[ARC5] R-26 BFO injection adjustment

[J Mcvey]

Removing c45 gave me enough BFO that it can work pretty well with medium -strong signals. No reason that I can see to disable the AGC. In fact I wish it worked better than it does.
Made contact with a SSB station 400 miles away last night amidst QRN, QRM and poor propagation with my paltry 25 watts of AM.While these sets were designed before SSB existed, SSB can be demodulated by an ARC-5 receiver with patience and a "light touch".
Even though it takes some patience to get an SSB station tuned in, it takes a lot more patience to wait for an "AM station" to stop talking!I wanted to throw my call out to one last night, but I gave up after he talked continuously for for 15 minutes without a break. I don't think he cared if anybody was still listening! It seem that AM ops are "long play" talkers in general...jeesh!

 

    On Friday, May 12, 2017 12:54 AM, WA5CAB--- via ARC5 <arc5 at mailman.qth.net> wrote:
 

 The R-26 is the only model that has C45.  In the R-25, the diode is open (NC).  In the R-27, the diode is tied to ground.

Disabling the AGC for tests would seem to be a simple matter of shorting either R5 or C15A to ground.

In a message dated 05/11/2017 21:37:38 PM Central Daylight Time, arc5 at mailman.qth.net writes: 

Well, after some experimentation, i found that C45 on the second diode had the effect of loading the BFO.
Adding capacitance to the 11 pf made little difference. Removing it helped improve the injection and the ability to 

beat against strong SSB signals at room volume. It still distorts with very strong signals, but I'd have to turn down the sensitivity anyway.
I can run the control at 3/4 most of the time now. ( I run a speaker, not headphones).


I'm still not convinced that the AGC is working properly, but it passed the "ohms to ground test." . It's not that bad that I want  to dive into
it at this time with live voltage tests. etc, but maybe it will be a good rainy day project.



Thanks for the insights into this issue.





Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
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