Topband: Re: [CQ-Contest] Re: Topband: TOP BAND RECEIVING ANTENNAS

i4jmy@iol.it i4jmy@iol.it
Tue, 8 Jan 2002 17:31:42 +0100


> >but efficiency too low compared with low signals.
> 
> Low band receiving antenna efficiency is limited by outside noise 
> which should be received some 10 dB stronger then own RX noise.
> 
> This is very easy to achieve with any of the present solid state RX 
> but some hams prefer additional preamps...
> 
> 73 de Mario, S56A, N1YU

I'm not convinced that any low band antenna has enough efficiency for 
all receivers, all cases, and expecially if the receiver BW is not for 
a narrow CW.
This is also a great opportunity to explain the difference between 
antenna efficiency and system efficiency.
The antenna pattern is a 3D solid and not a 2D plot.
Overall antenna efficiency might lead to acceptable absolute numbers in 
term of efficiency but because collecting some energy from unwanted 
directions. (i.e straight upward)
Like this the final efficiency, let's better say negative gain at 
desired heading and wave angle, might be already too low to produce a 
favourable S/N in spite the RX gets well alive when connected to the 
antenna.
Playing with N stacked beverages (1 to 2 WL beeing probably best choice)
insures a good pattern control and offers an output level that surely 
meets or exceed PY5EG system needs.
I agree that antenna preamplifiers should be avoided when it is 
possible.

73,
Mauri I4JMY