[ARC5] The BC-221 low frequency tank circuit puzzle.

[Mike Feher]

199.82 kHz. 

 

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell, NJ, 07731

732-886-5960 

 

From: ARC5 [mailto:arc5-bounces at mailman.qth.net] On Behalf Of J Mcvey via ARC5
Sent: Sunday, February 14, 2016 10:28 AM
To: Leslie Smith; ARC-5 List
Subject: Re: [ARC5] The BC-221 low frequency tank circuit puzzle.

 

I pulled up the schematis od the BC-221 and I assume that you are referring to item 1, 2 and 3 with 150, 2 and 10 pf ) a MAXIMUM combined parallel capacitance of 162 pf. This is from TM-11-300.

 

Item 1 is a 150pf VARIABLE cap. 10.4 mH (tm 300 -11 says 10.1 mH)needs a 61pf cap to resonate at 200kHz. This should be in the range of the variable cap.

Does that seem reasonable?

 

On Sunday, February 14, 2016 5:51 AM, Leslie Smith <vk2bcu at operamail.com> wrote:

 



              BC-221 Frequency Meter.

A number of web pages provide information about the BC-221 hetrodyne
frequency meter.  Some provide circuit diagrams - well drawn & with a
readable parts list.  I have one of these diagrams.  

Be warned!  Item 15 - the low frequency coil - is shown as 10.4uH - yes
ten point four micro-Henries.  This is an obvious mistake - the coil in
a tank circuit operating at 200 kHz MUST be larger than 10.4uH

Tracking back to an original manual, item 15 - the low frequency tank
coil - is given as 10.4mH - and that value solves the mystery.  Well,
not quite.  175pF and 10,400uH (according to calulation) resonate well
below 200kHz. 

Beyond this - the 10.4 uH vs 10.4mH difference nicely illustrates one of
my pet peeves.  This is  a failure to distinguish corretly between unit
designators.  By this I refer to those pesky prefixes - such as "u"
(properly mu, not "u") or 10e-6 and "m" (milli, one one-thousandth),
Mega (x10e6)  and so on.  On the web we often see MegaHertz abbreviated
at mH.  Please!  milliHertz (mHz) and MegaHertz (MHz) differ by a factor
of 1,000,000,000!  I'm certain ARC-5 list-readers would NEVER make the
mistake of confusing MHz with mHz!

For the benefit of non-list readers who are inclined to argue "it
doesn't matter" - it's obvious that mHz means MegaHertz - let me remind
you it DOES matter.  NASA lost a Mars orbiter as a result of confusion
about the correct understanding of units.  Millions of dollars!  Ouch!  
Closer to home the same problem arose with Air Canada flight 143, - The
Glimli Glider.  Confusion of units.  I rest my case.  Units of
measurement MUST be expressed accurately.

Back to the BC-221!  

Can anyone solve the mystery of how a 170pF and 10,400 microHenry
coil-capacitor combination resonates at 200kHz.  
Freq equ sqrt(25330.29/LC) What's going on here?

Les

-- 
http://www.fastmail.com  <http://www.fastmail.com/> - Send your email first class

______________________________________________________________
ARC5 mailing list
Home: http://mailman.qth.net/mailman/listinfo/arc5
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:ARC5 at mailman.qth.net

This list hosted by: http://www.qsl.net <http://www.qsl.net/> 
Please help support this email list: http://www.qsl.net/donate.html



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20160214/45af90fd/attachment.html>