[amsat-bb] Re: Arrow and EME?
ka1rrw at yahoo.com
Thu Apr 1 11:06:28 PDT 2010
Good points Mark,
--- On Thu, 4/1/10, Mark Lunday <mlunday at nc.rr.com> wrote:
> From: Mark Lunday <mlunday at nc.rr.com>
> Subject: RE: [amsat-bb] Arrow and EME?
> To: "'MM'" <ka1rrw at yahoo.com>, AMSAT-BB at amsat.org
> Date: Thursday, April 1, 2010, 1:11 PM
> 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
> something like 6 dB. Many folks intentionally use
> moonrise and moonset
> attempts for this reason.
MM: I have heard the same comments and some theories. The Ground Gain is very much dependent on your local Geography. I live 30 miles from the Massachusetts coast line. I can work Mir/ISS on 2-meters to the North East all the way into the Ocean with solid copy. However, my Geography does not favor the Moon. I cannot hear any JT65B signals on 2-Meters until the moon is more than 10 degrees above the horizon.
Will your location benefit from Ground Gain, the only way to find out is to try it. You may get lucky.
> 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.
MM: I now call RG-8 style coax 10-Millimeter coax. When comparing Name brand coax in the 10-millimeter size range, the loss at 2-meters (100 feet), will be very similar. If your loss is too high, the next step is to go with thicker cable. The Diameter of the cable, is one of the limiting factors. The LMR-400 has possibly the lowest loss of all of the flexible 10-millimter coax cables, and it does not kink like the Belden 9913. LMR makes several sizes of thicker cables, with lower loses.
Just like your antenna, Size is important, so too is the size of your coax.
Typical loss values for 100 feet at 145 MHz
LMR-400, 1.5 dB loss, 10 mm
RG-213, 2.5 dB loss, 10 mm
LMR-600, 0.9 dB loss, 14 mm
> 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:
> Mark Lunday
> Greensboro, NC - FM06be
> wd4elg at arrl.net
> -----Original Message-----
> From: amsat-bb-bounces at amsat.org
> [mailto:amsat-bb-bounces at amsat.org]
> 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
> 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
> 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
> Other Hardware:
> A good Receiver Preamp (similar to ARR)
> A good SSB 2-meter Transceiver (the best ever made Yaesu
> 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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