[R-390] Differences between the balanced antenna and unbalanced antenna inputs

[Jim Whartenby]

DavidI see what you mean.  The balanced antenna input is actually a link coupling to the antenna coils in both the R-390/URR and the R-390A/URR.  The balanced and whip antennas still use the antenna tuned circuits.  
Something I didn't notice before is an error in the Figure 5-13 Sheet 1 of NAVSHIPS 0967-063-2010.  6.3 volts is applied to the whip antenna center conductor.  This does not show up in any of the other schematics in this manual.  Strange.Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    On Monday, November 4, 2024 at 04:44:56 PM CST, David Wise <d44617665 at hotmail.com> wrote:   

 It's not tuned in the sense of resonance.  The two small caps make a voltage divider (center tap grounded) which you adjust so common-mode interference is nulled out.

________________________________
From: Barry Scott <72volkswagon at gmail.com>
Sent: Sunday, November 3, 2024 6:24 PM
To: David Wise <d44617665 at hotmail.com>
Cc: Tisha Hayes <tisha.hayes at gmail.com>; R390A <r-390 at mailman.qth.net>
Subject: Re: [R-390] Differences between the balanced antenna and unbalanced antenna inputs

So that's why the primary is tuned to a null?

Thanks,
Barry - N4BUQ

On Sun, Nov 3, 2024 at 8:15 PM David Wise <d44617665 at hotmail.com> wrote:
>
> I used to think that, but not anymore.  The unbalanced input is meant to be used with an antenna with a specific capacitance, which acts as part of the capacitance that resonates the secondary winding of whichever transformer is selected for your band.  The primary winding that the unbalanced input skips is nonresonant.  The caps there don't resonate, they just establish a center tap for balance.  You get the same number of tuned circuits either way.
>
> Dave Wise
> SWL (inactive)
>
> ________________________________
> From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of Tisha Hayes <tisha.hayes at gmail.com>
> Sent: Sunday, November 3, 2024 10:44 AM
> To: R390A <r-390 at mailman.qth.net>
> Subject: [R-390] Differences between the balanced antenna and unbalanced antenna inputs
>
> There is one advantage of using the 125 ohm balanced antenna inputs; You
> get a little bit more pre-selection through RF transformers T201 to T206.
>
> When using the 50 ohm unbalanced connector (the C connector) it bypasses
> those RF transformers.
>
> You can see this on diagram 5-14
>
> *Ms. Tisha Hayes, AA4HA*
>
> *Senior RF engineer (4RF USA, retired)*
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