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Author Topic: I got a taste of Mobile HF, am hooked, and need your advice.  (Read 3542 times)
KD0MBL
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Posts: 9




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« on: August 11, 2010, 03:05:43 PM »

Hi guys,

I'm a noob to this forum and to Amateur Radio having just gotten my Tech in June and my General in July.

I have an FT-857D with separation kit installed in an 02 Avalanche.  I've been running some inexpensive mag mounts while I figured out a permanent solution.  

Recently I tagged along with the Colorado 14er event and operated from the summit of Pikes Peak.  It was a blast.  My mag mounts only covered 2m/440 and 10m so a local elmer and I threw together an inverted V dipole on bream buster to get me by on other HF bands.  

Long story short, I am now ready for a serious multi-band vertical for this truck.  I would like something that could be removed or tilted back somewhat easily.

Can I trouble you to offer your advice for such an application?  

I'd also like to throw in a scenario that I'm trying to plan for.  I'm considering adding a Yakima or Thule type base rack on the roof to mount two solar panels.  If these solar panels are roughly 5" above the roof, will this have a negative effect on an NMO antenna between them?  

In the solar panel scenario, I was wondering about using some sort of angle bracket to attach the antenna between and above the panels vs an NMO.  Thoughts?

For an idea of the size of the panels, check out the photo from Pike's Peak below.  The panels are angled on the back here, but I'm planning to move them straight forward and horizontal atop the roof onto the rack system I mentioned:

http://www.facebook.com/photo.php?pid=6254028&l=dcb8b5f948&id=663967017

I've been lurking for some time so I've read enough to be confident you guys will have some good advice!

-neal

KD0MoBiLe

EDIT:  To summarize, what antenna would you recommend?  What mounting system?  Would an NMO mount suffer from the solar panels?





































 
« Last Edit: August 11, 2010, 03:33:07 PM by Neal A. Tew » Logged
K0BG
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« Reply #1 on: August 11, 2010, 03:20:44 PM »

You'll probably never notice any degradation.

I used to live in the Denver, area (late 1973 through mid 2001), and I have operated from Pikes Peak. To be honest, it's fine for VHF roving, but FM operation leaves a lot to be desired. As for HF, it isn't any better than being down in Colorado Springs, except for a little bit better signals to the west. Travel to Fountain, and you'd never notice the difference.

You might want to visit my web site.

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AA4PB
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« Reply #2 on: August 11, 2010, 03:34:28 PM »

There are 4 major considerations in an HF mobile (in motion) antenna installation.

1) The efficiency of the antenna. Generally, larger antennas with bigger loading coils are more efficient.

2) How much "size" are you personally willing to tolorate in order to maximize efficency.

3) The antenna mounting location - check K0BG's web site for information.

4) How much money are you willing to invest in the antenna and the installation.
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KD0MBL
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« Reply #3 on: August 11, 2010, 03:40:48 PM »

You'll probably never notice any degradation.

I used to live in the Denver, area (late 1973 through mid 2001), and I have operated from Pikes Peak. To be honest, it's fine for VHF roving, but FM operation leaves a lot to be desired. As for HF, it isn't any better than being down in Colorado Springs, except for a little bit better signals to the west. Travel to Fountain, and you'd never notice the difference.

You might want to visit my web site.



Thanks, Alan.  I've already been on your website this afternoon and plan to spend more time there.  I appreciate the time and effort you've put into it. 

I made more HF contacts in 3 hours on Pike's Peak than considerably more hours from my home using the same and similar antennas.  The difference was either the elevation or simply the statement of my location.  Either way, it made a huge difference and I plan to do it again.  Grin

Is Scorpion your recommendation?  Wink
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KD0MBL
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« Reply #4 on: August 11, 2010, 04:21:13 PM »

There are 4 major considerations in an HF mobile (in motion) antenna installation.

1) The efficiency of the antenna. Generally, larger antennas with bigger loading coils are more efficient.

2) How much "size" are you personally willing to tolorate in order to maximize efficency.

3) The antenna mounting location - check K0BG's web site for information.

4) How much money are you willing to invest in the antenna and the installation.



Thanks so much for your response! 

