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
