Hi Jon. I've seen exactly the same effect that you have , but with
different power meters - with and without tuners. What you describe is no
surprise. Without a tuner and a mismatched load, the power meter reads a
forward power that includes the incident power plus the re-reflected power
caused by the mismatch. If your meter can separately read forward and
reverse (reflected) power, take both readings, then subtract the reflected
power from the forward power reading. The result will approximately be the
power output of the amp.
With a tuner after the power meter, the reflection due to the mismatch
still occurs, but it occurs at the output of the tuner, so the meter
doesn't see any significant reflected power at all. You can test this by
adjusting your tuner for best match and take power readings while the meter
is between the amp and the tuner. Next, move the power meter to the
output side of the tuner and take new readings (don't change the tuner
settings). You'll probably find that the forward power has "increased".
The G5RV presents a highly reactive load on almost every amateur band and
therefore a mismatch almost everywhere. It was never the intent of the
designer to provide an antenna that provided a match on any band; his
intent was to provide an antenna that could simply be reasonably used on
lots of bands. Less than optimum efficiency from a G5RV is normal. Your
vertical will be efficent if you have a ton of radials under it to minimize
ground loss, and if the electrical length is sufficient tp present a
resistive load ( with little reactance), somewhere close to 36 ohms for a
quarter wave. As the design departs from these ideals, efficiency goes to
hell.
Phil
At 11:05 PM 4/27/99 -0500, you wrote:
>
>Hi all,
>
>Got a question for you about power meter readings.
>
>I have a Daiwa NS-660PA cross hair power meter. I have taken everyone's
>advice and eliminated my antenna tuner for the time being. I am just
>loading the PA directly into my antennas - matched or unmatched.
>
>How accurate is the power reading on my meter? The reason I ask is that
>with a tuner in line by fiddling with the controls, you can change the
>value of your forward power even though you've done nothing to increase
>output from the amp.
>
>Also, why would loading into my beam give me much better efficiency than
>when loading into my G5RV or vertical? I get much more power out when
>loading into my beam than into the other antennas.
>
>Do these cross-hair meters read correctly when the SWR is not under 2:1?
>
>73,
>
>Jon
>KE9NA
>
>
>-------------------------------------
>Jon Ogden
>KE9NA
>
>http://www.qsl.net/ke9na <--- CHECK IT OUT! It's been updated!!!!!
>
>
>"A life lived in fear is a life half lived."
>
>
>--
>FAQ on WWW: http://www.contesting.com/ampfaq.html
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>
>
>
--
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Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
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