[AMPS] Power Meter Readings Question

[Steve Thompson]

In message <199904280400.AAA12656@contesting.com>, Jon Ogden
<jono@enteract.com> writes
>
>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.  

Adjusting the tuner changes the load impedance which the amp, and thus
the output tube sees. Changing the impedance will change the power it
delivers.

>
>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?

The forward power readings are sometimes reasonable on these types of
meter, but I've yet to measure one which had sufficient directivity
(isolation between forward and reverse power measurements) in the
coupler to make it worth displaying the reverse power or VSWR. Phil's
mental arithmetic bit will get you the best measure of how much is
really going into the antenna.

Steve

--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm