CHEMANDY ELECTRONICS

FLEXI-BOX Broadband Amplifier 1 GHz

    The 1 GHz broadband amplifier is built in a FLEXI-BOX on a dedicated PCB. The box has one 50 Ω input and one 50 Ω output. It can be used as a test measurement aid or a general purpose wideband amplifier, but is mainly intended to be part of the Standing Wave Kit. The DC input can be fitted with a feed through capacitor with a solder tag, or a standard DC Connector for a 7.5 Volt mains power adaptor. The RF connectors can be selected from BNC, N and SMA. They could also be Belling Lee (Television Type 75 Ω!) or Type F to special order. Other connector types could be fitted if required in quantity. It could therefore be used in many applications that require a broadband amplifier not just in the lab. We can build and test these at Chemandy with a gain of approximately 15 dB and an output power of approximately 15 dBm, the 3 dB bandwidth is from 300 KHz to 1 GHz.     

Circuit

   The amplifier is built around the Sirenza SGA-7489 DC - 3000 MHz Silicon Germanium HBT Cascade able Gain Block. The basic performance is therefore similar to that achieved in their datasheet which can be obtained at http://www.sirenza.com/products_detail.asp?model=SGA-7489&line=Gain%20Block&menu=amplifier  This component performs very well but has the disadvantage that it is really designed to be embedded within a circuit. When it used as a free standing component, it is very easy to destroy the device. We have added reverse supply protection and a current regulation circuit which affords some DC protection and also softens the adjustment of the supply volts. A further addition of a 6 dB attenuator on the output reduces the 1 dB compression point from approximately +22 dBm to something greater than +15 dBm and this helps protect it from output mismatches. This does of course reduce both the gain and the output power level. It also gives an expected improved output return loss and isolation. It is however, still a very useful test aid and the 6 dB attenuator is required in all measurements made with the Standing Wave Kit anyway. So the need for an external attenuator in this case is avoided. The SGA-7489 is specified to 3 GHz and the performance to this frequency is shown in the following figures, but the conventional bandwidth is 1 GHz within a 3 dB output power bandwidth.

Figure 1

Figure 2

      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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