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KC9LWC
06-07-2008, 05:49 AM
Well here is my dilemma ...

I am a poor college student and buying a $100 mobile antenna is a real stretch for me. So I have been thinking how I can get by with a fantastic antenna and save myself some money. The terrain in my portion of the state is rather rough, and with storm spotting a solid signal is a real nice thing to have. I have a homebrew j-pole built from 1/2 inch diameter copper pipe, 58 inches w/ 19 inch tuning stub. The 'mounting post' on the bottom is 11 inches long, this is the copper pipe which falls below the tuning stub. The J-pole is 1.2:1 or less through out the 2 meter band. Now to the punch line.

I want to mount it for mobile operations. I have heard recommendations of a bumper mount of some kind or perhaps I could find some mount to put it on the trunk lid.

A goofy looking antenna? YES! A stout performer? YES!


Let's hear your thoughts on this..

SWR issues with it being near the trunk?

Performance vs. 5/8 wave mag mount or trunk lid mount

Ways to mount it, mount ideas?????

73s all --- have fun with this one :D

KD5QFL
06-07-2008, 06:21 AM
LWC, I have a copper j-pole at the house and a Tram 5/8($20) on a fender mount.
The J-pole is 3X the height of the 5/8 and the 5/8 outperforms the j-pole by a wide margin. There's quite a few stations/repeaters that I can hear on the mobile that I can't hear on the J-pole.

In fact, I'm thinking about setting a 5/8 as a base antenna and delegate the j-pole to the parts pile.

Will

p.s. I'm not sure, but I believe the J-pole has the same gain as a dipole whilst the 5/8 has 3dB gain.

WA9SVD
06-07-2008, 10:02 AM
Well here is my dilemma ...

I am a poor college student and buying a $100 mobile antenna is a real stretch for me. So I have been thinking how I can get by with a fantastic antenna and save myself some money. The terrain in my portion of the state is rather rough, and with storm spotting a solid signal is a real nice thing to have. I have a homebrew j-pole built from 1/2 inch diameter copper pipe, 58 inches w/ 19 inch tuning stub. The 'mounting post' on the bottom is 11 inches long, this is the copper pipe which falls below the tuning stub. The J-pole is 1.2:1 or less through out the 2 meter band. Now to the punch line.

I want to mount it for mobile operations. I have heard recommendations of a bumper mount of some kind or perhaps I could find some mount to put it on the trunk lid.

A goofy looking antenna? YES! A stout performer? YES!


Let's hear your thoughts on this..

SWR issues with it being near the trunk?

Performance vs. 5/8 wave mag mount or trunk lid mount

Ways to mount it, mount ideas?????

73s all --- have fun with this one :D



Sorry, old man... the monicker started before Amateur Radio with landline telegraphers. It's not, and never was meant, to refer to or imply a person's chronological age. (Besides, "young squirt" takes WAY too long to send via CW!) Similarly, a female operator is typically referred to as a "YL," and although a female operator may be somebody's 80 year old grandmother, you had BETTER call her a "YL" or your career in Amateur could well be cut short by an irate, ummm... let me phrase this properly... "YL!"

The J-Pole is NOT a "magic antenna." And a "copper cactus" construction made with copper plumbing materials is WAY too heavy to use in a typical mobile installation, the mounting of an antenna of that weight is unwieldy to say the least.

A quarter wave whip, mounted as high as possible on the vehicle would probably outperform the J-pole, as would a 5/8 wave. Any bumper mount (of particularly the J-Pole) would severely distort the radiation pattern.

N5USR
06-07-2008, 10:38 AM
I knew a couple of people in college who used a J-pole mobile, but they used stainless steel whips and some spacer blocks to make the whole thing so it would be MUCH lighter and flexible as well. By the time you get the copper one mounted high enough to clear the metal of the vehicle, I can guarantee you WILL hit something, and it's not going to give - something will break!

You mention rugged terrain, if it's quite hilly then a quarter wave would probably do best for you. If you have relatively flat terrain as I do here, then a 5/8 wave gets a bit of gain to the horizon, at the expense of higher angles. Either one mounted in the center of the roof would be about as good as you can hope for, I think.

FWIW, I find J-poles work quite well. I've certainly read plenty of people saying they are junk, but the ones I made performed nicely. No, nothing "magical", certainly the 17 foot repeater antenna I have now beats it handily, but still good. There are quite a few different designs out there, perhaps some aren't as good as others, I don't know.

W4HAY
06-07-2008, 12:32 PM
Shop around. I live in the mountains and have always used those $20 quarter-wave roof-top mag-mounts. The lower radiation angle of a 5/8 wave can actually work against you, sending a larger portion of your signal into the hillside.

