[TenTec] Amplifiers or system efficiency.

[Dr. Gerald N. Johnson]

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.
> 
> -Stuart
> K5KVH 
> 

-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer