Topband: 160m Mobile whips as a dipole, or a beam ?

[Tom Rauch]

>         Tim, since these are for RX only, you might
> consider a 75:50 ohm transformer based on the Mix 73
> binocular cores.

I would not use a small resonant whip. The reason being 
reactance changes far too fast with frequency. This means 
each antenna contributes a different phase shift to the 
system if not perfectly resonant. Bandwidth of the antenna 
is far too narrow.

The sharp tuning may be helpful in a multi-multi where the 
antenna is close to transmitting antennas if tuning never 
changes or if the operating frequency range is very small, 
but as a general rule I'd avoid it.

I'd also never use a transformer to change impedance. If the 
base impedance is too high, I'd use a shunt resistor. If the 
base impedance is too low, I'd use a series resistor for 
matching.

The concept behind each element is to have the widest 
possible SWR bandwidth. This means a feedpoint located 
loading coil is strongly advised rather than placing the 
loading coil up high in the element, and the element should 
have as much capacitance as possible up as high as possible. 
This is a very important guideline.

Again the concept is to use a broadly tuned antenna, not a 
narrow one. Think base loading coil, a reasonably tall 
antenna, capacitance hat at the top, and resistors for 
impedance matching. The goal for best performance is 75 ohms 
over the widest possible frequency range.

73 Tom