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More 5/8 hombrew questions about tuning

C

cjruger

Active Member
Aug 13, 2012
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So antenna is up and im having some trouble with swr. At 2 watts its good 1.2:1 20 watts 1.5:1. And 80 watts and up 1.8:1 no worse than that.
I have a gamma ring for a match. Im considering redoing the match with a coil. I cant get swr any better with length adjustment or the center wire tap location. Im thinking maybe because my tap wire is about 1' long and the gamma ring between tap and end of radiator is 1ft this is adding to the swr problem. Would cutting the matching ring at the tap point and reattaching it to the end of the radiator and shortining the center wire/ tap by going right to end of radiator help?
Is the purpose of ring to make resistance between the center wire and sheild? If so can i remive the excess ring between tap point and radiator and tap at the base of radiator?

Hope this question makes sense to someone
 

do you have a analyzer like the mfj 259B? or find someone with one locally?

if you change to a coil style,, look at pic of the sirio tornado, it has a 22' radiator and is not dc grounded from the coil or radiator element to ground,, just a small coil that taps to the radiator 6-8" from the bottom of the radiator element,,, this antenna tuned in very nice right at 22' long
 

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No analyzer, what do you mean by not dc grounded?. So that coil slides up and down on radiator for adjustment and tge end just goes thru that hole? I might make up something similar
 
it has no adjustment,, it just connects from the center pin of the so239 connector and runs up to where it connects to the mast it is not connected to the ground side of the so239 or the ground plane radiator elements

if you measure resistance/continuity from the center pin of the so239 to the threads it is open circuit

the ring match that you have will measure short circuit from the center pin to the threads on the so239,, just like the maco 5/8 antenna


I don't have the exact dimensions of the matching coil of the sirio,, I should have taken some measurements before I put it up
 
no coil adjustment,, it was pre-set and installed when I got the antenna, no adjustment points for it,, the only adjustment was the length of the antenna, and that is set with the very top section(for what band it is used on),, I did measure from the tip to where the radiatior element goes into the insulated base and it was right at 22' long and probly another 6-8" that are in the insulated base that you cant see that support the radiator
 
So i can go with a coil either attached from center wire to radiator or from ground to radiator and tap center wire in proper place. Seems like a big difference. One way the shield and center wire are completly isolated from each other and the other they are connected with a certain amount of resistance between them? Does ine way match better than the other?
 
And if that coil is as you described, it is a loading coil, not an impedance matching coil as it should be.
- 'Doc
 
I am saying that if that coil is as you described it to be, then it is a loading coil, not an impedance matching coil as found on 5/8 wave antennas. If that means that I'm saying that it was built wrong, then it means it was built wrong -or- the description is incorrect.
There are more than one way to produce the required inductance at the feed point to bring the input impedance to 50 ohms (or close). That loop and shorting bar is one, an inductance to ground is another.
If the antenna is acting correctly then I have to conclude that the description was wrong, wouldn't you?
- 'Doc
 
all I know is what I explained about the coil is correct, and with a dmm the antenna is an open circuit design, and others on this forum and other forums have noted the same when testing the tornado. we know the antenna works so there must be something to this coil design

I would like to know how it works as well,, I haven't been able to find any other info online just others that have done the same continuity test and came up with the same results
 
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camaro1 said:
all I know is what I explained about the coil is correct, and with a dmm the antenna is an open circuit design, and others on this forum and other forums have noted the same when testing the tornado. we know the antenna works so there must be something to this coil design

I would like to know how it works as well,, I haven't been able to find any other info online just others that have done the same continuity test and came up with the same results
Click to expand...

Camaro, I seem to recall we had a discussion in an older thread about this particular antenna sometime in the past, did we not?

I think you were telling us if we checked the continuity, we would find it had an open circuit when testing the feed point shield and center conductor.

Seems I recall that Bob85, posted that he once had an old Avanti Sigma II, and that it likely had a similar design to what the Sirio Tornado has, and that is why it shows an open circuit. I think Bob85 further claimed there was some additional matching device inside the base that provided such a circuit, aside from the exposed coil we see. Am I right?

I also seem to recall that I and a couple of other's questioned your claim, or was that discussion about some other antenna? IMO, I think you got us all to realize that the Tornado is probably different, that you were right...and what you explain is why you see an open circuit when doing your ohm's check.

CJruger and speak for himself, but I think your presenting the idea of the Tornado type coil design to Cj could be confusing the issue for him. I think he is building a standard 5/8 wave with a coil inductor in series with the radiator, and it will likely be showing a short at the feed point and not an open.

I would be a good discussion to talk about what is going on with the Tornado that makes it different, but maybe it needs to be in another thread...so as not to be so confusing for me at least, and maybe for Cj and others.

How say you?
 
So.... Now im confused. I should do the coil in series with radiator and sheild, just like the ring?
 

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