[R-390] Detector tests followup

[Barry]

----- Original Message -----
From: <Flowertime01 at wmconnect.com>
To: <r-390 at mailman.qth.net>
Sent: Thursday, September 21, 2006 7:11 PM
Subject: Re: [R-390] Detector tests followup


<snip>
>
>
> Have you got the distortion out?

I think so.  It sounds fine to me.

> Is the receiver sounding good?

Yes, I think it does.

> Is MGC giving stronger audio signal than AGC?

Yes

> Are you getting a good 1/2 watt output with the TS585?
> Both line and local audio channels?
> When you get a 1/2 watt out on the line with the TS585 and back the line
gain
> down to read 100 Milliwatt Zero DB on the TS585 does the VU line meter
read 0
> VU?

I need to test the above scenarios.

I did do something tonight, though.  Attempting to follow the mil manual, I
ran the sensitivity test.  With modulation off, I set the TS585 to 1mW.
Then with modulation on, set signal generator to get 10mW.  After going back
and forth a couple of times to get things levelled out, I ended up with 4uV
sensitivity.  This is somewhat uncalibrated as the signal generator is
putting out 50 ohms into the balanced input and my IF gain wasn't set
exactly right (I had fiddled with earlier and had not reset it properly).

This isn't too bad a performance indicator, though, is it?  I'd be worried
if it took 10uV or 20uV to get the 10dB increase and I realize 3uV is the
spec, but I'm not completely unhappy with 4uV at this point.

Also, I tried the test of injecting modulated100mV @ 455kc at pin 7 of V507
on my other R390A (all '56 Motorola).  It does the same thing.  There's
enough noise to get nearly full-scale VU readings with the Line Meter at -10
and Line Gain at 10.  When I inject the signal (using a 0.1uF cap between
the signal generator and pin 7), the audio goes nearly dead and the VU meter
goes to full left scale.  I'm beginning to wonder about the validity of this
test.  Anyone else try this?

Enough for tonite.

Thanks again for all the advice!

Barry - N4BUQ

>
> Roger AI4NI
>