•−•  ••−•    −•−•  •−  ••−•  •
RF Cafe Morse Code >Hear It<

Job Board

About RF Cafe™

Sitemap

Yagi Antenna Question - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

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 
 
Lieutenant

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


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

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 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 :smt024
RF Cafe Progenitor & Webmaster


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

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
Custom Search
More than 10,000 searchable pages indexed.

Your RF Cafe
Progenitor & Webmaster

Click here to read about RF CafeKirt Blattenberger... single-handedly redefining what an engineering website should be.

View the YouTube RF Cafe Intro Video Carpe Diem!
(Seize the Day!)

5th MOB: My USAF radar shop

Airplanes and Rockets: My personal hobby website

Equine Kingdom: My daughter Sally's horse riding website