[aprssig] Re: [OZAPRS] S points and satellite signals

Ray Wells vk2tv at exemail.com.au
Wed Nov 28 15:01:24 EST 2007


How much gain will the yagi's have?
If you are receiving a plane polarised signal the gain will be that of a 
single yagi and will be related to the number of elements (assuming mear 
optimum element spacing). However, unlike a single yagi, a crossed pair 
won't exihibit (much) polarisation loss as the antennas are rotated 
about the axis of the boom.
No.   gain (dBd) (approximate)
2      3
3      5-6
4      6-7
5      8-9

If you are receiving a circularly polarised signal the gain will be that 
of the two yagis. If, however, the sense (right-hand vs left-hand 
circular) of your antenna is opposite to the transmitting antenna the 
loss could be in the vicinity of 20dB, or more.

As for the S meter increase, that will depend on the calibration of the 
meter. A true S-meter is 6dB (twice, in voltage terms) for each S point, 
but amateur rigs rarely (ever?) use that calibration standard. If you 
have access to a calibrated signal generator (a service monitor) you can 
easily draw up a calibration chart.

Suffice it to say that you will experience a not insignificant increase 
with the yagis, assuming they're working as intended, and the increase 
will probably be more noticeable at smaller S-readings than at the high 
end of the scale.

Ray vk2tv

>On the weekend we are going to compare a crossed yagi and a vertical for
>satellite signals.
>Is there a rule of thumb for what we should expect with regards to S points
>of signal increase ?
>Andrew Rich VK4TEC
>vk4tec at people.net.au
>Ozaprs mailing list
>Ozaprs at aprs.net.au

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