[Amps] LP filter effects

[Gary Schafer]

Steve Thompson wrote:

> ----- Original Message -----
> From: Steve Lawrence <smlx@earthlink.net>
> To: <amps@contesting.com>
> Sent: 16 November 2002 07:19
> Subject: [Amps] LP filter effects
>
> > I have an old Drake 1KW LPF in line running 1500w output from an Alpha 87A
> > to a TH7DX. It's worked fine for several years. I've pulled the LPF out of
> > the line. At 28000 with 1500W out, the reflected power dropped from 200 to
> > 100 watts. There is also an improvement on 20 and 15.
> >
> > Comments appreciated.
> Assuming the power meter is between the LPF and antenna, it's difficult to
> see how the LPF could be increasing the harmonic level. Another possible
> cause is that your meter has poor directivity and heightened sensitivity to
> harmonics. I'd say that's much more likely.
>
> Steve
>
>

A low pass filter does not necessarily have a flat 50 ohm response. Especially
when you get to 10 meters. It is already starting to roll off some. This
produces some reactance which will show up as a higher or lower swr when
inserted into the line, depending on how much reactance is already on the line.

73
Gary  K4FMX