Amateur (Ham) Radio BS and Callsign Thread!

It will be a vehicle system, but im experimenting with mounting the antenna on a 2.5' aluminum mast that will be raised via pneumatic cylinder. My worry is that with the Larsen 5/8 wave, where its longer, when I hit bumps it tends to flex much more and transfer the energy down the mast, where a short 1/4 wave wouldn't flex as much. I really just need to build the thing and see what happens, but I was just curious as to what type of difference in performance I might experience when going with a shorter 1/4 wave.

 

If you mast mount the antenna you will lose your ground plane and will cut the performance of the antenna. They do make ground plane independent antennas, that you could look into

 

A 5/8 wave antenna is not as dependent on a ground plane as 1/2 or 1/4. So a mass mount would be fine. If he wanted to put radials on it to help the ground plane than he could, but they would be very exposed to being damaged on the trail.

 

I was wondering about the ground plane with this. The mast will extend up where the antenna base would be above the cab and the mast about 6" back from the rear window. IThe mast will be aluminum so I had planned on grounding the mast to the body really well. Would this help the ground plane?

 

Could make a set of ground plane radials like previously mentioned.

http://www.csgnetwork.com/antennagpcalc.html


http://www.antenna-theory.com/tutorial/smith/chart.php

 

grounding the antenna and ground plane are two different things. Ground plane is the metal around the antenna base, like if you mounted it in the middle of your roof. a 1/4 wave MUST have have an awesome ground plane, a 1/2 wave needs one, but a 5/8 or or 7/8 wave don't need one.

I was on a Net about portable antennas last night. This topic came up.

 

Thanks, I'll look into it. Not sure what I can fit just yet.

 

Interesting stuff I was hoping this was the case and I could get away with a mast one way or another, im kind of obsessed with the project now. I was Looking at these door-jam type mounts, like on SUV's where they bolt into the trunk lip but are not flat on a metal plane, like this one:



Would these normally be used with 5/8+ wave? In this example it looks like he has the same 5/8 larsen there. Even if I have to beef up the mast system to carry a 5/8 through the bumps I will. I just want to optimize the design for the best reception without it being on the plane of the roof. I had heard tale that 1/2 wave seems to be what many ppl use for motorcycle rigs, but then others say 5/8. I guess another idea would be to make retractable/foldable radials, of course then the engineering nightmare grows

 

I like you project. I think the debate over 1/2 or 5/8 wave depends on were you live/will be using it. Some people can get away with a 1/2 wave all day long and other needs the properties of 5/8 wave.

I am installing a bed bar and putting a 5/8 waves antenna on it. That will work best for me. I currently have a 1/4 wave mag mount on my roof, but I am going to use that for APRS in the future.

The radial angle changes with the different lengths. One is better for flat areas and another works better for mountain areas. With radials on a 5/8 waves antenna it will work like a rock star over any 1/4 or 1/2 wave. Maybe get an antenna with the options to put radials on it. Run without most of them time and if you find yourself unable to communicate, than you pull out a bag and put the radials on.

I am sure there is someone smarter than me that can chime in on this topic. Maybe post up on 4x4ham.com or offroadham.com

Keep us posted on this project!

 

Cool stuff & thanks for the info/links. I will definitely post some pics/video once I figure this thing out, hopefully it will work like a precision James Bond device. That's the vision anyway. I emailed Larsen about my 2/70B and they replied:
[FONT=&quot]The

$104 NMO2/70B Pulse Larsen 144-148/440-450 MHz Dual Band 37.25" Antenna - Black

NMO2/70B isn’t Ground Plane independent.[/FONT]
[FONT=&quot]Thanks![/FONT]

Sooo I may need to go with something like the

$59 Comet SBB-5NMO SBB-5 SBB5 Comet Original 146/446 MHz Dual Band Mobile Antenna

Comet SBB-5NMO which seems to get good reviews without a ground plane. Luckily there are a lot of repeaters around so hopefully I can make something work. The hardest part will be figuring out some way to mechanically lock/unlock the mast in place if the air pressure is not enough to hold it erect.

 

http://metalschnitzel.com/RoboMast/Robomast.htm

Or use a couple of wheels and an RC type control to extend and retract the mast. I saw a video of a couple of kids that built a reverse thing like that. It was a HF antenna designed to climb up light poles.

So many ways you could go with this. Did I miss why you want a retractable antenna?

 

That's unfortunate about the MURS channels being used in that way. Did you know that Walmart uses them? Although I've only heard walmart personnel on the wideband channels (4+5). Just this last weekend, I led a caravan from San Diego to Joshua Tree and we used MURS channel 1 the whole way. Two watt HT's, DCS turned on. They worked great!

I know projects can be fun and I don't want to dampen your exuberance, but I fail to see the point of using such a short mast on a mobile install. It's one thing if the mast extends your range by say 20-30 miles, but I would wager that it will probably do almost nothing for you and maybe even make things worse. If it were me I'd just mount that Larsen on the roof and call it good! All mobile installs are a series of compromises and you just have to make the best choices you can given the circumstances.

Now, where masts make a lot of sense is in portable installs. Such as this one:



Portable 2M mast to extend range.

 

You can't have a duel band antenna with a 1/4 wave on either band.

 

I know projects can be fun and I don't want to dampen your exuberance, but I fail to see the point of using such a short mast on a mobile install. It's one thing if the mast extends your range by say 20-30 miles, but I would wager that it will probably do almost nothing for you and maybe even make things worse. If it were me I'd just mount that Larsen on the roof and call it good! All mobile installs are a series of compromises and you just have to make the best choices you can given the circumstances.

Now, where masts make a lot of sense is in portable installs. Such as this one:



Portable 2M mast to extend range.[/QUOTE]

Yes. And please note the radials.

 

Hmmm I seem to missing something here...

http://www.diamondantenna.net/nr72bnmo.html

 

So, basically the idea of the mast I have in my mind.. would be not to raise the antenna to an advantage elevation, but just to get it above the metal shield of the cab, to that of a roof-mount antenna. The reasoning behind the retractable design... is that I work in a building where I drive under a 7ft ceiling of a parking garage daily. These limitations sparked my mind to build a (cab controllable) retraction-mast design that I have never seen ever.

It's hard to explain now without uploading drawings, but those might (who knows) be proprietary one day. I know this can work, I just need to select the right antenna that can ride..and still perform on this aluminum member I call a mast.

So other than the parking garage, I do like the look of my truck without a permanent antenna. This design will be tactically hidden 2 inches below the bed wall. And this is just another excuse to use a pneumatic system to make something I love even more awesome. Basically.

 

That is a 1/2 over 1/4 with a matching coil.

 

i'm out in Indio on top of Chuckwalla mountain- I wanna test out my new ham radio
can someone jump on
McGilvry
157.545 and say hello? I wanna see the range of my setup

 

Like to listen to pagers do ya?

 

Had the set screws back out on my NMO Larsen 150B somewhere on a trail in Montana..

Scored a Larsen 2/70C w/ NMO kit for $15 in Bozeman! She basically said, "Well, I don't know what this is, how about $15?"

Werd!

Going to be out in Yellowstone, there should be an IRLP node nearby..