[amsat-bb] Re: Arrow and EME?
mlunday at nc.rr.com
Thu Apr 1 10:11:53 PDT 2010
I have been doing some reading on this also. Although I have not yet made
any EME contacts, I have been uncovered the following:
1. Moonrise/moonset will enhance signals because of ground reflections,
something like 6 dB. Many folks intentionally use moonrise and moonset
attempts for this reason.
2. Mast mounted pre-amp is essential
3. Higher frequencies need more gain (so I have been told). But the 440 MHz
part of the arrow antenna should have a LOT more gain than the 2 meter part.
4. Low loss coax is very important, esp at VHF. Keep the runs short and use
something equiv to LMR 400 (50 foot of the good stuff is probably under
$100, and worth it.
5. Definitely try to set up a sked with W5UN. If you can hear him, then you
are halfway there!
6. Monitor websites like http://www.chris.org/cgi-bin/jt65emeA
7. 2010 appears to be a promising year for EME, here is a good calendar:
Greensboro, NC - FM06be
wd4elg at arrl.net
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of MM
Sent: Thursday, April 01, 2010 8:37 AM
To: AMSAT-BB at amsat.org
Subject: [amsat-bb] Arrow and EME?
Arrow Antenna and EME:
It is possible to work Earth Moon Earth with an Arrow Antenna.
Of course, it is. You just need to make a schedule with someone on the
other side of the link with enough Antenna Gain. You also need to be
running the new digital text messaging mode called JT65B
Link for JT65
In this document I will refer to all antenna gain values based on the number
Example: A Single half-wave Dipole = 0 dBd
Elements 2 = 3 dBd
Elements 4 = 6 dBd
Elements 8 = 9 dBd
Elements 16 = 12 dBd
The Arrow antenna (Model 146/436-10) has 3 elements on the 2-meter band, so
its maximum theoretical "Element Gain" is 4.5 dBd.
With the invention of the JT65 protocols, thousands of Amateur Radio
stations running a Single Yagi 2-meter antennas, now have access to the Moon
and EME contacts.
To make a contact on Moon bounce, the "Total Antenna Gain" from both
stations is added up and will need to be in the approximate range of 25-30
dBd. With this gain and the average transmitter power of (100-400 watts)
you will have a 10-20+ percent chance of completing a 2-way EME JT65B link,
with another station.
Note: There are many other factures used in EME gain calculations. For
simplicity, we will just focus on the antenna Gain.
The amount of Total Antenna Gain required depends on the mode you wish to
use. The wider the mode, the more gain that is required. The mode JT65B is
a very narrow mode and requires less gain. I am not going to go over all of
the details of JT65 in this article, look it up.
Gain required by mode: (All values are approximate)
JT65 28-30 dBd (1-Yagi + 4-Yagi)
CW 30-40 dBd (4-Yagi + 4-Yagi)
SSB 40-50 dBd (8-Yagi + 8-Yagi)
FM 60-70 dBd (16 + 24) Guess
The Mode JT65B requires approximately 30 dB of Total Antenna Gain for an EME
If we assume the average 12-element 2-Meter Yagi has 10.5 dBd (round to 11
for easy math) of "Element Gain", then the more Yagi's you stack, the more
gain you will have. In EME lingo, 1x12 means, you have One Yagi, with 12
elements, 4x12 means you have a stack of 4 yagis with 12 elements each (48
elements total) and an approximate gain of 17 dBd.
1-Yagi = 11 dBd
2-Yagi = 14 dBd
4-Yagi = 17 dBd
8-Yagi = 20 dBd
16-Yagi = 23 dBd
32-Yagi = 26 dBd
64-Yagi = 29 dBd (W5UN)
A Single-Yagi station (11 dBd) calling a 4-Yagi (17 dBd) station will have
approximately 28 dBd Total Antenna Gain. The 4xYagi stations are very
common on JT56B EME.
Let's go back to the Arrow Antenna:
We need 30 dBd of total antenna gain.
The Arrow antenna has 4.5 dBd.
The Arrow also has a Maximum power limitation of 150 watts (10 watts if hand
If you are running the maximum 150 watts on your Arrow antenna, you should
be able to work stations with 32 to 64 Yagi's. There are not very many 64
Yagi stations out there, however Dave W5UN has been active on JT65 EME
If you want more of a challenge, you can try QRP at 5 watts and your Arrow
Reducing you power from 150 watts to 5-10 watts, will reduce your
performance by 12 db.
To compensate for the reduce power, you will just need to find a station
with a bigger antenna.
There is another big gun on EME. Two weeks ago, Arecibo was on EME, running
CW, working EME stations on the 440 band. The antenna used at Arecibo is a
simple 1,000 foot dish. The actual gain for 2-meters is not known, however
I will assume it is more than 64-Yagi's.
So here is your chance. Make a schedule with Arecibo and go for QRP, EME,
with a held Arrow antenna, or if you know of any good contacts at Arecibo,
send me the data and I'll try to arrange a schedule and try it from my
A good Receiver Preamp (similar to ARR)
A good SSB 2-meter Transceiver (the best ever made Yaesu FT-736R)
Good Coax (RG-8 coax is 11 Millimeter coax. That is ok for 50' EME runs,
for longer runs use 12+ Millimeter coax)
Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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