[Moon] [Moon-Net] 3 cm circular polarisation

Chuck Smallhouse w7cs at theriver.com
Mon Sep 22 09:37:34 CEST 2014


I also question whether a W/G switch has truly enough isolation to 
protect a LNA, by it's self.  An additional SMA type relay, in 
series, may need to be added.

Several years ago I had numerous LNAs (converted TVRO LNBs) fail 
while using a 10W PA and an SMA relay for TR switching.   I had 
supposedly measured the SMA's isolation at approximately 60 dB, the 
limit of my measuring equipment then.

I now will have a W/G switch and considerably more power.  I hope not 
to loose too many more LNAs, sequencing will be in use, as it was before.

Chuck, W7CS




At 12:07 AM 9/22/2014, Charles Suckling wrote:
>Hi Ben
>
>Just wanted to add one slightly out of the box thought.
>
>Linear has one advantage over CP for 10GHz in that there is a recent 
>growth in stations participating in 10GHz EME using "tropo" sized 
>systems with associated linear pol feeds. The DL0SHF beacon, running 
>linear, is often their first point of contact with 10GHz EME and I 
>think this trend would be less likely to develop with the added 
>complication of needing a CP feed.
>
>Luis brings up some interesting points about depolarisation that on 
>one test with G4NNS we did not observe.  With linear, we saw a clear 
>null when trying cross polarised linear.  The fit between offset 
>angle and received S/N matched the expected behaviour quite closely 
>as if there was no depolarisation.  Observations of signal spreading 
>being less on CP is interesting and is something to look at 
>again.  The paper did not make clear that the tests were done at the 
>same time or at different times.  If the latter, then one would need 
>to check that the libration rate was the same at the different times.
>
>73
>
>Charlie
>
>
>----------
>From: moon-net-bounces at mailman.pe1itr.com 
>[mailto:moon-net-bounces at mailman.pe1itr.com] On Behalf Of SM6CKU
>Sent: 21 September 2014 21:10
>To: Dom DEHAYS; Moon-Net; moon at moonbounce.info
>Subject: Re: [Moon-Net] [Moon] 3 cm circular polarisation
>
>Yes, you are right Dom
>----- Original Message -----
>From: <mailto:f6dro at wanadoo.fr>Dom DEHAYS
>To: <mailto:ben at sm6cku.se>SM6CKU ; 
><mailto:moon-net at mailman.pe1itr.com>Moon-Net ; 
><mailto:moon at moonbounce.info>moon at moonbounce.info
>Sent: Sunday, September 21, 2014 8:59 PM
>Subject: Re: [Moon] 3 cm circular polarisation
>
>Hi Ben ,
>
>of course , there's no pb for U to use what U want. Just one thing : 
>0,5db loss in front of the preamp is NOT 0,5db loss on signal , but 
>probably closer to 1dB....so your monn noise could be 3dB.and 
>something like 2dB more on sun noise
>
>73
>Dom
>----- Original Message -----
>From: <mailto:ben at sm6cku.se>SM6CKU
>To: <mailto:f6dro at wanadoo.fr>Dom DEHAYS ; 
><mailto:moon-net at mailman.pe1itr.com>Moon-Net ; 
><mailto:moon at moonbounce.info>moon at moonbounce.info
>Sent: Sunday, September 21, 2014 8:44 PM
>Subject: Re: [Moon] 3 cm circular polarisation
>
>Dom,
>My preamp (DB6NT) has a NF of 0,75 dB, the SMA to SMA male connector 
>is 0,1 dB, the isolation relay is 0,15 dB and the coax between relay 
>and LNA is 0,15 dB. A total of 1,15 dB which has been confirmed by 
>measurements. I agree that a WG version will improve these figures, 
>but I prefer not to use WG pieces. I can accept the 0,5 dB loss 
>compared to that solution. 2,5 dB of moon noise instead of 2.
>But this has nothing to do with linear or CP....
>I will try to take some photos tomorrow.
>
>73 de Ben
>----- Original Message -----
>From: <mailto:f6dro at wanadoo.fr>Dom DEHAYS
>To: <mailto:ben at sm6cku.se>SM6CKU ; 
><mailto:moon-net at mailman.pe1itr.com>Moon-Net ; 
><mailto:moon at moonbounce.info>moon at moonbounce.info
>Sent: Sunday, September 21, 2014 12:15 PM
>Subject: Re: [Moon] 3 cm circular polarisation
>
>Hi all ,
>
>I have no personnal objection to go CP on 3cm eme BUT it should be 
>done with a waveguide access on the RX side of the feed.Most feeds 
>with a polarizer I have seen yet use an SMA connector on the RX side 
>, it is a problem as we need to use a coaxial sma relay for 
>isolation and a cable ( and/or adapter(s)) to connect a coaxial 
>preamp . This will give  significantly reduced Rx performances 
>compared to a waveguide system.
>
>73
>Dom
>
>
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