[Moon-net] 2.40m dish

Edward Cole kl7uw at acsalaska.net
Sat Sep 27 08:48:06 CEST 2008


For what its worth, I wonder if any out there have looked at the eme 
pathlink as frequency increases?  Pathloss rises by the square of the 
frequency and so does dish gain by square of diameter.  So a ten foot 
(3m) dish should work as well at 10-GHz as it does at 1296.  From 
what I have gleaned from reading, ten foot is the minimum "standard" for CW.

Opting for an 8-foot dish (2.4m) reduces gain by 20Log (8/10) or ~ 
1.9 dB down from a 10-foot dish.  That being said one would expect 
the same performance if sky noise, preamp NF were the same.  But it 
seems that the smaller dish does just a bit better with higher 
frequencies.  Could this be due to slightly lower sky 
temperature?  Or is it because the Moon is better illuminated by the 
smaller beamwidth?

Ironically, today my wife tells me that there is a 14-foot mesh TVRO 
dish available in our neighborhood for the taking.  Since I have two 
1.8m, a 2.4m, and a 4.9m dish, I certainly need another one ;-)  I 
will probably retrieve the 14-foot dish if only to hold for some 
future eme'r or amateur radio astronomer.

Re the 4.9m dish:  We are fabricating and welding the az-el mount 
tomorrow.  This mean we should have the dish installed in about two 
weeks.  Give me two more weeks for installing feed, running cables 
and 60w PA at the dish.

73, Ed - KL7UW

At 08:31 AM 9/26/2008, Mark GM4ISM wrote:
>Hi Phil, es All,
>For what its worth, my observations on the use of 2.4m dishes.
>On 23cm, this is enough to work many stations IF the dish is well 
>illuminated (not too difficult these days)  with 120W or so.
>My best QSO was with a station using a 3m dish the other end (it was 
>very hard going, my RX performance was not the best , but was offset 
>by the high power TX the other end.. )
>This I would consider the limit of my system on CW at this power 
>level.   It puts most stations active on 23cm in reach and if JT 
>modes were used I think I could work other 2.4m stations.
>There are many stations with 4m and up dishes that are really rather 
>easy to work, and a few QSOs on random CW have been made.
>
>Not tried 2.3GHz yet, but the same dish on 3.4GHz is pretty good, I 
>have about 45W and a sub optimal feed (septum without choke) and 
>have had some nice QSOs. With more work on the dish, PA and preamp I 
>will probably be able to work other 2.4m dish stations in the 100W class
>Even on my modest system I have detected my own echoes on a waterfall trace..
>
>On 5.7 GHz I operated with a 1.8m dish, (also not fully optimised) 
>and was just marginally unable to make QSOs with several stations.. 
>my 2.4m dish will be fine.  more work required!
>
>on 10GHz again I operated with a 1.8m dish, and worked 3m dish 
>stations and above..    a 2.4m dish is big enough.. one day I will 
>get the feed fitted and get back on.
>All my EME QSOs so far have been on CW
>My conclusion..
>A 2.4m is well worth putting on EME on all the microwave bands.  It 
>will require a bit more effort to optimise, both on the dish and the 
>PA and preamp front, but you will work a good number of stations and 
>have a great time! on the plus side its easier to point than a bigger dish!
>Having successfully got a 2.4m dish running, you will have a really 
>good station if you are later able to upgrade to a larger antenna.
>my system can be seen at www.dc2light.co.uk
>
>
>----- Original Message ----- From: "FR5DN-Phil" <fr5dn at izi.re>
>To: <moon-net at list-serv.davidv.net>
>Cc: <moon at moonbounce.info>
>Sent: Thursday, September 25, 2008 3:59 PM
>Subject: [Moon-net] 2.40m dish
>
>
>>Hello All,
>>
>>I may have a possibility for a 2.40m TRVO dish, and wonder if it's worth
>>the effort to try on 23cm and/or above with it.
>>
>>My feeling is that it would be marginal on 23cms; and above 23cms the
>>efficiency would be too low?
>>23cms activity is very nice but i need a bigger dish i guess...
>>
>>Just a note on the ZS-FR tropo qso mentionned in the NL. It was the
>>first between africa and reunion, and a record for ZS...and FR.
>>Longer paths have been worked on some other areas.
>>
>>Vy73 - Phil
>>FR5DN - LG78qs
>>
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>
>
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