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Author Topic: 2m Yagi for mobile use? Suggestions?  (Read 18634 times)
KJ4RQX
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Posts: 7




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« on: October 31, 2013, 08:47:10 PM »

I've recently been given an old service truck, you know the ones with toolboxes all along the sides.  It came with ladder racks and mounts, and i'm looking for a 2m yagi that is sturdy enough to be permanently mounted to the truck maybe usinging the ladder racks as support and with a small rotator.  I'd like to the truck hilltopping and possibly roving.

does anyone have any suggestions on brand/size yagi that would be good to use for this application?
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W8JX
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« Reply #1 on: November 01, 2013, 04:41:03 AM »

440 would be more viable for this than 2 meters do to size of antenna. I would suggest you maybe consider a Hustler 2 m mobile colinear antenna. I have used on and it works well and notably better than a 5/8 wave real world.
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N6AJR
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« Reply #2 on: November 01, 2013, 10:00:15 AM »

probably a pair of stacked halo's for 2m, 440 and 6m would work better,  look at M squared ( M2inc.com or something like that, google is your friend) fo their antennas  they make some that will handle 65 MPH on a vehicle.
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K0BG
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« Reply #3 on: November 01, 2013, 11:03:43 AM »

Assuming you're speaking about SSB (not FM), then the suggestion for a horizontally-polarized antenna is a good one. Even a stacked pair of 6 meter halos is easily doable, and will give you about 6 dB of omnidirectional gain over a dipole. You also get about a 20 dB advantage over a vertically-polarized antenna if you're working tropo-scatter.

The single M2 loop I have on my Ridgeline has about 50k+ miles of highway driving, it is it still in one piece despite hitting several birds along the way. I wouldn't waste my time with anyone else's.

If you're talking FM operation, then a collinear array is better in some respects, but not by much.
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WB6BYU
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« Reply #4 on: November 01, 2013, 11:44:44 AM »

My first concern would be the lateral force on the rotator.  Having driven down the
freeway with a 5-element 2m quad sticking out my window, I can say there is a
LOT of wind drag on such an antenna, and you'll probably need a thrust bearing
or a greatly oversized rotator to withstand it.

A reasonable approach may be to take the beams off the mast while driving and lash
them to the top of the ladder racks - that takes the lateral force off the rotator and
spreads it around the frame.  Then to set up you can bolt the antenna to the mast
and slide it up above the frame and you're ready to go.  I've seen some clamps for
scaffolding poles that would make a quick connection to the mast without having to
remove U-bolts and nuts, or you if the mast were appropriately placed you may be
able to leave the antenna clamps around it and just lower the antennas down to the
rack for transport.  With an appropriate thrust bearing to protect the rotator you could
still drive around with the antennas up when needed, but wouldn't need to do it all
the time.


Physical dimensions will depend on the vehicle laws in your state, especially for the
allowable overhang on the sides.  I know one transmitter hunting team that used an
11-element 2m yagi on their car, but they couldn't rotate it while driving.  (This could
be a problem for the element length on a 6m yagi as well.)  Side overhang limits are often
something like 6" beyond the edge of the vehicle (sometimes only allowed on the passenger
side) or 8' overall width - that's why you need to check.

If you plan to rotate the antenna while moving the you'll need one that fits within the
legal limits for your state (and those others in which you plan to drive.)  This may limit
you to 5 or 6 elements on 2m, and a Moxon on 6m (to reduce the element width.)

For mountain topping, where you are not operating while in motion, then you can use longer
beams as long as they conform to the requirements for overhand on front and back of the
vehicle, and something with about a 12' boom may be practical.  Again you'll have to make
sure that the 6m elements don't stick out too far on the sides, or do something to shorten
them (like bending the ends down).


You'll probably need something that will withstand 100mph winds (70mph highway speed
with a 30mph headwind).  I don't know who makes such antennas, but I'd probably check
M2 first.
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G8YMW
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Posts: 256




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« Reply #5 on: November 01, 2013, 05:23:54 PM »

Not a beam but is the biggest omni for 2 metres that is practical. A "cloverleaf", Wimo's Big Wheel (Dont have one for 6 metres, its ten feet diameter)
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73 de Tony
Sent by WW2 Royal Navy signal lamp
KJ4RQX
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Posts: 7




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« Reply #6 on: November 02, 2013, 08:23:29 PM »

I don't intend to rotate the antenna while underway  So I thought I could just lash the front or the back to the ladder racks while in motion to keep them from breaking the rotators

WB6BYU, N6AJR -- Thank you, I was looking for brands that build antennas that are stronger than the regular antennas, but 100mph winds could be expected if I took the truck on the highway, excellent advice.

What about some of those tilt antenna masts, I wonder if they would be practical for mounting an antenna, obviously not deployed while in motion, but more of a rover style drive and park.
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W8JX
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« Reply #7 on: November 03, 2013, 06:45:37 AM »

I don't intend to rotate the antenna while underway  So I thought I could just lash the front or the back to the ladder racks while in motion to keep them from breaking the rotators

WB6BYU, N6AJR -- Thank you, I was looking for brands that build antennas that are stronger than the regular antennas, but 100mph winds could be expected if I took the truck on the highway, excellent advice.

What about some of those tilt antenna masts, I wonder if they would be practical for mounting an antenna, obviously not deployed while in motion, but more of a rover style drive and park.

