[R-390] Official specs

Fri Oct 4 12:53:33 EDT 2024

It seems convincing. A measurement without an exact definition of the setup is not replicable.

In the meantime, I made some other tests. My R-390A gives a 10 dB S/N with -104 dBm (1.41 uV) signal applied to one half of the balanced antenna input, using the DA-121 (@7,580 kHz).

If I use the unbalanced antenna input, which should have a high impedance, I use a 50 ohm terminator for the generator. In this case, I get 107 dBm (1 uV), i.e. a difference of 3 dBm, which I attribute to the insertion loss of the DA-121.

Larry said that the correction factor should be 0.55, and I follow him in this, simply calculating the voltage divider in the DA-121 (100 + 125 ohm), so I would expect a difference of 5 dBm (if I am right), but  maybe that the unbalanced antenna introduces some other difference.

BTW, when I bought my R-390A, the seller gave me also this strange object, which should unbalance the balanced antenna, I suppose with a 50 ohm input. In this case I didn’t add neither the DA-121 nor the 50 ohm terminator; despite this, it requires -101 dBm for the same 10 dB S/N. Not very useful, I would say.

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> Il giorno 4 ott 2024, alle ore 16:38, Bob Camp <kb8tq at n1k.org> ha scritto:
> 
> Hi
> 
> The gotcah here is that we really don’t know what the interface between the signal generator and radio looked like for these official tests. Despite the document going into a lot of detail, they did not include a schematic or a part number. (or at least not one that I could find). There are a *lot* of ways they might have been doing things …..
> 
> Bob
> 
>> On Oct 4, 2024, at 10:19 AM, Ing. Giovanni Becattini via R-390 <r-390 at mailman.qth.net> wrote:
>> 
>> But when we perform the classical sensitivity test with a modulated signal, do we get the AM or CW value?
>> 
>> Following the instructions I got a value of -104 dBm, i.e. 1.41 uV. Because I used the DA-121, the real value should be even better, far from 5 uV. And surely my R-390A is not as good as it could be .
>> 
>> Is my reasoning correct?
>> 
>>> Il giorno 4 ott 2024, alle ore 16:13, Barry <n4buq at knology.net> ha scritto:
>>> 
>>> I don’t think of 1uV as “bad” but most of these radios will beat that. 
>>> 
>>> Thanks,
>>> Barry
>>> 
>>>> On Oct 4, 2024, at 8:55 AM, Ing. Giovanni Becattini via R-390 <r-390 at mailman.qth.net> wrote:
>>>> 
>>>> Wow, thanks!
>>>> 
>>>> By the way, do you know why the sensitivity values were so bad? Are we the ones who are taking measures that are too lenient or are they the ones who were too conservative?
>>>> 
>>>> Thanks again
>>>> 
>>>> Gianni
>>>> 
>>>>> Il giorno 4 ott 2024, alle ore 15:37, Larry Haney <larry41gm2 at gmail.com> ha scritto:
>>>>> 
>>>>> Hi Gianni and Barry,  Tom Marcotte and Al Tirevold (SK) obtained and cleaned up the specs for the 390A and put it on our website.  Here's the link: mil-r-13947b– (r-390a.net) <https://www.r-390a.net/mil-r-13947b.pdf>. Unfortunately, the entry in References page indicates it is for the R390(), but it is also the the 390A.  I will be changing that shortly.
>>>>> 
>>>>> Regards, Larry
>>>>> 
>>>>>> On Fri, Oct 4, 2024 at 4:49 AM Ing. Giovanni Becattini via R-390 <r-390 at mailman.qth.net <mailto:r-390 at mailman.qth.net>> wrote:
>>>>>> Have ever been released official specs for the 390A?
>>>>>> 
>>>>>> The manuals report few data and neither too correct, for what I can understand (e.g., sensitivity)
>>>>>> 
>>>>>> Thanks
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> 