[R-390] R-390 IF Deck

[Jim Whartenby]

Les
No, I meant the R-725/URR, see:  https://sv7apq.blogspot.com/2019/03/the-r725urr-and-tropicon-project.html

The story was that the phase distortion caused by mechanical filters when the R-390A was used for direction finding caused errors in the DF circuits.  Using the R-390 IF in the R-390A chassis and a few mods to make it work eliminated these location errors.  There are other stories in the above article but one comment supports the DF story.
Jim

Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    On Sunday, January 12, 2025 at 03:08:42 PM CST, Les Locklear <leslocklear at hotmail.com> wrote:   

 The R-390/URR predates the R-725/URR. you’re thinking about the R-390A/URR…

Sent from my iPadFrom: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of Jim Whartenby via R-390 <r-390 at mailman.qth.net>
Sent: Sunday, January 12, 2025 2:57:26 PM
To: 'R-390 Mailing List' <r-390 at mailman.qth.net>
Subject: Re: [R-390] R-390 IF Deck OH, so it is an R-725 wannabe?
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    On Sunday, January 12, 2025 at 01:12:01 PM CST, Jacques Fortin <jacques.f at videotron.ca> wrote:  

 Jim, with all due respect, Byron is asking about the IF deck of a R-390 (a non-A, if you prefer).
No mechanical filter in there, but a 6 stages IF strip....

73, Jacques, VE2JFE in Montreal

-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la part de Jim Whartenby via R-390
Envoyé : 12 janvier 2025 13:56
À : 'R-390 Mailing List' <r-390 at mailman.qth.net>
Objet : Re: [R-390] R-390 IF Deck

Where is S504?  I see S501, S502 and S503 but no S504 in the schematic or parts list.
I personally think that the 8kc mechanical filter now has a high insertion loss due to the internal "rubber" isolator turning into goo or perhaps a weld connecting a wire to a disk has failed.  I have seen both.  If one has any mechanical skill and patients, the filter can be repaired by careful disassembly and replacing the "rubber" isolator.  If it is a broken weld, the filter is toast.  The filter repair info is in the Pearls of Wisdom, IIRC.Regards,Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    

  
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