PDA

View Full Version : 10 meter beam



kk4fpx
04-09-2012, 01:42 PM
Anyone know if its ok to use two different dia for the REF and the DE?

kk4fpx
04-09-2012, 01:43 PM
It's a two element.

N8YX
04-09-2012, 02:11 PM
Yes, it is. You won't really get into problems with L/D ratios using normally available element tubing until you get into the VHF region. One can model the effects using NEC or similar software.

N2RJ
04-09-2012, 02:40 PM
It's kind of interesting because SteppIR kinda does this with its trombone style elements.

I was talking to K7IR and he was telling me that with the DB36 they were basically "modeling the piss out of it" and they found that not only did they save space and the gain difference between a full size and the trombone was not that much... but that the F/B was actually BETTER because the trombone had better capacitive coupling with the other elements close to it. Now I wish I got one... well, there's always room for another tower. :)

K6BSO
04-09-2012, 02:54 PM
Tapered elements like you get when you use telescoping tubing can affect how an antenna behaves but I don't think that using a reflector that's a different diameter from the driven element would matter much. It might tune a little differently but there would be no major difference in the pattern.

kk4fpx
04-09-2012, 04:15 PM
I'm trying to use what I've got on hand.I think I'm going to have to use the bigger dia for the driver because of the length.How close should the two haves of the driver need to be and is the gap concidered part of the overall length?

N8YX
04-09-2012, 05:26 PM
I'm trying to use what I've got on hand.I think I'm going to have to use the bigger dia for the driver because of the length.How close should the two haves of the driver need to be and is the gap concidered part of the overall length?
At HF, a difference of 1/4" or less is desirable. The gap is part of the overall length.

What type of matching arrangement are you considering? If you employ one that allows for grounding of the driven element to the boom, the antenna will be a lot less susceptible to static noise (QRN).

kk4fpx
04-09-2012, 08:02 PM
I am planing on just useing a poor mans coiled balun and hope I acn get a match.

kk4fpx
04-10-2012, 03:34 PM
Never mind.I don't have as much tubing as I thought.So.... I'm going to try a horizontal vee dipole.

WTKX
04-10-2012, 04:13 PM
Hmmm. I've made these for 6 meters... they are easy to do.

http://www.moxonantennaproject.com/index.html

W5GA
04-10-2012, 05:29 PM
The only time I've ever seen tubing diameter cause an issue was some years ago when the original maker of the KT-34 goofed. They put the wrong diameter tubing in some of the linear loading elements, and the antenna became a dummy load on 15m.

K6BSO
04-10-2012, 07:27 PM
Hmmm. I've made these for 6 meters... they are easy to do.

http://www.moxonantennaproject.com/index.html

I've got a 10m Moxon in the backyard. As soon as my medical insurance kicks in, I'm going to put it up on top of the garage.

WTKX
04-10-2012, 07:41 PM
Moxons give you a little bit of gain, and a kick ass front to back ratio. PVC tinker toy methods work great for the smaller ones.

As a plus for a camping antenna, they have a wide beam width. The Armstrong Rotor works well, you don't have to spin it much. :mrgreen:

I've got some sketches for a combo vertical/horizontal combo Moxon for VHF. You know, a "rover special".

K6BSO
04-10-2012, 07:44 PM
Moxons give you a little bit of gain, and a kick ass front to back ratio. PVC tinker toy methods work great for the smaller ones.

Exactly how I made mine:

http://i815.photobucket.com/albums/zz79/gyrogeerloose/10mMoxonMedium.jpg

kk4fpx
04-12-2012, 09:54 AM
Could you give me the dimensions of the 10 meter version.I can't seem to get it to load.

WTKX
04-12-2012, 01:11 PM
What won't load? The Moxgen calculator program? The dimensions will change a little depending on wire size and design frequency. Tell us more about how you at gonna build it.

FWIW, there are a lot of 10 meter examples on that website.

kk4fpx
04-12-2012, 02:00 PM
Yes the calculator won't load.I have enough 12 g wire for it.I plan on useing the pvc boom style with smaller pvc spreaders.

WTKX
04-12-2012, 02:25 PM
What frequency?

K6BSO
04-12-2012, 06:46 PM
Here's something to get you started:

http://i815.photobucket.com/albums/zz79/gyrogeerloose/moxon.jpg

The dimensions are in inches and the feed point should be at the middle of the top element (I was in kind of a hurry when I made the drawing).

My experience with these dimensions is that they result in an antenna tuned a bit low, so you'll probably end up trimming a bit but I always prefer building antennas that way anyhow.

kk4fpx
04-12-2012, 08:26 PM
Thanks for the drawing.I'm tech so 28.300 to 28.500 for the other ans.

kk4fpx
04-12-2012, 08:48 PM
I also noticed most had the wire running outside of the pipe instead of in side.reason?

WTKX
04-12-2012, 08:50 PM
Hmmm. Moxgen results with 12 ga and 28.4 as the mid freq:

https://lh4.googleusercontent.com/-mTzxIVA0Tgo/T4eF1Ev0jyI/AAAAAAAAAus/TeOd2Xx1Mdg/s681/10MeterTechMoxon.jpg

WTKX
04-12-2012, 08:55 PM
I also noticed most had the wire running outside of the pipe instead of in side.reason?

Strength. It puts the structure under a bit more "tension", so it doesn't wiggle and whip around so much.

Of course you can do it any way you want to. Pulling it taught on the inside wall of the pipes would work too...

K6BSO
04-12-2012, 09:31 PM
I also noticed most had the wire running outside of the pipe instead of in side.reason?

The pipe is just the stretcher to hold the wire. If you wanted to make a big pipe rectangle and put the wire inside, I guess that would work too (although it would be a lot heavier). In fact, my friend AE6QW and I built a 20m Moxon for our club's Field Day site out of 1/2" copper pipe and compression fittings. The pipe was the antenna and it worked very well; due to the broad main lobe and our location in the extreme southwestern corner of the U.S., we were able to aim it in a generally northeasterly direction and cover almost the entire country without need for a rotator.

Funny thing, though: that antenna was built from dimensions from the same program and it resonated low as well.

kk4fpx
04-13-2012, 07:06 AM
One more thing before I start rounding up parts.Would the gain be that much more than a single element horizontal v beam?

W5GA
04-13-2012, 08:00 AM
One more thing before I start rounding up parts.Would the gain be that much more than a single element horizontal v beam?
Wouldn't be much point to a single element beam, vee or otherwise.....it's still called a dipole whether it's made from wire or tubing. Any gain at all is a significant improvement.

WTKX
04-13-2012, 08:25 AM
I experimented with a 6 meter Vee beam.

In QSO across town with a guy running QRP for testing, there was little change on the front to back, RX and TX. It worked, but it did not work as well as the Moxon. When trying the Moxon, the TX to the RX station induced a 2-3 S unit change on his end. I could not hear him at all on the back of the Moxon.

His signal with a 6 meter dipole was about S5...

He was running 3 watts, I was running 5.

Bottom line, the Moxon did well, for a simple antenna.

kk4fpx
04-13-2012, 11:44 AM
Ok,I'll give the Moxon a try.And thanks to everyone for all the help.

K6BSO
04-13-2012, 04:00 PM
A Moxon should give you about 3dB of gain over a dipole, equivalent to doubling your RF power out. Also a very high (~20dB) F/B ratio, although I think that's really an overrated concern unless you have a major source of QRM nearby.