[ARC5] Visual alignment connections

[Kenneth G. Gordon]

On 26 May 2013 at 20:05, Fuqua, Bill L wrote:

> Kenneth,
>   There seemed to be so much information being provided that I decided
>   to set back and see what was going to happen. Of all the O'scope displays 
> the one with raw IF signal looked most likely to be a real one, albeit with 
> that one the sweep range was perhaps less than desired.

Yes, it certainly was. See below.
 
>   How are your experiments coming along now?

Absolutely excellently....finally!

Yes. The sweep range is much less than necessary, and not only less than 
"desired".

The problem is that these 3 - 6 MHz receivers have a 1415 KHz IF, and at 60 
db down, they are 26 KHz wide. 

The widest sweep I can get out of my HP-8640B at that IF frequency is no 
more than 15.6 KHz. before it starts "bitching" at me. I am certain that there 
is something in the HP-8640B that is interlocked with the output frequency 
which prevents "over deviation". 

I really need about 30 KHz. for this particular IF frequency.

Secondly, as far as I can tell, all three displays are accurate and true. They 
essentially show exactly the same information, and as far as I am concerned, 
what you wish to see, and the way you wish to see it is a matter of personal 
preference.

All three photos (at http://www.w7ekb.com/Personal/BC454/) were arrived at 
with identical signal input to the receiver IF strip by injecting the swept signal 
at the mixer grid. Also, all equipment was identical: an HP-1720A scope, a 
B&K Model 3025 Sweep/Function generator, and an HP-8640B signal 
generator.

The first photo (*****3.jpg) was taken at the tap on the last IF can to which 
the detector diode is normally connected, but with the detector tube 
removed, and the probe used was my Heathkit PK-3 RF probe. This is 
simply a diode-detector followed by a simple RC low pass filter. Also, the 
scope was set up for the X-Y mode.

The second photo (*****5.jpg) was taken at the same point as photo 3, but 
the probe was my standard HP 11 meg ohm scope probe, and I had 
connected a 1N34A diode between the IF tap and ground. There was no LP 
filter in the circuit, so the trace is "filled in" and since there is no LP filter, 
there are also no obvious artifacts or non-linearities to deal with. For this and 
the following one, I set the scope up with the sweep input to the external 
horizontal input connection rather than the X-Y mode.

The last photo (*****6.jpg) was taken across the TRUE "diode load" resistor 
(after I finally figured out what I was doing) while the probe is my standard 
HP 11 megohm scope probe as used in the setup of photo 5.jpg. This 
connection is exactly the same as that which I have read about since the 
1960s, and could never get to work quite right. Now I know why.

Here, the diode load resistor and its associated capacitors form an LP filter 
so the trace is not "filled in".

Although the photo 6 connection provides probably the most information of 
the bunch, I like photo 3.jpg best as it is the cleanest.

At this point, I need to figure out how to measure bandwidth and gain from 
the info I have there. I also really need to be able to inject a moveable 
marker.

I wish I could afford a real spectrum analyzer...

Ken W7EKB