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Change in antenna causes change in power?
- Thread starter The Jerk
- Start date
If you really want to bake your noodle, you could add in a 6 to 9 foot jumper of coax between your radio to antenna and see what happens there.
Your wilson and 102" could have different coax lengths each, causing part of the discrepancy you see.
maybe this antenna puts out less harmonicas?
Try using a baloon to connect it, like a 1:1 baloon.
Try using a baloon to connect it, like a 1:1 baloon.
I'd rather have one too, but (unless I was looking at the wrong place) they were around $300. Too much to play around with antennas once every 6 months...maybe one day.
I don't really care how much power I'm throwing (or I would have a different setup besides a 959 driving a straight 4-pill), I'm not into bragging rights for chest beating. I just found it odd that the SWRs stayed the same and the power changed significantly (almost 20 watts in a setup only doing 80 is fairly significant). I get good reports, that's all that really matters.
I'm going to stop by a local shop, have him put an MFJ analyzer on it (hopefully he knows how to work it correctly)...maybe even later today.
Time was mentioned and that is a factor. The Wilson 5000 uses a loading capacitor and coil to make the shortened whip load effectively and the impedance is close to 50 ohms . The 102 inch is a quarter wave and the impedance at the feed point is about 50 ohms. All that electronics in the Wilson makes sort of a bottleneck and throws the timing off and the final tank has to emit more power to to "load" the antenna with out high SWR...
mechanic
mechanic
First I must apologize for not getting to the local shop to check each antenna...he was closed the day I thought about having it done and my ride currently has a slipping clutch (that's what 435hp and 190k will do for you), not to mention I was in Florida last week.
Hopefully I will be hitting up DTB when I take the truck down for the clutch next week. Funny thing is now I'm getting more power out of the 102 than before...right around 80 watts (similar to the Wislon). I have been watching it closely, and it has been steadily increasing since the change, and finally platuea'd right about the same power as the Wilson.
I did shoot some skip, seems to be fine...doing ground plane everyone says it sounds good and that the distance is really good.
Hopefully I will be hitting up DTB when I take the truck down for the clutch next week. Funny thing is now I'm getting more power out of the 102 than before...right around 80 watts (similar to the Wislon). I have been watching it closely, and it has been steadily increasing since the change, and finally platuea'd right about the same power as the Wilson.
I did shoot some skip, seems to be fine...doing ground plane everyone says it sounds good and that the distance is really good.
Sounds like it needs to be a tad longer still. It is a lot harder to make it longer than it is to make it shorter. Does any company make parts to extend this setup a couple of inches?
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I honestly think I'd leave things alone until you can find out more (as in someplace that has an analyzer).
Depending on the particular mount you're using, that 102" whip could certainly be long enough. For instance, a typical ball mount will add about 4" to the whips overall length, a spring about the same. That would make that whip a tad longer than necessary, but like was said, they're a whole lot easier to cut off than add too.
The input impedance depends on the mount and everything around that antenna. You honestly can't know what it is without measuring it. That 25 - 35 ohms thingy is a typical range for a typical 1/4 wave antenna, don't bet your life savings on it being exactly anything. An SWR meter doesn't know squat about what that impedance is composed of (resistance and reactance) so can't really tell you much of what you need to know. (That's what's so nice about those antenna analyzers, they -can- tell you what you need to know. That's also why they ain't cheap. I also don't think everybody needs to go buy one. Bribe me! I'm susceptible to beer!)
Good luck and have fun.
- 'Doc
By the way...
That clutch is a lot nicer than putting the wrong fluid in the braking system. You really don't want to know about that.
Depending on the particular mount you're using, that 102" whip could certainly be long enough. For instance, a typical ball mount will add about 4" to the whips overall length, a spring about the same. That would make that whip a tad longer than necessary, but like was said, they're a whole lot easier to cut off than add too.
The input impedance depends on the mount and everything around that antenna. You honestly can't know what it is without measuring it. That 25 - 35 ohms thingy is a typical range for a typical 1/4 wave antenna, don't bet your life savings on it being exactly anything. An SWR meter doesn't know squat about what that impedance is composed of (resistance and reactance) so can't really tell you much of what you need to know. (That's what's so nice about those antenna analyzers, they -can- tell you what you need to know. That's also why they ain't cheap. I also don't think everybody needs to go buy one. Bribe me! I'm susceptible to beer!)
Good luck and have fun.
- 'Doc
By the way...
That clutch is a lot nicer than putting the wrong fluid in the braking system. You really don't want to know about that.
Why would the length need to change if (without power) I get a flat 1:1 SWR??
I followed a post on here about making a spacer for the 102 to eliminate the spring, and that's what I have done...my spacer is about 6 inches long and provides that 1:1 match...
The coax is new(er) mini-8...
I followed a post on here about making a spacer for the 102 to eliminate the spring, and that's what I have done...my spacer is about 6 inches long and provides that 1:1 match...
