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Author Topic: Mobile Antenna Mounting  (Read 290 times)
W1SCB
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Posts: 28




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« on: May 14, 2003, 11:46:30 PM »

I have a Jeep Liberty, and just ordered an Icom 706.  I'm planning on using a new Maldol HMC6s which is a 66" 6band 20m-70cm all vertical  through a comet 706 freq splitter and LDG RT11 tuner for HF.  My question is on the antenna mounting and placement.  I was going to make a braket to go across the two unused mounting holes on my rear mounted spare with and L braket out of 1/4" stainless bar stock.  My concern is that it isn't high enough and won't have sufficient ground-plane.  I'm toying with getting some an aluminum sheetin and mounting it across the 'roof-rack' though the overall height may be prohibitive and very inconvenient for garages and drive-thru's.  The last option I was considering is one of the motorized lay-down mounts attached to the roof-rack's rail, but again I'm worried about the ground-plane and would prefer not to drill, not for value, but to avoid both rust and/or water leaks over time.  I know nothing is perfect, just looking for any ideas and/or creative suggestions.
Thanks
Sean
W0SCB
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KA9ZIM
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Posts: 63




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« Reply #1 on: May 15, 2003, 08:51:14 AM »

Mobile HF setups are always a compromise.  I suggest you start with the easiest mounting method and see if you like the results.  As for the ground plane concern, do your best to bond the spare tire carrier to the body of the jeep with a short jumper.  Braiding is better but a wire jumper will work too.
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K0BG
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« Reply #2 on: May 15, 2003, 08:52:12 AM »

The antenna at just barely 5 feet in length is already lossy compaired to a host of others you could pick. Its selling point is its band width. You won't need the LDG tuner either for several reasons.

All mobile antennas are compromises and if the only convenient location is the tire mount location, sobeit. Just understand this adds to the overall loss of the system and is one of the reasons you won't need the tuner.

Alan, KØBG
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W9WHE
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Posts: 254




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« Reply #3 on: May 15, 2003, 12:42:49 PM »

With that tuner, you could save a bunch of $$ and gain some efficency by using a 102" whip (fiberglass or SS). Moreover, by simply folding it over to the rain gutter/roof rack clip (does the Jeep have gutters?) you can solve the garage/drive through problem!

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W9WHE
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« Reply #4 on: May 15, 2003, 12:47:23 PM »

Last post assumes you have a seperate UHF/VHF antenna!
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K0BG
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« Reply #5 on: May 15, 2003, 03:10:48 PM »

The is a problem problem with your suggestion John, the LDG does not have the range to tune a 102" whip except for 12 meters and maybe 15. It takes an AH-4 Icom or one of the SGC units to do that.

Incidentally, if you were to use the LDG RT11 (which is equipped with SO239s) to retune the whip to the 12 meter band, with just one foot of coax between the antenna and the tuner, the efficiency would be cut by nearly 50% due to the shunt capacitance of the coax.

Alan, KØBG
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W1SCB
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Posts: 28




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« Reply #6 on: May 15, 2003, 09:39:20 PM »

Well, I'm using 2" x 5/16" stainless bar stock across the two empty wheel holes held on with 1/2 stainless bolts.  Used a torch and bent an 11" piece to an L, bolting them together and using a diamond PL259/coax through a 5/8 hole on the end.  Will mount the Maldol to that, it seems sturdy and has a few inches before it'd hit the tire if it whipped around in the wind so the vehicle seems clear.  I'm hoping no guying is necessary(Chose the Maldol over the comet as it seemed sturdier and didn't have the horizontal elements).  The LDG and 706 should arrive on Sat, so I'll let everyone know how it goes maybe on Sunday.  Any further comments or suggestions are as always appreciated.
'73
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W1SCB
Member

Posts: 28




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« Reply #7 on: May 15, 2003, 09:39:37 PM »

Well, I'm using 2" x 5/16" stainless bar stock across the two empty wheel holes held on with 1/2 stainless bolts.  Used a torch and bent an 11" piece to an L, bolting them together and using a diamond PL259/coax through a 5/8 hole on the end.  Will mount the Maldol to that, it seems sturdy and has a few inches before it'd hit the tire if it whipped around in the wind so the vehicle seems clear.  I'm hoping no guying is necessary(Chose the Maldol over the comet as it seemed sturdier and didn't have the horizontal elements).  The LDG and 706 should arrive on Sat, so I'll let everyone know how it goes maybe on Sunday.  Any further comments or suggestions are as always appreciated.
'73
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