[R-390] DA-121 and R390/URR

[Larry Haney]

Hi Barry,  Yes, the DA-121 is what's recommended for the 390A when doing
alignment, but it does not make any difference if you use the adapter or
not for that, but it should be used for sensitivity and SNR measurements.
At least, that's been my experience.

I believe that the balanced antenna coils are a little different on the
390, but the DA-121 should be close enough to work correctly for it.  But,
there again, I doubt that an adapter is necessary for alignment on the 390,
either.  It should be used for sensitivity and SNR measurements though.

Regards, Larry


On Sun, Nov 3, 2024 at 6:04 PM Barry Scott <72volkswagon at gmail.com> wrote:

> In the last few weeks, there were several posts regarding using the
> DA-121 to determine sensitivity for, presumably, an R-390A/URR.  The
> DA-121 uses a 68-ohm in parallel and a 100-ohm in series with the
> signal generator's output.  Is this the recommended adapter also to be
> used for the RF alignment of the R-390A/URR when using the balanced
> input?
>
> I ask because the R-390/URR manuals say to use a 75-ohm parallel
> resistor with a 95-ohm series resistor when performing the RF
> alignment.  I realize there's not enough difference between those two
> networks to matter that much but I am curious as to why the two values
> are different between the models.  Are the RF transformers slightly
> different between them?
>
> Just curious.
>
> Thanks,
> Barry - N4BUQ
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