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

Barry n4buq at knology.net
Mon Nov 4 12:40:02 EST 2024


Larry,

I currently have just the one R-390/URR.  Not sure if I'll ever venture again into another R-390 of either version.  I do enjoy them and the R-390A/URR is definitely easier to work on so who knows.  I might get fancy (or, more correctly, OCD) and put a switch in the box with all four resistors...

Thanks,
Barry - N4BUQ

> Barry,  I'd say that if you are going to work more on As, then do the
> da-121.
> 
> Regards, Larry
> 
> On Mon, Nov 4, 2024 at 6:36 AM Barry Scott <72volkswagon at gmail.com> wrote:
> 
>> Okay, I agree.  I think as long as one can get a signal into the RF
>> deck, it can be used to align the coils and trimmers as necessary.
>>
>> I'm going to make a matching network and wondered if there was any
>> really good reason to use 68 and 100 ohm resistors or 95 and 75 ohm
>> resistors.  Probably doesn't matter...
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> On Mon, Nov 4, 2024 at 12:52 AM Larry Haney <larry41gm2 at gmail.com> wrote:
>> >
>> > 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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