Yagi Antenna Question  RF Cafe Forums

canuck1

Post subject: Yagi Antenna Question
Posted: Fri Jun 10, 2011 9:20 am


Joined: Sun May 22, 2011
6:02 pm Posts: 2 
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





Kirt Blattenberger

Post subject: Re: Yagi Antenna Question
Posted: Sun Jun 12, 2011 5:29 pm



Site Admin 

Joined: Sun Aug 03, 2003
2:02 pm Posts: 451 Location: Erie, PA

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 fronttoback 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





canuck1 
Post subject: Re: Yagi Antenna Question
Posted: Wed Jun 15, 2011 5:21 pm


Joined: Sun May 22, 2011
6:02 pm Posts: 2 
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.


Posted 11/12/2012


