Re: Hi Z Antenna Amplifiers

Chris Moulding

I've been surprised at the amount of advice and help following my post on the Topband contesting email reflector. I've had several direct emails with advice too.

What I'm proposing to manufacture is a Hi-Z antenna amplifier. This is is designed to be used with a 5m vertical element (aluminium tube or wire up a fishing rod and a ground or earth rod into the ground. This antenna arrangement can be used on it's own as a low noise receive antenna or with anywhere from 2 to 9 identical antennas in a phased array to produce a steerable directional beam for DX work on 160 or 80m (or the other HF bands).

The amplifier has to have a very accurate and repeatable gain and phase relationship between input and output so that users only have to adjust the coax lengths between several antennas and a central switching unit to construct a phased array.

It also has to have the highest IP3 performance possible so that it isn't overloaded by local medium wave stations.

I've built a prototype using a recently introduced IC from Analog Devices originally intended as a high IP3 buffer stage in front of ADCs in SDR receivers or similar products. During initial testing at the workshop signal to noise tests on a local medium wave station 20 miles away are the highest of any antenna I've tested there.

The design will allow it to be used with 12V or 5V bias tees and there will be two options 75 ohm F type or 50 ohm BNC connectors.

The production PCBs are being designed over the next few days so I expect to have some ready for sale in about a month.

The amplifier will be mounted in the same polycarbonate box used for the Loop Antenna Amplifier and I'm aiming to sell it at the same price.



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