[Elecraft] Insulated Backstay

[brianb]

Mike,

As past comm officer and board member of the Pacific Cup Y.C. I have had 
occasion to rig  about 10 offshore race boats for SSB ops (follow the 
action in this years race at SF_to_Hawii_race_underway 
<http://www.pacificcup.org/> ) . They have ranged in size from 24 ft to 
50 ft. The typical number you see for a backstay or other vertical on a 
small vessel is 21' to 23'. This is chosen to avoid 1/2 wave resonance 
on marine ssb frequencies (located typically just above and below the 
ham bands). This number is recommended by many auto tuners so that the 
feed point impedance doesn't approach several thousand ohms (a 1/2 wave 
at resonance) leading to several hundreds of volts at the feed point 
(assuming a 100+ watt rig) and possible breakdown within the tuner. 
Refer to the SGC 230 manual and I believe the ICOM manuals as well. 

Having used the above dimensions on many occasions my experience has 
been that they work well on the marine frequencies as well as amatuer 
frequencies  from 80 MHz (4Mhz SSB) up to 28 MHz. Of course that 
wonderful ground plane is a huge help in making contacts from the deck 
of  a little boat all over the planet. The other side of the equation is 
getting a real good ground connection. There is literature as well about 
technques that can be used that don't involve drilling through and 
adding extra weight or drag  to the hull via an extenal bronze plate.

If you have any other questions feel free to ask.

brian n6iz

>-----Original Message-----
>I'm this >||< close to buying a cruising sailboat (a Westsail 32) and can't
>seem to find any info/detail on the recommended length for an HF (insulated)
>backstay antenna.
>
>I thought I'd rememberd this topic being discussed in the maillist before
>but I've searched the archives and nothing pops up.
>
>Since I know nothing about them I thought I'd ask if anyone has any
>experience/advice/tips/suggestions/pointers/websites concerning insulated
>backstay antennas?
>
>Thanks,
>Mike K5PU
>
>
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