May 2013 - AMSAT-BB - mailman.amsat.org

Helical Antenna on 70 cm
by Rolf Krogstad 14 May '13

14 May '13

I am new to satellites and new to the design requirements for UHF and am looking for advice. I am looking to build a Helical antenna for the 70cm Band. I am considering the plans for such an antenna from the 2010 edition of the ARRL Satellite Handbook. The plans call for a 235 cm (7' 8") long, 2.5 cm (1") diameter center support made of either a wooden dowel which has been treated or a fiberglass tube. It also requires multiple 7.6 cm (3") spacers for the helical element. My question is would fiberglass rods made of "Isophthlic Polyester Resin" be a good choice of material at UHF frequencies? I hesitate to use treated wood because I plan to mount this on the top of a 15 meter high tower and it isn't very accessible. Thanks Rolf NR0T [EN34]

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Re: ISS HamTV Frequencies
by Matty Cunningham 14 May '13

14 May '13

This looks very interesting, wondering if it would be possible to tweak the tuners in DVB-S reveivers so no conversion would be needed? >From http://amsat-uk.org/ :- It is planned to transmit DVB-S signals on 2.4GHz at either 1.3Msps or 2.3Msps with 10 watts of RF from the ISS Columbus module. The IARU Amateur Satellite Frequency Coordination Panel have announced frequencies of 2422.0 MHz and 2437.0 MHz. Most of these receivers use 'L-Band' and can do 950Mhz to around 2Ghz - would be great if we could tweak this, or perhaps inject the 2.4ghz signal after the internal tuning stage, with a bit of buffering /amplification ?? :) Looking at this:- http://www.tbsdtv.com/products/tbs8920-dvb-s2-tv-tuner-pci-card.html or this:- http://www.proftuners.com/review_prof_7301.html - Just as a quick search - it looks like we could use these type of devices for 'decoding' the DVB stream, rather than going for the physical 'lump' and extra expense of a set-top box. Matty MD0MAN Date: Mon, 13 May 2013 21:33:13 +0100 (BST) From: M5AKA <m5aka(a)yahoo.co.uk> To: Daniel Schultz <n8fgv(a)usa.net>, amsat-bb(a)amsat.org, Greg Dolkas <ko6th.greg(a)gmail.com> Subject: [amsat-bb] Re: ISS HamTV Frequencies Message-ID: <1368477193.60216.YahooMailClassic(a)web172303.mail.ir2.yahoo.com> Content-Type: text/plain; charset=iso-8859-1 --- On Mon, 13/5/13, Greg Dolkas <ko6th.greg(a)gmail.com> wrote: > Is there something about the DVB-S modulation that makes it > astoundingly better for this application?? For > something that is intended to be widely received, they sure > are making it difficult... DVB-S receivers are in use in hundreds of millions of homes around the world. Apart from DVB-S2, which is not yet so widespread, I'm not aware of any other standard that would deliver better performance in a 2 MHz bandwidth. 73 Trevor M5AKA

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Up-tilted beams (15 degree optimum)
by Robert Bruninga 14 May '13

