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CX2SA > SATDIG 21.07.14 14:03l 491 Lines 17316 Bytes #999 (0) @ WW
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Subj: AMSAT-BB-digest V9 244
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From: CX2SA@CX2SA.SAL.URY.SA
To : SATDIG@WW
Today's Topics:
1. Re: ANS-199 AMSAT News Service Special Bulletin - AMSAT
Fox-1C Launch Opportunity Announced (Phil Karn)
2. Re: 432 10-13 -Element Antenna? (Jim Jerzycke)
3. Re: ANS-199 AMSAT News Service Special Bulletin - AMSAT
Fox-1C Launch Opportunity Announced (Phil Karn)
4. Re: going digital (Phil Karn)
5. Re: The root of all the problems (Phil Karn)
6. An exciting afternoon on the birds!!! (Hector, CO6CBF)
7. Re: 432 10-13 -Element Antenna? (Steve)
8. Re: 432 10-13 -Element Antenna? (Gary Mayfield)
----------------------------------------------------------------------
Message: 1
Date: Sun, 20 Jul 2014 21:26:28 -0700
From: Phil Karn <karn@xxxx.xxx>
To: amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] ANS-199 AMSAT News Service Special Bulletin -
AMSAT Fox-1C Launch Opportunity Announced
Message-ID: <53CC9674.8080505@xxxx.xxx>
Content-Type: text/plain; charset=windows-1252
On 07/20/2014 10:00 AM, Paul Stoetzer wrote:
> A good number of
> amateur radio operators are only vaguely aware of the amateur
> satellite program and consider it to be quite esoteric.
Precisely. Huge az/el yagi arrays don't help that image either.
Nor does an occasional, brief, noisy pass of an FM voice-only satellite
carrying 1 QSO at a time do much to impress a young person with a mobile
phone in his pocket that he can use to talk or message anywhere in the
world. The term "easysat" doesn't seem appropriate when said FM voice
satellite requires pointing an ungainly-looking 2m antenna at the sky
even if that antenna is very small by usual ham satellite standards.
Most mobile phones don't even have visible external antennas anymore.
I'm not trying to make ham radio into a utility to compete with either
the Internet or mobile phones. That's not what it's for. But for those
who'd like to learn, hands-on, about modern communication technology --
for which ham radio *IS* still uniquely suited -- you have to offer
something that's actually halfway modern!
I can't do anything about the occasional, brief passes of a LEO without
going to a higher altitude orbit. But I certainly *can* do far better
with a LEO satellite and a ~1/2 meter ground antenna by:
1. Adding 3-axis attitude control to the spacecraft.
2. Moving up to the microwave bands.
3. Going digital.
Instead of one voice conversation (interrupted by deep, noisy fades) you
could support many. Although the LEO passes would still be occasional
and brief, alternatives to real-time voice would be available. Bulk data
(including recorded and possibly lengthy voice messages) could be sent
up and delivered to an entirely different part of the globe. For those
who don't really care to talk, satellite-generated data (e.g.,
telemetry, imagery) can be multiplexed with the downlink data.
> The bottom line is that AMSAT-NA needs a significant boost in
> membership and visibility and that boost needs to be soon. Putting two
> satellites into orbit that nearly every single ham will be able to
> easily hear (even a $30 Baofeng and it's stock duck should hear high
> passes of the Fox-1 satellites) along with the accompanying publicity
> should provide that boost.
Suppose it were just as easy and cheap to build or buy an amateur
digital microwave satellite earth terminal? In this age of mobile
microprocessors that would at one time have been considered
supercomputers; handheld GPS receivers; Sirius/XM receivers with
postage-stamp antennas; and direct broadcast satellite dishes -- just to
mention a few now-widespread consumer items -- do you really think it so
impossible to set our sights as hams just a little higher than 1960s
technology?
--Phil
------------------------------
Message: 2
Date: Mon, 21 Jul 2014 04:37:46 +0000
From: Jim Jerzycke <kq6ea@xxxxxxx.xxx>
To: les@xxxxxxxxxxxx.xxxx AMSAT Mailing List <amsat-bb@xxxxx.xxx>,
Star-Com BB <starcom-bb@xxxxxxxx.xxx>
Subject: Re: [amsat-bb] 432 10-13 -Element Antenna?
Message-ID: <53CC991A.30508@xxxxxxx.xxx>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi, Les
I've been using an M2 420-50-11 for satellite use for years now, and it
works great.
