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Re: How much better with circular polarization?





On 4 Oct 2001, at 21:08, Floyd Sense wrote:

> The current AO-40 pass is in open sky for me (a hole in the tree cover) and
> the beacon is peaking at S6 with frequent fading to S3-4 and often dipping
> to S1.  This is with a 2x3' barbecue dish antenna and linear feed system
> (AIDC 3733).  I wonder if anyone has compared this setup to a mesh or solid
> dish of similar size and circular polarized feed system?  Should I see about
> the same peak signal strength, but with less QSB?  Substantially less QSB?
> 
> Several signals heard on CW tonight, but only heard one successful QSO.  One
> SSB station heard, plenty strong enough to copy.
> 
> K8AC
> Floyd Sense - Angier, NC
> 
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Hi Floyd

I just wire mesh the same antenna and with also an aidc 3733 (stub cut and filter mods) at squint below 15 deg i also received AO-40 
peaking at S6 with no rapid QSB only slow variation in signal from S4 to S6. I was able to make my first CW QSO using my UHF 9 DB 
omni antenna and 50 watts got 559 report.

I will let you know if there is any change in sigs i readjust the aidc from minimum to maximum distance in the holding bracket. I try to 
measure focal point distance with a lazer light but need to test it over the air to confirm best focal distance.

I also send you some data to calculate gain on a solid circular dish antenna

K = Performance factor 60% average 70% for commercial built antenna
D = Dish diameter in meters
R = Variation of light speed in meter per second on wave lenght in meters 

                     ( pi x D )2
 gain G = K x  ( ------ )
                     (    R   )

EX: dish antenna of 1.80 m diameter at 11.4 Ghz

R = 300 000 000 / 11 400 000 000 = 0.0263
 pi x D = 3.14 x 1.80 = 5.652
5.652 / 0.0263 = 214.9 square at  46182
with a performance factor of 60%  46182 x 0.6 = 27709

To get gain in DB we make 10 log base 10 of 27709 = 44.4 db

CAUTION
==============
	On dish antenna surface imperfections (bumps, paint deposit, dust) can reduce overall gain performance as per table below.

Average height of imperfections in mm        Gain losses in % for Ku band
                0.1                                                               3
                0.5                                                               16
                  1                                                                30
                1.5                                                               41
                2.5                                                               59
                3.5                                                               71

As per this table after 1.0 mm i'ts more a trash can cover than a dish...

It's theory and i dont know whats the gain losses is on 10 GIG as this came as is from notes i got from french packet network.
Wire meshing BBQ grill produce some bumps on antenna edges i dont know if this can have an impact on gain. and i'm using the same 
aidc dipole dont know also effects on a solid surface regarding polarisation.



Luc Leblanc VE2DWE (AMSAT 33583)
SITE WEB:http://www.sorel-tracy.qc.ca/~luclebla/
C.P.341
Sorel
J3P 5N6

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