On Thu, 14 Jul 2005 15:31:14 GMT, Bill Janssen
wrote:



Check the frequency (or frequencies) coming out of the amplifier. I will bet
that what comes out is not equal to what goes in. The antenna is not a
good match for those other frequencies.

Bill k7NOM


Smart guy you are! I never thought of that, but it makes perfect
sense. I don't have a spectrum analyzer, but since the 2nd harmonic
and higher lands above 30 MHz then I should be able to place my Barker
and Williamson low pass filter (30 MHz cut off) between the amp and
the SWR meter. Hopefully the low pass filter will allow the
fundamental through, and stop the higher frequencies (assuming they
are normal multiples of the fundamental frequency). If the
attenuation is great enough the SWR meter should not show the SWR jump
since the unwanted frequencies should be attenuated before they get to
the SWR meter.
Assuming you are correct my next problem will stopping the extra
frequencies from getting out of the amp in the first place.

J.

Joeseph wrote:
On Thu, 14 Jul 2005 15:31:14 GMT, Bill Janssen
wrote:


Check the frequency (or frequencies) coming out of the amplifier. I will bet
that what comes out is not equal to what goes in. The antenna is not a
good match for those other frequencies.

Bill k7NOM



Smart guy you are! I never thought of that, but it makes perfect
sense. I don't have a spectrum analyzer, but since the 2nd harmonic
and higher lands above 30 MHz then I should be able to place my Barker
and Williamson low pass filter (30 MHz cut off) between the amp and
the SWR meter. Hopefully the low pass filter will allow the
fundamental through, and stop the higher frequencies (assuming they
are normal multiples of the fundamental frequency). If the
attenuation is great enough the SWR meter should not show the SWR jump
since the unwanted frequencies should be attenuated before they get to
the SWR meter.
Assuming you are correct my next problem will stopping the extra
frequencies from getting out of the amp in the first place.

J.

Be sure to verify that it's not oscillating, and that any excessive
harmonics don't indicate some other problem with the amp (if you're in
the process of homebrewing it then it just means you forgot the dang
lowpass filter, but if the amp is a commercial unit & you're using it as
intended then there may be something broke).

--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Joeseph wrote:
, , ,
Assuming you are correct my next problem will stopping the extra
frequencies from getting out of the amp in the first place.

No, your problem should be figuring out how to prevent them from getting
generated in the first place. If the harmonic or spurious content is
that high, there's something seriously wrong.

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
Joeseph wrote:
, , ,
Assuming you are correct my next problem will stopping the extra
frequencies from getting out of the amp in the first place.

No, your problem should be figuring out how to prevent them from getting
generated in the first place. If the harmonic or spurious content is that
high, there's something seriously wrong.

Nice answer, Roy. That was my knee-jerk, too.

Joseph, remember, the problem isn't only "stopping them from getting out of
the amp...". Those other frequencies are some sort of parasitic in the
amplifier. Besides being stuff you don't want going to the antenna, they
are robbing your amp of the ability to amplify the frequencies you DO want
amplified, and they are unnecessarily heating up your transistors and
sapping their life.

So first, keep them from being generated, then stiffen up that low pass
filter so anything that does get created is way, way down. Far lower than
what will show up as an apparent SWR problem.

...