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Message |
    
Creator
Junior Member
Username: Creator
Post Number: 34
Registered: 1-2004
| | Posted on Sunday, February 22, 2004 - 9:10 pm: | 
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Hi,
Was looking into getting an antenna matcher for my future Imax-2000 & came acroos this statement online, please let me know if this is true..
"Antenna Matcher: A device used to compensate for a high standing wave ratio(SWR); contains coils of wire which deceives the radio into thinking the antenna is matched properly.
An antenna matcher, as discribed above, decieves the radio into thinking the antenna is either longer or shorter than it really is. This is done by a set of coils inside the box. By adjusting the tightness of these coils you are changing the way your SWR meter and radio perceive the antenna."
Is this true?
Thanks,
Rob
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Cm3885
Intermediate Member
Username: Cm3885
Post Number: 211
Registered: 12-2003
| | Posted on Sunday, February 22, 2004 - 10:22 pm: |
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Kinda.. Hams use them all the time.. But for CB they are a waste... Only way to get a good SWR is to tune the antenna and feedline to a good SWR and a good ground helps as well..... |
Bigbob
Senior Member
Username: Bigbob
Post Number: 1643
Registered: 12-2001
| | Posted on Sunday, February 22, 2004 - 10:51 pm: |
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All an antenna matcher is is a variable impedance device,radio 50 ohms,antenna who knows? enter the matcher,the antenna can be virtually any impedance and the matcher makes it 50 ohms,from a coathanger to a sheet metal roof,of course a roof may also require a 4 to 1 balun to get a good match.Bigbob |
ELCO Guy. (Unregistered Guest)
Unregistered guest
| | Posted on Monday, February 23, 2004 - 12:06 am: |
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An Antenna Matcher does not change your antenna. The only thing that can change your antenna is to change the antenna (no pun intended).
The antenna matcher only changes what your radio sees as an antenna. In other words your antenna stays the same allowing the rado to see the load that makes it (the radio) happy. The antenna is just as efficient with or without the antenna tuner.
That ELCO Guy |
Ca346
Advanced Member
Username: Ca346
Post Number: 601
Registered: 8-2003
| | Posted on Monday, February 23, 2004 - 12:36 am: |
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Creator:
I agree with the above posts. If your only antenna is the IMAX2000, then you don't need an antenna tuner. Just tune the IMAX when you get it ... by the rings at the base. Now if you add other antennas that are for other bands,(as in Ham Radio) then you might want to think about a tuner. |
Tech833
Moderator
Username: Tech833
Post Number: 566
Registered: 8-2002
| | Posted on Monday, February 23, 2004 - 2:02 am: |
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All a matcher does is change the match from one side of it to the other.
If you have the matcher hooked up between your radio and antenna, then it matches whatever the antenna load is to what makes the radio happy. In this case, 50 ohms, j0. If there is coax between the matcher and the antenna, you still have a mismatch which will distribute standing waves in the cable between the matcher and the antenna. These standing waves (called voltage standing waves) will turn reflected transmitter power into heat. If you mount the matcher right at the antenna, then the voltage standing waves will not exist. That is why the hams use remote tuners at the base of the antenna. |
Pig040
Intermediate Member
Username: Pig040
Post Number: 289
Registered: 7-2003
| | Posted on Monday, February 23, 2004 - 9:57 am: |
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I think the biggest advantage, is it makes your radio happy. So even if something happened to your antenna, and the swr was too high, you wont burn up your radio. My question is do these antenna tuners take wattage away from your power? If you put in say 500 watts, then use an antenna tuner, does it restrict the watts?? |
Bigbob
Senior Member
Username: Bigbob
Post Number: 1645
Registered: 12-2001
| | Posted on Monday, February 23, 2004 - 7:32 pm: |
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The tuner,if rated for output,will restrict very little,but as Tech833 said it is the voltage standing wave ratio at the coax end that will restrict power,actually it does not really restrict power it just turns it to heat in the coax instead of radiating it from antenna.I have a maco matchbox that I used to use to get a flat match on all six bands untill I got my boomer 400,then it started arcing inside because the matchbox is rated at 300 watts and with 75 feet of coax and a 2.5 to 1 mismatch lots of heat.The next step is a 1.5kilowatt matcher,too much money for this kid and a remote matcher,out of the question,so the little matchboxes are fun to play with but if you run serious power forget them.Bigbob |
Ca346
Advanced Member
Username: Ca346
Post Number: 603
Registered: 8-2003
| | Posted on Monday, February 23, 2004 - 7:49 pm: |
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Another thing to consider is LOSS OF POWER. Some meters show forward and reflected power. If your antenna (with NO tuner) meter is showing 100 Watts forward and the SWR is 1.5:1, then on my meter you are losing 15 Watts reflected power. Now admittedly that's not much, but the antenna is only radiating 85 Watts. When you 'tune' the match down to 1:1, you can watch the forward power needle go UP to 100 Watts. |
Mdiver
Junior Member
Username: Mdiver
Post Number: 45
Registered: 11-2003
| | Posted on Tuesday, February 24, 2004 - 9:33 am: |
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The other day I was talking from Nothern California to Texas I ask for a radio check,before and after I unhooked my Ant.Tuner..with the tuner unhooked I gained 1 on his end..
