Amplifier Module Prototype In the Shop

The prototype amp is in the shop. I ordered the proto board with a 10 day delivery schedule for the lowest quote price. I will have to gather a set of parts and have the thermal block fabricated. Maybe I can find someone that can mill the small block. All though I will have 3 boards, I usually have some sort of error to correct so I never build the spares.


I have decided to break the pieces up into logical modules. The MPU Module contains all the analog and digital circuitry used to monitor and control the amp. Rather than kit it, I decided to go for the smallest possible size finished module. It has been my experience that this is the weakest link. We are pushing the limits with features that do not lend themselves to non-surface mount technology. I created a little module that mounts on the back of the front panel away from the RF. It measures 2.8 x 3.8 inches. See schematics: File Attachment: sch MPU HFSP V3.pdf (39 KB) Description: The PIC18F is the processor is the controller. It is programmed through the USB link. The digital outputs all operate relays. We have a serial to 16–bit parallel register to accomplish that (6B595). There is one 16–pin flat cable that connects to the Amplifier Module. We control the gain, the MOSFET bias. We monitor the current and the MOSFETs temperature. A 10–pin flat cable connects to the Low-Pass Filter Module. A 12–pin flat cable connects to the rear panel RF Path Module. This is a module that mounts across the back and contains the switching for dual transceiver, dual antenna and TX. File Attachment: sch RF PATH.pdf (21 KB) Continuing with the MPU description, we have a 6–pin flat cable that attaches to the touch screen Graphics Display. Our design combines the Controller and QVGA display as one module. The RF Carrier is measured and sensed by this module and includes a PTT input from the transceiver if desired. The Module is low power and is local regulated to 5V. The second sheet of this design shows the interface to the RF Power Measurement analog circuits where the RF Input power is measured and RF Output power and reflected power is measured. In addition, we support the FT817 Band Data Input to control the low pass filters.

Description: RF Path Module. The schematic shows the signal flow paths from left to right. Starting with the RF Inputs selection we pass through the Input metering sensors. The outputs of these sensors are coupled by coax using SMA connections from the RF Path to the other Modules. For instance, the AMP IN jack goes to the amplifier input. The amplifier output connects to the low pass filter and the output of the low pass filter comes back to the RF Path Module at LPF OUT jack. From their, the signal is passes through Output metering sensor and then to one of two antenna selections. There are other signals that are destined for the rear panel. Control of the three RF Modules is available and control of the Power Supply is also available on this module.

I hope these descriptions give you and idea where we are headed with this design. I will soon need to get this MPU Module also in the shop so that I can control the amp. If you have any questions, I would be happy to answer. The MPU Module and Graphic Display will be machined assembled and tested. The rest is the user construction assembly. This will leave manageable tasks for the builder with high probability for assembly success.

Thank you for supporting the project. You deposits help sustain this R&D effort to develop the amp. I am excited about the design. If you want to join or comment, send an email to

73 K5OOR –  Virgil  HF Projects




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