1.2GHz ( 23cm ) 2 Watt RF AMPLIFIER
With a modified Motorola SHL7008 Hybrid Module

A collection of info by VK3GE, VK3QL, VK3BFG, VK3BCU, VK3YLH, VK3IE, VK3TRX, VK5YYY

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Technical Information for SHL7008

A later version of the same module is the MHL7236 (Practically identical Specs). Click here for a MHL9236 Data Sheet.

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THE MODIFICATION

The first part of the operation is to take the module apart. The module's blue cover is glued on each corner. The cover is removed using brute force. A screwdriver under one of the corners of the plastic corners and some leverage is all that is required to pop the case off the module. BEWARE there are TINY components inside the module that are easily destroyed so be careful. The transistors on the interior of the module are unprotected from physical damaged once you have removed the cover and are easily damaged so beware.

Here are some hints that may improve your chance of not killing your module during the mod. Dont drop it with the cover off, dont touch the fines internal wires, dont use too much heat and be quick with your application of it. The very fne wires in the module are very easy to destroy.

SHL7008 Interior With Cover Removed

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Move the chip capacitor from its original position (in the red oval) toward the output side of the module so it it somewhere in the Blue oval (placement doesnt appear to overlly critical) as per the picture below. The ideal position has been different for alot of people, but the blue oval will get you very close.

SHL7008 Interior - capacitor move

Glue the blue cap back on the module and that is it for the mod. All the rest is mounting and powering the module.

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Practical implementation of the modified module

For the practical implementation the module should be bolted into a metal box with heat transfer compound to maximise heat transfer. The box will need a heat sink on the exterior. The input and output can be what ever connectors you want (SMA, BNC, N). If the box is not the right size (most likely) that connectors can be soldered directly to the PCB then some semi rigid coax can be used. Remember its 23cm RF were are playing with so the enclosure MUST be metal (no plastic allowed).

* Good earthing of the module and the PCB is essential. Remember to add an earth strap from the PCB to the module at each of the module mounting points. Refer to some of the construction pictures for ideas. *

The power supply is 24V at approximately 0.5A. The amp can be used with the standard 13.8V shack power supply if a buck/boost converter is mounted internally (these can be found on lots of web sites for around $4 - $5 AU delivered from asia).

The power supply should enter the box via a feed through capacitor or if not then a 1nF ceramic or chip bypass capacitor should be applied to the supply line where it enters the box.

Pins 2 and 3 of the modified module should have a single hole ferrite bead on each leg next to the module. Some people have used 6 hole ferrites with a couple of turns of wire.

The only other components are a 100uF electrolytic or tantalum capacitor, 2 X 10nF chip capacitors, 2 X 100nF chip capacitors, and 2 X 100pF chip capacitors. All components should be placed as per the component overlay picture (NOT ACTUAL SIZE). PCB design by VK3BFG.

Now mount the PCB with attached SHL7008 module into a suitable metal box with your chosen connectors. Remember to use good microwave construction techniques. Shown below is one operators amp as an example (Note the good low impedance earth strapping from the PCB to the module).

The modified module can very occasionally self oscillate when there is power applied but no drive (luckily the module does not normally kill itself when this happens). The fix appears to be to have a 3dB pad on the input of the finnished product (make your own or buy a ready made one from one of the many asian suppliers).

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TESTING

Check your work!! Cross your fingers. (Remember if you let the smoke out you cant put it back in)

Connect a 24V supply or your shack supply of 13.8V if you have used a buck boost converter internally.

Use an input signal of approximately 0dBm (1mW) at your desired 23cm frequency. The output should be around 1.7W - 1.9W if all is well. An input of 3dBm (2mW) should produce an output of around 2.5W

Around 2.5W is about the most you will get out of this amp and still remain linear. You can adjust the position of the chip capacitor you moved in the module above slightly if you are not getting the required output at the desired frequency.

Shown below are test results from one of the locals.