[amsat-bb] Re: Arrow and EME?
kl7uw at acsalaska.net
Thu Apr 1 09:46:35 PDT 2010
A few comments for accuracy (no criticism intended on what WF1F
wrote). I have been on 2m-eme since 1998 and have used digital mode
since 2003 when it first was made available. Insertions (below)
At 04:36 AM 4/1/2010, MM wrote:
>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 of elements.
>Example: A Single half-wave Dipole = 0 dBd
>Elements 2 = 3 dBd
>Elements 4 = 6 dBd
>Elements 8 = 9 dBd
>Elements 16 = 12 dBd
This is not entirely accurate. Yagi antennas increase gain in direct
relationship to length of boom and not exactly a function of number
of elements. I run four ten-element yagis with a total gain of 17.6
dBd (19.2 dBi). One such yagi has 11.6 dBd (13.2 dBi). It is
21-feet long (eme'rs usually refer to wavelengths for boomlength, i.e. 3 WL)
>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.
The rest of this pertains to 2-meter eme. 432-eme will take more
antenna gain since the path-loss is higher at increase
frequencies. This means antenna gain requirements go up
(approximately 6-dB more for stations working eme on 432). The norm
for two CW EME stations is 18-dBi with 1000w on 2-meters and 24-dBi
with 1000w on 432. (subtract 1.64 dB to convert antenna gain to dBd).
The requirements drop significantly for running JT-65 instead of CW:
144-eme: 13-dBi with 600w (min)
432-eme: 19-dBi with 600w (min)
this is for two such stations working each other. This not easy at
this level and may take several hours spread over several days to
make one contact for stations so equipped.
I ran my four yagis with 125w (at the antenna; 170w at the amplifier)
and made contacts with single yagi stations running 600w. I now have
600w. This is on 2-meters.
>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
Don't even give any thought to using FM for eme; it is too wide in
bandwidth to get reasonable sensitivity in receive. SSB has only
been done with one or two super-sized 2m-eme stations; it is more
common with large stations on 1296-eme. I expect to work 1296-SSB
with my 16-foot dish running 300w with stations running dishes >25-feet.
EME is done on CW or JT-65, predominately. Using an Arrow you will
HAVE to use JT-65.
>The Mode JT65B requires approximately 30 dB of Total Antenna Gain
>for an EME contact.
>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 held).
>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 recently.
>If you want more of a challenge, you can try QRP at 5 watts and your
>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.
Arecibo will be doing 432-eme, NOT on 2-meters! However, one could
try their 6-element UHF Arrow antenna with preamp (absolutely
necessary) to try hearing Arecibo which has 58 dBi (56 dBd) gain on
432-MHz. In a recent test folks with small yagis 7-10 elements were
able to hear Arecibo. Arecibo will be running 500w (from last
reports). it is not known if they plan to run JT-65; the focus is
using SSB with other large dishes around the world. Average sized
432-eme stations (8-yagi and up) are expected work them (maybe
requiring the use of CW for smaller stations). If you have 100w+ on
432 you might try CW with Arecibo with a small yagi (ONLY IF you can
hear them, first - DO NOT Transmit if you cannot hear Arecibo).
I will be using 100w with my 16-foot dish (24-dBi gain).
BUT I REPEAT Arecibo will NOT be using 2-meters; ONLY 432.045 MHz
(plus/minus for the expected QRM of stations wishing to contact them).
Arecibo will be doing eme on April 16-18 at times limited by their
Moon view (they can only point down to 70-deg elevation). I will
reprint the times once I find the e-mail that cited the exact operating times.
>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 station.
>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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73, Ed - KL7UW, WD2XSH/45
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
500-KHz/CW, 144-MHz EME, 1296-MHz EME
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