[R-390] RE: R-390 Digest, Vol 18, Issue 2

[Steve Hobensack]

Jim,
   The diode load is a  very sensitive hi-z circuit. Computer audio systems 
are at line-level impedance. Are you using a DC blocking capacitor and 10k 
to 250k ohm resistor in series between the diode load and audio input of the 
computer audio? How does the rig perform using the rcvr's own audio module? 
How does the rcvr hear its own 100 khz calibration signal?  If the 756 Pro 
will hear 455 khz, put it on the rcvr's IF output and listen. You can use a 
ricebox receiver tuned to 455 khz, with a blocking cap on the ricebox coax, 
move the make-shift probe back through the if deck until you find the 
problem. Here is where it helps to have tube socket test adapters.
    Use the balanced line antenna input even if you are using a single line 
antenna. Just ground one side of the input. The single line coax input 
doesn't perform good with a long wire. It was made for a whip antenna fed by 
short coax.
Good Luck
...Steve...N8YE


>Message: 7
>Date: Sat, 01 Oct 2005 18:47:58 -0700
>From: James Cottle <jim_cott at earthlink.net>
>Subject: [R-390] A little help on sensitivity - where to look
>To: R-390 at mailman.qth.net
>Message-ID: <433F3C4E.6000008 at earthlink.net>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>Hello to the group.
>I finally had the distinct pleasure of turning on my R-390A today after
>building a roll-around rack for it. I have the diode load output
>connected to an old Altec Lansing computer speaker system. Here is my
>problem:
>    The AM broadcast band sounds simply fabulous. BFO works, both meters
>work, Veeder-Root is very accurate. I can get NOTHING ELSE! There seems
>to be a distinct lack of sensitivity on most all other frequencies.
>    On my ICOM 756 proII, I had WWVH coming in today at a solid S-9 with
>some fading. When I swapped the antenna over to the R-390A, I could hear
>nothing. On further digging, I could hear with the headphone output
>(through some Sony headphones), the WWV signal but barely discernible,
>way down in the mud of the noise and only with the AF gain turned all
>the way up.
>     Obvious some work to do on the beast. Anyone have any ideas where to
>start? Thank you in advance for any advice.
>
>Regards,
>Jim
>AC4EA
>San Francisco
>ac4ea at arrl.org