Casey and Bdale, thanks for the info! RE " ... when another newbie ham asked a similar question" :-) you!
Ok, I think I understand most everything. I did some more poking around (Casey's thread and a little Googling) Which got me to thinking about moving the altimeter from rocket to rocket. I found a web page which seemed to suggest I could strip off (in my case) ~ 7" of the outer casing and outer conduct of a coax cable to form the equivalent of a 7" wire antenna. Does that sound right? Give that it is true (works reasonably well) I was thinking I could buy a (say) 5ft sma male to <anyConnector> coax cable cut off the <anyConnector> end, drill a cable diameter hole in the "main" side of the altimeter bay thread the cable through leaving enough slack to easily connect the sma male connector to the TeleMetrum. I would then epoxy the cable as it passes from the inside to the outside of altimeter bay. Then I would cut the cable to (say) 8" long on the outside of the altimeter bay and strip 7" of the outer case and out conductor to form the wire antenna. *Seems* like it should work. Thoughts? This seems like it would be a good solution because I could install a cable/antenna in each rocket for the price of a sma male to xx cable (~$10) On Thu, May 30, 2013 at 9:30 PM, Bdale Garbee <[email protected]> wrote: > Peter Hackett <[email protected]> writes: > > > Can I just bend the whip antenna into a horse-shoe shape to get it to fit > > into the altimeter bay? (I guess the really question is "Will this > > significantly compromise the performance of the antenna?") And if it > > is "a bad idea" what should I do? > > It's a bad idea for two reasons. One is that it'll dramatically impact > the radiation pattern, as you surmise. The second is that doing that > will put strain on the SMA connector's attachment to the board, which > isn't a good idea. I've had to repair boards that had the SMA damaged > or sheared off because of loads put on the connector by such an antenna > setup... sadly, one was one of my own boards that I stuffed in a 54mm > airframe in a hurry at a launch a couple of years ago .. /o\ > > > My first thought was to find a short SMA male to SMA female cable so that > > the whip antenna can be straight. Is this "a good idea"? (necessary?, > > etc) > > That's a better plan. > > > Next: in poking around the Altus Metrum and gag.com web sites while > > researching about my altimeter question, I saw a link to a "SMA To BNC > > adapter" on the Teledongle page. > > > > I bought an Arrow II Hand Held Portable Antenna 440-3 and in looking more > > closely at the product description page, it looks like it has a BNC > > connector. > > > > So it looks like I'll need to get either the SMA to BNC adapter or get a > > coax cable with a male SMA connector on one end and a male BNC > > connector on the other. Have I got that right? > > Yes. > > > If so, any recommendations? > > Ok. The SMA-BNC adapter is the optimal way to attach a TeleDongle to an > Arrow antenna. It puts the receiver as close to the antenna feed point > as possible, which minimizes the loss between the antenna and the > receiver, giving you the best possible system noise temperature. > > On the rocket end, I really prefer the wire whip. The only reason to > use an SMA is if you're installing the board in something like an > aluminum or carbon fiber airframe section (both are more or less opaque > to RF signals) where you need to remote mount the antenna(s). > > Given that you have the SMA connector on the board, the two most > plausible choices are to use a short SMA male to female cable to remote > the whip, or to make up a simple wire whip with an SMA on it to use as > an antenna. > > > Peter "I just got my ham radio technical license, so *clearly* I'm an > > expert on all things RF" Hackett > > ;-) > > No worries, we all started somewhere! > > 73 - Bdale, KB0G >
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