inverted V folded dipole

R

rob.bob.dave

Member
Has anyone had any experience or knowledge about the characteristics of combining an inverted V and folded dipole for an antenna? I have limited space (the roof of a mobile home, 40' x 10') and have enough knowledge of antennas to make a wonderful mess of things. The antenna would be used for receive only.
 
Hiya!

Will the dipoles be sharing the same feeder, or will you use a separate feed to each one?

Is this a VHF/UHF system, or an HF one, or both?

If they are on separate feeders then there should be little problem, just fan out the dipoles, or if possible arrange them in a cross-like manner.

If they are fanned out and you use them on harmonically related bands to each other then you might get some unwanted coupling between the two, leading to matching problems. Worst case scenario on a receive only system is that you will loose a little of the received signal.

If you have both the standard dipole and the folded dipole on the same feeder things get a little more complex since you will need a suitable balun to match the 300 Ohms impedance of the folded dipole to the 50-75 Ohms of the coaxial feeder (assuming you are using coax of course!). Again, you need to watch out for coupling between the antennas on bands that are directly harmonically related.

Also, if the two antennas are sharing the same feeder, either coax or open wire feeder, you might find that the folded dipole will act as a short circuit (or at least modify the impedance of the system by acting as a stub). As before, on a receive only system you might at worst loose some (or all) of you received signals at and around odd spot frequencies, determined by the characteristics of the folded dipole upon the overall antenna system.

You say that you "have enough knowledge of antennas to make a wonderful mess of things". I guess that's why they call us amateurs! :cool:

Best 73, Mark.
 
Your reply indicates I did not clearly explain exactly what i am asking so i am going to attempt to clarify.

What I meant to ask was; If you construct an inverted V antenna and make it a folded dipole would it work?

That is to say, build an inverted V antenna then extend the conductors folding them back on themselves to meet back near the antenna feed point, or take a huge folded dipole and bend it down into an inverted V.

I understand the inverted V is good for broadband shortwave, I am just trying to lengthen it in a confined space. What I am not sure of is the characteristics of a folded dipole. Is it a narrow band antenna? If so, I would imagine I would defeat the broadband qualities of the inverted V by making it a folded dipole.

I realize my error in the wording of my original query. Thanks for the reply, interesting answer.

See, I told you I could make a mess of it. :cool:
 
Dude!

Ah, it all makes sense now. I did think from your original post that you were attempting to combine a folded dipole with a standard dipole antenna.

Yes, you can quite happily fold the ends of the dipole back on itself to create linear loading, but beware of allowing the sections to be too closely spaced. You need about a foot or so of separation between the conductors, in a similar manner to a T2FD antenna. The T2FD antenna has a resistor placed across the ends to give a wideband response, but you need not worry about that.

I have added a picture below of a T2FD antenna arranged as a straight dipole, and the dotted image is a T2FD antenna arranged as a folded dipole. The second dotted image is what you might want to aim for in your dipole antenna construction.

You don't need to fold the antenna back on itself though, you could create a large open triangular antenna, with the feed-point at either the top of the 'point' of the triangle, or at the centre of the flat base, either will work fine.

Also you could 'loose' the extra wire length in your dipole antenna by zig-zagging the wire down opposite ends of the attic space, thus avoiding any return wires, and allowing you to add a lot more wire to the ends than would be possible if you adopted a simple folded approach.

Hope the above helps. Any further questions then do please ask, that's what the forum is all about!

73, Mark.
 

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Thanks for the reply and the T2FD information. After a little research, I realized what I was describing is a T2FD antenna. I just did not know it.
 
I finally got around to actually building the antenna. It seemed to work well, but unfortunately most of what I could receive seemed to come from south america, in spanish??? The good news was my alarm clock radio became very sensitive and I could regularly listen to the southern states and chicago without interruption. It wasn't even connected to the antenna.
 
Hiya

Thanks for the update! It's great to get some feedback of members' projects.

I wonder if the reason for the South American reception was due to the direction of the antenna layout?

Another thing comes to mind, if it's broadcast AM stations, especially on medium wave/long wave that you were trying to receive, maybe the poor pickup was due to the polarity of the antenna not being correct?

For example, in the UK pretty well all medium wave/long wave broadcasting is vertically polarised, so maybe the stations you are after are using vertical polarisation (because they would have the funding for large vertical antennas), whereas the South American ones maybe have a more limited budget and so are using horizontal polarisation?

If your T2FD is set up horizontally it would then tend to favour the South American broadcast signals.

If so, then maybe a small active receiving antenna would better suit your needs.

Just a thought...

73, Mark.
 
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