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Looking to go 10K. Dual or single coil?

"there's no such thing as an antenna with NO reactance....except at resonance."

wrong. you still don't "get it"........even when resonant an antenna still has EQUAL AMOUNTS of BOTH INDUCTIVE and CAPACITIVE REACTANCE. the frequency at which these EQUAL amounts of BOTH TYPES of reactance occurs IS THE FREQUENCY AT WHICH THE ANTENNA IS RESONANT. whenever TWO IDENTICAL VALUES of Xc AND Xl are subtracted from each other regardless of which is subtracted from the other the result = 0. reactance does not only exist in a resonant antenna but it also exists in equal amounts of each. to say that there is "no reactance" in a resonant antenna is absolutely incorrect.
 
freecell,
If/when you find a new 'nit' to pick at, please let me know. This one is really getting to the point of the absurd. If you have $100 dollars in one pocket, and bills amounting to $100 dollars in the other pocket, then you are effectively broke. I don't care what you have in either pocket. Now, do you get that? Don't bother explaining how/why that isn't true, I really couldn't care less. It may be that I'm more conserned with the principal of the thing, you know? Oh crap, don't answer that either!
- 'Doc
 
the word here is principle. you didn't understand it three years ago when it was discussed in rec.radio.amateur.antenna among the likes of Hagen, Lewallen, Harrison, Blanarovich and Moore and if your dollar analogy is any indication you still don't get it. at least Harrison knew what he was talking about. balanced or "zero" reactance and no reactance are two different things entirely. i just hope that my time explaining this here hasn't been totally wasted.
 
( analogy ) think about a half bucket of acid and a half bucket of alkali, when mixed in just the correct quantities they neutralise each other giving ph of around 7 neither acid or alkali but they are both still there in the bucket,

back to the original post " My question is does it really make a damn bit of difference in whether i go w/ single or double coils? I know it affects the overall height but does it ever affect the performance?"

yes it does :!:

some people claim the dual coil outperforms the single and some even claim the single outperforms the straight 1/4wave, some even claim the wilson beats the single coil 10k,
in my own experience this is not the case, i have never tried a loaded mobile antenna that is the equal of a full size 1/4 when stationary though the 27" 10k does on my vehicles come very close and has many phyical advantages in everyday mobile use that cannot be overcome with a straight stick such as weight and stiffness when actually mobile,
i am not saying the full 1/4 is unbeatable i am saying none have done it for me so far

never in our many tests has a wilson even matched either of my 10k's or my coily dx and i would like to know how the antennas were tested to come up with that conclusion because that is almost the funniest claim second only to
"your signal is the same but that antenna is a much louder talker", i guess i just dont get american comedy huh,

mounting position clearly effects how a particular antenna works for the individual and since the only place i would ever consider mounting a mobile antenna is roof centre that will SKEW my opinion of what works best so here goes

stationary
1, full size 1/4
2, 27" 10k single 86"
3, 22" 10k/ 17" coily dx single 82"
4, sirio hp4000 base load ( shunt feed ) 82"
5, wilson 5000 trucker long shaft / 22" 10k dual
6, wilson 5000 base load ( shunt feed )

mobile at 70+mph
1, 27" 10k single
2, 22" 10k single
3, 17" coily dx single
4, full size 1/4
5, wilson 5000 trucker long shaft / 22" 10k dual
6, sirio hp 4000 base load ( shunt feed )
7, wilson 5000 base load ( shunt feed )

This is how things work out for me and i doubt you will get the definitive answer for your particular application without some experimenting.
 
freecell said:
the word here is principle. you didn't understand it three years ago when it was discussed in rec.radio.amateur.antenna among the likes of Hagen, Lewallen, Harrison, Blanarovich and Moore and if your dollar analogy is any indication you still don't get it. at least Harrison knew what he was talking about. balanced or "zero" reactance and no reactance are two different things entirely. i just hope that my time explaining this here hasn't been totally wasted.
Click to expand...

Just don't forget about the vast numbers of "others" that read this info...time not wasted on either side :)

So, is it possible to build an antenna with zero reactance?

Is it possible to measure the capacitive and inductive reactances independantly when both are present?

When my analyzer tells me that I have a net reactance of -100 ohms, how do I separate the terms? Remember, I'm the guy making the fancy Smith charts :)

I'm still mulling over how I can cancel out that teeny weeny bit of inductive reactance (Xl=0.001) on my straight 1/4 wave whip with a capacitor?

