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KB2VXA > TECH 16.03.05 07:52l 51 Lines 2215 Bytes #999 (0) @ WW
BID : 35264_NJ2AR
Read: GUEST
Subj: Re: VE1EX > marine antenna
Path: DB0FHN<DB0MRW<DB0WUE<DK0WUE<7M3TJZ<UA6ADV<HB9AK<K1UOL<K1UOL<WB2QJA<
KC2COJ<NJ2AR
Sent: 050315/2236Z @:NJ2AR.#CNJ.NJ.USA.NOAM #:35264 [Lakehurst] $:35264_NJ2AR
From: KB2VXA@NJ2AR.#CNJ.NJ.USA.NOAM
To : TECH@WW
Hi Andrew and all,
Being marine antennas are tuned for marine frequencies of course you need
a tuner to fool the rig into thinking the antenna is resonant. At
resonance depending on design an antenna feedpoint impedance may be
usually 50, 70 or 300 ohms, some unusual ones may be 400 to 600 ohms so
the tuner simply matches impedance.
Now what you have is a non resonant antenna and is therefore inefficient
even if the aparant impedance is matched. Using a marine antenna on ham
bands really doesn't make sense considering a proper antenna may be
bought or built. I'm sure you changed it's resonance and unless you have
aken proper measurements without the tuner of course you have what
amounts to a random wire. If you're serious about this antenna make sure
it works properly, you just may have a dummy load.
Marine HF antennas of this type are mounted high on the superstructure
without radials, the steel provides the counterpoise. Take a trip to any
harbor where there is a fishing fleet and you'll see plenty of them, the
superstructures look like antenna farms. The steel is of course connected
to a metal plate under the keel on wooden hulls for grounding so to
duplicate conditions only a grounding (counterpoise) wire is needed. The
angle (droop) of radials determines feedpoint impedance too, 90 degrees
equals 50 ohms and 45 degrees equals 70 ohms. Most hams never notice the
difference, a 50 ohm transmitter feeding a 70 ohm antenna only sees a
1.5:1 SWR at resonance.
I hope you now have enough info to work out that antenna, don't be afraid
to ask more questions.
BTW, I live within walking distance of the docks and can tell you the
whole place, boats and buildings are growing antennas at an alarming
rate. It won't be long before the trucks hauling fish will be hauling
antennas to market as well. (;->)
73 de Warren, KB2VXA@NJ2AR.#CNJ.NJ.USA.NOAM
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Message timed by NIST: 22:51 on 2005-Mar-15 GMT
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