[Moon-Net] 2.4M PRIME FOCUS / 2.4M OFFSET/ ALSO SEPTUM FOR 1296

Paul Andrews w2hro.fn20 at gmail.com
Tue Nov 22 15:48:42 CET 2016


Peter,

I just acquired a new 2.4m Channel Master 2 piece Ku-band TX certified
fiberglass dish.  Unfortunately, I did not get the factory feed
support hardware so I will need to build that here at home.   Based on
your comments, this Ku-band offset fed reflector will perform better
than my other dish which is a 3m mesh primary focus C-band RX-only.

The 2.4m is heavy compared to the 3m mesh.   The offset dish has a -23
deg offset so the feed point will be very close to the ground at moon
rise so the antenna will be mounted higher so the feed doesn't hit the
ground.

I would like to know which feed you used for 23cm.   The offset fed
dish has a flatter 0.6 F/D.   Is this a special issue to be handled?

Pictures of your offset fed antenna would be good to see.    I'm also
interested in your AZ/EL drive design.

73 - Paul - W2HRO






On Tue, Nov 22, 2016 at 2:36 AM, Hansen Peter
<peter.hansen at dk.saabgroup.com> wrote:
> Hi All I am an extensive user of a Offset dishes.
>
> I started out with a 1.8meter offset dish (6foot) with 35W in the feed. I
> worked easily 35initials on CW and it would have been going on. But 1½ year
> ago I changed to a 2.4meter Offset dish and this really opened the world. I
> use the dish on 3 and 6cm currently but will do 24Ghz also. My dish is
> channel master/Andrew dish. The mesh is small enough for use on 24Ghz.
>
> I can confirm most of the things KL7UW states. The dish is easy to feed
> linear on 3cm as there are waveguide feeds used originally that works great.
> On 6cm where I am circular I designed my own feed type as I find W2IMU feed
> little off peak being used for my dish. I had 0.2dB too little Moonnoise on
> 6cm. I know I could have tried with larger W2IMU feeds but I went another
> way.
>
> Efficiency is much better on the Offset dish due to low blockage and higher
> efficiency in the Feed to illuminate a higher F/d.
>
>
>
> What can be worked on a 2.4meter ??
>
> 3CM
>
> I worked a 90cm that was using 12W in JT4F EME
>
> I worked a 90cm that was using 25W in CW
>
>
>
> 6CM
>
> I worked a 1meter and 10W in CW
>
>
>
> Many qso is possible just try it out.
>
>
>
> All forgot one VERY NICE feature on Offset dish. When I work on my Feeds,
> Change system etc I simply sit on the ground and have the feed just in front
> of me. Or I can tilt the dish and work on it standing up.
>
>
>
>
>
> 73 Peter OZ1LPR
>
>
>
> From: moon-net-bounces at mailman.pe1itr.com
> [mailto:moon-net-bounces at mailman.pe1itr.com] On Behalf Of Edward R Cole
> Sent: 22. november 2016 00:55
> To: serge; moon-net at mailman.pe1itr.com
> Subject: Re: [Moon-Net] 2.4M PRIME FOCUS / 2.4M OFFSET/ ALSO SEPTUM FOR 1296
>
>
>
> Serge,
>
> Just my opinion but if you can acquire an offset feed dish I suggest its
> slightly better:
> 1.  Feed does not block part of the dish surface (no apparent shadow)
> 2.  It requires a narrower beamwidth feed that may improve rejection of
> ground noise pickup (lower sidelobes; better G/T)
> 3.  You can mount all the electronics at the feed eliminating feedline
> losses (max bang for the buck)
> 4.  Often these dish surface are rated to 10-12 GHz so multi-band use is
> greater.
>
> The feed support would need to be robust to handle the higher weight at the
> feed.
> Dish may be fiberglass vs mesh so heavier weight.
> Cost may be higher
>
> Az-El requirements are the same.
>
> Offset dish needs a feed designed for a F/d of 0.6-0.7 (W2IMU would work).
> Ordinary septum would not be good.
> I believe VE4MA is using one on 24/47 GHz so ask him about feedhorns.
>
> I have a idle 1.8m offset feed dish I am considering for 10-GHz use.  It
> used to be our satellite-TV dish until recently switching to Direct-TV
> (which included free dish and HD receiver).  Recently occurred to me that
> 6-foot (1.8m) makes it a candidate for portable use with our RV trailer.
> http://www.kl7uw.com/1.8m_dish.jpg
>
> 73, Ed - KL7UW
>
> At 12:00 PM 11/21/2016, serge wrote:
>
> Which is best a 2.4M prime focus dish or a 2.4M offset dish? & WHY? What
> kind of septum would you use on both dishes for 1296???
> Thank you
> Serge, VE1KG
> _______________________________________________
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>
> 73, Ed - KL7UW
> http://www.kl7uw.com
>     "Kits made by KL7UW"
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>     dubususa at gmail.com
>
>
> _______________________________________________
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