Beetle says not to think of adding a lumped capacitance, but eludes to perhaps subtracting some inductance, which might be more practicle. freecell told me that a short radiator will have high capactive reactance (at least in the 102" whip centered on a vehicular model), so I surmise that a long antenna would have a high inductive reactance.
 
bob85 said:
( analogy ) think about a half bucket of acid and a half bucket of alkali, when mixed in just the correct quantities they neutralise each other giving ph of around 7 neither acid or alkali but they are both still there in the bucket,

mobile at 70+mph
Click to expand...

I don't know if that is true, about the acid base scenario either. Perhaps the two react and create new substances, such as plain water and salt?

I'm glad I have not forgotten all my chemistry :)


Definitions of acids and bases
Arrhenius
acid: generates [H+] in solution
base: generates [OH-] in solution
normal Arrhenius equation: acid + base <---> salt + water
example: HCl + NaOH <---> NaCl + H2O

Mobility--I've often wondered what relative difference it really does make to a full 1/4 whip when in motion. I've proved to myself anyway that the SWR changes are just about insignificant. Perhaps the resonant frequency can be found a bit higher than when stationary, so you will have a bit of a mismatch at the resting resonant frequency, but then you are not looking at inductor losses, as you have pointed out exist.

So how would you reconcile those consequences into a positive conclusion for the coiled radiator? Based on SWR alone?
 
bob85,

good analogy. can you edit your antenna listings in your previous post to include the length of the shafts in any of the other antennas (where applicable) that weren't mentioned?

"So, is it possible to build an antenna with zero reactance?"

if by "zero" you are understanding that what is represented is equal amounts of both types of reactance cancelling each other while only leaving the pure resistive component then absolutely. i believe that you have already built one. "I'm still mulling over how I can cancel out that teeny weeny bit of inductive reactance (Xl=0.001)" see my reply to this below.

"Is it possible to measure the capacitive and inductive reactances independantly when both are present?"

an analyzer does that and indicates resonance when X = 0. if there is any "net" reactance one way or the other it's fairly easy to determine whether the "remainder" is inductive or capacitive.

"I'm still mulling over how I can cancel out that teeny weeny bit of inductive reactance (Xl=0.001) on my straight 1/4 wave whip with a capacitor?"

if it were me i wouldn't worry about it. you can safely assume that 1/1000 of a henry doesn't represent much opposition to the flow of an ac signal. THIS IS the nit picking part.

"Beetle says not to think of adding a lumped capacitance, but eludes to perhaps subtracting some inductance, which might be more practicle."

you can subtract inductance by shortening the vertical element. the small amount required might make it almost impossible to clear everything to the right of the decimal point to all .0000. like i said previously, for all intent and purpose the antenna is resonant.

"a short radiator will have high capactive reactance (at least in the 102" whip centered on a vehicular model), so I surmise that a long antenna would have a high inductive reactance.

correct. if the ¼ wl antenna is shorter than what is required for resonance at a particular frequency it is said to be capacitively reactive and visa versa if it is longer. both types of reactance are dependent on capacitance, inductance and frequency, alteration of the length of the radiating element not withstanding.

i want to add something to a statement that i made at the beginning of this thread: whenever TWO IDENTICAL VALUES of Xc AND Xl are subtracted from each other regardless of which is subtracted from the other the result = 0. please note that when the operation of addition is applied to the two identical values utilizing their "signs", - for Xc and + for Xl the result is still 0.
 
c2 i dont use a vswr meter while im driving so i cant comment on how much it alters at highway speeds,

when comparing 2 near identical stationary performers there seems to be a direct relationship between how much the antenna bends in the wind and how stable your signal is while moving,
since its not realistic to use a solid shaft 1/4wave on your car roof and not bend the roof when you clip a bridge or tree then for me its got to be a stainless 1 piece which when compared to the 10k bends way more in the wind at the typical speeds we drive causing the signal to float up and down as the antenna flexes this way and that in the turbulance,

maybe there is some other explanation other than just how much they flex that i am not aware of?.
 
I have the original version of Reflections in front of me. I pulled it out to reference chapter and page where Walt discusses changes in SWR in a mobile environment. In my few minutes flipping through pages, I wasn't able to find it. I'll give it a closer look and when I find it, I'll post it here.
 
im pretty sure its nothing to do with the antennas coupling to conductive things you drive past as all antennas do that but at under 100mph our steel whips and most other antennas are laying back at 90 degrees,
at anything up to 126mph the 27" 10k is perfectly useable,
i always imagined the severe bend would screw up the radiation pattern of a mobile antenna?,
you should see a sirio 4000 hypower magmount at 150mph :shock:

i know i know speed kills :!: and radiating youreself with 2000+w of rf through the rear window with a trunk mount dont do you or the rear seat passengers any good either :)
 

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