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Chris Hughes
| | Posted on Friday, September 06, 2002 - 7:08 pm: | 
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Does anyone have any idea on how to create a "small 11 meter mobile beam?" Or any idea on how to create a small 11 meter beam at all. I would think that a coil would have to play in this some where, but not sure or even where to start. Any help would be great!
Chris! |
Taz
| | Posted on Friday, September 06, 2002 - 8:26 pm: |
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The PDL-II is an awesome design to re-make for yourself. |
Beam-me-up
| | Posted on Friday, September 06, 2002 - 9:09 pm: |
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Mosley makes a great small 11 Beam but it will cost you. |
bruce
| | Posted on Friday, September 06, 2002 - 9:20 pm: |
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sure co phase antennas i have a hygain flyer that tells you how to even though its base antennas it dosnt take a NASA engineer to convert to a cb station E-mail me its a large file
WA4GCH@YAHOO.COM |
10ring
| | Posted on Saturday, September 07, 2002 - 4:49 am: |
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check out the ultimate guide to 11 meter CB antennas. This is a great place to learn the basics on beam antennas I dont have know the web addres just do a serch you should find it with no problem. This will answer many of your questions it's a great read. 73's 10ring |
Tech833
| | Posted on Saturday, September 07, 2002 - 11:19 am: |
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Chris,
One of the things I do for a living is design and build (and maintain) AM broadcast directional arrays (all antenna elements fed). I can help you create a directional array for your vehicle that will have real gain (Not Antron gain) if you are willing to do a little more work that the typical co-phase system.
If interested, email me here at copper. My email address is tech833 (at) copper dot com. If not, no sweat. |
Hoosier Cardinal
| | Posted on Saturday, September 07, 2002 - 1:58 pm: |
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mosley made a "mini beam" back in the mid 1970s. I think they still do but they cost an arm and a leg!!! |
Mosley
| | Posted on Saturday, September 07, 2002 - 5:32 pm: |
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Two arms and 3 legs |
bruce
| | Posted on Saturday, September 07, 2002 - 6:01 pm: |
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hoosier its still made but by butternut
10/11 Butterfly Beam Antenna
Interested in a small lightweight beam for the 10 or 11 meter band? Butternut's Model 10/11 mono-band was derived from the HF5B. The antenna can be tuned for either band. A TV antenna rotator and mast are all you need for this fine performer.
Wing Span: 10 ft. 6 in. (3.2 m)
Boom Length: 4 ft. (1.2 m)
Turning Radius: 6 ft. 6 in. (2 m)
Vertical Spreaders: 5 ft. (1.5 m)
Shipping Weight: 14 lbs (6.3 kg)
Feed Point Impedance: Nominal 50 ohms. Includes RF connector for direct connection to any length feed line terminated in PL-259
VSWR at Resonance: 1.5:1 or less
Power Rating: Legal limit
Wind Loading: 3 ft2 (.3 m2)
Unguyed Wind Survival: 80 mph (129 kph)
Bandwidth for VSWR 2:1 or Less: 10 m - entire band
11 m - entire band
Gain: 5 dBd
Front-to-back: 15 dB+
Front-to-side: 20 dB
Accepts up to a 1-1/2 in (38.1 mm) mast. Light enough to be turned with a TV rotator. |
Marconi
| | Posted on Saturday, September 07, 2002 - 8:18 pm: |
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Hey Tech833, if appropriate, why not publish your piece about the mobile array in the Subscribers section. I am sure there are several that would be interested in your ideas. I know I am.
Marconi
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Delerius
| | Posted on Saturday, September 07, 2002 - 9:56 pm: |
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I second that... I am interested as well in building a small beam that I can mount on the truck when sitting still. I would appreciate any info you can provide Tech833. |
Ironmask
| | Posted on Saturday, September 07, 2002 - 11:28 pm: |
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Many years ago I used five [5] 3' francis fberglass antennas with a 360 degree switch. I mounted two on the mirrors of a cab over, two on the headache rack and one in the middle of the cab. By switching I could change the radiator thus creating what I called a stationary beam. I pulled heavy equipment. I didn't have to worry about the van trailer being in the way.
This might give you an idea. |
2600
| | Posted on Saturday, September 07, 2002 - 11:56 pm: |
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I remember an outfit long (20 yrs?) ago who made yagi antennas with continuously loaded elements. They used a fiberglass element (NOT pvc) with copper foil wrapped in a coil along its length. This made the elements short, but three elements takes the same length boom either way.
73 |
Tech671
| | Posted on Sunday, September 08, 2002 - 8:15 am: |
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An easy way for a mobile beam that's not permanent....
Get two 5" mag mounts and two 102" stainless whips.
(This works best on a van or suburban, something with a long roof line)
Mount on magnet at the most rear point of the roof. Mount the other magnet 7' forward. Take 1st 102 and mount it in the rear magnet, then short it to ground both center and shield. Mount front 102 and hook coax to your meter. You'll likely start by trimming 5" off, keep trimming until you get the lowest swr or reflection.