The coax is new(er) mini-8...
"Why would the length need to change if (without power) I get a flat 1:1 SWR??"
Because SWR doesn't tell you anything about resonance, or how well an antenna radiates. It can only tell you if the antenna's input impedance -appears- to be 50 ohms. Why "-appears- to be 50 ohms"? Because there are a bunch of times when what that meter 'thinks' is 50 ohms, isn't really 50 ohms, but a combination of some resistance and a reactance (this is all AC, not DC, and why it's called impedance and not just resistance). The biggy is that reactance doesn't produce any power, it doesn't radiate. An SWR meter doesn't know anything about reactance and that's why it can't tell you that there's a difference in radiated power (which that watt meter told you). The watt meter doesn't have to be wrong, that SWR meter -can- be every time. An SWR meter -by it's self- doesn't tell you much that's really useful. I'll bet you can guess what kind of meter -can- tell you what you really need to know...
- 'Doc
Because SWR doesn't tell you anything about resonance, or how well an antenna radiates. It can only tell you if the antenna's input impedance -appears- to be 50 ohms. Why "-appears- to be 50 ohms"? Because there are a bunch of times when what that meter 'thinks' is 50 ohms, isn't really 50 ohms, but a combination of some resistance and a reactance (this is all AC, not DC, and why it's called impedance and not just resistance). The biggy is that reactance doesn't produce any power, it doesn't radiate. An SWR meter doesn't know anything about reactance and that's why it can't tell you that there's a difference in radiated power (which that watt meter told you). The watt meter doesn't have to be wrong, that SWR meter -can- be every time. An SWR meter -by it's self- doesn't tell you much that's really useful. I'll bet you can guess what kind of meter -can- tell you what you really need to know...
- 'Doc
First of all there is no way a 102" steel whip is going to give you a 1.1:1 swr period end of sentence !!! It's more like around 1.4:1 / 1.5:1 is what you should be seeing, Unless your using a antenna tuner between your meter and antenna.
The length of your coax is probably showing you a better swr than what is actual there. You need to calculate the electrical length to get the rite swr reading.
This is the rite way to calculate the electrical length not the physical length,
of the coax.
#1 The coax needs to be 1/2-wavelength or it's multiple 2/2, 3/2, 4/2, 4/2, ect.
#2 You need to know what the coax velocity factor is, for a example RG8/x has a VF of 78, RG8/U -80, RG213/U -66
#3 SO a 1/2-wavelength ( in feet ) = 468 divided/ the freq.(MHz) x the velocity factor say of 0.66
So say 1/2-wavelength of coax at 27 MHz is about 11.44' physical length, when using this length of coax it would be like checking the swr reading at the antenna.
The length of your coax is probably showing you a better swr than what is actual there. You need to calculate the electrical length to get the rite swr reading.
This is the rite way to calculate the electrical length not the physical length,
of the coax.
#1 The coax needs to be 1/2-wavelength or it's multiple 2/2, 3/2, 4/2, 4/2, ect.
#2 You need to know what the coax velocity factor is, for a example RG8/x has a VF of 78, RG8/U -80, RG213/U -66
#3 SO a 1/2-wavelength ( in feet ) = 468 divided/ the freq.(MHz) x the velocity factor say of 0.66
So say 1/2-wavelength of coax at 27 MHz is about 11.44' physical length, when using this length of coax it would be like checking the swr reading at the antenna.
A couple of corrections.
VF of RG-8 is about .66, not .80.
That 468 number is an electrical 1/2 wave at 0.95 VF. use 492 x VF for a closer estimate of an electrical 1/2 wave.
And since all coax is subject to variations in manufacturing, be prepared to do some adjusting to get close to that 'electrical' length of any part of a wave length. It'd sure be nice if you could count on that VF being constant, but you can't.
- 'Doc
VF of RG-8 is about .66, not .80.
That 468 number is an electrical 1/2 wave at 0.95 VF. use 492 x VF for a closer estimate of an electrical 1/2 wave.
And since all coax is subject to variations in manufacturing, be prepared to do some adjusting to get close to that 'electrical' length of any part of a wave length. It'd sure be nice if you could count on that VF being constant, but you can't.
- 'Doc
Again, I have tuned the antenna to the mount, its not just thrown on there and assumed to be 108"...it took me quite a while to adjust the 102 to get a flat 1:1 SWR.
I agree about the length, and will check the coax lengths, as I have had this discussion before. I'm pretty sure its a standard 18 foot length of Mini-8.
I know the local shop has an MFJ analyzer...is this a quality piece or are there others that are as good/better? Can anyone tell me the model number I should search for?
Might as well dive in head first...$1800 for the clutch and throw in an antenna tuner...its only money...
Might as well dive in head first...$1800 for the clutch and throw in an antenna tuner...its only money...