[ARC5] What the heck is a "1/2 harmonic Q-5er?

[Hubert Miller]

No - you're right, that's the way it has to be, regardless of what the dial says. 
You need at the BC-384 either  915 + 85  or 915 - 85 kcs.  Which means you need 1000 or 830 kcs. 
The BC-453 has to generate either 500 or 415 kHz. It does that when it is tuned to 500 - 85 or 415 - 85 
and that means dial = 415 or 330 kHz. 
Assuming the BC-453 osc is on the "high end", above F0. Which I think it has to be, to cover the 
200 - 550 kcs stretch with the size tuning cap.
-Hue 

>Folks,

Don't try to confuse me.  That's my job!

I think the problem is that the subject should have read "2nd-Harmonic Q-5'er."

1. Assuming the BC-453 uses high-side local-oscillator injection, if we tune that receiver to 415 KHz, the  LO will be 415 + 85 = 500 KHz, and the LO second harmonic will be 1000 KHz.  

2. The IF of the BC-248 is 915 KHz. which is 85 KHz below the BC-453 second harmonic. 

 3. If we bypass the preselection in the BC-453, by feeding the signal to the mixer grid, the receiver will have a response at 915 KHz.

(So Jeep's dial was off by 8 KHz.)

Where did I go wrong?

VY 73,
Al
On 5/10/2020 8:47 AM, Doran Platt wrote:
OK... herewith positively confirm that the BC-453 was tuned to 407 kHz.  Fortunately, I have some high res photos of my ARC-8 setup.  Looking at the dial, and a placard I made up, its clearly 407 kHz.  BTW, there was no hacking of the BC-348.  A small insulated pickup loop was positioned at the base of the last IF.  The connectorized RG-174 coax is routed to the grid cap of the BC-453 mixer via a tacked on 10pf dipped mica. The reason for going to the mixer was to bypass the front end of the BC-453 which would attenuate the 457.5 kHz signal from the BC-348. That was the setup and it works marvelously well.  
Jeep K3HVG



On May 9, 2020 at 7:53 PM Hubert Miller mailto:Kargo_cult at msn.com wrote:


So maybe I finally understand this, maybe not.
In the video, the guy's BC-453 is tuned to 420 kHz. That means osc = 420 + 85 = ~505.
Harmonic = 1010.  
Harmonic - 915 kHz BC-348 IF = 95 kHz. Maybe one or the other is not aligned quite right ?
Should be 85 kHz. 

There should be another point, I think, on the 453 dial where this would work.
BC-453 dial = 330 kHz. Osc = 330 + 85 = 415. 
415 x 2 = 830;  915 - 830 = 85 kHz.  

For the ARC-2, the challenge is, the IF continuously varies with the main tuning. What fun 
that is. I think, IF the above stuff is correct:
3885 kHz = ARC-2 IF  @ 1295 kHz.
1295 kHz - 85 kHz = 1210 kHz. 
If BC-453 is set to 520 kHz, osc is at 520 + 85 = 605 and second harmonic is 1210 kHz. 

Of course, I may have gone of the rails at point A. 
-Hue 
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-- 
Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/