"Richard" wrote in message ...
Hi. Is there a standard way to measure antenna bandwith? Is it within 3dB
down of maximum gain, or is it between SWR limits?

I'm looking at an FM receiving yagi that is advertised as covering the
frequency range 87.5 - 108 Mhz. And I'm wondering what this means. Is the
received signal going to be 3dB down at the band edges or what?

I notice that there are commecial yagis (that are probably suitable for
transmission) that have 150-174 Mhz in their description. Yet they are
stated as having a bandwidth of say 1.3 Mhz. What's the deal here?


What it means is that they have an antenna that will provide all the
signals
on a 1.3 Mhz frequency spread at the same time. It is incumbent on the
user to provide equipment that discriminates against unwanted signals
that the antenna supplies thru out the 1.3 Mhz frequency span even tho
it is resonant on only one frequency.
This makes it a very low 'Q' antenna where a very high 'Q' is desired
for a particular mode of communication is used such as audio.
Idealy one wants an antenna that is resonant on any frequency of
choice and where the band pass is tailored around audio carrier if
audio is the mode of communication. The latter is the antenna I use.



Cheers
Art