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RE: L Band Uplink Experience - AO40

Hi John,

I would say it is "good" to "very good."  About the only thing that keeps 
it from being "excellent" is the fact the wire in the helix is soft 
aluminum, and its cost :)  It wasn't cheap--I bought both a 30 turn 2.4 GHz 
helix and 20 turn 1.2 GHz helix at the same time.  It was about $300 US 
total for the pair by the time I paid for shipping, etc.  I did have to 
reshape the end of the helix a bit, as it had been squished a bit during 

I would call the matching part perhaps a little fragile?  The aluminum wire 
is flattened, and a hole is drilled through it so a small bolt passes 
through and is attached with a washer/nut.

While I can't truly measure the SWR, I have pretty good faith in the "power 
out" indication on my TS-790A.  If it's reading about 80-100% of full 
scale, it's a good match (as measured/tested on 2M and 70cm).  The match 
appears to be good, and it appears to work pretty well as I worked a couple 
of stations today with what has to be less than 5 watts at the antenna.

I expect at least several years of good service from it, so overall I'm 
happy with it.  If I were to do it again, I might have built one and saved 
some good money.  However, I didn't like the idea of burning up my $600 
1.2GHz module with a poorly matched antenna ;-)

As for the 30 turn helix--it's in the closet since the 2'x3' BBQ style dish 
I bought with my TranSystem converter clearly+ out performs the helix.  I'm 
thinking it might be fun as the receiver side of a portable setup.


Mark N8MH

At 03:52 PM 5/9/2001 -0400, you wrote:
>Hi Mark, I was wondering what your thoughts were on the
>Wimo helix antenna.  I'm thinking about purchasing one
>but you're the first I heard that actually put one to the
>test.  How's the quality and construction, etc. ?
>TNX & '73,
>         ----------
>         From:  Mark L. Hammond [SMTP:hammond@surrealnet.net]
>         Sent:  Wednesday, May 09, 2001 6:19 AM
>         To:  DA1LA@t-online.de; amsat-bb@AMSAT.Org
>         Subject:  Re: [amsat-bb] L Band Uplink Experience - AO40
>         Currently, I can uplink on mode U with a homebrew 9 turn helix and
>35 watts
>         (out of the rig) and on mode L with a 20 turn Wimo helix and 10
>watts (out
>         of the rig).  My feedline is about 70' of 9913FX(flexi), so I'm
>guessing I
>         have about 5 watts or less actually reaching the antenna.  Not bad!
>         rig is a Kenwood TS-790A with the 1.2 GHz module (10 watts out).
>         I could hear myself pretty well on mode U, and out of curiosity, I
>         mode L uplink for the first time ever.  Surprise!  I could hear a CW
>         carrier.  It was tough hearing myself on SSB, but I did hear myself
>         enough that I hoped somebody with a hot receiver could answer my
>calls.  I
>         got a few people's attention, but nobody replied.  L mode CW would
>         been quite doable, but SSB was marginal indeed.
>         I did successfully work DF4PV as my first AO-40 QSO this AM on
>         U/S!  Thanks!!! :-)
>         BTW I heard you this pass Larry, but couldn't get a reply :)
>         73,
>         Mark N8MH

Mark L. Hammond  [N8MH]

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