[ARC5] Visual alignment connections

[J. Forster]

This is a rough block:

                          #1        #2         #3      #4
ANT --- RF AMP --- MIXER --- 1st IF --- 2nd IF --- DET --- AUDIO AMP ---
                     |
                    LO


You want to align a stage at a time, ie:

#1 to #2
#2 to #3

#3 to #4 is just a LPF to reject the IF carrier.

The books may say inject at #1 and measure at #4 to get the IF center
frequency right.

If you align from #1 to #4 you are trying to adjust 4 tuned, cupled in
pairs, tuned circuits. This is damn near impossible.

You need to set the CF to nominal and inject at #2 and monitor at #4 (or
#3 w/ an RF probe). When 2nd IF is proper, move injection to #1.

You can do it in the other direction, but to align 1st IF, jou need to use
the RF probe on #2

-John

==================







> On 24 May 2013 at 6:50, J. Forster wrote:
>
>> By 'diode load at 2nd detrectot' you mean the point where the top of
>> the volume control is often connected?
>
> Yes. In the case of the BC-454, that would be R-18. The 'scope would be
> connected "across" R-18 .
>
> And that is exactly where the entire collection of methods of doing this
> tell
> me to connect the 'scope. Yet, when I do that with this receiver, I get
> nothing
> recognizable. My continuing question is: "Why?". Why are my results so
> unlike what "they" have gotten?
>
>> If that is the case, you would be seeing the response of the entire IF
>> strip.
>
> Yes. But that is exactly what I want.
>
>> To align a receiver, looking only at that point, you need to inject
>> the swept IF starting at the end furthest from the antenna, and align
>> stage by stage, moving toward the antenna.
>
> Well, that method is exactly backwards from what all the references tell
> me
> to do.
>
> They ALL say to connect the swept signal to the mixer grid, the 'scope
> (synced to the sweep) to the diode load resistor, and align as one would
> if
> using a VTVM or a DB meter across the diode load resistor or the speaker
> (with the AVC off).
>
>> If you monitor at the tail end and inject at the antenna end you will
>> get garbage.
>
> How so? I don't understand 1) why you say that, and 2) why that would be
> so. This is EXACTLY how all the references I have say that it MUST be
> done.
>
> Further, this method has, apparently, been used since there were 'scopes
> and superhets. It was always done for TV set IF strips, less often for AM
> or
> FM receivers, but it was still done for those too.
>
> I want to see the response of the entire IF strip, and so far, that is
> what I
> seem to have gotten, as far as I can see.
>
> Have you had a chance to look at my photos?
>
> I am beginning to wonder if I have a bad 12SR7...
>
> Kenneth G. Gordon W7EKB
>
> "Courage is being scared to death but saddling up anyway."--- John   Wayne
>
>