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Author Topic: 2 meter log skidder antenna  (Read 3915 times)
KD8PNE
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Posts: 9




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« on: July 10, 2012, 09:52:14 AM »

hey everyone I run a John Deere log skidder here in west virginia need to build a antenna thats practicaly indestructable I can destoy just about anything I put on it in a matter of days I have an old steel whip I can cut down to a half wave I only need about 3 ft or so of coax the roof has pre drilled 3/8 hole in it just for that does anyone have some good ides on antenna length,coaxlength to get me in the ballpark. MFJ sells a 1/2 wave 3/8 mount 2 meter whip looked at it could rip it off in about 15 minutes
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KG4RUL
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« Reply #1 on: July 10, 2012, 10:12:10 AM »

Are we talking 2M Amateur frequencies or VHF business band radios?
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WB8VLC
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Posts: 116




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« Reply #2 on: July 10, 2012, 11:35:34 AM »

http://www.antenna.com/apg_products.cgi?id_num=10953

If your serious and don't mind paying more than your average whip antenna then I would look at some of the low profile transit style antennas such as the model above to get an idea as to how rugged they are.
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AD4U
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Posts: 2150




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« Reply #3 on: July 10, 2012, 12:12:44 PM »

Assuming you are talking about VHF (HAM or business) and understanding that you will tear any externally mounted antenna off in a matter of days, I would suggest that you mount a 1/4 antenna inside the "cage" or cab.

Even if the cage is partially enclosed in expanded metal, there will be enough RF getting out of the enclosure to work local repeaters and several miles on simplex. 

Dick  AD4U
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KD8PNE
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« Reply #4 on: July 10, 2012, 02:25:54 PM »

Are we talking 2M Amateur frequencies or VHF business band radios?
    no I,m talking Amateur I wouldn't care about business radio
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WB6BYU
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Posts: 12980




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« Reply #5 on: July 10, 2012, 03:39:56 PM »

What type of mechanical damage typically destroys the antennas?  Rubbing them off
against branches?  Vibration?  Excessive swaying back and forth as the skidder drives
over rough terrain?  Each of these might argue for a different design.

How much gain do you need to make the desired contacts?

The antenna I've seen used the most in rough-service vehicles is the simple quarter
wave whip.  That would be about 18" to 19" long.  In your application, I don't think
you will find anything that works much better, assuming that you are planning to put
it on a 3/8"-24 mount.  (An NMO mount takes a bigger hole, but allows a wider
variety of antennas.  And even at that, the quarter wave whip is still a good choice.)
It has minimum length and no concentration of weight high in the antenna that can
cause problems with swaying.  By making it out of relatively flexible material it can
survive a lot of contact with branches, etc.  (I knew one ham who had 2" of clearance
under his garage door and the antenna survived for years driving under it every day.)

If you cut down a standard stainless-steel whip, it will be pretty stiff at such a short
length.  That would hold up pretty well for anything other than direct physical
contact.  Otherwise I'd look for a couple feet of #18 or smaller Copperweld(r) and
some way to secure it to the base.  (For example, find a 3/8-24 bolt, drill a hole
in the top for the wire and one or two in the sides of the head for set screws.)  Many
VHF antennas have a base with a whip that adjusts using set screws - just remove
the whip and stick the flexible wire in its place.  Or get a few pieces of brass brazing
rod that fit the mount and cut them in half - when you break the whip off the base or
bend it to far over that it breaks when you try to straighten it, just remove it and stick
a new piece in.  Half a standard length (18") should be a pretty good match. There
are other sorts of flexible whips that work as well - you want it stiff enough to stand
up without fatiguing, but flexible enough to bend when it hits a branch.

But don't get fooled and use copper-coated welding wire instead - the thin outer
coating will corrode off quickly, and the underlying steel doesn't radiate very well.

Otherwise, Antenna Specialists makes a line of antennas specifically for the rough
environment of commercial equipment that might be worth the expense, but they
might not have one that fits on a 3/8-24 mount.  (Most commercial antennas would
use an NMO mount at 2m / VHF-HI band.)

Good luck!
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KD8PNE
Member

Posts: 9




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« Reply #6 on: July 11, 2012, 03:04:43 AM »

What type of mechanical damage typically destroys the antennas?  Rubbing them off
against branches?  Vibration?  Excessive swaying back and forth as the skidder drives
over rough terrain?  Each of these might argue for a different design.

How much gain do you need to make the desired contacts?

The antenna I've seen used the most in rough-service vehicles is the simple quarter
wave whip.  That would be about 18" to 19" long.  In your application, I don't think
you will find anything that works much better, assuming that you are planning to put
it on a 3/8"-24 mount.  (An NMO mount takes a bigger hole, but allows a wider
variety of antennas.  And even at that, the quarter wave whip is still a good choice.)
It has minimum length and no concentration of weight high in the antenna that can
cause problems with swaying.  By making it out of relatively flexible material it can
survive a lot of contact with branches, etc.  (I knew one ham who had 2" of clearance
under his garage door and the antenna survived for years driving under it every day.)

