[amsat-bb] EsHail Microwave transponder satellite

Thu Jun 2 22:24:35 UTC 2016

The S-band RX antnna at Es´hailsat-2 is a RHCP antenna
NB and WB TWTA´s are feeding a Orthomode transducer (OMT) with horn antenna
So X band TX NB is V and X band TX WB is H polarisation.

73 de

Michael R. Lengruesser, DD5ER

AMSAT-DL e.V.

-- International Satellites for
Communication, Science and Education --

mlengruesser at amsat-dl.org
http:/www.amsat-dl.org

Am 02.06.2016 um 23:02 schrieb Edward R Cole:
> Comments *** inserted, below:
> ---------------
> Date: Thu, 2 Jun 2016 12:05:13 +0200
> From: Remco <pa3fym at amsat.org>
> To: amsat-bb at amsat.org
> Subject: [amsat-bb] EsHail Microwave transponder satellite
> Message-ID: <201606021205.13732.pa3fym at amsat.org>
> Content-Type: text/plain;  charset="us-ascii"
> 
> Having posted my setup at the end of last month and
> seeing that my mail program wrapped line feeds, decreasing
> readibility, here again my description and perspective.
> 
> 
> Es'hail2 will not differ from any other geostationary broadcast satellite
> in a sense that it's a 'full duplex' repeater with some time delay.
> 
> 
> I reckon this time delay inhibits actual full duplex operation,
> just like the TV reporter for a 'live stand up' in the TV news via
> a satellite link having an earplug with all audio except himself ('N-1').
> 
> ***Why?  Duplex is totally possible - just listening to your own
> retransmitted voice might mess up your mind too much.  I suggest
> probably muting the receiver when you talk (simple VOX controlling Rx
> audio).  Rx resumes immediately upon cease of talking.  Disable to tune
> in your signal using carrier.
> 
> ====snipped
> 
> 
> Feed:
> From my perspective the only challenge lies in the 2.4 GHz uplink.
> That is, to make an S-band feed which phase center coincides with the
> 10.5 GHz LNB (which has its own 'feed' ;-)
> 
> ***LNB "is" a feed with block down-conversion (e.g. Low Noise
> Block-down-converter)
> 
> I've no fear for isolation issues due to the large frequency difference.
> 
> ***Probably true as wg for 10-GHz LNB cuts off way above the uplink
> frequency.
> 
> I am told that circular polarization (CP) is 'mandatory' for S-band
> uplink's in general but can't find a verification for this,
> perhaps somebody else?
> 
> ***Generally, I am hearing that the s/c will have linear antennas whose
> orientation will change depending on your lat-long on earth.  Common
> issue for eme'rs separated by large differences in coordinates (term is
> called spacial loss but refers to polarization angle shift with apparent
> location in respect to the other station).
> 
> ***CP should solve this for the ground station; but designing and
> building a mw CP feed is not easy.
> 
> Anyway, we're amateurs and creative. So when RHCP uplink is too
> difficult we make a linear antenna and increase uplink power with 3 dB ;-)
> 
> ***Huh?  That would only be true if s/c is circular pol.  If it is
> linear you could have a loss all the way to 20-dB depending on polarity
> mismatch (see spacial loss referred to above)
> 
> But, I follow the published receiver specifications . . .
> Last week I made a 6 turn LHCP 2.4 GHz helix.
> (Rule of thumb seems to be 1 turn per 0.1 f/D)
> Phase center of such a helix is a bit 'foggy' but from what I read lies
> somewhere between the first and second turn.
> 
> I've some issues with matching it due to some mechanical boundary
> conditions
> of the helix feed point in conjunction with the mounted downlink LNB and
> relative position of the helix.
> There is an additional 'transmission line' involved and
> a 'normal' 1/4-wave stub doesn't give me the desired return loss.
> So, this needs some fiddling, perhaps with a gamma match or so.
> 
> ***I used a 33-inch offset fed dish on 2.4-GHz with a 6-1/4 turn helical
> feed for AO-40.  I used brass strap for the first 1/4 WL to match the
> feed to coax.  Matching is done by adjusting the height of the matching
> section from the ground plane.  I ended up with 3/16 inch separation at
> helix end of matching line.
> 
> My approach is, the downlink LNB is mounted in the dish 'as usual' and
> looks through the centre of the uplink helix.
> 
> ***If the 10-GHz feed is generally cylindrical and smaller diameter than
> the Helix this will work fine.  I used a metal tube with heat sink
> covering as center support for my helix.  0.7-inch ID tubing is proper
> diameter for 10-GHz wg.  But not sure how well the typical 12-GHz LNB
> will work inside a helix.
> 
> ***Other geosat designs are for 5-GHz/10-GHz so not sure how well a
> Helix will work there.  Perhaps the 10-GHz cylindrical wg could serve as
> center conductor of air-insulated coaxial feed with a simple dipole feed
> on 5-GHz and 10-GHz horn extending a small way beyond the dipole.  This
> would work better with center-fed dishes of f/d ~ 0.35.
> 
> Pictures of the prototype feed arrangement can be provided soon.
> They are on a camera not present here at this moment of writing.
> 
> ***Attachments to Amsat-BB probably will not go thru; post http link to
> the photos, instead - please.
> 
> Remco PA3FYM
> 
> 
> 73, Ed - KL7UW
> http://www.kl7uw.com
>     "Kits made by KL7UW"
> Dubus Mag business:
>     dubususa at gmail.com
> 
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