Tuning Capacitor Rating Part Two

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• Hello Everyone Referring to my message: https://groups.yahoo.com/neo/groups/Electronics_101/conversations/topics/87771
Message 1 of 20 , Jul 13, 2014

Hello Everyone

Referring to my message:

https://groups.yahoo.com/neo/groups/Electronics_101/conversations/topics/87771

Something went the opposite way than I expected. Holding L at the same place (0.44874 MicroHenrys in my 11-6 meter I.C. receiver circuit), I found that a tuning cap of a HIGHER pF rating gave me a LOWER frequency- I expected the opposite to be true.

Thinking of this, I remembered that the 365pF tuning cap took us down to the BCB in kiloHertz range (at about 540 kilohertz to 1700 kilohertz), but with a different coil).

And got the following results (if you can stand the headache of reading my notes):

Given INPUT MegaHertz (I used highest frequency for this project -i.e. 56 MegaHertz)

Find Inductance:

4.4874e-7 Henrys, or 4.4874e-4 MilliHenrys, or 0.44874 MicroHenrys.

This is where the 0.44874 MicroHenrys came from.

Okay. I set about finding the frequency for a higher 36 pF rating as the tuning cap:

The answer is (I THINK) Frequency = 39.598 MegaHertz. RATS!

This is a LOWER frequency than the 18pF tuning cap!

I tried again with a LOWER rated (LESS than 18pF) tuning cap and got:

Find frequency with:

Inductance 0.44874

Frequency= 75.132 MegaHertz!

The lower tuning cap value gave me a HIGHER frequency.

I was sure that a higher rated tuning cap would give me a higher frequency.

Now my head hurts A LOT. I'm going to let it rest.

Ideas? Am I THAT lost?

Thanks

Patrick

p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are present.

• Hello Two additional points: 1). After my last message on this thread, I looked up the number of turns on the coil. It s only 13 turns of #20 enameled wire.
Message 2 of 20 , Jul 14, 2014

Hello

1). After my last message on this thread, I looked up the number of turns on the coil. It's only 13 turns of #20 enameled wire. That's a fairly small number of turns. It occurred to me that (maybe) I could use different values completely for the coil and tuning cap and end up with the same thing frequency wise*. In other words, I could come up with my own combination of the coil and tuning cap. If this is true, it would be great for working out of a junk box when it comes to parts. I would be inclined to leave the coil tapped at 2 1/2 turns from the ground end...at least for starters.

2). I suspect I might need to change a diode, too, if one is used, but I'm uncertain about this part.

Am I right as far as number 1 goes??

Patrick

*See parts list...it's the image at the bottom of the Web page.

p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are present.

• Freq = 1 / 2 / PI / SQRT( L * C ) Freq = 1 / 2 / 3.14 / SQRT ( 4.4874e-7 * 18e-12 ) = 56e+06 From the above formula, if C is doubled (to 36 pF), the frequency
Message 3 of 20 , Jul 14, 2014

Freq = 1 / 2 / PI / SQRT( L * C )

Freq = 1 / 2 / 3.14 / SQRT ( 4.4874e-7 * 18e-12 ) = 56e+06

From the above formula, if C is doubled (to 36 pF), the frequency decreases to 56/SQRT(2) = 39.598 MHz.

If C is halved (to 9 pF), the frequency increases to 56 * SQRT(2) = 79.2 MHz.

• Kerim Thanks for the workable units. 4.4874e-7 What does the E stand for? Does SQRT stand for square root ? Thanks! Patrick p.s. NOTE: NO TYPO CHECK WAS
Message 4 of 20 , Jul 14, 2014
Kerim

Thanks for the workable units.

"4.4874e-7"

What does the "E" stand for?

Does "SQRT" stand for "square root"?

Thanks!

Patrick

p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are present.

• Yes, SQRT stand for square root . 4.4874e-7 = 4.4874E-7 . Now what about “e” or “E”? “3,000,000” could be shortened to “3e6”. Here,
Message 5 of 20 , Jul 14, 2014

Yes, "SQRT" stand for "square root".

