The low pass filter should be placed where the SWR is least. That is before an
antenna tuner. High SWR probably burns up more filters than anything else.
Also, filters rated for 1000watts (in the old days) were good for 3KWPEP. That
is because they were rated for plate input power and not output power. So if
you had an AM transmitter with 1000 watts plate input power you could expect
to get about 750 watts carrier out. However, at 100 % plate modulation the peak
envelope power is 4 time that or 3KW.
As far as harmonic generation goes the worst offenders were the
electronic TR swithches.
73
Bill wa4lav
-----Original Message-----
From: "Joe Giacobello, K2XX" <k2xx@swva.net>
To: Steve Thompson <g8gsq@qsl.net>
To: <amps@contesting.com>
Date: Sat, 16 Nov 2002 10:25:33 -0500
Subject: Re: [Amps] LP filter effects
Steve, my experience with the Drake LPF's is that after sustained use at
1.5 KW, they start to fail. Probably capacitor dielectrics are breaking
down or something similar. They are really only rated for 1 KW and they
were manufactured when the legal power was 1 KW input. So they were
probably designed to routinely handle 750W or less.
73, Joe
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
>
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>
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