14 May '13

Did you look at the antenna plot on that web page?: http://aprs.org/rotator1.html At the proper 15 degree tilt of a fixed beam, the gain is down only 1 dB at the horizon. At your proposed 35 degree tilt, the gain is down 4 dB on the horizon where you need it most (70% of all pass times are below 22 degrees). To me, it makes no sense to sacrifice 4 dB in the area where the satellites spend most of their time. The only benefit to the high tilt angle is improved performance during the 3% of the time the satellite is above 60 degrees. And is that worth giving up gain for the 70% of all other pass times? Further, when the satellite is that high the signal is already 6 to 10 dB stronger than it was on the horizon anyway. How much better does one need to hear an already excellent signal? (so as to sacrifice the other 70%)? But again, if the antenna is in a hole and cannot see anywhere close to the horizon anyway, then of course, tilt the main beam up to point right at the lowest available horizon where the gain is needed most. Bob, WB4aPR > Bob, depending on the antenna pattern and the ground, as you say, > 15 degrees might be too low for any additional help toward the horizon. > 30 to 35 degrees will give you a little better results for stuff that isn't just > right at the horizon, I feel. As with all things in this hobby, experimentation > with your equipment will allow you to find the best combination. Also why sacrifice 3 dB for all terrestrial operations too which are also on the horizon? On 5/13/2013 11:29 AM, Robert Bruninga wrote: >> As has been said many times, most satellite passes are never >> "directly overhead", but rather on some inclination across the sky. >> A 5 element yagi antenna, at a 35 degree angle from the horizon, >> with only an asmuth rotator, will let you work far more satellites >> for > the money spent. > > Except that the correct angle is 15 degrees not 30 or 35. At 15 > degrees, the main gain lobe of the antenna still has excellent gain on > the horizon where you need it most and an equal gain all the way up to 30 > degrees or so. Below 30 degrees is where satellites spend 80+% of their > in-view times. This is where you need the gain most. But when the > satellite is above 30 degrees, the satellite is at least 6 to 10 dB > closer and so it makes no sense to sacrifice gain on the horizon > (where you need it most) by placing it at 30 degrees where you need it least. > > See http://aprs.org/rotator1.html > > Ignore the topic of the page but look very carefullyl at the SCALE > drawing (Yes, that is drawn to scale) of a LEO satellite pass Notice > how 95% of all satellite access times are below 50 degrees and 70% of > the time they are below 22 degrees. That is where you need the gain. > Do not waste it by tilting the antenna up more than 15 degrees. > > The only exception is that if your beam antenna cannot see the horizon > anyway, then, yes, tilt it up a little more since you wont hear the > low stuff anyway... > > Bob, WB4aPR > > > > Gregg Wonderly > > On 5/12/2013 12:48 PM, Jeff Moore wrote: >> I wouldn't recommend a J-pole for satellite work unless you expect to >> only work sats on the horizon. The J-Pole antenna has a low take-off >> angle and almost NO radiation overhead, an plain 1/4 wave ground >> plane antenna would work better for the sats. >> >> >> >> J-poles are great terrestrial communications antennas, not so much >> for working overhead satellite passes. An Eggbeater or quadrifiliar >> antenna would be a better choice. >> >> 7 3 >> >> Jeff Moore -- KE7ACY >> >> On 5/12/2013 8:00 AM, Werner, HB9BNK wrote >>> Thank you all for your valuable hints and advices ! >>> >>> I will now build such an antenna and then supply here the results. >>> >>> 73 Werner, HB9BNK >> >> _______________________________________________ >> Sent via AMSAT-BB(a)amsat.org. 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(a)amsat.org. 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(a)amsat.org. 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 >

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Re: ISS HamTV Frequencies
by Daniel Schultz 14 May '13

14 May '13

I would research the matter carefully before buying any equipment, does anyone in the ISS HamTV group have any data on which DVB-S receivers will work? This is pretty much beyond what the gear was designed for! Dan Schultz N8FGV ------ Original Message ------ Received: Mon, 13 May 2013 10:52:22 PM EDT From: Greg D <ko6th.greg(a)gmail.com> To: M5AKA <m5aka(a)yahoo.co.uk>Cc: Daniel Schultz <n8fgv(a)usa.net>, amsat-bb(a)amsat.org Subject: Re: [amsat-bb] Re: ISS HamTV Frequencies > 2 mhz? Yeah, that would be tough... Ok, DVB-S it is. > > Thanks all for the education. There's a swap meet coming up in a couple > of weeks... Sounds like I have a now have a mission. :-) > > Greg KO6TH

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ISS - HAMTV - Tutionne Software for DATV
by I0ELE 14 May '13

14 May '13

Daniel the software I mentioned can be downloaded here: http://www.vivadatv.org/viewtopic.php?f=60&t=63 Emanuele I0ELE

