On Sun, 06 Apr 1997 01:39:19 -0800 Harry Bump <bump@redrose.net> writes:
>Hi Gang,
>
>Built an NN1G (Mk II) rig fer 20m a couple (2-3) years ago and have
>enjoyed using
>it very much; however it has recently developed a problem.
>
>When on my dummy load it shows one watt output and (almost) no
>reflected power, but
>when switched to the antenna SWR shoots up to above 4:1.
>
>When I do the same with my main station rig (same antenna, meter,
>switch, and cables)
>the antenna appears to be resonant and SWR very near unity.
>
>The same situation appears at the mobile antenna on my vehicle...
>
>Any ideas?
>
>
>73,
>
>Harry, KM3D
>
>Outlaw Wireless League
>QRPARCI #3875
>Norcal #1295
>QRP-L #637
>
>
Harry,
Sounds like spurious signals appearing on the output. Since the dummy
load is resistive at a wide range of signals, the SWR will look fine.
The antenna, on the other hand, will provide a good match at a very
narrow band of frequencies, thus the high SWR reading. Judging by the
high readings, the spur level is probably very high, compaired to the
desired frequency. I am not familiar with this rig but it sounds like an
oscillation in the driver or final stages. A spectrum analyzer would be
helpful but given the probable degree of spurious signal, an oscilloscope
will likely reveal a quite distorted output. Take a look at the signal,
with dummy load connected, on the 'scope.
----------------------------------------
Charles R. (Randy) Ott
K5HJ - QRP-L #1040
----------------------------------------
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