[Amps] Dummy Loads & Wattmeters

[Steve Katz]

Yep, there is.  An accurate power measurement with the model 43 is P(actual) = Pf (indicated) - Pr (indicated).  With a 70 Ohm load you should have a VSWR of 1.4, a return loss of about 15.6 dB, or about 3% reflected power, so the Bird should read "high" by about 3% when viewing indicated Pf.

But I'd look into why the load measures 70 Ohms!  Check your Ohmmeter if you can to verify its accuracy, and if that seems good, probably the load's been overheated and the resistor should be replaced.

WB2WIK/6

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
Behalf Of David C. Hallam
Sent: Wednesday, December 02, 2009 9:16 AM
To: AMPS List
Subject: [Amps] Dummy Loads & Wattmeters


A little education, please.

I am working on restoring an old transceiver and linear.  I have a Bird 
43 wattmeter and a Heath Cantenna dummy load.  The wattmeter is for 50 
ohm impedance and I measure the DC resistance of the Cantenna at 70 ohm.

Is there any effect on the wattmeter reading from this mismatch?

David
KW4DH
-- 
National Health Insurance
* Compassion of the IRS
* Efficiency of the Post Office
* Cost Control of the Pentagon


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