You could also install several verticals and phase them to make them steerable and usable on highway.
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WB6BYU
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Posts: 13489




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« Reply #8 on: November 03, 2013, 08:30:42 AM »

Lashed to the frame, the wind rating doesn't have to be as high.  A bit of an aerodynamic
shield on the front of the rack will help to reduce the stress on the individual elements as
well.

There are other options:  the boom of the Cushcraft 11-element 2m yagis, for example,
comes apart into 3 sections, and can be laid flat in the back of a pickup truck.  Only takes
a couple moments to slip the end sections on and tighten the clamps when you're putting
it up.  (Color-coding the ends makes it more likely that you'll get them right each time.)

I have 6- and 7-element VHF yagis made from PVC pipe and aluminum wire.  Not only
does the boom come apart into sections, but the elements pull out of the holes in the
boom so the whole thing fits into a 6" diameter tube less than 5' long.

I regularly carry a 6-element 6m yagi to Field Day in my minivan, though the boom and
elements have to stick out the passenger window a bit.  This requires removing the
elements from the boom, but a few minutes with a wrench is enough to put them back on.


There are lots of mast options, depending on required height, how much weight you
want to put on it, how long you want to spend putting it up, and how much you want
to spend.  We used to be able to get 5' TV push-up masts, which are a good size for
being able to stand next to it and push it up.  You could use one with 10' sections if
you can stand on the truck to reach the top.

I like using the 4' military mast sections, which I put up by stacking them vertically.
(Lifting the stack and inserting the next section underneath.)  I use guy ropes to
hold it in place, but a bracket off your ladder rack could be used as well.

Tilting up a mast with an antenna on top can generate a lot of force - I've seen
a couple push-up masts bent that way on Field Day.  But for lengths up to 20' or
so you can probably get by with aluminum or steel pipe or tubing of whatever length
you can put on top of the truck, especially if you can use the ladder rack as a gin
pole to pull it up.


As far as a rotator goes, I've seen a couple that are DC powered, but most will require
an inverter or generator to power them.  A simple solution that we use on Field Day is
to tie a rope to the back of our antenna and pull it around manually to the desired
direction.
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KJ4RQX
Member

Posts: 7




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« Reply #9 on: November 03, 2013, 08:08:30 PM »

Excellent ideas,  I recently found a piece of what i'd call a sleeve (not a coupling) its about a 1ft long piece of galvanized pipe that is just perfect to couple two peices of 1 1/4" EMT together.  I'm thinking I could mount the yagi to one shorter peice of EMT, and then, when needed whip out that sleeve and add another 10' of mast height.  That would give me about 20ft of height above the ground, and from what I can tell, thats about all that one person can handle easily.

I've actually got one of those cushcraft 11element 2m yagis, I do like the way it works on my home location but its those clamp connectors that also make it weak, it wants to droop when stationary, I could only imagine what shaking from the road would do to it.  Can anyone do any side by side comparisons between the cushcraft and the M2 antennas?

Having AC power isn't an issue, The truck has one of those quiet inverter generators mounted to it.  Would you put the rotator at the bottom of the mast and brace at a ladder rack, or put the rotator at the top?  Having never used a rotator that part confuses me.  Also do the compasses in the rotators self calibrate or is it a user defined thing?
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AA4HA
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Posts: 1599




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« Reply #10 on: November 06, 2013, 05:23:12 AM »

The windrose on a rotor is manually set. It will not detect the difference between truck orientation and antenna orientation.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
KJ4RQX
Member

Posts: 7




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« Reply #11 on: November 08, 2013, 03:10:41 PM »

Thank you very much, That helps knowing that even if I put a rotor on the truck it will need calibration every time I move. That limits its effectiveness in this application.  AA4HA in your experience are the windroses on rotors easy to change or is it a tedious process?
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N0MLR
Member

Posts: 74




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« Reply #12 on: November 10, 2013, 10:11:14 AM »

I have seen this done. It was back in 1978 while I was in high school. W0ERE Al Gallo had a 3 element 2 meter yagi on top of his station wagon. Al still lives in Missouri. I am sure if you contacted him he could give real world information on this.
Good Luck.

73
Greg

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WB6BYU
Member

Posts: 13489




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« Reply #13 on: November 10, 2013, 11:08:49 AM »

Once it is properly set, the rotator display will show the bearing of the antenna relative
to the direction the truck is pointing
.  So if you can always part pointing North you're
all set.  Otherwise there are a couple of options:  first would be to make an adjustable
cardboard cutout to go on the display with a new set of directions printed on it.  Then
you can rotate the markings to coincide with the way you parked.  Another way is to
simply mount the antenna on the mast pointing North each time, regardless of how the
truck is aligned.  A magnetic compass is good enough for this, as long as you hold it
far enough away from the truck and sight down the boom of the antenna.

Or just turn the antenna for strongest signal and don't worry about what the actual
direction is.
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N6AJR
Member

Posts: 9921




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« Reply #14 on: November 22, 2013, 11:40:18 AM »

well in my car I use a pig tail antenna for 900 MHz and a ATAS 120 for the ft 857. in the truck  ( I have 5 radios, ) so I have 2m/440//220/1.2 g antennas on the roof with 4 nmo mounts and on the bed rails on both side I have a 2m separate 2m/440/6m antenna on one side and an ATAS 120 and a DK-3 on the other bed rail, ( Look at the pictures on my call on QRZ) to cover all bands from 1.2g, 900MHz, 440 MHz, 220 MHz, 2m, 6m, 10m, through 160. (160 mobile really doesn't work). I have also been thinking of adding 2m 440, and 6 m halo's I have sitting in the shack to my ladder rack. We'll see.
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