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The Remotely Powered VHF Pre-amplifier is built in a FLEXI-BOX on a dedicated PCB. The box has one 50Ω input and one 50Ω output. It is intended as a general purpose VHF amplifier and could be used in a VHF radio installation or for boosting low level signals. The input power is sourced from the center conductor of the co-axial cable, thus avoiding the need to have a nearby power source or an additional power supply cable. This amplifier is intended to be used with the Bias Tee FLEXI-BOX. The RF connectors can be selected from BNC, N and SMA. They could also be Belling Lee (Television Type 75 Ohms!) 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 VHF Pre-amplifier not just in the lab. The remote power facility allowing it to be placed near to the receiving antenna where mains supply may be unavailable, such as a loft or cupboard. Although robust and well screened the FLEXI-Box is not intended for outdoor installation and this would require a weatherproof enclosure. We can build and test these at Chemandy with a gain of approximately 13 dB and an output power of approximately +5 dBm, the output ripple is less than + 0.5 dB from 88 MHz to 108 MHz.
The amplifier is built around the BFS17, which is a NPN 1 GHz wideband transistor manufactured by Philips. The datasheet for this device can be obtained at http://www.nxp.com/acrobat_download/datasheets/BFS17_2.pdf The circuit for this amplifier and a description are available at VHF Amplifier Description.
Figure 1
![[Gain and Isolation Loss Graph - S21 and S11 v Frequency]](../../images/prod121.gif)
Figure 2
![[Return Loss Graph - S11 v Frequency]](../../images/prod122.gif)
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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