| Author |
Message |
    
Heavy_chevy
New member
Username: Heavy_chevy
Post Number: 6
Registered: 12-2004
| | Posted on Monday, January 03, 2005 - 6:18 pm: | 
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And does what about those antenna tuners? Can they be used instead of a gamma on a set of beams? I am interested in trying to build my own beams. |
Bruce
Senior Member
Username: Bruce
Post Number: 1979
Registered: 9-2003
| | Posted on Monday, January 03, 2005 - 7:38 pm: |
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Heavy
Even though they... tuners ... do the same thing Gamma and Beta matches are the way to go. Most tuners have several changing ot tunable components while most beta or gamma matchs have only ONE and you dont need any more up their in the rain or snow to change value on you. |
Heavy_chevy
New member
Username: Heavy_chevy
Post Number: 7
Registered: 12-2004
| | Posted on Tuesday, January 04, 2005 - 12:03 am: |
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Is a beta a balun, or something different? I'm a bit confused as to the " up in the air, with the rain & snow". Here's what I was getting at...I wanted to know if I could build a set of, say, 4-element beams, and run coax from the beam to my desk top, to an antenna tuner, to control the match. Make any sense? I'm no tech by any means, just trying to learn, and I like to fabricate. |
Bruce
Senior Member
Username: Bruce
Post Number: 1980
Registered: 9-2003
| | Posted on Tuesday, January 04, 2005 - 4:35 am: |
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the beta match is like balanced gamma matches
http://www.qsl.net/dk7zb/dk7zb-match.htm |
Bruce
Senior Member
Username: Bruce
Post Number: 1981
Registered: 9-2003
| | Posted on Tuesday, January 04, 2005 - 7:39 am: |
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also one more problem would be your coax using the tuner is part of the antenna unless you mount the tuner at the driven elm. |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 151
Registered: 9-2004
| | Posted on Tuesday, January 04, 2005 - 8:56 am: |
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Balun....This is really coiled coax or similar wire wound around a ferrite core usually. It is used to go from a balanced line (like wire) to a unbalanced line (like coax) Very good for WIRE beams. It does normally not transform impedance. A 1-1 Balun means you already should have a 50 ohm wire line ready to convert to a 50 coax feed line. There are 2-1, 4-1, and even 6-1 Baluns availbale but these are inflexible as far as Impedance goes.
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Beta Match...provides adjustable impedance match as well as transformation from balanced to unbalanced mode, generally for impedance matches between 10 - 50 ohms. The Beta match usually involves using a piece of coax as a matching trasformer. It usually involves shorting the shield to the driven element, and adjusting the lenght to get a good match.
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Gamma Match...very similar to the Beta match except usually involves a bar with a capacitor placed parallel to the driven element and a piece of shorting bar between them. This is usually your BEST choice for a aluminum element beam.
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Omega match...very similar to Gamma match with a shorter parallel bar, you move the capacitor instead of the bar as in a Gamma Match.
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Yagi beams can be built to use Baluns with a 1-1 ratio, they will work just fine. However most commercially made antennas use a Gamma/Beta match type because the general public usually puts together their antenna with slightly off measurements, or the antenna was constructed so that it needs a Gamma/Beta match. |
Pig040
Advanced Member
Username: Pig040
Post Number: 622
Registered: 7-2003
| | Posted on Tuesday, January 04, 2005 - 11:37 am: |
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Heavy Chevy, If you dont care about the technical stuff they are all talking about the answer is yes, you can tune almost anything with a good tuner, I have a MFj antenna tuner that will tune anything, up to and including a metal shed!! How the perfomance is as compared to a normal matching system on an antenna, I do not know. I can tune my homeade vertical that is matched on 27mhz to 80 meters without a problem.
Rich |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 152
Registered: 9-2004
| | Posted on Tuesday, January 04, 2005 - 5:37 pm: |
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NO NO NO
Pig040 The above statement does nothing for the antenna. Your antenna tuner is tuning the coax not the antenna! It is making your rig THINK that it is seeing a 50 Ohm load. This does NOT make your antenna resonant. Once your power gets up to the antenna it will still radiate poorly unless it is resonant to the frequency you are trying to use with it.