"4.4874e-7" = "4.4874E-7".

Now what about “e” or “E”?

“3,000,000” could be shortened to “3e6”.

Here, “e6” means (x 1,000,000), i.e. “1” followed with 6 zeros.

So R=2.2e3 Ohm is equivalent to 2.2 x 1000 = 2200 Ohm.

Could you guess now the value of 4e0?

It is 4 x 1.

"4" is multiplied by "1" only

because “0” after “e” means there is no zero’s after it.

Now if the number after e (or E) is negative,

the multiplication becomes division.

For example, 3e-6 means 3 / 1,000,000.

Therefore if 3e-6 is a capacitance value,

it means 3 uF ( 1uF = 1 / 1,000,000 F )

Similarly 4.7e-9 is 4.7 / 1,000,000,000.

For capacitors it means 4.7 nF.

Another example:

4.4874e-7 H = 4.4874 / 10,000,000 H

But this value could be written as:

(4.4874 / 10) / 1,000,000 => 0.44874 / 1,000,000 H

Or

0.44874 uH ( since 1uH = 1 / 1,000,000 H )
• Or, read E as times 10 to the... 1.0E06 means 1 times 10 to the 6th power - a million 1.0E-06 means 1 times 10 to the minus 6th power of one millionth. One
Message 6 of 20 , Jul 14, 2014

Or, read E as "times 10 to the..."

1.0E06 means 1 times 10 to the 6th power - a million

1.0E-06 means 1 times 10 to the minus 6th power of one millionth.

One way to deal with negative exponents is to put them in the denominator

1.0E-06 is identically equal to 1 / (1.0E+06)

Richard

• Kerim & Richard et al So E indicates exponent and refers to the following numeral and it is a power of ten; the sign + - of the numeral indicates whether
Message 7 of 20 , Jul 14, 2014
Kerim & Richard et al

So "E" indicates "exponent" and refers to the following numeral and it is a power of ten; the sign +\- of the numeral indicates whether the power of ten is plus or minus power of ten.

And "SQRT" indicates "square root".

Got it, thanks!

Patrick

p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are present.

• QUOTE So E indicates exponent and refers to the following numeral and it is a power of ten; the sign + - of the numeral indicates whether the power of ten
Message 8 of 20 , Jul 14, 2014

QUOTE

So "E" indicates "exponent" and refers to the following numeral and it is a power of ten; the sign +\- of the numeral indicates whether the power of ten is plus or minus power of ten.

And "SQRT" indicates "square root".

/QUOTE

Yes

I keep thinking back to the days where the sliderule was king.  We kept a running "power of ten" in our head while dealing two or three significant digits on the sliderule.

Richard

• Hello My idea about the Two additional points above must have REALLY missed the boat badly. And I thought I was on a hot trail. I should have known it
Message 9 of 20 , Jul 15, 2014

Hello

And I thought I was on a hot trail. I should have known it couldn't be that easy.

Best Regards

Patrick

p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are present.

• Write down the resonant frequency equation: f = 1/(2*PI*Sqrt(L*C)) As L or C increase. the SQRT(L*C) increases (eg, the square root of 5 is greater than the
Message 10 of 20 , Jul 16, 2014

Write down the resonant frequency equation: f = 1/(2*PI*Sqrt(L*C))

As L or C increase. the SQRT(L*C) increases (eg, the square root of 5 is greater than the square root of 4) so, with the denominator getting bigger, the frequency is going down.  The equation says it all.  The problem with writing it out in a Fortran-ish way is that it isn't as obvious how it works as it would be if the equation was written in textbook form with the wide dividing line.  One over big dividing line over the 2*PI*Sqrt(L*C)) bit.

Not a good analogy and one I wouldn't hope to defend but here goes:

Consider inductance and capacitance as inertia - a resistance to change.  If C or L increases, there is more inertia so the resistance to change goes up.  Frequency is the change in voltage.  Inertia goes up, frequency goes down.