Not as much gain as the old KLM 30-element CP antenna I have, but then
it's not 10' long either!
Check it out at the M2 website:
http://www.m2inc.com/index.php?ax=amateur&pg=103
73, Jim KQ6EA
On 07/21/2014 04:18 AM, Les Rayburn wrote:
> I'm limited to indoor antennas for all my amateur operations,
> including satellite operation. Right now, I'm running a 6 element 2
> Meter yagi, along with the 7 element 432 beam (part of an arrow
> antenna). I have room to rotate a larger, and longer 432 antenna, and
> I'd love to have more gain.
>
> Most of the commercial antennas seem to be either small and portable,
> like the Arrow or much longer intended for weak signal operations. Is
> anyone aware of something in between, such as a 10 to 13 element
> antenna available commercially. No time or interest in homebrewing one
> right now.
>
> Even better, does anyone have one that is surplus to their needs that
> they'd like to sell?
>
>
>
------------------------------
Message: 3
Date: Sun, 20 Jul 2014 22:53:19 -0700
From: Phil Karn <karn@xxxx.xxx>
To: amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] ANS-199 AMSAT News Service Special Bulletin -
AMSAT Fox-1C Launch Opportunity Announced
Message-ID: <53CCAACF.5080405@xxxx.xxx>
Content-Type: text/plain; charset=windows-1252
On 07/20/2014 04:58 PM, Robert Bruninga wrote:
> Hummh,
>
> We get an equilibrium of a cube to be about 55F (13C) when exposed to the
> sun on one side and all the other sides radiating to cold space. (assuming
> they are thermally connected).
>
> I wonder why the big difference between our calculations?
Well, here's mine again:
Stefan-Boltzmann law:
P = A*e*s*T^4, where
P = radiated thermal power in watts
A = radiating area in m^2
e = emissivity (dimensionless)
s = Stefan-Boltzmann constant: 5.6703e-8 W/(m^2 K^4)
T = absolute temperature, kelvins
Solving for T:
T = (P / (A*e*s)) ** (1/4)
The solar constant at 1 AU is 1367.5 W/m^2.
For a 10 cm cube with a = e = 1.0 (blackbody) at 1 AU, with the sun
normal on one surface, the absorbed solar thermal power is 1367.5 * .01
= 13.675 W. The radiating surface is six times the absorbing area, or
.06 m^2, because it radiates from all six sides (including the side
facing the sun).
Plugging into the previous formula:
T = (13.675 / (.06 * 1.0 * 5.6703e-8)) ** (1/4)
= 251.8 K = -21.4 C.
Shape matters a very great deal. If you have a blackbody sphere instead
of a cube, then the ratio of radiating to absorbing area is only 4:1
instead of 6:1 and the equilibrium temperature rises to 278.7K = +5.5C.
A thin flat plate (normal to the sun) is only 2:1 so it's even warmer:
331.38K = +58.2 C (quite toasty).
Here's why we may get different answers. If the sun shines on an edge of
the cube instead of normal to one surface, the effective absorbing area
increases to sqrt(2) times that of a single face. In that case, the
equilibrium temperature increases to 274.5K = +1.4C.
And if the sun shines directly on a corner, the absorbing area becomes
(3/4) * sqrt(3) times the area of a single face and the equilibrium
temperature is 268.8 K = -4.3C.
But without active attitude control you can't count on *any* specific
orientation with respect to the sun, and that's precisely the problem.
Even a random average is not necessarily useful if the cube is small
(with a low thermal mass) and turning very slowly. Add the ~90 min
periodic changes due to eclipses and the much slower periodic changes
with the seasons and you can see why the thermal design of a 1U
unstabilized cubesat is such a challenging problem.
It's much less of a problem on a larger spacecraft because you don't
have to cover every surface with solar cells to maximize power
generation, you have a much greater thermal mass to smooth out eclipse
(but not seasonal) variations, and you have room for insulation to
thermally isolate the external surfaces from the interior components.
--Phil
------------------------------
Message: 4
Date: Sun, 20 Jul 2014 22:57:40 -0700
From: Phil Karn <karn@xxxx.xxx>
To: amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] going digital
Message-ID: <53CCABD4.9010305@xxxx.xxx>
Content-Type: text/plain; charset=windows-1252
On 07/20/2014 08:00 PM, Gus wrote:
> I'd hazard to guess that the 'average' shack has multi-mode HF
> capability, along with VHF/UHF FM. Some lesser number of 'average'
> shacks will have multi-mode VHF/UHF, or could readily acquire that
> capability without too much expenditure in resources (time, effort, money).
