22 Inch shaft with Comp Coil and it mounted on top of the car should do you nicley
the 17 inch shaft will have you in a 1.2 to 1.3 swr
the 22 should be flat
the 17 inch shaft will have you in a 1.2 to 1.3 swr
the 22 should be flat
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Predator 10k vs shaft length
- Thread starter sp5it
- Start date
sp5it, my 17" tunes out flat 1:1 on my roof mount. Maybe you can buy both shaft along with the 10K and try them out. Dont get the comp coils just get the Reg 10k.
James. 1-5
James. 1-5
IMO- the 17" shaft is the best compromise for roof mounting...It tunes good, and you don't have 3' of aluminum rod sticking up begging for a tree branch to come along and whack...
Mirror bracket mounting? I would go with the 12"...
And I still stand behind what I posted back in 2011 in the earlier post..."the 17" lower shaft works just fine on roof tops..."
I have used the 27" and 22" shafts before on the roof of my Suburban, and they do tend to tune a bit lower on a MFJ 259b analyzer...But eventually this is what will happen to one with the longer shafts.
Just takes one good hit, and they will snap at the base everytime...By the way, I have 3 more shafts that look just like this one...
Those 10K's are a nice antenna...
I used to run the 27" shaft and single coil on my toolbox I had in my truck, and it was easy getting the antenna tuned as well, only thing was it did hit the trees been on the back side of my toolbox, but it did out perform the 102" ss whip I used to run..
But the 10k is a nice antenna for the money..
I used to run the 27" shaft and single coil on my toolbox I had in my truck, and it was easy getting the antenna tuned as well, only thing was it did hit the trees been on the back side of my toolbox, but it did out perform the 102" ss whip I used to run..
But the 10k is a nice antenna for the money..
I recommend to anyone the 27" shaft if you have room to mount it, if not go for the 22" shaft. Out of all of the shaft lengths I have used, these two tune the best when using the MFJ.
Long ago there was a some testing done with the 10K antennas and the 22" shaft and 27" shaft came out on top of the list, I do not know if anyone here remembers because it was so long ago.
Jessie I have yet to break one, maybe I have just been lucky.
I also agree with what 15 posted, don't get the comp coils just get the Reg 10k, there is no need to spend more money on the larger coil.
You ALWAYS want to get the coil above the roofline of the vehicle if at all possible .
73
Jeff
Long ago there was a some testing done with the 10K antennas and the 22" shaft and 27" shaft came out on top of the list, I do not know if anyone here remembers because it was so long ago.
Jessie I have yet to break one, maybe I have just been lucky.
I also agree with what 15 posted, don't get the comp coils just get the Reg 10k, there is no need to spend more money on the larger coil.
You ALWAYS want to get the coil above the roofline of the vehicle if at all possible .
73
Jeff
The longer shaft everytime, not that I own a Predator, now here's the thing, the closer the coil is to the vehicle bodywork the less efficient the coil is, this is due to greater capacitive coupling of the coil to the vehicle body, however when you raise the coil away from the car body it's efficiency increases, but that's not all.
Because the coil efficiency increases, due to less capacitive coupling to the car body, then the more inductive loading is required in the coil, still with me?
This may seem counter intuitive, however we replace this extra inductance, required by the coil, with the longer shaft, it's entirely possible that your VSWR won't change when you go from a 17" to a 22" shaft, however any change in VSWR is taken care of by adjusting stinger length.
The length of shaft below the coil is more important than the length of stinger above the coil, here's a couple of simple graphics that should help explain why:
Here's the current distribution for a full 1/4WL antenna, notice the curved current profile:
Here's the current distribution for a base loaded antenna, notice how the current drops off sharply from the coil to the tip:
Here's the current distribution for a centre loaded antenna, notice the current distribution remains almost constant up to the top of the coil, then drops off sharply towards the tip:
Ideally we would use a 1/4WL whip for maximum efficiency, a centre loaded whip for near 1/4WL efficiency and reduced length, and a base loaded antenna for convenience.