If you cut down a standard stainless-steel whip, it will be pretty stiff at such a short
length.  That would hold up pretty well for anything other than direct physical
contact.  Otherwise I'd look for a couple feet of #18 or smaller Copperweld(r) and
some way to secure it to the base.  (For example, find a 3/8-24 bolt, drill a hole
in the top for the wire and one or two in the sides of the head for set screws.)  Many
VHF antennas have a base with a whip that adjusts using set screws - just remove
the whip and stick the flexible wire in its place.  Or get a few pieces of brass brazing
rod that fit the mount and cut them in half - when you break the whip off the base or
bend it to far over that it breaks when you try to straighten it, just remove it and stick
a new piece in.  Half a standard length (18") should be a pretty good match. There
are other sorts of flexible whips that work as well - you want it stiff enough to stand
up without fatiguing, but flexible enough to bend when it hits a branch.

But don't get fooled and use copper-coated welding wire instead - the thin outer
coating will corrode off quickly, and the underlying steel doesn't radiate very well.

Otherwise, Antenna Specialists makes a line of antennas specifically for the rough
environment of commercial equipment that might be worth the expense, but they
might not have one that fits on a 3/8-24 mount.  (Most commercial antennas would
use an NMO mount at 2m / VHF-HI band.)

Good luck!
   Yeah it just gets beat to death I have a Maxrad magmount after about a month looks like it was drug down the hard top I'll check Antenna Speialists out thanks for the info
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KC9NVP
Member

Posts: 64




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« Reply #7 on: July 11, 2012, 06:25:00 AM »

Have you looked at relocating the antenna to an area where it would be protected bow the roof line of the cab (if there is a enclosed cab)?  Not know what type or model you are driving, but a search of the internet showed several with enclosed cabs and glass windows plus protection bars over the engine area.  This may be an area where you could mount an antenna instead of on the roof of the cab.
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KG4NEL
Member

Posts: 373




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« Reply #8 on: July 11, 2012, 06:44:37 AM »

The idea about having the antenna be as flexible as possible is good - I've bent 1/2" steel plates on my tractor before in the course of things, and I'm sure your application is 100x more demanding Smiley I have a feeling anything that puts up a fight, contact-wise, is going to lose.
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KG4RUL
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Posts: 2676


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« Reply #9 on: July 11, 2012, 08:24:59 AM »

So, the next question is are you using 2M Amateur for personal communications?
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KCJ9091
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Posts: 0




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« Reply #10 on: July 11, 2012, 01:45:01 PM »

What, someone can't yak on the local two meter repeater while dragging logs out of the woods?

My solution to the problem would be to put an NMO mount on the roof panel.  For the antenna I would use the cheap SS wire whip Motorola includes in the quarter wave kits that are held on with the chrome nut.  It is soft enough to bend instead of break and you can straighten them out many times before they do finally work harden and snap.

Like this:   http://www.motorola.com/Business/US-EN/Business+Product+and+Services/Accessories/Two-Way+Radio+Accessories/Antennas+and+Antenna+Accessories/Portable+Radio+Antennas/HAD4007
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W5DQ
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Posts: 1209


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« Reply #11 on: July 11, 2012, 03:04:21 PM »

Hope you're not trying to handle a skidder and ragchewing at the same time Shocked  Better get a headset and run VOX if so

If so, may be more than your antenna that takes a beating. You might need 'circular' polarization as you go tumbling down the slope Smiley

Good Luck!! I never run a skidder but have seen one in action before .... not for the faint of heart Smiley

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
KD8PNE
Member

Posts: 9




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« Reply #12 on: July 11, 2012, 05:29:32 PM »

Hope you're not trying to handle a skidder and ragchewing at the same time Shocked  Better get a headset and run VOX if so

If so, may be more than your antenna that takes a beating. You might need 'circular' polarization as you go tumbling down the slope Smiley

Good Luck!! I never run a skidder but have seen one in action before .... not for the faint of heart Smiley

Gene W5DQ
well thanks havent turned it over Smiley this week but it's only wednesday
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KD8PNE
Member

Posts: 9




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« Reply #13 on: July 11, 2012, 05:35:02 PM »

What, someone can't yak on the local two meter repeater while dragging logs out of the woods?

My solution to the problem would be to put an NMO mount on the roof panel.  For the antenna I would use the cheap SS wire whip Motorola includes in the quarter wave kits that are held on with the chrome nut.  It is soft enough to bend instead of break and you can straighten them out many times before they do finally work harden and snap.

Like this:   http://www.motorola.com/Business/US-EN/Business+Product+and+Services/Accessories/Two-Way+Radio+Accessories/Antennas+and+Antenna+Accessories/Portable+Radio+Antennas/HAD4007
yeah relly If it was a company radio it would never work as far as I'm concerned falls a coming soon hoping the 2 meter propragation awesome these w.v mountains sure are tall I'm checking on some mounts on ebay now
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