[amsat-bb] Re: loop yagis

[Greg D.]

Hi Ed,

I do have a hardline run from the shack, at least for most of the 60' path.  
Need some flexible stuff at either end, so that will eat some signal.  
You're right, I'm going to loose a lot before it gets there.

I managed to snag an ICOM 1271 rig, so I am "native" on that band, but I 
could trade for a transverter up on the roof I suppose.  Does anyone make a 
6m to 23cm transverter?  I have about 10w on 6m that is going pretty much 
unused.

I do remember how wonderful the S1 downlink was on AO-40, but S2 was still 
quite usable.  My BBQ grill, preamp, and Drake converter managed a usable 
signal at apogee if the squint was right.  More uplink wasn' always the 
right answer, as Leila would point out.

Probably I should just sit tight and wait until we know more about P3E and 
Eagle.

Greg  KO6TH


----Original Message Follows----
From: Edward Cole <kl7uw at acsalaska.net>
To: "Greg D." <ko6th_greg at hotmail.com>, amsat-bb at amsat.org
Subject: Re: [amsat-bb] Re: loop yagis
Date: Mon, 07 May 2007 22:40:39 -0800

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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