The reason why the likes of the base loaded Sirio HP antennas work so well is because of their overall length, they rely on minimal inductive loading and a long whip.
I know this is the CB section, however when you look at any high performance HF antennas, they are almost always centre loaded, it's not practical to use full 1/4WL antennas due to their length, however that doesn't stop me mounting 1/4WL antenna to my car for as low as the 40m band, static of course.
Another way to increase efficiency of short loaded antennas is to add capacitance to the tip, but I don't know anyone that would do this on 10/11m, there's no point.
Want to know the complex circuit created by the antenna, the car and the ground, here's a graphic from Les Moxon's book; HF Antennas For All Locations:
Just a for info, the car in the picture is a drawing of a Triumph Dolomite, a classic British saloon car from the 70's, I think most on here would call it a compact
Because the coil efficiency increases, due to less capacitive coupling to the car body, then the more inductive loading is required in the coil, still with me?
This may seem counter intuitive, however we replace this extra inductance, required by the coil, with the longer shaft, it's entirely possible that your VSWR won't change when you go from a 17" to a 22" shaft, however any change in VSWR is taken care of by adjusting stinger length.
The length of shaft below the coil is more important than the length of stinger above the coil, here's a couple of simple graphics that should help explain why:
Here's the current distribution for a full 1/4WL antenna, notice the curved current profile:
Here's the current distribution for a base loaded antenna, notice how the current drops off sharply from the coil to the tip:
Here's the current distribution for a centre loaded antenna, notice the current distribution remains almost constant up to the top of the coil, then drops off sharply towards the tip:
Ideally we would use a 1/4WL whip for maximum efficiency, a centre loaded whip for near 1/4WL efficiency and reduced length, and a base loaded antenna for convenience.
The reason why the likes of the base loaded Sirio HP antennas work so well is because of their overall length, they rely on minimal inductive loading and a long whip.
I know this is the CB section, however when you look at any high performance HF antennas, they are almost always centre loaded, it's not practical to use full 1/4WL antennas due to their length, however that doesn't stop me mounting 1/4WL antenna to my car for as low as the 40m band, static of course.
Another way to increase efficiency of short loaded antennas is to add capacitance to the tip, but I don't know anyone that would do this on 10/11m, there's no point.
Want to know the complex circuit created by the antenna, the car and the ground, here's a graphic from Les Moxon's book; HF Antennas For All Locations:
Just a for info, the car in the picture is a drawing of a Triumph Dolomite, a classic British saloon car from the 70's, I think most on here would call it a compact
Just to add a detail or two to northern35's post.
The higher on the vertical antenna the coil is the larger it needs to be to achieve the same shortening effect. This effect goes up exponentially as you move up the antenna itself, and is especially noticeable as you pass the midway point.
Typically the best place to put a coil on an antenna is as close to the middle of the whip as you can get it.
The DB
The higher on the vertical antenna the coil is the larger it needs to be to achieve the same shortening effect. This effect goes up exponentially as you move up the antenna itself, and is especially noticeable as you pass the midway point.
Typically the best place to put a coil on an antenna is as close to the middle of the whip as you can get it.
The DB
A couple of pictures I should have added at the time:
20m 1/4WL attached to the tow hitch on my car, you can see the need for a shortened antenna.
And a large capacitance hat in use on the 40m band.
I must stress I'm not trying to convert anyone to amateur radio I just mentioned both subjects in my previous reply and thought it important to add a visual reference.
20m 1/4WL attached to the tow hitch on my car, you can see the need for a shortened antenna.
And a large capacitance hat in use on the 40m band.
I must stress I'm not trying to convert anyone to amateur radio
I just mentioned both subjects in my previous reply and thought it important to add a visual reference.If I had the shorter 9 inch section, and just put on the 27 inch, would I expect her to go up and have to trim the whip?
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