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Yagi Antenna Question - RF Cafe Forums
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| canuck1
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Post subject: Yagi Antenna Question
Posted: Fri Jun 10, 2011 9:20 am
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Joined: Sun May 22, 2011
6:02 pm
Posts: 2 |
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Not sure if this needs to go into education section
or antenna question but here is the question:
Question:
Yagi
Antenna Gain = 10dbi
Front to back ratio = 15
db
Distance between Tx and Rx = 15KM
Frequency
= 10 MHz
Transmitter ERP = 100KW
Rx feedline
loss = 2db
Calculate Signal power supplied
to Rx if the antenna is:
a. Pointed directly
towards the transmitting antenna
b. Pointed directly
away from the transmitting antenna
This is what I've done
I calculated
free space path loss using the equation
FSPL(dB)
= 20logd + 20logf + 32.45 (where d = distance in
KM and F = Frequency in MHz)
FSPL = 23.5
+ 20 + 32.45 = 75.95dB
Rx Feedline Loss =
2dB
Total Loss = 77.95
Antenna Gain
= 10dBi
Net loss = 77.95 -10 = 66.95dBi
Tx Power = 100 KW
10 Log (Rx Power/ Tx
Power) = -66.95dBi
Rx Power = 20.18mW
But given answer
is 414uW
So what am I doing wrong
here?
Thanks
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Kirt Blattenberger
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Post subject: Re: Yagi Antenna Question
Posted: Sun Jun 12, 2011 5:29 pm
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| Site Admin |
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Joined: Sun Aug 03, 2003
2:02 pm
Posts: 451
Location: Erie, PA
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Greetings canuck1:
I get just about the same
numbers you do (I get 15.96 mW on the first calculation).
The 414 uW vs. 20.18 mW is 16.9 dB - very close
to the front-to-back ratio. Using my 16 mW vs. 414
uW is 15.9 dB. Methinks the answer was for using
the FtB ratio. What say ye?
_________________ - Kirt Blattenberger
RF Cafe Progenitor & Webmaster
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canuck1 |
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Post subject: Re: Yagi Antenna Question
Posted: Wed Jun 15, 2011 5:21 pm
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Joined: Sun May 22, 2011
6:02 pm
Posts: 2 |
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Thanks for getting back, Kirt.
This is an awesome
forum.
I was thinking along the same line.
Maybe, the given answer was for part B.
This
is an old book so I don't know if I will be able
to get in touch with the author.
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Posted 11/12/2012
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