[ARC5] BC-221-AKs

[Jay Coward]

Bill,
 You remind me of tech school! Thanks,
   Jay KE6PPF



-----Original Message-----
From: Bill Fuqua <wlfuqu00 at uky.edu>
To: jfor <jfor at quikus.com>; Jay Coward <jcoward5452 at aol.com>
Cc: arc5 <arc5 at mailman.qth.net>
Sent: Sun, Nov 25, 2012 10:12 pm
Subject: Re: [ARC5] BC-221-AKs


    Technically, it would not be a square wave but a rectangular waveform 
f it did not have a 50% duty factor.
he shorter the pulses the more even in amplitude the harmonics would be.
 square wave (50% duty factor) would have only fundamental and odd harmonics
eceasing in amplitude as the harmonic number. The third harmonic would be 
/3 the
mplitude of the fundamental, the 5th would have 1/5, etc, in voltage 
evel. This is the downfall of
ome of the newer solid state crystal calibrators since they use a divide 
y 2^n
C. So if you have a 100kHz solid state calibrator of this sort by the time 
ou get to
0.1 MHz the harmonic would be 1/201 of the fundamental, 46db below the 
undamental.
nd at 100.1 MHz 60db down. Naturally at 20MHz (even harmonic) there would 
e little or nothing.
he only reason there is something at the even harmonics is that due to 
ome slight delays in
he ICs they don't produce a perfect 50% duty factor.
    Just about all RF LC and crystal Vacuum Tube oscillators are class C. 
nd by having
 high cutoff bias the plate current would be fairly short pulses compared to
 50% duty factor.  The oscillators usually are self biased via grid 
ectification often
eferred to as "grid leak bias".
    If you want a nearly harmonicless waveform you pick your signal off 
he LC directly,
f you want harmonics you take it from the plate.
    Looking at a schematic of a BC-221M, it appears that the LC oscillator 
s a electron coupled
artley oscillator. The signal going to the antenna terminal and to the 
nput of the
ixer tube is directly off the plate with no LC in the plate circuit.
    73
ill wa4lav
At 08:00 PM 11/25/2012 -0800, J. Forster wrote:
I heard back from my signal processing expert friend, and it is indeed the
asymmetry of the square wave on the low band that produces the nice comb
with lines at both the odd and even frequencies.

Best,

-John

============



 >
 > Square wave would give high odd harmonics.
 > Jay
 >
 >
 >
 > -----Original Message-----
 > From: Kenneth G. Gordon <kgordon2006 at frontier.com>
 > To: Arc5 <Arc5 at mailman.qth.net>
 > Sent: Sun, Nov 25, 2012 12:48 am
 > Subject: [ARC5] BC-221-AKs
 >
 >
 > By the way, I would have thought that we did NOT want a pure sine-wave
 > output
 > rom these
 > n the interests of maximum harmonic output. Am I wrong?
 > I would have thought that the output should be as close to a square-wave
 > as
 > ossible.
 > Ken W7EKB
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