[R-390] R-390A balanced input question

[Larry H]

Hi Craig,  Jim's right.  The balanced input is for balanced or unbalanced input for low impedance input. You would hook up your antenna coax as he suggests for the signal generator (left side grounded with the coax shield grounded and coax center to the right contact).  In this scenario, the adjustment of the balancing cap is not necessary.  If you need a twinax connector, I can send you one.  The unbalanced input is for high impedance antennas (very short coax is ok).

Regards, Larry


On Sunday, September 21, 2014 10:26 AM, Craig Heaton <hamfish at efn.org> wrote:
 


Jim,

One item I believe is missing in the Y2K; the procedure to adjust the
balance caps in the RF deck. This could be part of the issue. Then consider
the antenna vs. the antenna input connection? Are you using a balanced
antenna? How did you align/peak the RF section?

The local RFI noise level is too high here in Springtucky, OR to even see a
difference. So considering the fact the antenna/tuner presents a 50 ohm
unbalanced connection to the transmitter & RX; the sig-gen is cabled up
straight to the balanced input of the R-390/A, center conductor to the right
side, other side grounded, per Chuck Rippel's website & the RF section is
peaked. All hoping for the best. YMMV

Craig,

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of JAMES GREEN
Sent: Sunday, September 21, 2014 9:40 AM
To: r-390 at mailman.qth.net
Subject: [R-390] R-390A balanced input question

I have way too many projects to work on and just want to have a good
receiver to listen to when I'm not in the shop. I have an EAC R-390A that I
used to listen to quite regularly about a year ago. I put it aside for a few
months and started listening more to 2 channel Hi-Fi. I had the yen to catch
the BBC out of ascension Island again so I pulled it out and ran into a
small problem.

Knew exactly where the radio was stored. I can't for the life of me find the
"C" to so-239 adapter I used before to hook it to my antenna. I did find a
balanced to SO-239 adapter, but I found I could not get a signal from the
balanced input. Upon close inspection and some dis-assembly I found the
plastic insert in the balanced connector was twisted. This twisted the relay
contacts so there was no connection. I replaced the antenna relay with one
from my parts radio & have verified it is now passing a signal. 

Here is the problem:

I still am unable to pick up anything through the balanced input. Upon
looking in the R-390A Y2K manual schematics it looks like the unbalanced
connector bypasses several tuned transformers that the unbalanced input does
not bypass. I suspect these tuned transformers are in need of alignment.
However, the alignment procedure in the Y2K manual instructs one to connect
the sig gen to the unbalanced connector. & aligning from there.

Am I missing something? Is there a separate alignment procedure that I did
not find that shows how to align from the balanced input?

Cash flow at the moment prevents buying another "C" to SO-239 adapter, & I
have heard some extra sensitivity can be gained by using the balanced input.


Jim
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