[amsat-bb] Antennas for Satellite & EME

[Edward R Cole]

Rich,

Progressing to eme from satellite is not uncommon for folks looking 
for further challenges.

But antenna requirements for eme are considerably different than for eme:
1.  Obviously eme signals are much weaker thus require more sensitive 
(lower noise figure) receivers, larger antennas, and much more 
transmit power.  Frequency and time requirements are higher 
especially if doing digital modes.
2.  Antenna tracking speed is greatly reduced for eme; swinging a 
large eme array fast enough to track satellites might present 
additional challenges.
3.  2m-eme is much easier now days since it has almost completely 
gone to digital mode (WSJT10-JT65B).  This helps running smaller 
antennas and less power due to 10-dB sensitivity advantage over CW.
4.  A single large yagi and 1kW will work 2m-eme fairly well using JT65B.
5.  Power requirement is best understood as EIRP (effective isotropic 
radiated power).  EIRP = Po x gain ratio, where one calculates the 
gain ratio by taking gain = 10^(G/10), G = gain in dBi.
e.g. a 15 element yagi on 28-foot boom G might be 17 dBi, g = 50
if Po = 1000w, EIRP = 1000x50 =50kW
6.  My opinion of minimum 2m-eme requirements is EIRP = 12kW
7.  A standard 2m-eme array has 20-dBi gain; 432 it becomes 24-26 
dBi; 1296 30-dBi
with those gains one is in the maintime for doing eme.  You can work 
some of the bigger eme stations if you have smaller arrays than that.
8. yagis work well on 144 & 432 but a dish is better for 1296.
four 10-element yagis on 144, eight 8-element yagis on 432, and a ten 
foot dish on 1296 will produce these gains.
9.  I recommend you try 2m-eme first.  There is a steep learning 
curve and 2m is easier to achieve eme with off shelf equipment.  But 
be prepared to construct parts of the system.
10.  Az-el tracking is assumed for eme.  Satellite az-el rotators are 
not strong enough to take the loading of a good sized eme array.
11.  What I have for 144-eme:
4x M2 2mXP20 (21.3 dBi) + 1300w (8877 amplifier); 0.1 dB NF preamps, 
DEMI transverter to K3 running on 28-MHz.
I ran for several years with 150w linear amp (100w at antenna array).
12. What I have for 1296-eme:
16-foot dish with 35 dBi gain, special circular polarity feed, HB 
az-el tracking, 0.32 dB NF preamp, 125w

Guess this will give you a start.

73, Ed - KL7uW


----------------
From: Richard Lawn <rjlawn at gmail.com>
To: Amsat BB <amsat-bb at amsat.org>
Subject: [amsat-bb] Antennas for Satellite & EME
Message-ID:
         <CADQmrTGP-YME_CKUi=0TjbPx6s5WY30DNujEn6jhMcT=orA54g at mail.gmail.com>
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I've never devoted much time to VHF/UHF operation aside from satellite
operation and now in retirement I'm thinking of exploring this new
dimension. Since I don't have a lot of space for really long boom yagis and
separate installations for satellite and EME operation I'm looking for an
antenna system that would do double duty. I'd be interested in any
suggestion the group might have in terms of antennas that would work well
for both activities as I could replace my current M2 yagis with something
else for 2/435 and maybe 1.2 ghz.

TNX
73
RIck, W2JAZ


73, Ed - KL7UW
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