[R-390] GR Adapter and Signal Generator findings

[Joel Richey]

Hey there old buddy, sensitivity is all in the front end, IF gain is just
that, if the front end isn't able to hear a .2uV signal they all the if gain
in the world wont have anything to amplify.  The abality of a reciever to
hear weak sigs is a function of the RF amp and the Mixer stages and the only
reason there is an RF amp is to overcome the noise generated by the mixer,
thats why alot of high end recievers made today don't have an RF amp, the
mixer is so quiet that one isn't needed.

I doubt if anyone on this list has the abality or the equipment or the
shielding to come anywhere close to measuring levels as low as .2uV with any
degree of accuracy and furthermore, unless you live on the moon that amount
of sensitivity would be usless on the freq covered by the R390 series.

Joe W2DBO
----- Original Message -----
From: "Barry" <n4buq at aol.com>
To: "R-390 reflector" <r-390 at mailman.qth.net>
Sent: Friday, June 03, 2005 10:06 AM
Subject: [R-390] GR Adapter and Signal Generator findings


> All this talk about the GR1001A reminds me that I need a GR 874 to BNC
> Female adapter.  Does anyone know where I can get one of these?
>
> Last night, I was playing around with the IF Gain control.  I'm not
> convinced I have it set right, but I think it's pretty close.  It's about
at
> 2/3 full CCW.  After setting it and with the radio set to 15.2mc, I
> connected the signal generator through my impedance matching network and
> started listening to the signal.  With the output level set to 1uV, I
could
> hear the modulated signal.  I began decreasing the output and could still
> hear the signal as low as 0.2uV.  I realize this isn't exactly scientific,
> but I was kind of surprised to hear the signal at that low level.  Also, I
> didn't have the series 40-ohm or the parallel 50-ohm resistors in place
yet
> so I'm not sure how this works into the overall equations, but I was
pleased
> to be able to hear a signal that small.
>
> I also realize there is (can be) signal leakage from the generator, but if
I
> turn the output down below 0.2uV, the signal is inaudible so I'm not sure
> I'm hearing leakage or not.  I have the 2V output on the GR1001A plugged
so
> I don't think there's much (if any) juice getting out from that point.
>
> What really surprised me was with the signal generator as my "antenna",
> signals on the 9mc band came blasting in.  I've heard some signals with
the
> generator connected before, but not that loud.  Does this indicate the
> generator could be really leaking more than I suspect?  It was pretty cool
> nonetheless.
>
> Thanks for listening to my longwinded post.
>
> Barry - N4BUQ
>
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