories are mounted within the front panel ,and the plug-in modules which come with the set mount in receptacles on the main chassis.The overall construction is of high quality.

CT501 Lid Assembly. Inside Lid of CT501

The picture above shows the lid which holds some of the accessories and leads,you can clearly see the thumb screws which clamp the lid to the main assembly.

CT501 Main Panel. CT501 main panel

This picture shows the controls of the CT501.

Bottom left we have the mains input socket with the voltage selection connector which is behind the plastic"window",below it are the mains fuse and on/off switch.To the right is mounted the amplifier/demodulator unit,next to that are the ext calibrator input,the calibration marker selection switch,and above that the sweep range switch.To the right of all this is the variable attenuator unit.The rest of the controls mainly refer to the setting of the display,focus,brilliance etc.

There is one switch,mounted in the center of the four knobs above the attenuator,which selects between RA17-SCR70/RAD10 equipment.The RA17 position speaks for itself,the SCR70/RAD10 is, I think,radar equipment.

The main display is pretty obvious,this shot showing 39.35 MHZ to 40.65 MHZ sweep for RA17 40 MHZ filter alignment.

To the left of the display is a drawer which houses the additional units that plug into the front panel,such as the amplifier calibrator unit and probe panel,used for impedance measurement also houses the probe assembly used with the RA17.

An additional unit is the Frequency Convertor Unit which extends the range down to 1 MHZ.

Brief Technical Details

Frequency Range 16-215 MHZ (1-215 with convertor)
Output Level 1uv--100mv
Attenuator 99db in nine 40db and nine 1db steps
Calibration Markers 500 KHZ,1MHZ,5 MHZ *
Marker Accuracy 0.25 % (2.5 khz/mhz)
Y-Input Sensitivity 0.1V pp of 6.5 cm deflection on CRT

* Additional markers for RA17/SCR70-RAD10 Ranges

The CT501 In Use.

The CT501 may be used for many of the purposes you would have for any swept frequency equipment.As our main interest is in the RA17 I shall describe only this use.

Alignment of the 40 MHZ filter is relatively easy using this equipment as it has been made with this in mind.

The 40 MHZ filter is made up of eight over-coupled tuned stages and is just about impossible to align properly without equipment such as the CT501.I have included here an extract from the Royal Air Force alignment manual which I hope will give some idea of the procedure used.

40 mhz filter alignment lin

40 mhz filter alignment log

It is also possible to align the 37.5 MHZ filter

37.5 mhz filter alignment

The descriptions above will,I hope,illustrate the procedure for realigning the main IF filters using this equipment.The 37.5 MHZ filter can be aligned without using sweep equipment but for best results the 40MHz filter should be tuned this way, because,as you can see the, 40MHZ filter has a much wider response.If you just peak the filter for maximum you will end up with a response like the 37.5 MHZ filter and this may be too narrow for a drifting 1st VFO

You can of course use any equipment that will sweep the required range such as a Spectrum Analyzer but BEWARE of the HT present at the ends of the filter,get that into the mixer and.......well don't even think about it..!

The RA117 of course can be realigned the the same way with the addition that you can check the 2-3 MHZ bandpass filter,the same is true for the MA79.

Updated 15/02/2000.

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