[Amps] 50 Ohm Loads

[jeremy-ca]

As one forum member pointed out 50KW BCB water cooled dummy loads use 
nichrome elements with a fixed cap to cancel the reactance. That is not a 
"narrow range".

Measuring a true non inductive resistor with an Ohmeter should not be any 
different than using more elaborate methods at MF or low HF frequencies. We 
are not interested in calculating out to several decimal places; simply 
establishing a baseline is sufficient. At VHF and above Bird and others use 
sophisticated techniques in their dummy loads to cancel or minimize VSWR 
degradation.

Carl
KM1H





----- Original Message ----- 
From: "Jim Brown" <jim at audiosystemsgroup.com>
To: <Amps at contesting.com>
Sent: Monday, November 12, 2007 2:24 AM
Subject: Re: [Amps] 50 Ohm Loads


> On Sun, 11 Nov 2007 14:27:36 -0500, jeremy-ca wrote:
>
>>For low frequencies a regular wire wound can be used with a capacitor to
>>cancel the inductive reactance.
>
> At a single frequency (or depending on the Q, a relatively narrow range).
> The laws of physics, as described by the classic resonant frequency
> curves, apply in full. Wire wound resistors as an RF dummy load are a
> really bad idea.
>
> Those of you saying you have 55.xx ohm loads. How did you measure them?
> With an ohmeter?  What counts is the Z at RF, not at DC. Only in
> Wonderland do resistors have a constant value from DC to daylight.
>
> 73,
>
> Jim K9YC
>
>
>
>
>
>
>
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