[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Satgate Omni Antenna plots

About the 19" vertical for Omni RX at 435 MHz:

>>> John Ronan <jronan@tssg.org> 08/05/05 2:16 PM >>>
>I was reading
> http://web.ew.usna.edu/~bruninga/pec/pc2ops.html 

>just now and at the bottom of the page you have the elevation plot.   
>I was trying to reconcile the text with the plot.  The text talks  
>about a 3/4 wave antenna, and the plot has a 1/4 wave antenna.  
>I  assume that is supposed to be 3/4. I was about to go cutting an  
>antenna to length, hence I was reading it.

One has to intepret that plot carefully.  ALL plots are done
at the frequency of 435 MHz.  Even if it says it is a 1/4
wave at 2m, it was still being used to receive 435... where
it is a 3/4 wave vertical.

See how that antenna is poor below 30 deg, but it has
very good +7dBi gain above 30 deg.

See also how the 5/8 wave gives its gain below 30 deg
and less gain too.

That is why, I receommend the vertical 19" whip over
a ground plane for fixed omni antennas for satgates.

1) Because PCSAT2 is so weak (1W) that you will never
hear it strong enough on a 5/8 wave vertical at low

2) When it is closer and stronger, notice tht the 5/8
wave has negative gain!  So it is useless when you
can actually have a strong enough signal to hear

3) Since you cant hear it at low angles with any
common antenna, then may as well forget about
hearing the horizon, and concentrate your gain
when it is high up and close in by using the
3/4 wave vertical (19") whip.

This receommendation is ONLY for unattended
capturing of packets into the internet.  Because
we dont care what you DONT hear, but we do
want to get good packets for what you do hear.
This combined with what everyone else captures
over their station combined over the internet
will give us a good system of data cpature...


I hope its going well for you all.

de John

John Ronan <jronan@tssg.org>, +353-51-302938
Telecommunications Software &  Systems Group,  http://www.tssg.org 
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org