[amsat-bb] Re: Easy to make, low cost omni-directional antennae

[Edward Cole]

At 11:17 AM 3/27/2008, Bill Dzurilla wrote:
>I have just been involved with the sats since February
>and also wanted an omni for base station use.  I
>started with a simple 1/4 wave ground plane (19" for
>2m, 6 1/2" for 70 cm), later tried homebrewing Jerry's
>Eggbeater II, and then bought a second-hand M2
>eggbeater and the ARR preamp.  I noticed little or no
>difference between the 3 antennas, certainly not
>enough to justify the relatively high price of a new
>M2 eggbeater.  The preamp helps a lot but, as Jeff
>says, SO-50 is still quite weak.

For a simple omni the 19-inch ground plane works as a 1/4 or 3/4 
wavelength vertical on either 2m or 70cm respectively.  I used one 
with a P432 ARR preamp ($79.95) to record AO-51 telemetry very 
well.  This is a plain GasFet preamp with 0.5 dB NF so do not 
transmit into it.  The 25w switching ARR preamp is worth the piece of 
mind in that respect.  I think you get much better low noise 
performance with ARR over the cheaper preamps.


>Have not tried the Lindenblad.  Not many are using it
>or talking about it, so I doubt it is all that great.
>Same for the turnstile.

I am thinking to build a set of these antennas for non-tracking 
use.  Tony AA2TX design looks good.
(http://www.arrl.org/qst/2007/08/monteiro.pdf).



>I do far better with a 5w HT and a handheld Arrow than
>I do with an IC-7000, ARR preamp, and any of the omnis
>I have tried.  However, unlike some people, I don't
>really enjoy standing in the yard holding the Arrow
>antenna for 15 minutes.  So I usually work from
>inside.
>
>If you do go omni, get it high enough to be in the
>clear.  And unless you get a preamp, use very good
>coax and keep the line as short as possible.  You can
>get a 70cm receive-only preamp from Ramsey Electronics
>for $17, but with that you'll need a separate coax
>line for the 2m uplink, or a duplexer.  The ARR is the
>cheapest RF switching preamp and it's over $125.
>
>I also homebrewed one of Kent's dual band LEO cheap
>yagis, see
>http://www.wa5vjb.com/references/Cheap%20Antennas-LEOs.pdf.
>It can be built for $10 and it works as good or better
>than the far more expensive expensive Arrow, although
>it's not quite as portable.  As Jeff mentioned, the
>Arrow unscrews into very small pieces and fits in a
>suitcase, very nice for air travel.  The cheap yagi
>elements are glued to the wood boom, will fit into a
>car trunk but is not suitable for air travel, unless
>someone comes up with a different way to attach the
>elements to the boom that allows easy removal.
>
>Have not tried this, but I'm almost certain that a
>cheap yagi mounted at a fixed 20-30 degree elevation
>and rotated with an old TV rotator will be less
>expensive and give substantially better results than
>any omni, even an omni with a preamp.

For couple years I had the 2m portion of my Arrow installed on az-el 
rotator and it worked well.  I would recommend the fixed elevation 
short yagi as next better than an omni for simplicity with Leo 
sats.  Either an Arrow or home-built will work.

I have the full AO-10/13 long x-yagi's on az-el rotator for the next 
Heo, but for simpler Leo operation the small fixed rotator or 
Lindenblad are fine.


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73, Ed - KL7UW              BP40iq, 6m - 3cm
144-EME: FT-847, mgf-1801, 4x-xp20, 185w
http://www.kl7uw.com     AK VHF-Up Group
NA Rep. for DUBUS: dubususa at hotmail.com
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