Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 3 Next   Go Down
  Print  
Author Topic: Brainteaser  (Read 8174 times)
W5DXP
Member

Posts: 3556


WWW

Ignore
« on: November 02, 2011, 06:34:06 AM »

Here's a graphic of a black box containing one real-world component along with lab measurements made on the current in and current out of the black box. What's in the black box?

http://www.w5dxp.com/branteas.GIF
Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
AC5UP
Member

Posts: 3835




Ignore
« Reply #1 on: November 02, 2011, 08:52:13 AM »

If the black box is a passive part, my best guess is a 4:1 Balun.......
That would explain the output current being greater than the input current in the first two cases if the black box performs an impedance transformation.

?

Hey, someone had to go first...........................  Tongue
Logged

Never change a password on a Friday                
W5DXP
Member

Posts: 3556


WWW

Ignore
« Reply #2 on: November 02, 2011, 11:09:35 AM »

If the black box is a passive part, my best guess is a 4:1 Balun...

Yes, it is a passive part and no, it is not a 4:1 Balun nor any N:1 turns ratio transformer.
Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
AC7ZN
Member

Posts: 42




Ignore
« Reply #3 on: November 02, 2011, 01:08:49 PM »

Hi Cecil,

Can we assume, since transformers are eliminated, that it is also not a saturating tapped inductor (which could be considered a  form of autotransformer)?

73,

Glenn AC7ZN
Logged
W5DXP
Member

Posts: 3556


WWW

Ignore
« Reply #4 on: November 02, 2011, 02:52:14 PM »

Can we assume, since transformers are eliminated, that it is also not a saturating tapped inductor (which could be considered a  form of autotransformer)?

There's no known non-linearity like saturation. It is an extremely common linear component and this brainteaser has absolutely no tricks involved.
Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K7STO
Member

Posts: 45




Ignore
« Reply #5 on: November 02, 2011, 08:36:28 PM »

I believe it is a capacitor. The answer I would like to know is how to change my Callsign after logging into the site to my new callsign.
Logged
W5DXP
Member

Posts: 3556


WWW

Ignore
« Reply #6 on: November 03, 2011, 04:47:44 AM »

I believe it is a capacitor.

How would a capacitor manage to effect a 60% increase in output current over input current?
Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
G3RZP
Member

Posts: 4467




Ignore
« Reply #7 on: November 03, 2011, 07:07:55 AM »

Are the phases all positive as suggested, i.e. input leads the output?
Logged
G8HQP
Member

Posts: 122




Ignore
« Reply #8 on: November 03, 2011, 07:59:46 AM »

Transmission line, impedance 1930 ohms, electrical length about 8.5m ?
Logged
W5DXP
Member

Posts: 3556


WWW

Ignore
« Reply #9 on: November 03, 2011, 10:26:49 AM »

Transmission line, impedance 1930 ohms, electrical length about 8.5m ?

Congratulations!!! Very close, but no cigar. The characteristic impedance is indeed 1930 ohms and the electrical length, assuming VF=1.0,  is indeed about 8.5m at 4 MHz, i.e. 41 electrical degrees.

But the device inside the black box was a 75m Texas Bugcatcher mobile loading coil.
Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
WS3N
Member

Posts: 686




Ignore
« Reply #10 on: November 03, 2011, 10:30:35 AM »

I believe it is a capacitor. The answer I would like to know is how to change my Callsign after logging into the site to my new callsign.

http://www.eham.net/about/loginhelp#new_callsign
Logged
AC5UP
Member

Posts: 3835




Ignore
« Reply #11 on: November 03, 2011, 12:46:21 PM »

But the device inside the black box was a 75m Texas Bugcatcher mobile loading coil.

...which makes it ready for burial. Excellent!
Logged

Never change a password on a Friday                
G8HQP
Member

Posts: 122




Ignore
« Reply #12 on: November 03, 2011, 02:20:24 PM »

I was wondering where you could buy 1930 ohm coax cable! A big coil will of course have a high inductance and a relatively low capacitance (when compared to coax) so at some frequencies can behave like a section of transmission line.

My initial guess, before I carefully read the question, was a pi network as that has impedance inverting properties but then I saw that only one component was present. A pi network is of course a lumped approximation to a transmission line.
Logged
K0BG
Member

Posts: 9866


WWW

Ignore
« Reply #13 on: November 03, 2011, 03:49:07 PM »

Someone's mathematics is a bit off.
Logged

K7STO
Member

Posts: 45




Ignore
« Reply #14 on: November 03, 2011, 04:41:26 PM »

I believe it is a capacitor. The answer I would like to know is how to change my Callsign after logging into the site to my new callsign.

http://www.eham.net/about/loginhelp#new_callsign


Thanks Jack I appreciated the assistance.

Mike
Logged
Pages: [1] 2 3 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!