Phil Clements wrote:
> It only took me 44 years to learn this little tidbit, so I thought
> I would pass it on as it is of interest to all bird Wattmeter users.
>
> The standard Bird HF slugs like we all use are marked 2-30 mhz. I
> always figured that 1.830 mhz was close enough to the edge to not
> make any difference. Not so...there is a 10% error on the low side
> in the reading!
>
As a student I worked on calibrating Bird 43's. 10% of FSD is not an
unusual error. In fact, I purchased a 70 cm slug for myself, and
checked it (at 432 MHz) the day after buying it. It was out of spec. I
took it back to the distributor, who re-callibrated it for 432 MHz (I
said I was not bothered at another frequency). I then retested it and
found it within the 5% spec at 432.
Birds are great for indication purposes, creating very little
disturbance to the line (unlike some ham power meters), but they can not
be relied upon to be within 5% of FSD. Most, but not all, will be within
10% of FSD.
G8WRB
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