[R-390] DA-121/U Dummy Antenna

Dallas Lankford [email protected]
Fri, 21 Jun 2002 17:43:21 -0500


Yes.  And if one uses a 50 ohm signal generator, and measures the R-390A
sensitivity by reading the signal generator setting, the number one gets
will be about 0.636 lower than the voltage across the antenna input.  Here I
am assuming that the signal generator is connected to the R-390A through a
UG-971/U (with no impedance matching or adapter).  So the method I have
recommended previously is wrong too.  That's really amusing.  The numbers I
have been getting should be multiplied by 1.57.  And that does not
necessarily give accurate values.  What one really has to do is measure the
antenna input resistance at the frequency where one measures sensitivity.

----- Original Message -----
From: "Roy Morgan" <[email protected]>
To: "Dallas Lankford" <[email protected]>
Sent: Friday, June 21, 2002 2:52 PM
Subject: Re: [R-390] DA-121/U Dummy Antenna


> At 01:56 PM 6/21/02 -0500, you wrote:
> >Thank you very much Roy.  It turns out I put the schematic in HSN 23 many
> >moons ago.  Duuuhhh!  And yep, you are right that the voltage across the
> >R-390A antenna terminal will not be the voltage on the sig gen.
>
>
> Just got back from lunch, and reading the HSN 23 article.
>
> If we assume the input impedance of the radio is 125 ohms (it does vary a
> lot from that value) then the actual input voltage will be 125/(125+100)
or
> 0.55.. of the input. Call it half, allowing for all variables.  If a
person
> takes the indicated signal generator output voltage as the value for
> sensitivity measurements, the measurement will be in error by being about
> twice what the actual input voltage is.
>
>
>
> - Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
> 7130 Panorama Drive, Derwood MD 20855
> Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
> [email protected] --
>
>