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Author Topic: a 9 mdb gain jpole?  (Read 1836 times)
WB6BYU
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Posts: 13585




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« Reply #15 on: March 29, 2009, 09:37:22 AM »

A 20' stack on 2m only gives about 6dBd omnidirectional gain
in free space.  9dBd presumes you have a reflector behind
it (like a tower) and is not omnidirectional.  You need
to more than double the height of the stack to get the
extra 3dB for an omni antenna.
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KE7YYB
Member

Posts: 41




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« Reply #16 on: March 31, 2009, 07:28:04 AM »

"BTW what is 9 mdb? 9 million d bees, 9 mega d-bees or what! "

No, it's 9 Mega-Gigawatt dB J-pole antenna fed with flux capacitor linear amp in my basement :-)
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AA4PB
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Posts: 13033




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« Reply #17 on: March 31, 2009, 10:31:30 AM »

Maybe mdb is "milli-decibels", which makes a 9mdb gain jpole quite possible :-)
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K9ZF
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Posts: 76


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« Reply #18 on: April 11, 2009, 09:45:06 PM »

>For what I know, the 11 meter J-Pole was compaired to >a know beam. The known Beam did 16DB gain. The J-Pole

16 db gain over what?  As the previous poster pointed out, you have to have a point of reference for db gain. Is it gain over a dipole?  Gain over an isotropic?  Or maybe gain over a wet noodle?  Stating the known beam has 16db gain without a point of reference is meaningless.


>at the same hight, 100 feet away gave 1 S unit less

What is an "s" unit?  "S" meters on a radio are not test instruments.  No two radios will respond with the same "s" reading, they are just not very accurate.   That one "s" unit of difference may equal 6 db, 3db, 1db, or more likely something entirely different.  And they are not very linear.  The difference between s5 and s7 maybe 3db, and s7 to s9 6db....

In the real world, it is very difficult to measure antenna performance.  I suppose if you had a field strength meter that would read out in uV/m, and a calibrated attenuator, you could get close.  But then you are ignoring stuff like noise and other on frequency interference adding or subtracting from your measurements.

>than the beam to several stations about 20 miles away. >Then an IMax 2000 was used and placed were the J-Pole >was, and it gave 2 S units less. Taking that, the IMax >was doing about 3 DB while the J-Pole was doing about >9db. Does this sound right?

No, unless your reference antenna is a light bulb.  The only thing you have proven in your test is the J-pole seems to be slightly better than the IMax, and neither is quite as efficient as the beam  FOR THIS ONE SPECIFIC SCENARIO.  Turn to another station in a different direction, and every single reading could be different.  Turn to a third, and get a third set of results.
>
>
>1326 - Gary
>1326@dxrw.org

BTW, I'm not trying to be critical, I'm trying to teach.  I have no prejudice against CB'ers.  I used to use CB myself, quite a few years ago.  I gave it up when the fun to crap ratio got out of hand.  Since then I discovered how much fun you can have with ham radio.  One of my favorite parts was learning to build my own antennas and other gear.  A big part of this was reading books and learning theory.  It's all part of the fun.


73
Dan
--
Amateur Radio Emergency Service, Clark County Indiana. EM78el
K9ZF /R no budget Rover ***QRP-l #1269 Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla> List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!

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--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
 ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Maili
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