[amsat-bb] Re: loop yagis

[Edward Cole]

Greg,

My experience was with my 144/1268 15w DEMI Tx-converter mounted on 
the elevation crossboom with 7-foot of 1/2-inch hardline to a single 
45-element loop-yagi.  I measured 9.5w at the feed with a Bird meter.

So I think anyone considering running mode-L uplink should consider 
the losses to the antenna.  10w in the shack will not do it unless 
you use a very big dish, since you may only get 1-2w to the dish 
(using hardline; don't even think 9913 or such for this 
frequency).  Above 432 it is standard practise to locate the 
equipment close to the antenna so you do not suffer high losses.

Directive systems makes a 6-foot loop-yagi with half the gain so one 
could stack two to get 20 dBi.  The M2-23CM35EZ should work well, also.

We do not know what the orbit and satellite 1268 antenna/receiver 
parameters are, so the only approach I have is to use AO-40 
experience as a guide.  If P3E is more like AO-13 then you get a bit 
more signal which will not hurt.  Let's all remember that the S1 
system failed after a very short period, and S2 used a lower gain 
helix antenna requiring better uplink capabilities.

One should always design in a little "wiggle" room in your 
station.  That way you can absorb some lowered performance on the 
satellite.  This is just good engineering.

At 08:34 PM 5/7/2007, you wrote:
>Hi Ed,
>
>Yeah, I thought a loop in front of my grill might be too good to be true.
>While probably fine for terrestrial work, I only have 10w in the 
>shack, so for satellite work there's no RF to waste on spillage and side lobes.
>
>The 12' Directive Systems antennas seem to be big and very well 
>built.  Too much of both, probably.  I only have a 4'-5' vertical 
>turning radius (cross-arm to sloped roof), so mid-span on a 12' boom 
>isn't going to work.
>And it weighs 5 lbs.
>
>M2 has a 35 element beam (23CM35EZ) with similar specs, but its a 
>little shorter and weighs half as much.  I might be able to squeeze 
>it in between the rotor and the tower cam.  Anybody have any 
>comparative experience between the two?
>
>Thanks,
>
>Greg  KO6TH

73,
Ed - KL7UW
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