I used a amplifier based on the PA0RDT "Mini-Whip" because of it's low input impedance and low noise floor.
You might be able to get away with just using the J-FET input stage and feeding the output to your SDR or, if that doesn't work, go with a plain jane PNP output transistor because you are not dealing with the wide range of signal strengths an antenna is exposed to.
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You could probably even get away with using a lower quality J-FET like the 2N3819 or MPF102 (or is it MPF101....been too long since I used one, I have oodles of 2N3819 so I use them for general purpose N-Channel J-FETs).
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I had a spare "PAR0DRT" "Mini-Whip" I prototyped for an oscilloscope low capacity wide bandwidth (to me 0 to 30MHz qualifies as wide bandwidth on my bench) scope probe. I built a compact version for the scope then reassembled the prototype as a general low input impedance buffer.
