CHEMANDY ELECTRONICS

FLEXI-BOX HF Amplifier

    The high frequency amplifier is built in a FLEXI-BOX on a dedicated PCB. The screened box has one 50Ω input and one 50Ω output. It can be used as a test measurement aid or a general purpose HF amplifier. The DC input is fitted with a feed through capacitor with a solder tag, or a standard DC Connector for a 7.5 Volt mains power adaptor that can supply 70 mA or more. The RF connectors can be selected from BNC, N and SMA. Other connector types could be fitted if required in quantity. It could therefore be used in many applications that require a HF amplifier not just in the lab. We can build and test these at Chemandy with a gain of approximately 14 dB and a 1 dB compression output power of approximately 11 dBm at 30 MHz, the gain ripple is less than + 0.2 dB from 3 MHz to 30 MHz. Input and Output return loss better than 20dB.    

Circuit

   The amplifier is built around the BFS17 in a shunt series pair configuration. A full description of this amplifier and how we built the prototype is available at Building a HF amplifier in a FLEXI-BOX Part 1. This article shows several photographs of using the FLEXI-BOX for circuit development. The amplifier is referred to as being an HF amplifier but it can be seen in Figure 1 that the 3 dB frequency response is far wider than the HF band and it could also be used for LF and MF.

Figure 1

Figure 2

     The isolation S12, has been omitted because it is better than -65 dB from 0.3 MHz to 50 MHz and would cramp the scale of the other measurements.

     The above results were obtained with SMA connectors and the performance will most probably be inferior with any other type fitted.

       This test aid is available Ready Built or in Kit form. The Kit contains the hardware only; i.e. box, pcb, connectors, screws etc. Components are not included because they are surface mount and  it is impossible to supply the correct amount because of the 'ping' factor. Anybody who has fitted surface mount components will know that when a component is being placed with a pair of tweezers there is often a 'ping' and the component disappears into thin air. We would have to supply at least two of every component thus doubling the cost.

A selection of escutcheon drawings are available for downloading as .zip or .bmp files.

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