[amsat-bb] Re: loop yagis

Mon May 7 21:34:41 PDT 2007

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

----Original Message Follows----
From: Edward Cole <kl7uw at acsalaska.net>
To: "Greg D." <ko6th_greg at hotmail.com>, kc6uqh at cox.net, amsat-bb at amsat.org
Subject: Re: [amsat-bb] Re: loop yagis
Date: Sun, 06 May 2007 23:59:19 -0800

For what is worth, my two 45-element loop-yagis give gain of 23 dBi.  They 
are 12-foot long and spaced about 16-inches apart.  They are sold by 
Directive Systems.

A loop fed element in front of  a 32-inch BBQ dish will not have anywhere 
near this gain and have many large side lobes.  A dish needs to be >10 
wavelength to exhibit nice clean beam pattern (23cm *10 = 230 cm or about 
7.5 feet).  I know many satellite folks are using a 4-foot dish so on 
transmit only this  may be sufficient, though the beam will not be nice and 
waste much radiation in other than the desired direction.

I used one of the loop-yagis (20-dBi) on AO-40 with 9.5w with a marginal 
uplink signal.  Either 15w or more antenna gain was indicated to produce an 
SSB signal comparable to mode US.  of course P3E and Eagle requirements  may 
not be the same as AO-40.  This is the best we can do without precise 
knowledge of the satellite parameters.

At 03:50 PM 5/6/2007, Greg D. wrote:
>I need a good uplink antenna for the new birds, and have no real space on 
>the boom to add a yagi.  This sounds like what I need; do you have any 
>pictures?  Also, more details on how you do the filtering to keep from 
>frying the 2.4 preamp!
>
>I have a screen-lined grill dish, with a canned helix feed to a Khune 
>preamp.  See:  http://home.jps.net/~gregd/Dsc00201.jpg.  Would I just put a 
>single 1-wavelength loop around the outside of the helix at about the focal 
>point?  That would be right at the front of the can...
>
>Greg  KO6TH
>
>
>
>----Original Message Follows----
>From: "kc6uqh" <kc6uqh at cox.net>
>Reply-To: kc6uqh <kc6uqh at cox.net>
>To: <w7lrd at comcast.net>, <amsat-bb at amsat.org>
>Subject: [amsat-bb] Re: loop yagis
>Date: Sat, 5 May 2007 23:19:29 -0700
>
>Bob,
>For ATV I have used a Conifer BBQ grill type 2.4 GHz antenna with a Loop 
>for
>1.2 GHz in front of the 2.4 GHz feed. The 1.2 side has plenty of return
>signal in the order of 18 dBi for ATV work. I haven't seen a loop yagi that
>will touch it in performance. I run full duplex with filters on both
>frequencies 1253.25 receive and 2441.5 transmit with 10 W. I am able to 
>work
>the W6ATN repeater from 40 + miles.
>
>Art
>KC6UQH
>----- Original Message -----
>From: <w7lrd at comcast.net>
>To: <amsat-bb at amsat.org>
>Sent: Saturday, May 05, 2007 4:13 PM
>Subject: [amsat-bb] loop yagis
>
>
> > Hello
> > What is the consensus regarding loop yagi antennas for L band uplink.  I
> > have 10 watts available from an IC1271 before the coax.
> >
> > --
> > 73 Bob W7LRD
> > AMSAT member 28498
> > Seattle
> > _______________________________________________
> > Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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> >
>
>
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73,
Ed - KL7UW
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144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
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