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mobile antenna to base !
- Thread starter stathis
- Start date
Like Beetle is fond of saying, "Determine this by experimenting. No two installations will EVER be identical."
Sorry, couldn't resist.
I think the most common and cheapest is the top load, but I would try base loaded.
I knew that was coming, binrat! But it will get really expensive comparing them all.
I, too, am leaning toward base loaded, mostly because there will be far less weight toward the ends of the antennas reducing sag and stress on the mounts.
Oh, and I've edited my original post to included one more:
center loaded.
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I think it would come down to whats is readily available and how much $$ you want to spend. It would be good to have the antennas adjustable. I have a personal preference for the Wilson Silverloads, but that's just me.
Am giving some thought to the Radio Shack Model 21-988.
Base loaded, 64" long, and gets crazy good reviews.
These would also make for a pretty stealthy antenna (something I need).
http://www.radioshack.com/product/index.jsp?productId=2102661#inTheBox
Anyone else have a thought on my original question?
When using two mobile antennas for a "hamstick" type dipole, is it best to use antennas that are:
a. base loaded
b. top loaded
c. center loaded
d. continuously loaded
Base loaded, 64" long, and gets crazy good reviews.
These would also make for a pretty stealthy antenna (something I need).
http://www.radioshack.com/product/index.jsp?productId=2102661#inTheBox
Anyone else have a thought on my original question?
When using two mobile antennas for a "hamstick" type dipole, is it best to use antennas that are:
a. base loaded
b. top loaded
c. center loaded
d. continuously loaded
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It can be a loaded question, plus where to load an antenna has been discussed before, including earlier today in another thread in the same section of this forum three hours before you posted your question the first time... I always recommend search, there is a ton of information on this forum, more than you ever knew you wanted to know...
In the realm of theory, moving the coil towards the tip will make it more efficient. That being said there is also a cost for moving the coil away from the feedpoint.
A coil is a current based device, and is the most effective where there is the most current. The feedpoint, in the case of your dipole, and in the case of mobile antennas, is the point where this current is the strongest. If you move the coil away from the feedpoint, there is less current for it to work with, which has the effect of making it more efficient, but also has the effect of making the coil less effective. To get the same amount of shortening further up the antenna, the coil needs to be larger. The problem with that is a larger coil will be less efficient than a smaller coil, so for a given antenna length, you end up with close to the same losses to efficiency.
In the real world, take your pick, you won't notice the difference between any of those...
Of course, the best option, if possible, is to use full length whips, but that wasn't the question...
The DB
I always recommend search, there is a ton of information on this forum, more than you ever knew you wanted to know...In the realm of theory, moving the coil towards the tip will make it more efficient. That being said there is also a cost for moving the coil away from the feedpoint.
A coil is a current based device, and is the most effective where there is the most current. The feedpoint, in the case of your dipole, and in the case of mobile antennas, is the point where this current is the strongest. If you move the coil away from the feedpoint, there is less current for it to work with, which has the effect of making it more efficient, but also has the effect of making the coil less effective. To get the same amount of shortening further up the antenna, the coil needs to be larger. The problem with that is a larger coil will be less efficient than a smaller coil, so for a given antenna length, you end up with close to the same losses to efficiency.
In the real world, take your pick, you won't notice the difference between any of those...
Of course, the best option, if possible, is to use full length whips, but that wasn't the question...
The DB
It appears no one has an opinion, or I have been blackballed for asking too many crazy questions.
My apologies if it's the latter.
1. I was waiting for somebody who knows what they're talking about
2. I was wondering if they were going to do to you like they did me in that I ended up having to do my own research.
Still here with ya!
Not a problem, wasn't blackballing you, but I can't monitor these forums every second of every day... Sometimes it takes a day or two to get an answer, but you will typically get an answer.
The DB
In my experience best way to get good performance out a base antenna is to make up an L shaped bracket, drilled with 4 holes for u bolts to mast mount it, Drill a 13mm hole to mount a sirio so239/DV type mount or whatever antenna you choose, then get 3 or 4 copper insulation coated wires 108" each,
Attach wires to corners of plate or one of the u bolts and use non conductive wires to guy them.mount to a 1,5" 35mm mast or 2" 50.8mm or anywhere in between, either 6m or more ground mounted, 4 meter or more building mounted or at least 2m chimney mounted.
set antenna for best swr and spread wires at equal spacing either 90 or 120 degree's depending if you use 4 or 3 and slope them around 35-45 degrees downward,
once you have best swr on antenna you may or may not have to trim groundplane wires to get swr lower, at 35/45 degrees a 1.0:1 swr should be achieveable no matter which antenna you choose, Obviously a 108" whip would be best, 102" is too short and will resonate at high end of 10m not 11m where you want it, 106" is closer depending on what band/s you want to cover.
