jacour
join:2001-12-11
Ypsilanti, MI
 ·Comcast
| Delta Beams
Since we are talking about antennas this week, I am wondering why delta beams are not more popular. The only time I used one was at a field day station, connected into a rig running barefoot power. We all know how busy those field day pile-ups get, and I busted every one on the first or second call. I was getting great signal reports all day and all night.
When I got home, I looked up the delta beam antenna on the MMANA software, and it calculated something like a 13dBi gain! So, given the relatively small footprint and great performance, why hasn't this antenna become more popular? It certainly kicks a regular multi-element beam all to hell.
Am I missing something? |
|
n1zuk
This Space Available
Premium
join:2001-10-24
South Burlington, VT
 ·Future Nine Corpor..
·Comcast
·ViaTalk
·Packet8
| Good subject. I had great success with a 2 element Delta on 6M. A 2-el Delta has about the same gain as a 3-el Yagi, with a very similar radiation pattern.
I feel that there are several reasons that Delta (and for the same reasons, Quad) beam antenna aren't favored over Yagis:
-- Mechanically, more of a bear to set up and maintain. Several spreaders for each element, then the wire element itself.
-- Wind loading. Even though the boom is shorter (and one less element for the gain) you do get a lot of surface area to catch the wind.
-- Impedance matching. Not the easiest setup to get a good match. Most everybody knows and understands the classic yagi Gamma Match.
For my 2-el 6M, I avoided most of it by fixing it facing SW (being in Vermont, where most e skip comes from), and building a very simple antenna. A 1x1 strip of lumber with two holes on the end to hang from some trees, and two more holes appropriately spaced for the elements. Cut wire for the driven and reflector. some 75ohm coax for a tuning stub. I used string to hold out the other corners, tied to other low branches and stuff. Ugly, but worked for over 300+ contacts, including VP6BR on 6M. Even though it was retired for a 5-el yagi that I could rotate, I still have that antenna. 
--
New to Forum Life? Click here and learn. |
|
GeekGirl1
The Medium IS the Message
Premium
join:2007-01-28
Morrisville, PA
 ·Verizon FIOS
 ·Verizon Online DSL
| I used to have a 2-el tri-band HF quad antenna. Fiberglass supports. Carried it up to the top of my 50' Rohn-25 tower over my shoulder (really!).
Then the wind hit it. Wind loading is an understatement.
One thing that you realize after a while is that the wire is stressed at the points it passes through the supports, i.e. the apex where it forms the "squares". Over time, the wire breaks. That will happen. A pain to fix. Hence, the popularity of rigid metal elements (yagi).
If you remember all those CB quad antennas from a long time ago- just about every one had broken wires on it. Not many were kept in good condition. |
|
jacour
join:2001-12-11
Ypsilanti, MI
·Comcast
| reply to jacour
The one I used was rigid all the way around. It had a thick piece of pipe on the bottom with welded supports for attaching to a rotor and a welded "V" configuration to hold the lightweight tubing that completed the triangle. This particular one was fairly big, because it was made for 20m, but man did it work!
I hadn't thought about the wind load, or the matching. The matching would not be that much of a pain, but I can understand the wind load problem is some geographies and especially permanently mounted on a tower. Wind was not a particularly big problem on field day because the weather was decent and we had it fixed to a portable man lift that got it up in the air about 40 feet. |
|