Kind of like a pebble versus a boulder.  It's pretty easy to skip a pebble (small capacitance, small inductance) on the water, but a boulder (large capacitance, large inductance)?  Not so much.

Another way to consider the alternatives is to create a spreadsheet with a column for resonant frequency, a column for capacitance (in Farads) and another column for inductance (in Henries).  Pay particular attention to the units and the powers of 10.  Now you can experiment with a range of values without all the grunt work.

Richard

• As stated in another post the resonant freq equation is: F = 1/(2 pi sqrt (LC))...1 over 2 pi times sq root of L x C So as you decrease L and/or C the
Message 11 of 20 , Jul 19, 2014
As stated in another post the resonant freq equation is:

F =  1/(2 pi sqrt (LC))...1 over 2 pi times sq root of L x C

So as you decrease L and/or C the resonant freq increases.  This works for both parallel and series LC circuits.

You can work with the Q, the bandwidth of the values of L and C to make narrower or wider.  For parallel the higher the C the higher the Q or bandwidth.  In series the higher the L the higher the Q.

I once made a notch filter for notching out that old interfering sig on cable TV HBO channel, the interfering sig the cable company put in the middle of HBO so if you did not have the filter it tore up the picture.  I made notch filter with large tunable cap and for inductor/L had 3/4 inch wire connected between the cap leads forming a parallel  LC tuned circuit.  Since C large and L small made high Q/narrow bandwidth circuit.  Worked ok, not as good as the cable company trap, but I got HBO for free, hi.

73, ron, n9ee/r
• Ron I m sure HBO and other such channels STILL haul in money by the truckload! Patrick p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are
Message 12 of 20 , Jul 19, 2014
Ron

I'm sure HBO and other such channels STILL haul in money by the truckload!

Patrick

p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are present.

• Hello What I m wondering is if I can change the LC specs and retain an unaltered circuit otherwise in the tuning section and amplifier sections and end up
Message 13 of 20 , Jul 19, 2014
Hello

What I'm wondering is if I can change the LC specs and retain an unaltered circuit otherwise in the "tuning" section and amplifier sections and end up with a receiver that works on a different frequency.

Best Regards

Patrick

p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are present.

• Patrick, That is exactly how it is done. Variable C and one or more Ls for band switching or vice-verse with a variable L and one or more Cs for band
Message 14 of 20 , Jul 20, 2014
Patrick, That is exactly how it is done. Variable C and one or more Ls for band switching or vice-verse with a variable L and one or more Cs for band switching.

As for how far you can take this from a given point/frequency that you know works, this depends on the rest of the circuit. There will be other elements, capacitance, inductance, resistance that will effect the LC tank circuit. Some circuits can operate over many decades of frequency and others will be more restricted. You can certainly experiment. You will probably find that, at some point, the frequency will not match what you calculate or the response will drop off or the circuit may break into oscillation.

Paul A.

---In Electronics_101@yahoogroups.com, <vw_beetle_fix_it@...> wrote :

Hello

What I'm wondering is if I can change the LC specs and retain an unaltered circuit otherwise in the "tuning" section and amplifier sections and end up with a receiver that works on a different frequency.

Best Regards

Patrick

p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are present.

• A question for Richard Hello Richard Is: resonant frequency equation: f = 1/(2*PI*Sqrt(L*C)) The exact same formula described (in blue) as the Resonant
Message 15 of 20 , Jul 21, 2014
A question for Richard

Hello Richard

Is:

"resonant frequency equation: f = 1/(2*PI*Sqrt(L*C))"

The exact same formula described (in blue) as the "Resonant Frequency Calculator" on this Webpage; and using the proper units?

URL:

Please forgive my being so slow to catch on to what you're telling me.

Thanks!!

Patrick

p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are present.

