I don't disagree with this. I was trying to explain intuitively why a directive antenna has a better s/n ratio than a non-directive one. I was assuming that the noise was evenly distributed. Then I r
The only thing to remember is that you can not have gain in an antenna unless you have directivity. Gain in a particular direction comes from reducing it in other directions. 73 Gary K4FMX
It depends on what the reference antenna is. An isotropic radiator has several dB gain over a GAP vertical on 80 meters, even though it is less directional. Gain is a function of efficiency and dire
Good points Tom. I was thinking more of the difference between 2 antennas of similar efficiencies. Dipole verses a multi element beam for instance. 73 Gary K4FMX
One point about receive antenna directivity is the Murphy factor - the peak noise source is always in the same direction and polarisation as the wanted signal. 73 Peter G3RZP
This implies that what Tom called the average gain of the antenna is not great enough to override the rx generated noise. A low-noise preamp would boost both signal and noise from the antenna and sol
yagi great both Rx noise figure measured 1.5-1.8dB. you I wouldn't expect the average gain, integrated over a sphere to be higher than the 2x9. If anything, there's more potential sources of loss. ou
Steve, Virtually every object emits background RF radiation that can be heard with a good antenna, although I'd be a bit puzzled that you could hear it on a freq as low as 144 mhz with a single yagi.
a good antenna, 144 mhz with a single antenna system. Point you hear sun noise. explanation that fits antenna will certainly on all azimuth objects - will prove or This was my original thinking, it w
Please don't attribute any statement noise should be the same regardless of directive pattern to me! That doesn't mean anything definitive. It might be sufficient, it might not be. When one receiver
I'm very sorry if I've misunderstood and/or misrepresented you. As a final clarification (and I'll shut up on the subject after this) - if I have two antennas with different directional characteristi
To: <amps@contesting.com> Steve, If both antennas have the same gain they will have the same directional properties. One could have a sharper vertical pattern and the other a sharper horizontal patte
No, that is not true. The antennas can and often do have vastly different directional properties even with the same gain. 73, Tom W8JI W8JI@contesting.com
I guess I should have qualified that a little better. I did say that one may have a sharper vertical pattern and the other a sharper horizontal pattern. What I meant by that over simplification was t
True, but the converse is not true, You can have directivity independent of gain as witness loop and other directional receiving antennas. Or yagis with lossy elements... 73 end Barry Kirkwood PhD ZL
I think it really boils down to 'what is the definition of directivity'? Witness Vertical antennsa used in the commerical world...they may have 10-15db of gain...as a so called OMNI directional anten
My point exactly. In this antenna the radiation is suppressed in the vertical plane to be put into the horizontal. This antenna is very directional in the vertical plane though it is omni in the hori
I know what you are trying to say, but that still is not true. Efficiency can be different and/or considerable power can go into spurious lobes on one and not the other. For example, Rhombics have v