[AMRadio] Watt meters

jeremy-ca km1h at jeremy.mv.com
Sat Feb 16 14:22:46 EST 2008

I have 2 of the rather scarce 75 Ohm Bird 43's and would sure like to obtain 
some more slugs of any description.

My feedlines thru 1296 are all 75 Ohm hardline and Ive been able to make do 
with 50 Ohm line sections and slugs on HF and low VHF. If the amps load up 
Im satisfied.


----- Original Message ----- 
From: "Thomas Adams" <quixote2 at ix.netcom.com>
To: <garyschafer at comcast.net>; "Discussion of AM Radio in the Amateur 
Service" <amradio at mailman.qth.net>; "'Discussion of AM Radio in the Amateur 
Service'" <amradio at mailman.qth.net>
Sent: Saturday, February 16, 2008 12:54 PM
Subject: Re: [AMRadio] Watt meters

>> >>> While a true wattmeter is an absorption type of instrument, the
>> wattmeters
>>like the Bird and many other thru line meters measure voltage and current 
>>determine power on the line. <<<
> Quite true...  thus the market for the Bird TERMALINE units, which combine 
> a
> line voltage measurement device with a terminating resistor of known 
> characteristics.
> Combine a Bird 43 with a well designed 50 ohm dummy load and you've 
> essentially
> got a TERMALINE instrument... even tho the 43 and similar "slug" 
> wattmeters use
> a different principle for measuring line voltage than a TERMALINE.
>>They will accurately measure at impedances
>>other than 50 ohms too. You just subtract the amount of reflected power
>>indicated from the forward power indicated for true forward power.  It 
>>doesn't matter if the load is reactive either as these type wattmeters 
>>read true within their capability.
> Yep, so sayeth the Book of Bird. I use that one all the time because I ran 
> into an
> offer I couldn't refuse on 1200 feet of RG11/U coax!    ;o)
> Mr. T. W9LBB
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