Sorry, there isn't one.

Roy Lewallen, W7EL

gregB wrote:
Anyone know the formula (if there is one)for
working out the spacing of the elements
on a UHF TV antenna?

Thanks, Greg

Roy, thanks for the reply.
So how do they do it?
Greg.


Roy Lewallen wrote:
Sorry, there isn't one.

Roy Lewallen, W7EL

gregB wrote:

Anyone know the formula (if there is one)for
working out the spacing of the elements
on a UHF TV antenna?

Thanks, Greg

So how do they do it?
Greg.

==============================

Easy!
They just copy somebody else's workmanship.
Very non-critical.
If it looks like an antenna it will work.

UmVnOg0KDQpUaGF0IGlzIGEgcHJldHR5IGNsb3NlIGFuc3dlci BhbHJpZ2h0LiAgUmV2ZXJzZSBl
bmdpbmVlcmluZyBpcyBhIHZlcnkgdmlhYmxlIG1ldGhvZCB0by Bwcm9kdWNlIGEgZ29vZCBmdW5j
dGlvbmFsIGFudGVubmEhDQoNCkkgaGF2ZSBzZWVuIGNoYXJ0cy BvbiBvcHRpbXVtIHNwYWNpbmcg
YmV0d2VlbiBlbGVtZW50cywgaW4gZnJhY3Rpb25zIG9mIGEgd2 F2ZWxlbmd0aCwgY2hhcnRzLS1w
bG90dGVkIGFnYWluc3QgbnVtYmVyIG9mIGVsZW1lbnRzLg0KDQ pOYXR1cmFsbHksIHNpbmNlIEkg
d2FudCBvbmUgbm93IHRvIHNob3ctLWNhbid0IGZpbmQgaXQsIG J1dCBJIHRoaW5rIGEgZGlsaWdl
bnQgc2VhcmNoIHdpbGwgcHJvZHVjZSBvbmUgb3IgbW9yZSBzdW NoIGNoYXJ0cyBvbi9mcm9tIHRo
ZSB3ZWIuDQoNCkpvaG4NCg0KIlJlZyBFZHdhcmRzIiA8ZzRmZ3 EucmVncEBaWlpidGludGVybmV0
LmNvbT4gd3JvdGUgaW4gbWVzc2FnZSBuZXdzOmRjMm5pcCQxZG ckMUBud3JkbXowMy5kbXoubmNz
LmVhLmlicy1pbmZyYS5idC5jb20uLi4NCj4gDQo+PiBTbyBob3 cgZG8gdGhleSBkbyBpdD8NCj4+
IEdyZWcuDQo+Pg0KPiA9PT09PT09PT09PT09PT09PT09PT09PT 09PT09PT0NCj4gDQo+IEVhc3kh
DQo+IFRoZXkganVzdCBjb3B5IHNvbWVib2R5IGVsc2UncyB3b3 JrbWFuc2hpcC4NCj4gVmVyeSBu
b24tY3JpdGljYWwuDQo+IElmIGl0IGxvb2tzIGxpa2UgYW4gYW 50ZW5uYSBpdCB3aWxsIHdvcmsu
DQo+IA0KPg==

gregB wrote:
Roy, thanks for the reply.
So how do they do it?
Greg.

Making a decent antenna that works over the very wide bandwidth of the
TV UHF band isn't at all trivial. And there's a great big handful of
tradeoffs -- gain, front/back ratio, impedance match, physical size,
number of elements, sidelobe levels, and bandwidth among them. The UHF
TV antennas I've seen are mostly a combination of log periodic, Yagi,
and corner reflector types -- something like a few log periodic elements
with some parasitic (Yagi) elements and a corner reflector. There *are*
some formulas which can be used for pure log periodics and corner
reflectors -- you should be able to find them on the web, and a
serviceable if not optimum antenna could be made with either or both
techniques. You'll have to decide how to best make the tradeoffs for
your application. The main difficulty with a corner reflector is making
a very broadband driven element.

I imagine that beyond designing a basic log periodic or corner reflector
structure, most manufacturers do a bunch of cut and try. These days, I'm
sure they use modeling programs for it. I'm also sure that after some
years of designing the things, the engineers get a feel for the general
effect of certain techniques -- say, how to improve the front/back ratio
with the minimal number of added elements. Some of the bigger companies
might have developed some optimization software. If they have, it's
probably kept as a trade secret.

Roy Lewallen, W7EL