When DirecTV designed their satellite broadcast system, did they worry
about backward compatibility with the multitude (or so it probably
seemed) of existing C-band BUD (Big Ugly Dish) owners? All of whom were
then receiving analog FM, I might add.
If not, then why are they still in business?
--Phil
------------------------------
Message: 5
Date: Sun, 20 Jul 2014 23:33:24 -0700
From: Phil Karn <karn@xxxx.xxx>
To: amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] The root of all the problems
Message-ID: <53CCB434.1030405@xxxx.xxx>
Content-Type: text/plain; charset=windows-1252
On 07/20/2014 08:42 PM, Bryce Salmi wrote:
> Cubesats are standardizing AMSATs satellites and there's much much more to
> the satellite than simply the amateur radio mode used to communicate. If I
> do my job right, and others working on their Fox-1 subsystems do their jobs
> right too, you will never know it... it will be invisible to the average
> user.
This is absolutely true, especially for the power subsystem you're
working on. So it's vital that the payload use that power as efficiently
as possible.
The biggest load in a communications satellite (most spacecraft,
actually) is the downlink power amplifier, and that's why it's so
important that the downlink use the most power-efficient communications
mode available. And that's not FM, SSB or any other analog mode, not by
a long shot.
Here are some numbers for comparison. NBFM typically uses 15 kHz
bandwidth, and a SNR of at least 10-12 dB in that bandwidth is required
for acceptable performance. That's a P/No (power to noise spectral
density ratio) of about 53-54 dB-Hz.
A CODEC2 encoded voice signal at its highest rate (and quality) is 3200
bps. (Codec2 was specifically developed for ham radio digital voice by
VK5DGR, and outperforms many commercial voice codecs.)
The CCSDS-standard turbo FEC codes require an Eb/No (energy per bit to
noise spectral density ratio) of -0.25 to +1.5 dB, depending on code
rate and block size (the lower the code rate and the bigger the block
size, the lower the required Eb/No). This is remarkably close to the
Shannon limit.
Assuming an Eb/No of +1 dB and a CODEC2 data rate of 3200 bps, a single
voice signal therefore requires a P/No of 10*log10(3200) + 1 = 36 dB-Hz,
17-18 dB less than the FM voice signal.
That's a power savings of something like 60x, which in a power limited
system like a communications satellite turns directly into a capacity
increase of 60:1. That is, you could carry 60 digital voice signals with
the power required by a single FM voice signal. Or you could carry a
single digital voice signal with 1/60 of the power required for a single
FM voice signal.
This should give some clue as to why almost the entire (non-amateur)
world has gone digital.
--Phil
------------------------------
Message: 6
Date: Sun, 20 Jul 2014 21:37:05 -0400
From: "Hector, CO6CBF" <co6cbf@xxxxxx.xx.xx>
To: <amsat-bb@xxxxx.xxx>
Subject: [amsat-bb] An exciting afternoon on the birds!!!
Message-ID: <002201cfa484$48e26a70$daa73f50$@xxxxxx.xx.xx>
Content-Type: text/plain; charset="us-ascii"
Hello to all!
It was an exciting afternoon on the birds! First, I worked Patrick, WD9EWK
on SO-50 in a new grid for me (FN56). Patrick, thanks very much for the
great QSO and new grid!
Then, I had my first contact on satellites with France. Michael, F6GLJ in
IN94qs and I completed a great QSO on FO-29. We had a maxim elevation of 0.5
degree at our ends. I believe it is the first contact between Cuba and
France on FO-29! It is a 7508 Km contact!
Our first attempt was on July 18 but Michael was not able to get a solid
copy of my signal. Fortunately, FO-29 offered us another opportunity, we
made a schedule again and I decided to use the ELK antenna instead of the
ARROW which I used in the first attempt.
I was operating portable from a tall building (45m over the ground), I had a
great horizon visibility. I was running half - duplex with my FT-817nd, a
homebrew 50W power amplifier and a homebrew preamplifier. Everything was
supplied by a 12V 7A gel battery.
Michael, thanks very much for the great contact, new grid and new country!
73!
Hector, CO6CBF / KF5YXV
El92sd
------------------------------
Message: 7
Date: Mon, 21 Jul 2014 12:32:42 +0100
From: "Steve" <steve@xxxxxxxxxx.xxxxxxx.xx.xx>
To: "'AMSAT Mailing List'" <amsat-bb@xxxxx.xxx>
Subject: Re: [amsat-bb] 432 10-13 -Element Antenna?