W4INF
06-07-2008, 12:43 PM
Ive got two of these and works great. Not as good as a real grounded NMO, but... easy solution and works FB.

http://cgi.ebay.com/DUAL-BAND-2-Meter-440-MAG-MOUNT-ANTENNA_W0QQitemZ200228912391QQihZ010QQcategoryZ46 72QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

It COULD get you by until your brave enough to drill a 3/4 roof hole.

http://cgi.ebay.com/Dual-Band-Mobile-Antenna-NMO-mount-5dB-gain-2-meter-440_W0QQitemZ350065865923QQihZ022QQcategoryZ4672QQ ssPageNameZWDVWQQrdZ1QQcmdZViewItem

http://cgi.ebay.com/2M-440-Dual-Band-High-Gain-Mobile-Antenna-NMO-UV-325_W0QQitemZ310056309472QQihZ021QQcategoryZ4672QQ ssPageNameZWDVWQQrdZ1QQcmdZViewItem

http://cgi.ebay.com/DUAL-BAND-VHF-UHF-144-148-430-450MHz-NMO-ANTENNA_W0QQitemZ310049263411QQihZ021QQcategoryZ46 72QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

Coax and NMO mount
http://cgi.ebay.com/ANTENNA-NMO-COAX-KIT-MOBILE-3-4-HOLE-UHF-VHF-RG-58-HAM_W0QQitemZ200229020192QQihZ010QQcategoryZ53107Q QssPageNameZWDVWQQrdZ1QQcmdZViewItem

http://cgi.ebay.com/NMO-Mount-and-coax-17ft-of-RG-58-Solid-Brass-NMO-NEW_W0QQitemZ200229564874QQihZ010QQcategoryZ53107Q QrdZ1QQssPageNameZWD1VQQcmdZViewItem

On the bottom of the NMO brass ring, there is a groove in which a rubber o-ring sits. These kits (Non-moto) do not include it, but use a dab of silicon grease on the ring to let it slip as you tighten it down, else it could bind and break.



HTH,
Andrew

W5DXP
06-07-2008, 12:44 PM
I am a poor college student and buying a $100 mobile antenna is a real stretch for me.

Find a hamfest and get a used one for $10. Or buy one new from MFJ for $20. A 19" whip (what I use) is all you need for 2m. Find a ham club or an elmer and probably get one for free.

AK7V
06-07-2008, 02:29 PM
Someone will correct me if I'm wrong, but I believe the J-pole has a pretty low radiation angle. It might not be ideal with your terrain.

You can make a quarter wave whip (or buy one) for probably $20 which will have a higher radiation angle. A 5/8ths wave whip will be lower than the 1/4. Are you trying to hit mountain top repeaters?

In some situations, a 1/4 wave will work better than a 5/8 or a J-pole. And they're simple, easy to drive with, and cheap. After that, I'd go with a 5/8. I don't really see the point of a mobile J-pole.

K8JD
06-07-2008, 03:12 PM
I agree that the quarterwave with a NMO style base is the more economical way to start out. Getting a used one at a hamfest or thru your local radio club meeting should be easier then buying nickle and dime hardware to try to mount a jaypole on your bumper, that may end up costing you that hundred bucks when you are done.
You will be able to find a used 5/8 base coil and whip later if you want to try the extra gain, just unscrew the quarterwave and screw on the 5/8 wave ant.

KA9VQF
06-07-2008, 06:53 PM
Over the years I have built a lot of J-pole antenna.

I use a 300 ohm TV tape J-pole that is taped to a stick and leaning in the corner most every day with my hand held rig here in my living room

A while back now a friend managed to break his snazzy Shakespeare marine mobile antenna on his boat. He didn’t want to pay the price for a new one so he talked me into building a J-pole out of TV tape, cut for the marine band of course.

I put the thing inside some PVC pipe and attached it to the fold down antenna mount that I talked him into buying for his boat.

It still cost him a few bucks but so far he hasn’t managed to break the home brew antenna. There were some real head scratching moments while I was trying to figure out how to attach the PVC with the J-pole inside to the new mount but somehow we managed.

WD8OQX
06-08-2008, 12:34 AM
When I first got into Ham Radio, I too, had a tight budget. (still do) & what I used was the whip off an old discarded CB antenna cut to 1/4 wave. I soldered it into a PL-259 & screwed this into an SO-239 I made a mount out of. Worked great & an amp cured the "fringe" problems if needed. (rarely did) - I still use this method today, especially for those "emergency" antennas. It also has the added benefit of being quick to make - if the tools are available & one can be resourceful on the mount.

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