In a post above Hams use them all the time WHY is it for the same reasons as posted. |
Creator
Junior Member
Username: Creator
Post Number: 36
Registered: 1-2004
| | Posted on Tuesday, February 24, 2004 - 12:39 pm: |
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I wonder if you did the same test for a low pass filter, if it would have the same results.. |
Bruce
Senior Member
Username: Bruce
Post Number: 1018
Registered: 9-2003
| | Posted on Tuesday, February 24, 2004 - 2:59 pm: |
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I use a MFJ tuner it does exactly what it was intended to..... If the SWR is realy high it loses power but tricks the radio into being happy with the antenna. Bottom line when all else fails use one. |
Bobs (Unregistered Guest)
Unregistered guest
| | Posted on Tuesday, February 24, 2004 - 6:02 pm: |
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You loose very little by using an antenna tuner. You are doing the same thing that matching networks built into the antennas do,only at the other end of the coax. The above is true if 2 conditions are met.
1.Your coax is heavy enough to handle the high voltages and currents that will be present on it with high swr.
2.Your coax has very low loss.
If number 1 is not met your coax may burn up or be damaged and if number 2 is not met any reflected power will be lost the same way transmitted power is lost in coax. But if both conditions are met any reflected power will be rereflected back at the antenna and reraidiated. It will not be lost. So if you use good low loss coax there is virtually no difference which end of the coax you match at. I'm sure some will diagree so you can check my source for this info. The ARRL publishes a book called Reflections. It is written by an antenna engineer and he spends several chapters on the subject of swr.If you like antennas this is a must read book.
Bob |
Tech833
Moderator
Username: Tech833
Post Number: 567
Registered: 8-2002
| | Posted on Saturday, February 28, 2004 - 1:57 am: |
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Quote: "if both conditions are met any reflected power will be rereflected back at the antenna and reraidiated. "
This is not true as unless the length of coax from the voltage reflection node to the antenan feedpoint is a multiple of a wavelength x velocity factor, it will be out of phase and will cancel out forward power. It will not radiate, it WILL be lost.
Just because ARRL prints it does not make it true. ARRL publications have been found to contain serious errors many times. |
Phineas
Junior Member
Username: Phineas
Post Number: 15
Registered: 4-2002
| | Posted on Saturday, February 28, 2004 - 10:27 am: |
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A resonant antenna will be resonant no matter what is happening on the feed line. The issue with matching is transfer of power. There are good antennas that do not have 50 ohms impedence at the feedline. Example
Long wires
1/2 and 5/8 waves(Like the IMAX2000)
Loops
Quads
Etc...
All of these antennas will not be 50 ohms at the feed point. If you notice, there are matching networks at the feed point of these antennas. Just because they dont match does not mean they dont work. There are 2 types of tuners.
High voltage, and line matching
High voltage tuners are setup to deal with the higher voltages present at the feed point of the antenna. Think of these as a substitute for the built in matching network. If used properly, these will give you the maximum transfer of power to your antenna with the lowest loss. High voltage tuners will also have a higher tuning range. You can use these as a line tuner, but you get stubstancial lose!
Line tuners are made to match the feed line. This makes just makes the radio happy, however the effects of a mismatch are still present on the antenna side. This is not a big deal when you are dealing with an antenna that is 2:1 or 3:1 but anything more, less than 50% of your power is getting to the antenna. The only exception is when the feed line is something like 450ohm ladder line, which really is part of the antenna itself.
As far as the COAX myth, I have found that the only time the length of Coax is a factor is when you have Common Mode issues(RF Feedback On the Sheild of the COAX). This is very common in automobile installations. RF chokes solve this problem quite nicely. This was not a problem until I started talking on different bands with the same feedline, and finally had to improve my antenna grounding system, and RF choke the feed lines. There are many ways to do this, but that is another thread.
Phineas |
Tech833
Moderator
Username: Tech833
Post Number: 575
Registered: 8-2002
| | Posted on Wednesday, March 03, 2004 - 8:45 pm: |
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Resonance means that there is no mismatch, and that the reactance is neither reactive or capacitive, the fields being zero at the transmitter or cable connection point. How could there be any need to tune a resonant antenna? There would be no standing wave in the cable of a resonant antenna.