Message-ID: <B90572A044D048D79724D1715F4801E0@xxxxxxxx>
Content-Type: text/plain; charset="us-ascii"
You could look at a 12 element ZL Special 1.1M long and gives 14dBd gain.
In the UK they are made by Moonraker
Steve
G6UIM
-----Original Message-----
From: amsat-bb-bounces@xxxxx.xxx [mailto:amsat-bb-bounces@xxxxx.xxxx On
Behalf Of Jim Jerzycke
Sent: 21 July 2014 05:38
To: les@xxxxxxxxxxxx.xxxx AMSAT Mailing List; Star-Com BB
Subject: Re: [amsat-bb] 432 10-13 -Element Antenna?
Hi, Les
I've been using an M2 420-50-11 for satellite use for years now, and it
works great.
Not as much gain as the old KLM 30-element CP antenna I have, but then
it's not 10' long either!
Check it out at the M2 website:
http://www.m2inc.com/index.php?ax=amateur&pg=103
73, Jim KQ6EA
On 07/21/2014 04:18 AM, Les Rayburn wrote:
> I'm limited to indoor antennas for all my amateur operations,
> including satellite operation. Right now, I'm running a 6 element 2
> Meter yagi, along with the 7 element 432 beam (part of an arrow
> antenna). I have room to rotate a larger, and longer 432 antenna, and
> I'd love to have more gain.
>
> Most of the commercial antennas seem to be either small and portable,
> like the Arrow or much longer intended for weak signal operations. Is
> anyone aware of something in between, such as a 10 to 13 element
> antenna available commercially. No time or interest in homebrewing one
> right now.
>
> Even better, does anyone have one that is surplus to their needs that
> they'd like to sell?
>
>
>
_______________________________________________
Sent via AMSAT-BB@xxxxx.xxx. Opinions expressed are those of the author.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
------------------------------
Message: 8
Date: Mon, 21 Jul 2014 06:36:15 -0500
From: "Gary Mayfield" <kk0sd@xxxxx.xxx>
To: "'AMSAT Mailing List'" <amsat-bb@xxxxx.xxx>
Subject: Re: [amsat-bb] 432 10-13 -Element Antenna?
Message-ID: <006f01cfa4d7$fb04e680$f10eb380$@xxx>
Content-Type: text/plain; charset="us-ascii"
Gulf Alpha has a 7 x 7 element 2 meter with a 10 x 10 element 70cm antenna
on one boom. I would love to hear from someone with one of those.
http://gulfalphaantennas.com/
I have one of his earlier / smaller antennas, and it performs very well and
is the most sturdily built antenna like this I have ever seen.
73,
Joe kk0sd
-----Original Message-----
From: amsat-bb-bounces@xxxxx.xxx [mailto:amsat-bb-bounces@xxxxx.xxxx On
Behalf Of Les Rayburn
Sent: Sunday, July 20, 2014 11:19 PM
To: AMSAT Mailing List; Star-Com BB
Subject: [amsat-bb] 432 10-13 -Element Antenna?
I'm limited to indoor antennas for all my amateur operations, including
satellite operation. Right now, I'm running a 6 element 2 Meter yagi,
along with the 7 element 432 beam (part of an arrow antenna). I have
room to rotate a larger, and longer 432 antenna, and I'd love to have
more gain.
Most of the commercial antennas seem to be either small and portable,
like the Arrow or much longer intended for weak signal operations. Is
anyone aware of something in between, such as a 10 to 13 element antenna
available commercially. No time or interest in homebrewing one right now.
Even better, does anyone have one that is surplus to their needs that
they'd like to sell?
--
--
73,
Les Rayburn, N1LF
121 Mayfair Park
Maylene, AL 35114
EM63nf
6M VUCC #1712
AMSAT #38965
Grid Bandits #222
Southeastern VHF Society
Central States VHF Society Life Member
Six Club #2484
Active on 6 Meters thru 1296, 10GHz & Light
_______________________________________________
Sent via AMSAT-BB@xxxxx.xxx. Opinions expressed are those of the author.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
------------------------------
_______________________________________________
Sent via amsat-bb@xxxxx.xxx. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
http://amsat.org/mailman/listinfo/amsat-bb
End of AMSAT-BB Digest, Vol 9, Issue 244
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