[Elecraft] Re: [Icom] Opinions re: HF Verticals?

Tue Oct 15 13:08:01 2002

Hi George

This reminds me of a DMM made by Tektronix with a display of 4 1/2 digits=
 but an accuracy spec of 0.1% The last digit is for all practical purpose=
s useless. In fact one of the technicians placed a little sticker over th=
e last digit so he could not see it on the meter at his bench. =20

Some times people take the readings too seriously on their test equipment=
 and forget the specifications. Just because it has a nice digital readou=
t does not mean it is as accurate as it might appear. As you know RF watt=
 meters (and SWR meters) are not very accurate. Within a few percent is q=
uite good (the industry standard is the Bird with 5%) - nowhere near as a=
ccurate as any of the cheapest DMM's are when measuring DC or resistance.=
 Does it really mater, NO because the type of measurements made with watt=
 meters, a small amount of inaccuracy probably won't matter.

Don Brown
KD5NDB

----- Original Message -----
From: George, W5YR
Sent: Tuesday, October 15, 2002 11:26 AM
To: [email protected]
Cc: [email protected]
Subject: Re: [Elecraft] Re: [Icom] Opinions re: HF Verticals?

<SNIP>

> =20
> RF Applications VFD  http://www.rfapps.com/vfd.htm

I note that no accuracy specification is given at the URL for your unit.
Rather they ask you to "compare with the Bird 43 . . ." The Bird is rated
at +/- 5% of full scale. If you will work with that accuracy figure and g=
o
through the equations for computing VSWR from forward and reflected power
measurements - which is what your instrument does wioth its microcomputer=
 -
you will find that there is no way that it could actually compute the
difference between a 1.01 and a 1.03 SWR. The instrument may well display
such readings, but they are an artificial artifact of the processing, not
reflective of the accuracy of the raw power data. =20

<SNIP>

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