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Re: Satellite Demonstration Passes for Dayton 2013
by Rolf Krogstad 14 May '13

14 May '13

What callsign will be used - W5IU? de Rolf NR0T >>> ---------- Forwarded message ---------- >>> From: "Keith Pugh" <w5iu(a)swbell.net> >>> To: <amsat-bb(a)amsat.org> >>> Cc: >>> Date: Mon, 13 May 2013 00:03:08 -0500 >>> Subject: [amsat-bb] Satellite Demonstration Passes for Dayton 2013 >>> Here are the Satellite Demonstration Passes for Dayton 2013, 17-19 May. >>> Times are in UTC. We will work as many of these passes as possible - >>> weather and equipment permitting. The days are Friday, 17 May, through >>> Sunday, 19 May. The original plain text file is attached with the original >>> formatting. See you on the "Birds" at Dayton 2013 this weekend. >>> >>> 73 - Keith, W5IU

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Re: ISS HamTV Frequencies
by Daniel Schultz 14 May '13

14 May '13

------------- Original Message ------------- >> Right. But what is that in terms of what normally gets described? >> For example, I have a Digital TV card for my computer (Pinnacle PCTV >> HD). It says it does "ATSC digital TV (HDTV up to 1080i, and SDTV)" >> and "Clear QAM (unencrypted digital cable)". >> >> Am I even close? >> >> Greg KO6TH No, you are not even close. ATSC (Advanced Television Systems Committee) is the proprietary over-the-air television broadcast standard used in North America. It is fundamentally incompatible with the open source "DVB-T" broadcast standard that the rest of the world uses for domestic TV. (The fact that it was designed by a committee should tell you all that you need to know about that particular political sausage.) The "Cheap and Easy SDR" article in January QST requires using a DVB-T USB dongle which you need to purchase from a supplier that knows that you want to use it for SDR. The ATSC USB devices sold at Best Buy or other retail stores in the USA cannot be used for this purpose. QAM is used only by cable TV and is never broadcast over the air. (Most cable systems use encrypted QAM so you will still need to rent the decoder box from the cable company). DVB-S is the digital satellite TV standard that the "free to air" (FTA) satellite receivers use. We are not talking about Direct TV or Dish TV, but the C band services. If you watch NASA TV or the foreign language TV broadcasts directly from your C band dish, you are using DVB-S. This standard has been used for terrestrial ham ATV in some US cities. It would be best to contact the ATV experts directly to see what receivers they are using. I don't know which FTA receivers will work with the ISS ham TV. Bottom line is: ATSC and QAM decoders are not useful for receiving the ISS ham TV signals, and DVB-S is not widely used in the USA except by dedicated "free to air" hobbyists. If you bought your receiver card or dongle from any US consumer retail store, it almost certainly is not what you need for ISS ham TV. Dan Schultz N8FGV

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J-Pole Antenna
by Werner, HB9BNK 13 May '13

13 May '13

Thank you all for your valuable hints and advices ! I will now build such an antenna and then supply here the results. 73 Werner, HB9BNK -- Werner, HB9BNK http://www.hb9bnk.ch http://www.hb9bs.ch

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Isle of Mull Grid IO76 on Satellites
by M5AKA 13 May '13

13 May '13

The Camb-Hams group GS3PYE/P are active until May 16 from the Isle of Mull, Grid IO76, in Scotland. Listen out for them on VO-52 and FO-29. GS3PYE/P http://www.southgatearc.org/news/may2013/gs3pye.htm 73 Trevor M5AKA

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Elk antenna review in QST
by Alan 13 May '13

13 May '13

Hi, There is an interesting, positive short review of the Elk 2M/440L5 in the June issue of QST, page 56. He covers both satellite and terrestrial VHF contest use. If you are a League member and don't have the paper issue, the article by Steve Ford, WB8IMY is available for download or on line reading at www.arrl.org/qst. These antennas, as well as a case, will be available at the AMSAT booth at Dayton, and are easily transported home when disassembled. 73s, Alan WA4SCA

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