" High voltage tuners are setup to deal with the higher voltages present at the feed point of the antenna. Think of these as a substitute for the built in matching network. If used properly, these will give you the maximum transfer of power to your antenna with the lowest loss. High voltage tuners will also have a higher tuning range. You can use these as a line tuner, but you get stubstancial lose! "
Who says the antenna feedpoint is always going to be the voltage node? On a 1/4 wave vertical, the base is the current node. The voltage is at the top. On a 1/2 wave, the base is a voltage node, but if you feed it from the center, it will be fed at the current node. No voltage there either.
"Line tuners are made to match the feed line. This makes just makes the radio happy, however the effects of a mismatch are still present on the antenna side. This is not a big deal when you are dealing with an antenna that is 2:1 or 3:1 but anything more, less than 50% of your power is getting to the antenna. The only exception is when the feed line is something like 450ohm ladder line, which really is part of the antenna itself. "
The first part of this is true. Reflected power between the tuner and antenna is lost as heat in the feedline and phase cancellation. The second part is untrue. 450 ladder line is not part of the antenna. Balanced line is naturally decoupled from the antenna by physics itself. There is no current or voltage or vector difference between the conductors of balanced feedline. In 450 balanced feedline, the RF current flows along the conductors rather than radiate from them. Not until the antenna does RF begin to build the crossed magnetic and electrical fields needed to radiate the RF over a distance. |
Phineas
Junior Member
Username: Phineas
Post Number: 17
Registered: 4-2002
| | Posted on Thursday, March 04, 2004 - 11:43 pm: |
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Tech833
"Resonance means that there is no mismatch, and that the reactance is neither reactive or capacitive, the fields being zero at the transmitter or cable connection point. How could there be any need to tune a resonant antenna? There would be no standing wave in the cable of a resonant antenna."
This is true, that is what a matching network is for. To say the an antenna is not a good antenna because it does not match the impedence of the radio output would be false. I will put a full wave wire with a matching network up against a 1/4 wave anyday of the week. Even thought the full wave length wire is not 50 ohms at the feed point, does not mean it is cannot resonate on a given frequency. Resonance is just a condition a TUNED circuit.
"Who says the antenna feedpoint is always going to be the voltage node? On a 1/4 wave vertical, the base is the current node. The voltage is at the top. On a 1/2 wave, the base is a voltage node, but if you feed it from the center, it will be fed at the current node. No voltage there either."
I never said anything about high voltage being at the feed point of EVERY antenna. What I did say was high voltage tuners have a higher range, and perform very well at the feed point of the antenna. These tuners are also geared up for a wider range of impedence.
"The second part is untrue. 450 ladder line is not part of the antenna. Balanced line is naturally decoupled from the antenna by physics itself. There is no current or voltage or vector difference between the conductors of balanced feedline. In 450 balanced feedline, the RF current flows along the conductors rather than radiate from them. Not until the antenna does RF begin to build the crossed magnetic and electrical fields needed to radiate the RF over a distance."
Well, from my experience with ladder line, I would have to disagree(Respectfully of course). Clip the elements off a G5RV, and it will still work. Just all depends what band you are on.
Phineas
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Ozzie
Intermediate Member
Username: Ozzie
Post Number: 115
Registered: 11-2003
| | Posted on Friday, March 05, 2004 - 9:13 am: |
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Phineas,
As far as coax not having much of an affect, I know of several antennas that are multi-band by using switched lengths of coax and or open line in order to present a better match at the radio |
Tech833
Moderator
Username: Tech833
Post Number: 581
Registered: 8-2002
| | Posted on Wednesday, March 10, 2004 - 9:07 pm: |
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Phineas,
I have not played with a G5RV much. Too frustrating. I may know why yours will radiate while disconnected, they are inefficient to begin with.
Anything will load up with the proper network. The difference between a full wave or 1/4 wave antenna becomes one of radiation pattern and angle once proper matching is met. Matching is the act of delivering the proper current and voltage ratio to the antenna element. That includes vector compensation in the formula for efficiency. |
Mr_rf
Intermediate Member
Username: Mr_rf
Post Number: 279
Registered: 12-2001
| | Posted on Wednesday, March 10, 2004 - 11:14 pm: |
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FYI...
"Resonance" and "match" refer to two totally different issues.
- Resonance occurs when the impedence of the radiating portion of an antenna equals the impedence of the atmosphere around earth, which is approximately 277 ohms, and this is where the maximum transfer of energy will occur between the antenna and the atmosphere.
- "Match" is achieved when the impedence of the radiating portion of the antenna equals the impedence of the radio and/or transmission cable, thus acheiving maximum transfer of energy between the RF device and the antenna.
