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

[Bob Groh]

The mixing takes place in the BC-453 - the BC-348's IF signal is loosely
coupled to the mixer tube in the BC-453.  The BC-453 is then tuned to 415
kHz - that means the 453's LO is 85 kHz higher or 500 kHz.  The 2nd
harmonic of the 453's LO is at 1,000 kHz and that 2nd harmonic mixes with
the 915 kHz IF signal from the BC-348 and the result is (Wala!!) 85 kHz.

This can all be done in a non-destructive way to either radio.

The article that goes into wonderful detail on all of this in Electric
Radio Issue #304 September 2014 (pg 18 on) and authored by Joe Long,
WA2EJT.  I have had a chance to look at the article (pdf copies are NOT
legitimately available!!!) and I am going to buy a copy of that issue for
my own use (as soon as I decide what else I want to get to make the minimum
$10 order threshold - shipping is free, by the way).  It is a wonderful
article with tons of great information including selectivity curves,
information on using the same idea with other radios, etc. As a long-time
ham and a retired electronics engineer with a long history in designing RF
radios, I whole heartedly recommend getting your own back issue!  After
I've gotten mine of course.

73
Bob Groh, WA2CKY

On Mon, May 11, 2020 at 8:11 AM Robert Eleazer <releazer at earthlink.net>
wrote:

> I thought I had a pretty good understanding of superhet technology until
> this 1/2 harmonic Q-5er business came up.  I even once changed both the 1st
> and 2nd IF's of a National NC-155 so I could use a different crystal for
> the 2nd LO.  I have never heard of receiving a subharmonic.
>
> But as I understand it now, you tune the BC-453 so the 2nd harmonic of its
> LO is 1000 KHZ.  That signal then mixes with the 915 KHZ IF signal of the
> BC-348 to get the 85 KHZ if of the BC-453.
>
> I am not clear whether the mixing takes place in the BC-453 or the BC-348.
>
> The original article about the 455 KHZ Q-5er use of the BC-453 said that
> it did not matter if you used the BFO of the receiver or the BFO of the
> BC-453, so I guess an R-11A/R-511 would work as well, in addition to taking
> advantage of the superor construction of the Type 12 set.
>
> Thanks!
>
> Wayne
> WB5WSV
>
>
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