"Richard Clark" wrote in message
...
On Fri, 18 Feb 2005 16:12:19 -0000, "Richard"
wrote:

Futher: Some time ago I did download 4nec2, and obtained some yagi
models. I
would have thought that all I have to do is scale one of these models and
then make corrections for the physical construction.

Hi Richard,

If you do this literally so (even to element thickness). Some slop is
tolerable in going from one VHF frequency to another, but from HF to
VHF you need to scale closely.

One of these designs got to be wideband and maximised for gain I suppose.

4nec2 should resolve this - it is its purpose after all.

All the models I have are VHF ones.

Actually the bandwidth of the marine band, in terms of percentage is
6/159.025 = 3.78%. So, any beam ought to have a useble range of 3.78% at the
operating frequency. (I guess though that for any particular design it's
bandwith could be a producy of your personal SWR tolerance). I'm not even
sure if a yagi I need is just a regular one or a wideband type.

Anyway, I guess in truth, of those designs I mentioned, quite a few would be
satifactory. ie:

DJ6BV
OWA
SM5BSZ
VK3AAU
W6SA
Wideband Yagi (eg such 220-4eleYagi.nec) Not sue what this design is.
Wideband yagi W4NRL
Yagi (eg 220-3eleYagi.nec) Not sure what this design is.


I think perhaps I could probably go for any, (not sure about that) but folks
seem to rave about DL6BV designs and I think they may have a the requied
bandwith, but I'm guessing here, not being much of an antenna buff.