[amsat-bb] Re: Arrow and EME?

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
>http://www.physics.princeton.edu/pulsar/K1JT/
>
>Definitions:
>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 
>Arrow antenna.
>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.

>http://www.naic.edu/
>
>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.
>
>Other Hardware:
>A good Receiver Preamp (similar to ARR)
>http://www.advancedreceiver.com/
>
>A good SSB 2-meter Transceiver (the best ever made Yaesu FT-736R)
>http://www.xs4all.nl/~ketel/ham/ft736.htm
>
>Good Coax (RG-8 coax is 11 Millimeter coax.  That is ok for 50' EME 
>runs, for longer runs use 12+ Millimeter coax)
>
>73
>
>WF1F
>www.marexmg.org
>
>_______________________________________________
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73, Ed - KL7UW, WD2XSH/45
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  BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
500-KHz/CW, 144-MHz EME, 1296-MHz EME
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