At 07:22 AM 2005-09-08, Luis Mansutti IV3PRK wrote:
>But I discovered that the problem is due to the KD9SV preamplifier. I don't
>know why but it introduces that s9+ noise only with the Flag, not with any
>Pennant, neither with the verticals. On all them the KD9SV is a great
>performer and I could not rise low signals without it.
>Leaving the preamplifier out, the noise level is the same as on the
>Pennants, but I can't get any S-meter reading.
When I was a young engineer, fresh out of college, designing and
breadboarding wideband amplifiers, my experienced mentors always had
me check for UHF or higher self-oscillation when there were strange
performance anomalies. Of course, it helped to have a spectrum
analyzer that covered up to 2 GHz to find the frequency of the
oscillation and to be sure it was fixed.
It is likely that the impedance presented to the input of the
amplifier at some high frequency is just the wrong value to make the
preamplifier oscillate with the Flag in the circuit. Try putting a
small value attenuator (3dB or so) at the input of the preamp to see
if it quiets down. Not a long term solution, obviously, but may help
troubleshooting. You could also try adding a few feet of
transmission line to change the source impedance.
73, Terry N6RY
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