sirio makes a 1/2 wave dipole that can be mounted verticle or horizonal
that would be my pick for your situation
that would be my pick for your situation
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mobile antenna to base !
- Thread starter stathis
- Start date
If the antenna is mounted far enough above the earth, approximately 45 degrees will provide a near perfect SWR match, if that is what you are seeking. Many people mistakenly presume that a lower SWR automagically means better performance.
Using modeling (I know, many people don't trust modeling at all..) as you start with horizontal radials and angle them down the antenna's gain goes up. This continues until the radials are at about 15 degrees or so off of vertical, then continuing past that point and gain begins to drop again as the radials approach horizontal. All that being said, the change in overall reported gains at any angle of the radials is so small you will never notice it. Getting the antenna higher, even a mere 10 feet (assuming that the antenna is less than 100 feet off the ground to begin with), will have more of an increase in gain than any change of radial angle.
I want to note here that the models and description used above is meant for 1/4 wavelength antennas, and do not apply to the radials of a 5/8 wavelength antenna, which angling down will actually be counterproductive...
When it comes to mobile antennas, most actually perform poorly compared to base antennas, and this is the case for several reasons. Very few vehicles provide an adequate "other half". To further complicate this very few people have taken steps such as RF bonding to allow the vehicle's body to perform as well as it can as the antenna's other half. You also have the proximity of the antenna to earth compared to most base antennas, in general, the closer your antenna is to the earth the more of the radiation from that antenna will be lost to heat, which also affects performance. This is only one aspect of why people accurately say that "height is might" when talking about antenna performance.
In reality, there really is no comparison between a mobile antenna mounted on a vehicle and a base antenna mounted, say 30 feet in the air. If the base antenna mounted that high only performs about the same as a mobile antenna then you have a problem with the antenna system that needs to be looked at...
The DB
Thanks for replying, Hotrod, but I think you misunderstood my question. What I'm wondering about is this: If mobile antennas can be mounted on nearly any surface and still work good, why is the angle of the radials on a ground plane base antenna critical?
Still not sure I worded that right.
Okay, DB. Got it. Although someone's mobile antenna might be performing "GREAT", it's really not doing all that well in actuality.
What about this: What angle should the radials be slanted for a ground plane using a fiberglass mobile antenna (i.e. Firestik) for the vertical element? Does it differ from one using a 1/4 wave steel whip?
What about this: What angle should the radials be slanted for a ground plane using a fiberglass mobile antenna (i.e. Firestik) for the vertical element? Does it differ from one using a 1/4 wave steel whip?
No real difference. The radial angles will have essentially the same effect on a shortened antenna as it will with a full sized antenna. One difference will be the angle of lowest SWR, but as I mentioned above, that really isn't something to be overly concerned with.
If you are curious, a loaded antenna will generally require the radials to be closer to vertical for an equivalent SWR match. This has to do with how a coil shortens the antenna. That being said, sometimes there are exceptions (some base loaded antennas have a built in circuit to counter this effect on SWR.)
The DB
As of yesterday, the IMAX came down (for simple maintenance) and I'm using the Workman hub with 4 - 102" whips for a Starduster type base antenna. I'm looking forward to talking to the locals and getting some anecdotal comparisons.
Are you using another 102" whip for the vertical element?
Let us know how it works, Rick.
Yes.
The Workman hub calls for three downward sloping radials. I'm using three of the Radio Shack 102" stainless steel whips. For the vertical radiator, I'm using an old Radio Shack fiberglass 102" whip. SWRs are around 1.28 on channel 40 but over 2 on channel 1. I'll need to add a spring to lengthen the vertical radiator and bring down the SWR on the lower end of the band.
Dang. That R/S fiberglass whip must be old! I don't even remember them making one that long. But that oughta work good!
It definitely is over 20 years old.
I took it off my boat, which is 20 years old. In 1995, I mounted a Radio Shack/Archer marine CB antenna, #21-976, that I purchased in March of 1994. The Radio Shack/Archer antenna came with a 4' whip. This fiberglass 102" whip that I am using now had been sitting in my garage a few years when I hooked it up to replace the stock 4' job. The fiberglass 102" came from an earlier version of the same Radio Shack marine CB antenna. The later version used the same hub, mount and coax, but replaced the fiberglass 102" whip with a 4' version.
I wrap my fiberglass antennas in automotive loom. The loom - not the fiberglass antenna - takes the UV rays and the punishment from the weather and the elements instead of the antenna. As a result, my fiberglass antennas tend to last me forever. At a different location, I have an old Radio Shack/Archer 1/2 wave fiberglass "Crossbow" base antenna. It is basically a blue Shakespeare Big Stick. It has been up and running for about 30 years now.
I took it off my boat, which is 20 years old. In 1995, I mounted a Radio Shack/Archer marine CB antenna, #21-976, that I purchased in March of 1994. The Radio Shack/Archer antenna came with a 4' whip. This fiberglass 102" whip that I am using now had been sitting in my garage a few years when I hooked it up to replace the stock 4' job. The fiberglass 102" came from an earlier version of the same Radio Shack marine CB antenna. The later version used the same hub, mount and coax, but replaced the fiberglass 102" whip with a 4' version.
I wrap my fiberglass antennas in automotive loom. The loom - not the fiberglass antenna - takes the UV rays and the punishment from the weather and the elements instead of the antenna. As a result, my fiberglass antennas tend to last me forever. At a different location, I have an old Radio Shack/Archer 1/2 wave fiberglass "Crossbow" base antenna. It is basically a blue Shakespeare Big Stick. It has been up and running for about 30 years now.
I brought the antenna down and added a heavy duty, Workman KA52 stainless steel spring. Here in South Florida, stainless steel over chrome is essential. With these few inches of added length, my SWR now runs from a low on channel 40 of 1.33 to a high on channel 1 of 1.51 across the 11 meter CB band - very respectable.
The ears when using this antenna are every bit as sensitive as when using my IMAX 2000. Unfortunately, I have not had enough local traffic recently to compare the two when it comes to getting out.
The ears when using this antenna are every bit as sensitive as when using my IMAX 2000. Unfortunately, I have not had enough local traffic recently to compare the two when it comes to getting out.
I bought 3 of them from Eagle1com.com. I don't remember where I bought the fourth, but it was from an internet amateur radio business.
They sell it as the "Workman 6hub." It screws onto standard thread 1" plumbing pipe. I'm using the standard Home Depot special, galvanized pipe which I protected just a bit further by giving it two coats of Rust-o-leum spray paint. I then bought stainless steel everything else - including Allen screws.
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