[R-390] Official specs

[Bob Camp]

Hi

When they are measuring “AM Sensitivity” are they running 30% modulation or 100%? 

If by some chance, they are running 30% and you are running 100% …. the numbers will off a bit. Will it be 3:1? Probably not. Still it’s going to impact things quite a bit. 

I’d doubt they switched techniques between the two plots. Switching them between a 1953 document and one from 1961 …. yup, could indeed happen.

Bob

> On Oct 13, 2024, at 5:12 PM, Jacques Fortin <jacques.f at videotron.ca> wrote:
> 
> The chart TM 856-91 attached.
> 
> 73, Jacques, VE2JFE in Montreal
> 
> -----Message d'origine-----
> De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la part de Jacques Fortin
> Envoyé : 13 octobre 2024 16:13
> À : 'Larry Haney' <larry41gm2 at gmail.com>; 'Jim Whartenby' <old_radio at aol.com>
> Cc : r-390 at mailman.qth.net
> Objet : Re: [R-390] Official specs
> Importance : Haute
> 
> Well...
> I found two diverging statements....
> In the first R-390/URR manual (Collins Radio, 23 October 1953) the Figure 95 on page 172 (Also IDed TM 856-91) shows that the sensitivity is higher for the Unbalanced input, compared to the Balanced one.
> This is the only manual I know that gives a "sensitivity" plot for the R-390/URR.
> On the R-390A/URR side, the TM 11-856A, on pages 173 and 174, seems to tell us the reverse from the charts M and J (More sensitivity on the balanced antenna input than on the unbalanced one) I do not exclude the possibility that one of those "sources" could tell the truth in reverse....
> 
> Bottom line: we have to test ! (once again).
> 
> 73, Jacques, VE2JFE in Montreal
> 
> Hi Jim,  My thinking in why the second 'balanced' entry is actually the Unbalanced info is that the Unbalanced antenna input is the high impedance input and therefore would have the higher microvolt readings.  And in the numerous other places in the spec where both are listed, the 'balanced' one is first.
> 
> Regards, Larry
> 
> On Sun, Oct 13, 2024 at 8:27 AM Jim Whartenby via R-390 < r-390 at mailman.qth.net> wrote:
> 
>> I agree that one list is mislabeled but I would think that the first 
>> "Balanced" list is the one that is actually the Unbalanced spec.
>> 
>> My reasoning is that the CW input voltage spec is lower in the first 
>> list and higher in the second for all frequencies.  We may disagree on 
>> the actual insertion loss of the DA-121 but it would still be higher 
>> for all frequencies then the DA-124 which uses a series capacitor to 
>> mimic a short antenna instead of a voltage divider to transform impedance.
>> 
>> Jim
>> 
>> Logic: Method used to arrive at the wrong conclusion, with confidence.
>> Murphy
>> 
> 
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