Last year a bought and measured the Radio Works Line Isolator in my in line
(isolation on the outer shield) balun test setup using an HP Network
Analyzer. It measured about 220 Ohm at 1.8 MHz and 500 Ohms at 3.5 MHz. NOT
ANYTHING TO WRITE HOME ABOUT!.
For comparison, 20 small ferrite beads (2673002402), the type recommended
by W2DU gave about the same performance on 1.8 and 3.5 MHz!
At 02:31 PM 1/28/2003 -0500, Chuck Counselman wrote:
>At 9:35 AM -0500 1/28/03, Mike Wetzel W9RE wrote:
>>To add to your RadioWorks info, I had 3 of their baluns...and found that
>>the baluns exhibited a very high swr on 10 [meters].... The baluns
>>seemed ok below that frequency (21 Mhz). I informed them and they ignored me.
>About three years ago, suckered by RadioWorks' advertising which seemed to
>say that the common-mode-choking impedance of their so-called line
>isolator at 3.5 MHz was _extremely_ high, of the order of 100 kohms, I
>bought two of these devices.
>In fact the complex impedance at 3.5 MHz is about ( 0 + 800 j ) ohms. Yes,
>zero ohms resistance plus eight hundred ohms reactance. The uncertainty
>in this complex value is a couple of ohms in the real part and a few
>percent in the imaginary part. In other words, at 3.5 MHz the device is a
>37-microhenry inductor with a very high Q, greater than 400.
>An exchange of email with RadioWorks' proprietor Jim Thompson eventually
>revealed his justification for advertising "100 kohms." In the parallel
>L-R circuit having the same impedance at 3.5 MHz, the value of L is about
>37 microhenries and the value of R is about 100 kohms.
>Since the complex impedance of such a device varies with frequency in the
>3.5-MHz range like that of a _series_ L-R circuit, not at all like a
>parallel L-R circuit, I told Jim Thompson that I thought his advertising
>was misleading. He ignored me, too.
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