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1-10 of 35 messages
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Parachute mobile HF QRP, need ideas
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by SWL377 on October 10, 2008
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I and some friends are hams and also skydivers. We have been kicking around the idea of deploying our canopy high (14,000 ft) and operating QRP HF during the descent under canopy. Many ham jumpers have carried HTs on jumps and communicated on VHF/UHF while descending, but I have not seen anything about HF ops. Rig currently available is an ICOM 703 with a built in AT. We have some prelim designs for a chest mounted pack for the rig and battery that will not interfere with the parachute gear. We need antenna ideas and general ideas and feedback from QRP experts. Trailing long wire? Wire dipole in sort of a V shape, one leg with a weight and the other with a very small drogue chute to get it roughly horizontal? What are the capabilities of the tuner in the Icom 703? Need to be able to jettison antenna at about 2000 ft to eliminate chances of snagging power lines on landing approach. Would like to use VERY small wire, perhaps enameled coil wire, needs to be strong enough not to break when we deploy it and trail it, but not big enough to carry significant current if it lands across power lines. We intend to do it on a no wind day and operate over a rural area with no power lines nearby, but you need to think about all possibilities. We also might go for an antenna that can be wound back up on a reel, rather than jettisoned. Will be using a helmet mounted headset and need a good noise cancelling mic as canopy forward speed is about 20 mph. Are throat mics practical? I hear that they are great and reducing wind noise, but have mushy audio. All ideas welcomed. No need to re-invent the wheel. If this has already been done let's hear about the details. Those who have operated motorcycle mobile will probably have addressed similar issues.
Why would anyone jump from a perfectly good airplane?
No jumpship is a perfectly good airplane. Besides, the door was open...
73,
AF6IM
af6im@arrl.net
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RE: Parachute mobile HF QRP, need ideas
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by W5FYI on October 10, 2008
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An interesting way to avoid a pile-up....
On jettisoning a wire antenna at 2,000 ft AGL, you still have to be careful that it doesn't fall across hot wires. I would worry, too, about it somehow getting caught in the rigging, and doesn't the nylon build up a static charge when the chute opens? Might it be enough to damage your radio?
I've never jumped from from an airplane like you, but I've always heard that parachutists are good to the very last drop. But, as a pilot, I know I don't want to be worrying about antennas and radios and other things when I need to be concentrating on having a safe landing.
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RE: Parachute mobile HF QRP, need ideas
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by KQ6Q on October 10, 2008
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Unless you have a sked with someone who will be listening while you drop, is even watching you, a contact during the couple of minutes you're in the air is unlikely. And if it's a sked like that, what's the point? It would have to be HF/SSB - you could just use a CB HT, rework it to 10 meters. Wire antennas - you'll cause hazards with power lines, electric fences, or get hurt yourself.
If you need a new challenge, how about using one of the visual communicator options with an VHF or UHF HT, and transmitting real time video while you're coming down. You'd have some folks really interested in watching what you see as you're coming down, while they can see YOU in the chute!
Fred Wagner, KQ6Q
(did 5 static line jumps at Ft Benning in summer of 63, all my takeoffs and landings have been equal since)
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RE: Parachute mobile HF QRP, need ideas
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by WB6BYU on October 15, 2008
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Check out the frequencies for the HF PACK group - that
might be a good place to make some contacts.
www.hfpack.com
While a trailing wire sounds like a good idea, you'll
want to make sure it doesn't tangle in your shrouds, of
course. A weight on the end might help. I suspect that,
due to the forward velocity, you won't be able to maintain
sufficient separation between two wires to make an effective
dipole, so some sort of end-fed antenna probably will be
your best bet.
I've seen the same reels used in the "Yo-Yo" antenna sold
at Wal-Mart as camping clotheslines. If you use stranded,
insulated hookup wire for the antenna you can wind up
the wire before landing. Or, to automate the process,
try a fly fishing reel with a spring-wound wind-up (so
you just squeeze the lever and the wire rewinds itself.)
If you keep the antenna length reasonable (under 40 feet
perhaps) it makes more sense to rewind it than to
jettison it. In fact, with those lengths you could
rewind it around your hand pretty quickly to secure it.
An end-fed J-pole for 20 or 17m might be a good choice,
or an end-fed half wave wire with a fixed-tuned
matching network. You don't have much ground available,
so you may have to use your body for that.
Given the circumstances, you probably want a setup that
requires minimum attention to operate. I'd suggest having
the radio preset to a given frequency, the antenna
pre-tuned, etc., so all you have to is deploy the antenna,
talk, then roll up the antenna again.
And if you are thinking of doing it more often, you might
look into one of the old Mizuho HF HTs that would be
smaller and lighter than the 703.
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RE: Parachute mobile HF QRP, need ideas
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by SWL377 on October 15, 2008
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Thanks for the comments and tips, please keep em coming. We will have roughly 17 minutes of operating time if we open at 14,000 ft, more if I use a larger canopy. I have jumped from 24,000 ft, (freefalling to 3000 ft) but it's too cold (for my California bones) to open at 24K and you'd need O2 which complicates mic setups. I was thinking of using onboard APRS so that people could watch the ascent on an APRS website and know that soon we'd be on the air during descent. Another ham skydiver will be jumping with me so we will at least be able to talk to each other if we cannot raise anyone else. The new skydiving gear has both canopies on your back so there is lots of room in front for a radio pack. Weight isnt a big deal with QRP gear.
73,
Mark
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RE: Parachute mobile HF QRP, need ideas
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by K9PU on October 29, 2008
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Use the chute, inbed some wire, or use the lines to the shute. Possibly sew wires into your jump suit. Don't radio during freefall, no time, wait for shute to open.
Test all this on the ground with some sort of fan to fill the shute. Remember, no ground plane in the air so look for an antenna designs without ground planes. Limit power, don't start your shute on fire. Carry a back-up shute. Safety first.
GL.
Scott
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RE: Parachute mobile HF QRP, need ideas
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by SWL377 on November 3, 2008
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Good point about fire safety.
http://www.youtube.com/watch?v=mDBhT1eaCjk
The video is real, chute deliberately ignited for a commercial. No RF involved, but plenty of testosterone!
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RE: Parachute mobile HF QRP, need ideas
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by K9TY on November 3, 2008
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I would say PAR Electronics end-fed 1/2-wave wires would be a simple and effective antenna. Just pick your band and freq ahead of time (hopefully jumping when the band has a good chance to be open). You might even find yourself in a quick pileup! :-D Might be worth adding some sort of digital voice recorder to capture the whole session for logging purposes after the jump. Would be a hoot to work you -- try 20m or 17m and let us know when you go!
Dave-K9TY
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RE: Parachute mobile HF QRP, need ideas
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by SWL377 on November 6, 2008
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Good antenna suggestion Dave. We will take digital audio recorders. The chances of synching good propagation and a good time for a HAHO jump aren't great, but we might get lucky. I am determined to make an HF QRP parachute mobile QSO, even if it means just talking with a friend operating from his car parked below.
73,
Mark
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RE: Parachute mobile HF QRP, need ideas
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by N8BOA on January 27, 2009
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Build a J-Pole from twin lead.....one wire...no ground...just let it deploy uner you
N8BOA
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