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Author Topic: Screwdriver antenna - mount on truck bed  (Read 8921 times)
HS0ZIB
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Posts: 424




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« on: February 19, 2014, 11:20:20 PM »

I have a Mazda BT-50 pick-up (SUV) and intend to mount an HF screwdriver antenna in the rear cargo area.

Various photos from the websites of manufacturers of screwdriver antennas show them mounted in this position, but I am a little concerned that the cab of the vehicle will adversely affect the radiation pattern of the antenna.

Specifically, where does a screwdriver antenna radiate from?  Is it primarily from the coil area, or is it from the whip, (or is it a combination of both)?

My antenna whip will be clear above the truck, but the screwdriver/coil region of the antenna will be mounted into the truck bed, fairly close to the rear of the passenger cab.

Any installation advice is appreciated.  I cannot mount the antenna on top of the passenger cab - it would be too tall for the low palm trees!

Simon
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N6AJR
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« Reply #1 on: February 20, 2014, 11:31:26 AM »

o to QRZ and see where  mounted 2 screwdrivers on my truck.   they work ok. tom N6AJR
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M6GOM
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« Reply #2 on: February 21, 2014, 04:05:16 AM »

The screwdriver radiates primarily from the whip. As long as the exposed coil and whip aren't masked by the body you're good to go.

Breedlove Mounts make some excellent antenna mounts for pickups with several options available. It won't come off one of those.
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N6AJR
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« Reply #3 on: February 21, 2014, 11:58:09 AM »

Go to.. Smiley
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K4FMH
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« Reply #4 on: March 07, 2014, 05:50:13 PM »

Just a follow-up Q on this....

I just bought a 2010 Chevy Silverado Extended Cab pickup. It has a center hitch mount in the truck bed (e.g., for a trailer, etc.) which would make a good mounting point for a screwdriver antenna. What if I temporarily removed the bedliner, installed a rectangular sheet of metal the size of the truck bed as the ground plane? Would this likely negate the need to bond everything underneath the truck?

The thinking I've read on relevant pages is that it's getting the most metal directly underneath the screwdriver antenna that matters to establish a viable groundplane. Since this would be fairly easy to install, is it a crap-shoot or a likely success?

73,

Frank
K4FMH
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N5UD
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« Reply #5 on: March 15, 2014, 03:35:14 AM »

My screwdriver is located above the bed near driver side wheel well. Has quick disco to remove whip. Top of coil is level with cab roof. Also it is directly over the frame below. Heavy duty ground strap run directly through bed to frame. Ground to frame. I have worked 300+ DXCC in 3 years of chasing DX from the Silverado.

My buddy got the HF mobile bug. He was having antenna problems.  He asked me what was wrong. He was only grounded to bed. I had him go straight to frame.
He is delighted with his radio ops now.

73 N5UD
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K0BG
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« Reply #6 on: March 15, 2014, 06:50:33 AM »

What really needs to be done, is the bed bonded to the frame, and to the cab. Doing so all but eliminates any ground loop issues.

It also eliminates the need to run a ground from the antenna base to the frame. In fact, doing so often causes more issues than it solves.

Another additional item not mentioned here, is the need for a common mode choke near the bee of the antenna.
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HS0ZIB
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Posts: 424




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« Reply #7 on: March 18, 2014, 04:26:42 AM »

Just an update to say that I've ordered a 'Shorty I' screw-driver antenna.  This choice was based both on eHam reviews and (most importantly), the overall shipping length, since that dimension is often an issue with international mailing.
Jerry at Breedlove is customising his Scorpion fold-over base mount to fit the Shorty I...

Now all I need to do is to complete the purchase of the Mazda truck.... Smiley

Simon
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K4FMH
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Posts: 255




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« Reply #8 on: March 23, 2014, 11:13:55 AM »

Hi Alan,

Could you respond to my post? The current QEX has an article describing mobile antennas, including HF models. The conclusion is that the most metal underneath a screwdriver model with a capacitive effect is optimal. Would my idea of sheet metal in the truck bed with the screwdriver mounted in the center via a trailer mount perform this way?

Frank
K4FMH

What really needs to be done, is the bed bonded to the frame, and to the cab. Doing so all but eliminates any ground loop issues.

It also eliminates the need to run a ground from the antenna base to the frame. In fact, doing so often causes more issues than it solves.

Another additional item not mentioned here, is the need for a common mode choke near the bee of the antenna.
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N5UD
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« Reply #9 on: March 25, 2014, 07:12:18 PM »

Frank, I don't think the sheet metal idea will negate the need of bonding bed to frame. In some cases the cab is not bonded to frame. So bond it too.
Also use the common mode choke at base of antenna.

GL on the install.
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K0BG
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« Reply #10 on: March 26, 2014, 07:39:43 AM »

There are two things here some folks need to do some research on.

The comment about most of the radiation is from the whip, isn't exacting.

There are two reasons why bonding the bed to the frame and cab are important. Lining a bed with aluminum doesn't negate either one.
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