October 27-29, 2000 - Klofas.com

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Ed Krome K9EK Columbus, Indiana kgek@amsat.org August, 2000 Phase 3D: A Primer on High Frequency Operatiou With the excitement over the impending launch ofPhase 3D, many people are working hard to improve existing satellite stations and add new capabilities. The AMSAT reflector is full ofdiscussions on higher frequencies, high speed digital, all kinds ofneat things! Last year, S-band (2401 MHz) downlink got a boost from the availability ofDrake 2880 downconverters, readily convertible to amateur service. I expect that S-band downlink will be a very popular band, indeed. The lower bands are all pretty well known. Even 1269 MHz uplink is much less exotic than it used to be, with the availability ofplug-in modules for popular satellite transceivers. The higher bands haven't had much discussion yet; uplinks on 240112446 MHz and 5668 MHz and downlinks on 10450 and 24050 MHz have great possibilities. As a long time high-frequency experimenter and general AMSAT enthusiast, these bands are ofgreat interest to me. This article will discuss some ofthe basics ofhigher frequency operation and discuss one man's approaches to operation on these frequencies. This is not supposed to be a construction article, though everything discussed has been built (and even works!), but rather to take some ofthe mystery out ofthings. Where to start Lesson one is that the sensible place to start is the one that costs you the least time, effort and money. The fact is that UHF receiving is a LOT cheaper and easier than transmitting. And the lower the frequency, the cheaper and more available the gear. Currently, 23 cm is the highest band supported by off-the-shelf ham gear, and that is an uplink-only band. For 13 cm and above, equipment shifts from one-piece boxes to distributed components. A fact ofphysics says that the higher the frequency, the greater signal loss in a piece of feedline. To a receiver, feedline loss looks like increased noise. And low front end noise is the most important part of a receiving system. The most practical method ofreducing feedline loss is to eliminate the line. We do this by mounting preamplifiers (and sometimes even whole converters) directly at the antenna. Since a 13cm downlink was active on A013, this mode has already been well documented. A good reference, also useful on all higher bands, is "Mode S: The Book" available from AMSAT. Higher yet The next downlink band beyond 13 cm is 3 cm .... quite a jump in frequency and complexity. Phase 3D has 2 separate antennas and amplifiers on 10450; one ofthem a 60 watt TWTA (Traveling Wave Tube Amplifier), the other a 10 watt solid-state amplifier. These should provide a booming signal to a small dish and make this frequency very popular with both techies and even "normal" people! 39
On 10450, it may not be enough to follow the "low frequency" (like 13cm!) techniques ofantenna mounted preamp and shack mounted converter. Feedline losses are so high that is will be necessary to mount the receive converter right up close to the antenna feed also. Probably the most physically satisfactory arrangement will be to mount the preamp right at the antenna feed, then use a short-as-possible length ofhigh-quality (RG-213 or better) coax. to get from the preamp, around the rotors to a weather-proof box containing the receive converter, mounted high on the tower. Then the lower-frequency connection to the IF receiver itself (in the shack) can be made through normal cable with minimal signal loss . . Details Following are discussions on the various parts common to S-band and higher satellite receive systems. The basic requirements are 1) the antenna 2) an antennamounted low noise preamplifier 3) the converter. Antennas Link margins done by Frank Sperber and shown on the AMSAT-DL web site indicate anticipated antenna sizes. On 10450, a 60-cm (24" diameter) parabolic dish antenna should be adequate. While other types ofantennas, such as hom and lens may find some users, the dish is probably the most readily realizable. Yagis aren't practical on 10 GHz. Dish antennas can be homebrew or purchased; sources should be advertised as P3D becomes a reality. It is possible that the small offset-feed TV dishes may be adequate, but we really won't know until P3D is up there. Dish antenna basics A common misconception about parabolic dish antennas is that the dish has some parasitic relationship (like the undriven elements on a yagi antenna) to the operation of the antenna. Not true; all the dish itself is is a reflector that concentrates signals on a particular point called the feedpoint. We place a small antenna ofknown pattern characteristics (hopefully matched to the reflective characteristics ofthe dish) at that feedpoint and call it a dish feed. A dish feed is never characterized by "gain" but by illumination characteristics, usually an angle between either -3db or -1 Odb field strength points. Parabolic dishes themselves are characterized by their diameter and their fld (focal length divided by diameter) ratio. The feed used must have an "illumination pattern" that is matched to the fld ratio ofthe dish to properly utilize the area ofthe dish. Note that, when matching a feed to a dish, only the fld ratio is significant, not the actual diameter of the dish itself. To give a feel for the meaning of fld ratio, a "low" fld such as .3 means that the feed is mounted quite close to the dish. A feed for a .3 fld has to have a very broad beam to illuminate the dish that it is very close to. A "high" fld such as .7, requires a narrower beamwidth feed to illuminate the dish, since the feed is mounted some greater distance in front ofthe dish. What is better? The "deep" dish (small fld) tends to pick up less background noise (the feed is more shielded from the hot and noisy earth) and is mechanically easier to support, but it is more difficult to illuminate properly. "Shallow" (large f/d) arrangements tend to have larger feeds (more directional) and are physically more difficult to support and counterbalance but are generally less critical. Whatever you 40
Page 1 and 2: jL 7££ $15.00 A MSAT RADIO AMATEU
Page 3 and 4: Copyright © 2000 by The American R
Page 5 and 6: Table of Contents (continued) APRS
Page 7 and 8: Welcome It is with great pleasure
