[ARC5] Quick sensistivity comparison

[Richard Knoppow]

>
>
>
> Since you didnt specify mode or receiver bandwith those 
> statements are rather ambiguous.
> When dealing with vintage receivers that have only fair to 
> poor IF filtering I use the AM test for a 10dB SNR at 30 
> MHz at maximum bandwidth for the models mentioned and even 
> .25 to .5uV is a very rare occurance. For CW I crank in 
> whatever maximum selectivity is available and of course 
> sets with selectable filters will have different results. 
> And then measure MDS which is described as 3dB above the 
> noise but many, myself included, can hear well below that.
>
> There is also minimal shielding inside most vintage 
> receivers, and impedance mismatches that add to the 
> generator and cable issues.
> In fact using the lowest range of a generators attenuator 
> is not considered good practice and using an external lab 
> quality step attenuator and a much higher generator signal 
> results in the expected accuracy with all other things 
> considered.
>
> A HQ-140X fully overhauled but unmodified will have a hard 
> time reaching 1 uV on AM while a slightly modified HRO-60 
> is an easy .25uV. Radios such as the 51J and R-390 
> families are rather poor at 30 MHz.
> I rate my minimally hopped up HRO-60 as the most sensitive 
> on 10M AM of the over 100 tube radios I own and a fully 
> overhauled NC-300 with a selected 6BZ6 and 6BA7 a very 
> close second. I do a lot of 10M AM operating.
>
> I disagree about SS having lower sensitivity at HF and it 
> has been proven many times by many people. The HRO-500 and 
> others without PLL phase noise are extremely sensitive 
> with very low internal noise. Those with a PLL vary 
> considerably but most are very sensitive on a test bench. 
> It is when the wide open untuned front ends meet 
> hundreds/thousands of strong signals that the PLL becomes 
> a noise generator.
> You can hear the noise during a contest by monitoring 
> outside of the ham band and the backround noise will rise 
> at the contest start and fall at the end.
>
> Carl
>
     I agree with all this. I am curious what the minimal 
modification to the HRO-60 is.  The stock receiver uses 6BA6 
RF amplifiers feeding a 6BE6 mixer.  This is the same 
arrangement used on the SP-600-JX and many other receivers. 
Whatever you have done has lowed the noise very considerably 
from what I get on these other receivers.
     30 mhz performance has a lot to do with losses in the 
RF stages. Evidently the HRO has very low loss coils an 
insulators, etc.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com