Topband: Amplifiers

[tracey.gardner]

For those people looking for an amplifier, the following extract
from the K9AY list might be of interest.

Tracey G5VU

>The reason why most active antennas have their amps fitted next to the
>antenna, is that the required impedance match is from several 100k ohms
to
>50 Ohms. This is not the case with either the K9AY or the Pennant
antenna
>where the antenna z is only 450 to 1k Ohms. Hence, low noise bipolar
devices
>can be use with the antenna matched to 50 Ohms.
>
>When selecting or building an Amp or an Active antenna  it is most
important
>that the IP3 is over +35dBm and more importantly the IP2 figure is well
over
>+60dBm to avoid intermod ( beware of any amp or active antenna that
does not
>specify an IP2 figure ). For home brew amps, only push-pull transistors
>should be considered  to keep the second order intermod to very low
levels.
>Single ended amps even with NFB; you will be very lucky to achieve more
than
>+35dBm for the IP2! Also MMIC devices offer poor IP2 figures.
>
>The Wellbrook K9AY amp ( IP3 +40dBm and IP2 +70dBm ) is still available
for
>home brew K9AYs in either 13dB or 20dB versions.
>
>73s
>
>Andy
>
>
>
>Andy Ikin   e-mail: sales@wellbrook.uk.com
>          andy@wellbrook.uk.com
>                      aikin@globalnet.co.uk
>     URL: http://www.wellbrook.uk.com
>
>Wellbrook Communications
>Wellbrook House, Brookside Road,
>Bransgore, Christchurch, Dorset          BH23 8NA. UK.
>Tel. 01425 674174 Int.+44 1425 674174
>
>Manufacturers of Broadband Loop Antennas


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