277 ohm resonance naturally occurs at the feedpoint of a 1/2 wave antennas. A "matching network" is used to maintain VSWR characteristics between the antenna and RF devices, hense, even 1/2 wave antennas need a matching network sincee most radios have a 50 ohm feedpoint impedence. Gamma matches, delta matches, L-C networks, stubs, matching transformers, etc. are all methods of matching the radiating portion of antennas to the feedline and earth's atmosphere.
Antenna tuners ("matchers") only fool the transceiver, and in severe mismatch conditions all you're doing in most cases is loading up the feedline which creates a whole new set of issues with harmonics, RF safety, etc. Bottom line, when the match doesn't occur at the point the radiating portion of the antenna connects to the feedline, then loss occurs...and loss = heat = burned up investments if too much power is applied to the "matched" mismatch! |
Tech833
Moderator
Username: Tech833
Post Number: 586
Registered: 8-2002
| | Posted on Thursday, March 11, 2004 - 12:54 pm: |
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I will try to help you.
""Resonance" and "match" refer to two totally different issues. "
*** Yes they are. See below.
"- Resonance occurs when the impedence of the radiating portion of an antenna equals the impedence of the atmosphere around earth, which is approximately 277 ohms, and this is where the maximum transfer of energy will occur between the antenna and the atmosphere. "
*** You are incorrect. Resonance is when reactance is at zero. Simplified: A length of wire is resonant as an antenna the same as for music, like on a piano. The feedpoint is the point where the string is 'plucked'. The finger that does the plucking is the current from the transmitter. The frequency the string vibrates is the resonant frequency. It works exactly the same for RF.
*** I have never heard this 277 ohm thing before. Who told you that? This is incorrect as well.
"277 ohm resonance naturally occurs at the feedpoint of a 1/2 wave antennas"
*** What? Where? If you end feed a 1/2 wave element, the feedpoint will be around 1,000 ohms. If you center feed a half wave element, it is around 70 ohms. You have been given bad information.
"Gamma matches, delta matches, L-C networks, stubs, matching transformers, etc. are all methods of matching the radiating portion of antennas to the feedline and earth's atmosphere. "
*** The first part of your sentence is correct, they are all forms of matchers. The second part is incorrect. It has NOTHING to do with matching to the Earth's atmosphere. This sounds like you are pulling my leg and I am apparently falling for it. |
Mr_rf
Intermediate Member
Username: Mr_rf
Post Number: 282
Registered: 12-2001
| | Posted on Thursday, March 11, 2004 - 11:23 pm: |
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Tech 833...
No, I'm not pulling legs. Simple logic: For an object to be able to pass AC electrical currents means there must be an associated impedence value for the object in question, right?
Therefore one must assume for the atmosphere to be able to pass electrical currents it must have an impedence value, right?
I don't have a lot of time to go into the deep theory but I searched a little to find yo references on the internet to this concept. Go here and search for 277 ohms in the text on this webpage and you will see the 277 ohm vaule referenced: http://home.netcom.com/~sbyers11/grav11k.htm
FYI... even man-made vacuums has a assigned value... 376.730313461 ohms. Go here and search "vacuum"...should be the second use of the word in the document: http://physics.nist.gov/cuu/Constants/Table/allascii.txt
That characteristic impedence that everyone talks about the feedpoint of antennas having is all referenced to the "impedence value you need to present to the point along the radiator that you are calling the feedpoint," usually one end of a certain length of radiating material. That value is the "feedpoint" value required for the antenna to load up in a world of 277 ohm atmospheric impedence!
Hope this isn't too deep to understand...everything has an impedence! |
Bigbob
Senior Member
Username: Bigbob
Post Number: 1734
Registered: 12-2001
| | Posted on Friday, March 12, 2004 - 5:49 am: |
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My boss assigns a very high impedance to me,on occasion,he hates impedance,but my radio loves it. |
Pig040
Intermediate Member
Username: Pig040
Post Number: 327
Registered: 7-2003
| | Posted on Friday, March 12, 2004 - 8:58 am: |
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The 277 Ohm thing is right, I read it while I was studying for the ham test. I dont understand it, but the book said it. |
Tech833
Moderator
Username: Tech833
Post Number: 589
Registered: 8-2002
| | Posted on Tuesday, March 16, 2004 - 1:28 pm: |
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I will respectfully bow out of this discussion since, apparently, actual RF physics is being rewritten by Art Bell fans.
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Creator
Member
Username: Creator
Post Number: 58
Registered: 1-2004
| | Posted on Tuesday, March 16, 2004 - 5:18 pm: |
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If the matcher is in line to protect the radio, and it works (makes SWR flat), then your getting your money's worth. Regardless if it deceives or not, right? even if your really not improving your output.. |
