I've been talking to a fellow over on the PDQ group that set up his unit on an upper stay using one insulator near the top and attaching the lead wire to a bolt on the chainplate. The resulting lead to the tuner is about 6' http://www.pdq36.blogspot.com . I get the part about RF burns but this seems like a neat install. The only question is if the vinyl shroud covers would have any effect on signal. Typically it is just my wife and I on the boat so I don't see personal saftey as a big issue as we are both reasonably concious people. We also tend to be minimalists so I also don't see us using the radio all that much - just another tool to use when needed. Bob PDQ 36 Peace
________________________________ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jim Richardson Sent: Monday, November 17, 2008 2:09 PM To: [email protected] Subject: Re: [Liveaboard] SSB antenna On Fri, Nov 14, 2008 at 8:35 PM, Norm of Bandersnatch <[EMAIL PROTECTED]> wrote: The length the antenna "should" be depends on the frequency, usually 1/4 of the wavelength. However, antenna tuners compensate for this so you can use just about any length antenna and the tuner adjusts the antenna system's reactance to make it resonate no matter the physical length (within limits). I suspect it is not a good idea to try to load up the entire rig. RF, and most HF SSB rigs put out about 100 Watts, will burn you ( I know this!). While the tuner will compensate for length, setting up a good impedance match. There is an efficiency cost. So your 100W won't go as "far" as it would with a well tuned antenna. But that's one of the trade offs. Frankly, You are generally better with a 1/4 wave Dipole, than a backstay antenna, but the backstay antennas work well enough if done correctly. The angle of the backstay does have an effect on the radiation pattern, but it's probably not too big a deal. If you are feeling adventurous, you can set up a pair of balanced dipoles, one half wave apart, and tune them to increase the F/B ratio to point fwd or aft, and pick up about 4-6 dB of gain. You also get two antennas in case of emergency. But you need to be able to put a pair of 23 ft whips 46ft apart to do so. You can use delay lines to reduce the spread needed. But honestly, it's a lot of work for a bit of gain, and unless you are careful, all you do is waste power. On the RF burn issue, these are *nasty* Since they often burn deep into the muscle, rather than just at the surface. In some cases. can leave the skin above pretty much unharmed. One thing you can do to avoid this is to set the backstay split far enough above your head that you aren't likely to grab the antenna portion. But the downside then is you have a length of line from the antenna tuner to the antenna that isn't included in the radiator element, but is included in the antenna tuning circuit. For best results, that length should be taken into consideration in the antenna tuner. But again, that's a bit tough to do if you don't know how. Another option is a simple dipole. But you are pretty much limited to the higher freq bands, about 12MHz for most boats w/40 ft masts. Remeber, with antennas, there's always a trade off. Gain<->Directionality. Efficiency<->Size (although at high enough frequency, size is less of an issue) and the higher up you get it, generaly, the better it will perform. Antennas are fun, but they can be a lot of work to figure out too. -- http://neon-buddha.net _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://www.liveaboardnow.org/mailman/listinfo/liveaboard To subscribe send an email to [EMAIL PROTECTED] To unsubscribe send an email to [EMAIL PROTECTED] The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
