Just a small clarification:
A 3 dB pad will increase the return loss byt 2*3dB = 6dB.
A 2.0:1 SWR is equivalent to a reflection coefficient of .333 and a
return loss of 9.542dB. Therefore it takes a 4.77dB pad to guarantee a
input SWR of <= 2.0:1.
However let's think of it like this: Assuming an original SWR of 3.0:1,
then a 2 dB pad will produce a resulting SWR of 1.922:1. A measly 6 ft.
piece of RG58 coax between the transmitter and the amp will have less
than 0.2dB of loss at 28MHz which will not improve the input SWR much at
all. Even if the 6 foot piece of coax is made from RG174 the loss at
28MHz will only be 0.3dB which still won't do much. Am I missing
something here?
73,
Larry, W0QE
k7fm wrote:
>One simple way to improve the input swr to any amplifier is to add a 1 or 2
>db attenuator at the input. The greater the attenuation, the greater the
>improvement in swr. It does not make sense to do this if you barely have
>enough drive power, but the Alpha 87a drives easily.
>
>A 1 db attenuator only needs a 15 watt continuous rating for most
>amplifiers. Either a T or pi type will work.
>
>A 3 db pad would mean that you would never have greater than a 2:1 swr into
>any amplifier, although the power dissipation would climb dramatically for
>the attenuator.
>
>And, Happy New Year
>
>Colin K7FM
>
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>
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