• Patrick wrote: Is: resonant frequency equation: f = 1/(2*PI*Sqrt(L*C)) The exact same formula described (in blue) as the Resonant Frequency Calculator on
Message 16 of 20 , Jul 21, 2014
Patrick wrote:

"Is:

"resonant frequency equation: f = 1/(2*PI*Sqrt(L*C))"

The exact same formula described (in blue) as the "Resonant Frequency Calculator" on this Webpage; and using the proper units?"

Yes, that is the same exact formula.  The "dots" mean multiplication, and Sqrt(X) means take the square root of X.

The formula works correctly with the units of Henrys, Farads, and Hertz.  Those are the "normal" engineering or scientific units.  Any time someone throws in a multiplier such as Milli or Pico or Mega, you probably have to compensate for it.  Sometimes you get lucky by having the same multipliers in both the numerator and denominator, and then they cancel one another.

Regards,
Andy

• While the resonant frequency equation has been discussed, nothing has been said about Q - the selectivity or bandwidth of the tuned circuit. Kerim showed this
Message 17 of 20 , Jul 22, 2014

While the resonant frequency equation has been discussed, nothing has been said about Q - the selectivity or bandwidth of the tuned circuit.  Kerim showed this with the RLC LTSpice circuit he submitted months ago.  There was a family of curves depicting the varying bandwidth.

For a series RLC circuit, Q is increased with a larger inductor and smaller capacitor.  For the parallel circuit, it is the opposite:  Q is increased with a larger capacitor and smaller inductor.

So, just picking arbitrary values of L & C to obtain a particular resonant frequency will not result in a particularly good tuned circuit.

Note that I left out the R (resistance) factor but it, too, affects the Q of the circuit.  For the series circuit, a higher resistance results in a lower Q, for the parallel circuit, a lower resistance results in a lower Q.

http://en.wikipedia.org/wiki/Q_factor

I suspect there is a reason why certain values of L & C keep showing up in radio circuits.

Richard

• Hello Special thanks to all who answered this post. I ve been really fuzzy with my symptoms of late and I ve been SLOW to catch on. My original question
Message 18 of 20 , Jul 22, 2014

Hello

Special thanks to all who answered this post. I've been really fuzzy with my symptoms of late and I've been SLOW to catch on. My original question happened on a "good" day.

In my fuzzy state, I do better with single word answers. I'll try to let you know when my symptoms are acting up. It may save you some typing.

I'm somewhat better today..., but I don't know if my thinking will clear up substantially or not.

Thanks Again

Patrick

p.s. NOTE: NO TYPO CHECK WAS DONE HERE; please forgive any that are present.

• On 7/22/14, rstofer@pacbell.net [Electronics_101] wrote: (snip) ... There are a lot of unstated assumptions in those rules of
Message 19 of 20 , Jul 22, 2014
On 7/22/14, rstofer@... [Electronics_101]
<Electronics_101@yahoogroups.com> wrote:
(snip)
> For a series RLC circuit, Q is increased with a larger inductor and smaller
> capacitor. For the parallel circuit, it is the opposite: Q is increased
> with a larger capacitor and smaller inductor.

There are a lot of unstated assumptions in those rules of thumb. They
assume that high Q capacitors are always available and high Q
inductors are not. They also neglect the impedance of any circuit
connected to the tuned circuits, or assume the impedances are
something like those found in tube amplifiers. Maybe a bit out of
date.

--
Regards,

John Popelish
• The math doesn t change with the passage of time or specs. What does change is the ability to measure/predict all of the parameters. Mutual inductance,
Message 20 of 20 , Jul 22, 2014
The math doesn't change with the passage of time or specs.  What does change is the ability to measure/predict all of the parameters.  Mutual inductance, distributed capacitance, circuit impedances, all are rather difficult to measure/predict.  So, they hang a little trimmer capacitor on the tuning capacitor to allow for matching to the display and the inductors will often have a tuning slug.

That's one of the cool things about LTSpice (or any other Spice for that matter):  We can get the wrong answer to several significant digits.

Richard

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