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

[Al Klase]

Hi Ken,

I was trying to figure out why people hadn't done it Ken's way. Just 
tune to IF/2.  I assume you can just come in on the BC-453 antenna 
terminal.  I guess it's counter-intuitive that the IF subharmonic even 
exists.  I would have never thought of that.

I think Jeep was set up using a BC-453 LO harmonic to receive the 915 IF 
fundamental as I suggested below.  In that case you would tune near 415 
on the BC-354 dial.

So there's more than one way to skin a cat.

Al

On 5/10/2020 6:53 PM, Kenneth G. Gordon wrote:
> On 10 May 2020 at 15:38, Al Klase wrote:
>
>> Folks,
>>
>> Don't try to confuse me.  That's my job!
> Heh heh....or mine...
>
>> I think the problem is that the subject should have read
>> "2nd-Harmonic Q-5'er."
> Well, yes...sort of...
>
>> 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-348 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?
> Well, first of all the BC-453's IF doesn't even matter. It is completely unimportant for our
> present purposes.
>
> You simply tune the BC-453 to the IF/2  (1/2 harmonic) of the BC-348, or 915/2 = 457.5 kc.
>
> If Jeep really does have his BC-453 tuned to 407 kc, then his BC-453 calibration is off by 50
> kc. I find that absolutely impossible to believe.
>
> But I'm betting either he didn't mark his dial with the "5", or his photo isn't clear enough to
> show the "5". Furthermore, if his dial settinig IS exactly 457, then his BC-453 dial is off by
> 0.5 kc, which is much more reasonable for a BC-453 in good condition.
>
> MY BC-453s MIGHT be off as much as 1 dial-marking width....maybe. Calibration in a
> properly restored and aligned BC-453 is unusually good.
>
> Ken W7EKB
>
>

-- 
Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/

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