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Discussion in 'CB Antennas' started by Number15, May 7, 2007.
Looking for pics for a direct feed antenna element. Thanks Guys . # 15.
Direct feed simply means connecting the feedline directly to the driven element without any matching system. This requires that the driven element be split in the middle and not grounded.Here is a sloppy example.
Find a typical picture of a 'Cushcraft' "A-3" beam's feed point, it's a direct feed (or was).
What's "direct feed"?
Like MC, the only one I'm aware of is a dipole.
Well, loops and such are too, but someone told me about a yagi using a "direct feed", no gamma.
I figured BS.
Nope, not 'B.S.', just not all that common anymore.
I should have thought of that. I have an A3.
Looky here at step #4 page #6.
I used to have an A4 (same as the A3 but with a separate reflector for 10). It was almost direct feed, but it incorporated a really crappy 1:1 voltage balun at the feedpoint. After a few months, the balun died. I removed it and went straight direct feed. It worked just fine, thankyouverymuch, and I worked several more years with it.
So the driven element is a dipole?
In a beam generally yes unless it is a quad and then the driven element is the loop. All direct feed means is that the coax is connected DIRECTLY to the radiating element,whatever it happens to be, without ANY form of matching system.
OK, it was BS as I thought.
I mentioned that I have a beam with the driven element being a dipole,could this be what he meant, I was told the coax was hooked to the yagi with a single driven element on a direct feed, gaining 5 db over a gamma. :frky
I figured why waste time telling him he couldn't gain 5db with anoter antenna just like it stacked.
This thread made me consider there was a method of feeding a yagi like he was trying to describe.
No 74in it is not BS. Mosely uses direct feed in some of their yagi antennas.
Check it out: Mosley Antennas!
74IN where is the BS? We have told you and provided links to antenna,yagis,beams, whatever you want to call them and they all have DIRECT FEED, NO GAMMAS or any other matching device. The only BS I see is a claim of 5dB over an identical antenna using a gamma feed.
The driven element of a yagi type beam is a dipole of some sort. It may be 'folded', or loaded (traps), but it's typically a 1/2 wave length, or dipole.
As other elements are added to the driven element, director(s), and reflector(s), the input impedance of the driven element is lowered. Depending on the number of 'other' elements, the input impedance can get down to something around 20-30 ohms. Depends on the number of elements, their spacing, (and at times the color of the sky I think). That's why a gamma (or beta, or delta) match is then used, they tend to raise the input impedance back to something around 50 ohms. Feeding a multi-element beam directly can still be done but usually a balun is needed to get that 50 ohms back (but then you may not consider it directly fed anymore).
There is no 5 dB difference between matching systems, that's about the only B.S. about the whole thing (unless it's MY antenna, and MY antennas are always 5 dB stronger than anybody elses! You believe that too, right?).
Ain't this electronic @#$% fun?
Marconi, I can't get the link to work.
The BS is, as I see it, is to simply eliminate a gamma and hook the coax to a one piece driven element.
Maybe I'm missing something.
For some reason adobe has gone to heck on this computer, so I couldn't see the pdf link above.