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

[Al Klase]

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 <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/

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