Adjustments for resonance

338_MtRushmore said:

f you tuned a typical antenna system for x, then swr dip, then field strength, would any receiving station notice the difference?

Obviously it is a hobby and we tend to strive for perfection, but does it really matter? Am I going to get 20% more power if I tune by field strength? Certainly a valve and bipolar wouldn't have the same gain at their optimum impedance?

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No, you won't notice a difference between any of these points. That is why in the past I have stated that I don't have a problem with people tuning to any of these points.

There are people that tune to the lowest SWR because they think it will make a difference, but there are those that know that as far as an antenna is concerned that an SWR of 2 is acceptable, and you won't notice a difference in performance if SWR is below that and tune for lowest SWR because they see themselves as a perfectionist.

When people get their first antenna analyzer suddenly it becomes X=0. The belief going around is X=0 will always lead to the best antenna performance because "resonance". Its strange to me that no one has actually demonstrated this, yet it is the predominant belief. If this is really the case, why do 5/8 wavelength antenna's not only exist but are touted as the best? They are literally as far away from X=0 as you can possibly get.

Then there is a third group, the one that @333_MtRushmore mentioned as his third stage earlier in this thread. This group has realized that tuning to X=0 doesn't actually benefit them in any noticeable way. Many of this group go back to using SWR.

There are also people like me who switched to using field strength. Why did I do it? It was something I haven't done before and I felt there there was more I could learn. I have since improved said method quite a bit. Yes, I am still being a perfectionist in my own way. That being said, I will also be the first to tell you that you won't notice and real world difference with this method over either of the other two.

Honestly, if their is one concept that I think is holding back the knowledge level of people in the radio hobby, its the 'X=0 means best possible performance' fallacy. This idea gets set in people's minds as absolute fact not to be questioned, yet they have never seen any actual real world evidence of such. This has lead to many misunderstandings of how things actually work in the radio hobby, and gave rise to fierce debates, such as weather an antenna tuner on your desk actually tunes an antenna.


The DB

Nick hatz said:

This is it. Doesn’t explain any of the values or anything. Power of the Internet I’ve been doing and digging and looking. Ordered the AARL.

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Well K0BG is an antenna GURU & I doubt the ARRL Antenna Handbook will tell you anything his website does not.If it were on the Amateur Radio bands he would be more than happy to assist you but he will not assist you with any CB Related issues.He does not have any desires to discuss the 11 meter band & I have no issues with his freedom of choice.Most everyone I know that has a mobile antenna issue goes to him for help & he never fails them.

SIX-SHOOTER

Slowmover,

what was/were your reason/s for avoiding them?

I have always just tried to tune for the lowest point in the SWR curve. Then I double check with another SWR meter. I have yet to spring for an antenna analyzer. I have been lucky anytime I have a vehicle checked with an analyzer then may readjust, but it may be just to make 1,6 to 1.4. I have not ever tried to tune outside CB band. And have had antenna installs with no SWR curve then I realized that something else is wrong and have to recheck my install. I have been trying to keep everything simple.
Then again I run everything barefoot. One thing I have noticed. I had witnessed a lot of professional land mobile installs for 50 or 100watt high band VHF for 155mhz. Never once have I seen a tech with a meter. They just cut the antenna for whatever the instructions say. Most were base loaded Motorola whips to NMO mounts to hood channel.

six-shooter,

some members of the ham community are still holding a grudge for the loss of their novice cw segment in the 11 meter band and the conversion of that band for use in the citizens band radio service.

Borrowed from k0bg in Antenna Matching

freecell said:

Slowmover,

what was/were your reason/s for avoiding them?

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Cabovers? Lousy ride, tiring to climb in and out of several times per day and you’re always first at the scene of the accident.

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fourstringburn said:

A 102 whip isn't 50 ohms, it's around 33 ohms so your analyzer is correct for 11 meters.

Read K0BG's chapter about antenna matching using inductive matching and shunt coils to bring up the antenna feedpoint impedance to 50 ohms on any given frequency within the range of your antenna.

Is this necessary?

If you're a perfectionist or like to experiment and learn, than yes!

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Looks useful in mobile.

MFJ-908 Mobile Impedance Matcher $55.
Or DIY

“Best” resonance, first, lowest SWR, second.
Per k0bg (with MFJ-259) in Antenna Matching.
(Details apply; read).

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Nick hatz said:

I got the whip adjuster and installed it today tuned the antenna to resonance on my frequency I use most.
x=0
Swr 1:1.5
Phase 180 deg
Ohms 34 I know that’s a little low.
This thing screams now.
I really appreciate everyone’s help it’s been a great learning experience. It was worth every ounce of sweat in this Texas heat getting this set up put together.

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Where the OP was satisfied.

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Slowmover said:

Where the OP was satisfied.

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based on the information provided, there is a measurable loss of power output from the fixed 50 ohm transmitter because it is looking into a line with approximately 30-35 ohms of input impedance. this mismatch will be eliminated with the use of a line approximately .640 wl. at the "mystery" operating frequency. this will restore the transmission line input impedance to 50 ohms allowing full output from the transmitter into the line.

The MFJ-908 sounds like the Dollar match with a switch to change inductance to ground,

To raise feedpoint impedance closer to 50ohm I seem to recall that you resonate the antenna then shorten it a bit to make it capacitive & add the right value of inductor to ground ?

or you can do just the opposite since inductors tend to have a lower Q and more loss than a variable capacitor, which can be used to cancel inductive reactance and return to X=0.. (and it's adjustable) lengthening the antenna also increases the radiation resistance of the antenna, which is also a good thing. any increase in the radiation resistance of the antenna improves the radiation efficiency of the antenna.

bob85 said:

The MFJ-908 sounds like the Dollar match with a switch to change inductance to ground,

To raise feedpoint impedance closer to 50ohm I seem to recall that you resonate the antenna then shorten it a bit to make it capacitive & add the right value of inductor to ground ?

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I’m going off of what I read. Applegate says, yeah, okay, but you’re better off with a DIY shunt coil.

Others remark that the shunt coil tends to get out of tune, so to speak, and you’re fiddling with it for mechanical and weather changes.

I’d get the MFJ piece if that’s the case (not a great difference in performance.

MFJ says it must be mounted at 2’ or less.

None of these comments are/were CB-centric.

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SIX-SHOOTER said:

Well K0BG is an antenna GURU & I doubt the ARRL Antenna Handbook will tell you anything his website does not.If it were on the Amateur Radio bands he would be more than happy to assist you but he will not assist you with any CB Related issues.He does not have any desires to discuss the 11 meter band & I have no issues with his freedom of choice.Most everyone I know that has a mobile antenna issue goes to him for help & he never fails them.

SIX-SHOOTER

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just ask him for help with 10 meter antenna systems and then adjust your calculations accordingly.

freecell said:

just ask him for help with 10 meter antenna systems and then adjust your calculations accordingly.

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