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Since you are on CB you should make your antenna resonant by using the correct measurements regarding height,lenght etc. Then use a Gamma Match to get a correct 50 Ohm impedance. Then you will not need a antenna tuner, because your antenna is already correct on 27 mhz.
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There is NOTHING you can do from the coax side to make your antenna resonant. |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 153
Registered: 9-2004
| | Posted on Tuesday, January 04, 2005 - 5:44 pm: |
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If you are a Shortwave Listener or a Ham with only 1 antenna, then you will need a Tuner to try and hear and or attempt to get out, because you have many different frequencys to cover with only 1 antenna. This is then the only way the Rig will "SEE" a 50 ohm load, but this is not the best way to try and get heard.
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Yes you can tune your shed out back with a MFJ tuner, but how good do you think it would work as an antenna? |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 154
Registered: 9-2004
| | Posted on Tuesday, January 04, 2005 - 8:46 pm: |
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If you only have 1 antenna, and need to hit multiple bands, like a Ham Op or shortwave listener, than you need a tuner. Because one antenna cannot be resonant on all bands.
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However if you are primarily concerned with CB radio...make the antenna resonant and don't even bother with a tuner. |
Pig040
Advanced Member
Username: Pig040
Post Number: 626
Registered: 7-2003
| | Posted on Wednesday, January 05, 2005 - 9:12 am: |
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Gonzo, I didnt say that a tuner was a panacea for antenna perfection, I said a tuner can tune almost any length antenna to almost any freq. Of course in my opinion in a perfect world we would all have a different antenna for each band, but this is not a perfect world, and an antenna tuner is a compromise.
Rich |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 155
Registered: 9-2004
| | Posted on Wednesday, January 05, 2005 - 11:06 am: |
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I understand, sorry about the double post |
Heavy_chevy
Junior Member
Username: Heavy_chevy
Post Number: 12
Registered: 12-2004
| | Posted on Wednesday, January 05, 2005 - 2:23 pm: |
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If using a tuner instead of a gamma, or balun will make your coax part of the antenna, why doesn't a dipole, or 102 inch whip cause the coax to be part of the antenna? I built a set of 2-element beams, using 2 whips for the front (radiating) element, conecting the coax center to one whip, and the other whip to the sheild, like a dipole. It had about a 1.3 match, and used no gamma, or balun, or anything else to acheive a match. JUst trying to learn. |
Bruce
Senior Member
Username: Bruce
Post Number: 1999
Registered: 9-2003
| | Posted on Thursday, January 06, 2005 - 7:03 am: |
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heavy unless you choke off the coax it IS part of the antenna ill bet your coax was RF hot! |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 156
Registered: 9-2004
| | Posted on Thursday, January 06, 2005 - 11:17 am: |
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"conecting the coax center to one whip, and the other whip to the sheild, like a dipole. It had about a 1.3 match"
Yes thats entirely possible, however as Bruce said, you should choke off the coax, either by winding it into a 8" circle below the antenna, using several coils and then running it, or by using Ferrite Cores
palomar.com
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The major point I think is...You want ALL of your power radiating from the antenna, this means usually using some sort of Gamma/Beta match (for Yagi's) at the antenna AND choking off the coax from radiating.
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Heavy_chevy
Junior Member
Username: Heavy_chevy
Post Number: 13
Registered: 12-2004
| | Posted on Thursday, January 06, 2005 - 2:01 pm: |
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Thanks guys. I'm just trying to learn. I have been on the cb since 1986, but I'm still learning. I built the makeshift 2-element beams, not necessarily to use, but to test an idea. I run a antron 99, but I just bought a imax 2000. I do want to build a set of 3, or 4 element beams, just because I like to build things. Here's a question for you.....would using larger diameter elements, like say, 7/8, or 1-inch radiate a better signal. How about recieve? The would definately be more durable, but heavier. Thanks. |
Bruce
Senior Member
Username: Bruce
Post Number: 2004
Registered: 9-2003
| | Posted on Thursday, January 06, 2005 - 3:05 pm: |
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Larger would have to be shorter now as long as you adjusted the length of the element for the changing diameter you would find very little change. There are limits to size ( DIA ) both ways but they would be so large and so small that you will never even be close to getting there. |