BAM.....2 element mobile beam. |
Chris Hughes
| | Posted on Wednesday, September 11, 2002 - 5:28 pm: |
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Thanks for all the information guys. Lots of great ideas out there. I figured this would be the best place to ask about it.
Tech833, I'll get that email right out to ya. Thanks!
A friend of mine was asking me about an antenna that he could mount in his attic, but was afraid of the large boom lenght and hight that comes with the 11 meter beams. Looks like with all this info, I might get both mobile and base as well.
Thanks for all the great info and keep it coming. My options are open! |
Znut
| | Posted on Wednesday, September 11, 2002 - 6:09 pm: |
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Don't forget, the rear element/whip, which is grounded, should be about 5% longer than the front one, which is hooked to the coax. Those good ole springs can help you play with the length. |
Tech833
| | Posted on Wednesday, September 11, 2002 - 10:37 pm: |
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Hi Chris.
In the usual configuration of 'co=phased' antennas, you mount one antenna on each side of the car and feed them with equal lengths of 75 ohm coax cable. This nulls signals to the side of you and increases signals to the front, rear, above, and below you. The front and rear signal increase are nice, but the above and below you are wasted power when transmitting.
If you instead mount one antenna on the front of the vehicle and the other toward the rear of the vehicle, then feed them with unequal lengths of cable, you then create the nulls to the side of you like the co-phase, but you also take the signal that would be wasted going above and below you and redirect it to the front and rear of you. This is actual system gain!
Now, let's assume you can get the antennas nearly 9 feet apart or so. If you feed the antennas 180 degrees out of phase, you will have a perfect figure 8 pattern with most signal going to the front and the back of the vehicle. As you get further away from 180 degrees and approach 0 (like co-phase) again, you make the nulls to the sides less deep, and the lobes to the front and rear lose gain. At some point near 60 degrees, you end up almost omni-directional again.
Using RG-6 (75 ohm, 78% velocity factor) coax to feed the antennas, if you made the coax to one antenna 10 feet long, you would make the coax to the other antenna 29.76 feet long to get 180 degree phasing (at CB frequencies). Shorten the longer coax to get the nulls on the sides to fill in.
Now, if you want to send signal one direction (say the front of the vehicle) more than the other in this configuration, we then adjust the ratios of the two antennas. Adding more power to the rear antenna than the front antenna would send the signal toward the front of the vehicle in the proportion of radio difference. You can do it the quick and dirty way with resistors, or you can use a variable capacitor across the coax where it connects to the bottom of the front antenna's base (from center conductor to ground). This will raise the drive impedance to that antenna and cause more power to be diverted to the rear antenna. Now, this also increases the common point resistance of the system (at the radio's coax connector), so don't get too crazy with the ratio differential unless you build a matching network for the other antenna too (a variable coil across the base would lower the drive impedance).
I can't provide parts values since the system would be different from one to the next. However, this will arm those so inclined to experiment with the ammo you need to get started.
Znut, A 2 element 'beam' with just a driven element and director (no reflector) is more effective in a mobile array (with the flat 'ground plane' instead of 1/2 wave dipole elements like on a yagi). That is how a Wullenweber DF array works. No reflectors. FYI. |
bruce
| | Posted on Thursday, September 12, 2002 - 11:42 am: |
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I have from hygain how to do it if you want a copy e-mail me at
WA4GCH@YAHOO.COM |
Znut
| | Posted on Thursday, September 12, 2002 - 6:22 pm: |
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OK, cool. Thanks.
Znut |
DeadlyEyes
| | Posted on Monday, September 16, 2002 - 8:34 pm: |
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Give this a try. Taz, I will per my policy of honesty and giving credit where credit is due put me onto the line of search.
The antenna is a quad but not a PDL 2. Make a quad/loop anenna with each side being 3 feet long for a total length of 12 feet. You will need to make a matching device. Get a weatherproof box a 150 pF variabale cap. Build an air coil on a 1 inch form to the value of 2.5 uH using bare copper wire. solder one end of the coil to one side of the variable cap. To this junction solder the shield of a length of 50 Ohm coax. The other side of the coil is connected to one side of the loop while the other side of the variable cap is connected to the other side of the loop. Tap the coil loop junction and attach it 3 turns down on the coil. Tap the bottom of the coil 3 loops up from the bottom with the center conductor of the coax. You are now ready to tune the antenna.
With this initial 3 turn top and bottom tap of the coil adjust the variable cap to the best SWR. Now fine tune the antenna by changing the top tap and the bottom coax tap on the coil for best SWR. Solder in place. Close and seal the tunner box.
One big drawback. The bandwidth per the article is only 20 kHz. So you are going to have to tune it for one frequency. You will not be able to move around very much.
Construction Note. To increase the band width of the antenna beyond 20 kHz you can increase the size of the loop and decrease the size of the coil. BUT as you approach full size loop why even bother with a smaller loop? Just go full size.
The PDLII is not that big of an antenna. |
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