I'd sugggest a 108" steel whip (preferrrably 2 piece tuneable one), sirio hp4000,megawatt 4000,performer 5000 or modultor/red devil type antennas or even a 7ft firestick if you can find one as top radiator, the long er the better, once you go shorter than about 5ft you start losing performance fast.
You have just built a 1/4 wave ground plane with full size/reduced radiator, one of the most underrated antennas in the world as any starduster owner will tell you. It can be built for pennies and all parts can be bought on e bay, will work as well as most commercial 1/4 wave ground planes and will easily cover the distance you want if mounted high enough, The higher the better, will also easily work dx skywave and isn't the most visible antenna in the world. Power handling will be limited by the mobile antenna you choose and coax,
a sirio starduster m400 is a good modern commercial version, a clone of the original antenna specialists starduster m400. And reasonably cheap.
Attach wires to corners of plate or one of the u bolts and use non conductive wires to guy them.mount to a 1,5" 35mm mast or 2" 50.8mm or anywhere in between, either 6m or more ground mounted, 4 meter or more building mounted or at least 2m chimney mounted.
set antenna for best swr and spread wires at equal spacing either 90 or 120 degree's depending if you use 4 or 3 and slope them around 35-45 degrees downward,
once you have best swr on antenna you may or may not have to trim groundplane wires to get swr lower, at 35/45 degrees a 1.0:1 swr should be achieveable no matter which antenna you choose, Obviously a 108" whip would be best, 102" is too short and will resonate at high end of 10m not 11m where you want it, 106" is closer depending on what band/s you want to cover.
I'd sugggest a 108" steel whip (preferrrably 2 piece tuneable one), sirio hp4000,megawatt 4000,performer 5000 or modultor/red devil type antennas or even a 7ft firestick if you can find one as top radiator, the long er the better, once you go shorter than about 5ft you start losing performance fast.
You have just built a 1/4 wave ground plane with full size/reduced radiator, one of the most underrated antennas in the world as any starduster owner will tell you. It can be built for pennies and all parts can be bought on e bay, will work as well as most commercial 1/4 wave ground planes and will easily cover the distance you want if mounted high enough, The higher the better, will also easily work dx skywave and isn't the most visible antenna in the world. Power handling will be limited by the mobile antenna you choose and coax,
a sirio starduster m400 is a good modern commercial version, a clone of the original antenna specialists starduster m400. And reasonably cheap.
jazzsinger, thanks for the info.
My problem is that I am limited to a 15' mast (wife and neighbors). My house eave is 10' and the roof is steeply pitched. As much as I'd love the antenna you describe (or a M400), there's room for only a single 108" radial slanted downward away from the house at 45 degrees. The roof is in the way of the others.
I think for the time being I am just going to stick with my Firestik dipole although I might replace the two 4' Firestiks with a couple of Radio Shack Model 21-988 antennas. This would increase the overall length by 32 inches and be even more stealthy than the Firestiks.
My problem is that I am limited to a 15' mast (wife and neighbors). My house eave is 10' and the roof is steeply pitched. As much as I'd love the antenna you describe (or a M400), there's room for only a single 108" radial slanted downward away from the house at 45 degrees. The roof is in the way of the others.
I think for the time being I am just going to stick with my Firestik dipole although I might replace the two 4' Firestiks with a couple of Radio Shack Model 21-988 antennas. This would increase the overall length by 32 inches and be even more stealthy than the Firestiks.
Not sure which forum to post this in and I know it's been discussed before, but here goes:
With all the talk about what angle ground plane radials should be pointed at (40-45 degrees seems to be the favorite), mobile antennas are mounted on vehicles in all sorts of places (roof, trunk, bumper, truck beds, hood, etc.) Flat surfaces. Vertical surfaces. And everything in between. Resulting, I'm guessing, in all sorts of impedances yet most seem to work fine. How's that?
With all the talk about what angle ground plane radials should be pointed at (40-45 degrees seems to be the favorite), mobile antennas are mounted on vehicles in all sorts of places (roof, trunk, bumper, truck beds, hood, etc.) Flat surfaces. Vertical surfaces. And everything in between. Resulting, I'm guessing, in all sorts of impedances yet most seem to work fine. How's that?
Never received a reply to this question so will try again.
There is much talk about what angle ground plane radials should be slanted at (40-45 degrees seems to be the favorite) however, mobile antennas are mounted on vehicles in all sorts of places (roof, trunk, bumper, truck beds, hood, etc.) Flat surfaces. Vertical surfaces. And everything in between. Yet they typically work fine. How's that?
There is much talk about what angle ground plane radials should be slanted at (40-45 degrees seems to be the favorite) however, mobile antennas are mounted on vehicles in all sorts of places (roof, trunk, bumper, truck beds, hood, etc.) Flat surfaces. Vertical surfaces. And everything in between. Yet they typically work fine. How's that?