Page 9 and 10: had characteristic perigee values o
Page 11 and 12: the digital experimenters will want
Page 13 and 14: Fig.1, P3E Rendered overvieW
Page 15 and 16: 10 Fig.3, P3E Line Overview
Page 17 and 18: Amateur Radio On-board the Internat
Page 19 and 20: of "transportable stations" which c
Page 21 and 22: The packet bulletin board system on
Page 23 and 24: Side view of the EVA handrail ada
Page 25 and 26: wishing to review the status of the
Page 27 and 28: 2. CUBESAT DEVELOPMENT PROGRAM Aft
Page 29 and 30: The P-POD is constructed using 7075
Page 31 and 32: N 0"1 4 .3 2 NOTES: IN..ESS OTI£RW
Page 33 and 34: Payload services are designed to pr
Page 35 and 36: Assembly is simple. The RF circuit
Page 37 and 38: Level 2) To receive some beacons fr
Page 39 and 40: Amateur radio frequencies (and lice
Page 41 and 42: 2. These organizations could move t
Page 43: 5 "Space System Developments at Sta
Page 47 and 48: Converters A converter converts one
Page 49 and 50: 44 falls offby 3 dB from the highes
Page 51 and 52: And higher still: S and C Bands Her
Page 53 and 54: Summary The higher bands on P3D off
Page 55 and 56: Mountaintop, P A 18707 (570) 868-56
Page 57 and 58: product using another media. Those
Page 59 and 60: Ground Track The unit vector (V LCH
Page 61 and 62: sin((J) = The velocity vector is th
Page 63 and 64: FIGURE 2 DEFAULT SETTINGS FOR A TIM
Page 65 and 66: identified under the AMSAT Output F
Page 67 and 68: The command and control mode VN dat
Page 69 and 70: Most of the TNC-2 based TNCs have a
Page 71 and 72: Ahstract Distributed Processing Goe
Page 73 and 74: SETI@)home's power derives from cle
Page 75 and 76: ARGUS@home won't happen overnight.
Page 77 and 78: Figure 3: Graham Vincent, SEll Leag
Page 79 and 80: o lola••ec("dmg1en'lth ~ 339 31
Page 81 and 82: On AO-27 and UO-14 the downlink is
Page 83 and 84: little planning even urban settings
Page 85 and 86: A Spread Spectrum Wideband Transpon
Page 87 and 88: nadir-pointing attribute of the Pal
Page 89 and 90: signal, one to monitor the station'
Page 91 and 92: Instanffune for the FT-IOO Anthony
Page 93 and 94: The flIst problem is that you canno
Page 95 and 96:
Due to the way that the FT-IOO work
Page 97 and 98:
Auxiliary Receiver InstantTune lets
Page 99 and 100:
Similarly, the "itstart.bat" file i
Page 101 and 102:
Step 1 Quit from InstantTrack putti
Page 103 and 104:
Once you have turned on , control t
Page 105 and 106:
DOWN step DATA 1 3 Tuning Complete
Page 107 and 108:
EXAMPLES: 1. Change COM 3 to use IR
Page 109 and 110:
The name of the satellite must matc
Page 111 and 112:
eacon 29.4081 cw Auxiliary Fixed Tr
Page 113 and 114:
• Check to see that the COM port
Page 115 and 116:
Even with P3D in orbit and operatin
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'atelllte :je:?lmJC!gNumbeet::'~ Ep
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REFERENCES Specific technical infor
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The potential of two-way satellite
Page 123 and 124:
Igates with operators that have vol
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any time while also monitoring the
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universal frequency where ALL APRS
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DISTRIBUTING LIVE SAT TRACKING DATA
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The Houston AMSAT Net I earned myHa
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VNIW Real Audio Geostationary Comme
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finnware (verses EPROM) and the EEP
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Rotor Calibration First and foremos
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Deadband Commanded Value ,/ For exa
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of dissimilar radio models. For exa
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Calibration Limits Command Meaning
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and the T APR EasyTrakTM AzlEI Ro
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Software Design If the world was fl
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Rotor Control Window 1 (Normal Mode
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Automatic Weather Balloon Tracking
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148
Page 155 and 156:
Camera Tracking Recent events have
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BEARING is only accurate if you are
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Applications of PIC Microcontroller
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TNC must simultaneously be in commu
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This leads to the selection ofa mod
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Distributed system for LEO satellit
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a sender and a lot of receivers, po
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Figure 2. Processes in the main app
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The new G3RUH software modem for th
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Figure 3. Multirate processing Figu
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MODE-V/I EASY-SATS FOR EVERYONE Bo
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usable downlinks across a 30 Khz ba
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• First is the requirement for a
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Thayer School of Engineering at Dar
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mechanical support as well as the s
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In tandem with data acquisition and
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opportunities. Modularity by design
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AMSAT SYMPOSIUM PRESENTATION PHASE
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emember awaiting the sun to go down
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communications, this will open up a
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About the Author ... Dominick ''Dee
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October 27-29, 2000 - Klofas.com

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