On Mon, 2007-08-06 at 16:16 -0500, Stuart Rohre wrote:
> Alan, absolutely a great post, and well said. You are right on the money!
> Effective power is the key. An improved or efficient antenna is the lowest
> cost route to effective radiated power.
And it also improves receive.
> A point was made in the QRP forum at the local ham convention Sat. Even if
> you are using one of the shortened antennas, you still have to keep the high
> voltage ends well away from conductors and screening foliage, or other
> detriments to the high near field levels.
> And the high current magnetic field concentration near the feed point should
> also be protected from coupling to conductors.
> A dipole can be shortened to 60 per cent of full length and maintain
> efficiency in the greater than 90 per cent
> value. You just have to have it in the clear of detractors from its field.
> Low profile antennas like the Moxon rectangles can provide beam performance
> in less than traditional Yagi dimensions. Use of low loss insulators,
> conductors, and fasteners is key to small antenna use.
Its false economy to use tiny conductors in a QRP antenna just because a
tiny wire will safely handle the current. A good QRP antenna needs as
large a conductor and insulator as a KW antenna, then it won't waste
power in resistive losses.
> An easily elevated small beam may be the answer for aging hams. The masts
> from Force 12 that were marketed for portable use come to mind. Motorizing
> such an elevating cable for that mast might be fairly simple.
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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