Bob
You are over thinking the testing. The generator is terminated but not in it's
characteristic impedance. Collins and the agency letting the contract agreed
on a test method and wrote it down in the test procedure. Anything that would
affect the testing like VSWR has already been considered and accounted for.
That Hams don't use the proper termination for the signal generator, according
to the spec, which affects the perceived sensitivity is another issue. Spec is
spec as they say.
Not all Government Source Inspectors are knowable about the equipment that they
are reviewing and putting their inspection stamp on. Not all Signal Corps
equipment is inspected by Army GSIs. Every once in a while, Army equipment
will have an anchor stamp on it and vice-versa. Sometimes certain specs are
wavered if not considered critical, most often they are not. Again, spec is
spec.
Regards,
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence. Murphy
On Friday, October 4, 2024 at 02:43:36 PM CDT, Bob Camp <kb...@n1k.org>
wrote:
Hi
Ok …. but …..
If it is simply a resistor, then the generator is unterminated. It’s designed
and calibrated to run into a 50 ohm load. If all that’s there is a series
resistor the generator is not properly set up (and thus not calibrated ….). Yes
some generators deal with this better than others.
My guess is that there’s more to the load circuit than just that resistor.
Without a schematic …. who knows ….
Bob
> On Oct 4, 2024, at 12:53 PM, Jim Whartenby via R-390 <r-390@mailman.qth.net>
> wrote:
>
> Bob
> But we do know what the interface is between the signal generator and antenna
> input. On document page 20, the balanced RF input is in series with a 125
> ohm non-inductive resistor and the unbalanced RF input is in series with a 50
> pF capacitor. Both interfaces do not include the generator's output
> impedance.
>
> As for the sensitivity not being what the R-390/URR or the R-390A/URR is
> capable of, well there are perhaps 100's of tests that the receiver must
> successfully pass before it is accepted. Tightening any of the specs to
> exactly what the receiver may be capable of passing will guarantee that no
> one receiver will ever pass all of the acceptance tests. Then there is the
> added problem of your test equipment's error tolerance and being traceable
> back to the NIST standards. Is your 10 microvolts from the signal generator
> really 10 microvolts?
>
> Unless otherwise stated, the specification calls out a value that the
> receiver must do better than. A sensitivity of just under 6.5 microvolts for
> a 10 dB S+N/N with an audio power output of 10 milliwatts seems reasonable
> over the range of 2 to 32 MHz for either balanced or unbalanced RF inputs.
> This is perhaps typical for just about all HF receivers built for the
> military, at least for what I am aware of, but I am sure that there will be
> the rare exception.
>
> Regards,
> Jim
> Logic: Method used to arrive at the wrong conclusion, with confidence.
> Murphy
>
> On Friday, October 4, 2024 at 09:39:26 AM CDT, Bob Camp <kb...@n1k.org>
>wrote:
>
> 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@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 <n4...@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@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 <larry41...@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@mailman.qth.net <mailto:r-390@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
>>>>>> ______________________________________________________________
>>>>>> R-390 mailing list
>>>>>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>>>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>>>> Post: mailto:R-390@mailman.qth.net <mailto:R-390@mailman.qth.net>
>>>>>>
>>>>>> This list hosted by: http://www.qsl.net <http://www.qsl.net/>
>>>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>>
>>>> ______________________________________________________________
>>>> R-390 mailing list
>>>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>> Post: mailto:R-390@mailman.qth.net
>>>>
>>>> This list hosted by: http://www.qsl.net
>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>>
>> ______________________________________________________________
>> R-390 mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:R-390@mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390@mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390@mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
