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Below are all of the forum threads, including all
the responses to the original posts.
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?
Post subject: Re: Yagi Antenna Question
Posted: Sun Jun 12, 2011 5:29 pm
Joined: Sun Aug 03, 2003 2:02 pm Posts: 451 Location: Erie, PA
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?