In regards to #3, mounting location..........I was planning to mount in the center of the roof.  Many years ago when I installed mobile cell phones, the antenna manufacturers always recommended a center roof mount.  That is the one mounting solution that I can't find addressed on K0BG's web site.  Is the notion of a center roof mount being a favorable location actually a myth? 
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AA4PB
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« Reply #5 on: August 11, 2010, 06:30:25 PM »

I doubt that you can mount a multiband HF antenna in the center of the roof unless its one of the very short ones, in which case it will be very inefficient. The ground plane of the roof won't be of any benefit on HF and the added loss of the short antenna will give you a net loss.

Now if you are talking VHF/UHF then the roof center is a good spot.
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KD0MBL
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« Reply #6 on: August 12, 2010, 07:55:33 AM »

I doubt that you can mount a multiband HF antenna in the center of the roof unless its one of the very short ones, in which case it will be very inefficient. The ground plane of the roof won't be of any benefit on HF and the added loss of the short antenna will give you a net loss.

Now if you are talking VHF/UHF then the roof center is a good spot.


Do you see any obvious downsides to mounting to a roof rack like the first picture in the thread below (but without all the bike mounting hardware):

http://www.chevyavalanchefanclub.com/cafcna/index.php/topic,94316.0.html
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AA4PB
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« Reply #7 on: August 12, 2010, 08:08:02 AM »

What kind of antenna are you considering? Antennas need a good RF ground connection to the vehicle. Mounting to roof racks generally prevent that by requiring that you run a ground lead of some length between the antenna and the vehicle.

When you talk about a "good" multiband HF antenna suitable for mobile in motion I think in terms of one of the big screwdriver antennas mounted to a custom bracket welded to the frame of the vehicle. Again, take a look at K0BG.com for some example pictures.

If you are thinking in terms of getting one of the really short screwdrivers and clamping it to the roof rack, it'll work "okay" on the higher bands (20/15/10M) but won't be very good on the lower bands (40/75M).
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WX7G
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« Reply #8 on: August 12, 2010, 07:02:05 PM »

The solar panels may affect the VSWR of the VHF/UHF antenna mounted between them. You will have to install it and measure the VSWR.

A short mobile antenna - such as the coil and stinger only of a Hustler RM "resonator" - can work well when mounted high on the vehicle. I use such an antenna on 40 meters. They can work well because the vertical dimension of the vehicle is part of the radiating antenna and is actually the main antenna. Mounting the short antenna near the edge of the vehical roof is best as it maximizes the antenna current along the vertical surface of the vehicle.

For 20-10 meters my measurements and simulations show the Hamstick performing essentially as well as a comparable length screwdriver. On 40 meters I measure a 3 dB difference with the screwdriver being better.
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KD0MBL
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« Reply #9 on: August 17, 2010, 10:33:51 AM »

The solar panels may affect the VSWR of the VHF/UHF antenna mounted between them. You will have to install it and measure the VSWR.
 

If the VSWR is adversely affected, would raising the VHF/UHF antenna mount to the level of the panels be a viable option?
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W5LZ
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Posts: 477




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« Reply #10 on: August 17, 2010, 11:27:23 PM »

There are lots of consideration when picking a mobile HF antenna.  In general, the bigger and the uglier the antenna the better it will be (within reason).  I've found that a 'Scorpion' is a very nice antenna.  It's well made and is at least as efficient as any other screwdriver type antenna (besides, it's prettier!).  The only real benefit to a screwdriver antenna is convenience (which is very nice!).
 - 'Doc
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VE3XKD
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« Reply #11 on: August 18, 2010, 06:23:48 PM »

Hi

I have a Hi-Q 3.5 short HF screwdriver centre-mounted on the roof of my Toyota Prius hybrid for the past two years. I find the installation works really well and I consistently get good signal reports. Monday evening  I worked the Azors on 20, and I generally have no problems working Europe. While roof mounting cuts down the length of the whip by several feet, and thus impacts efficiency, particularly for the low bands, I was able to add a Capacity hat and I manage to do fine on 80 meters. The problem with roof mounting is being able to re-enforce the roof so that the antenna will be sturdy. I managed, but it was a bit of effort.

Enjoy!

John VE3XKD
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KD0MBL
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« Reply #12 on: August 18, 2010, 06:51:52 PM »

Hi

I have a Hi-Q 3.5 short HF screwdriver centre-mounted on the roof of my Toyota Prius hybrid for the past two years.

John,

Thanks for the info! 

How long is your mast?  Did you shorten it or order it that way?

-neal
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