5 foot DBGH vs 7 foot DBGH design?

[Emerald_Boar]

Hi there.

Does the DBGH driven element need to be around 5 feet? I have a design that is 7 feet in length. 7"x12 bends. In fact why doesnt DBGH use like 7"x 20 bends? (or 7"x50).

Second quiestion, I need something to pick up ch 39 + 41 + 43 + 44+ 45. (Detroit digital channels.) How far should the reflector be from the driven element to pick up this channels?

TIA,
Al

[300ohm]

I have a design that is 7 feet in length. 7"x12 bends. In fact why doesnt DBGH use like 7"x 20 bends? (or 7"x50).

Have you computer modeled it ?

Jed has some designs that have more legs here : http://www.jedsoft.org/fun/antennas/dtv/xgh.html

[M.Satterfield]

142mm + 6*180mm + 142mm = 4.47 feet. I was cutting 5' sections of wire to work with as I made the bends on mine. There is a little left over (~6"), but it sure makes it a lot easer to work with a 5' section rather than a long run of wire!

Now two of these SGBHs placed closer together to form a DBGH will give improved gain on the upper channels of the UHF band while separating two two sections farther will improve gain on the lower end of the channels.

I have mine centered on channel 29 to improve the gain on channels 19 - 39 which will be the ones I need in N. Georgia.

See 300ohm's comments about all of that on my design here.

One other comment, a certain number of bends may maximize signal, while another number may actually cause a loss in gain. I say this based on the principle of superposition. You want the wavelengths to add together constructively to get gain increases, not destructively to cancel gain. This is all based on how many "wavelengths" can you get on that piece of wire. You want to always be able to get full standing waves on the elements and no partials (full standing waves are in phase)--partials (not in phase) reflect and result in destruction of the signal.

Note that in jed's versions one has 14 bent segments while the other has 6--> both are even numbers.

Of course, doing the computer modeling on it shows this kind of stuff, a heck of a lot faster than you do it the old fashioned way by hand!


HTH

Mike

[Emerald_Boar]

I do have computer modeling program. Now i need to figure how to use it.

hmmm
Been checking out the X-GH. Its exactly what i wanted to pick up Detroit stations with. <:

Read ya l8r,
Al