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 Ma5b help 
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Post Ma5b help
After using my ma5b beam this morning i noticed a high swr on 20m after checking 17,15,12 and 10 the rest seem to be fine

I checked the connections dimensions and traps and all seems to be ok

Is there anything else i can check to fix the swr

Running between the ma5b with rg213 and ic 7600

Thanks for any help


Sun Apr 19, 2015 9:01 am
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 Ma5b help 
Silent Key

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Post Re: Ma5b help
The only components that are unique to 20m are those outboard of the 21/28MHz traps on elements #1 and #3, so that would be the obvious place to look. Are all the hat spokes in place and making good contact?

Steve G3TXQ


Sun Apr 19, 2015 11:27 am
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 Ma5b help 
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Post Re: Ma5b help
thanks for reply

ive bn messing with it most of the day changing dimensions on certain elements to the build sizes the 7600 tunes it no bother on the other bands but dosent want to tune on 20

theres no water within the traps as far as I can see can these traps be dismantled to check them out I didn't want to burst the rubbers ?


Sun Apr 19, 2015 1:50 pm
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 Ma5b help 
Silent Key

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If the traps were the problem I think you'd have a high SWR on bands other than 20m.

Steve G3TXQ


Sun Apr 19, 2015 5:14 pm
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 Ma5b help 
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would I be right in saying the 5 bands are tuned via the sleeves on the outside of the traps on elements 1 and 3 ? and you tune on 20m and this swrs the rest?


Sun Apr 19, 2015 5:40 pm
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 Ma5b help 
Silent Key

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Post Re: Ma5b help
20m tuning is achieved by varying the length of the outermost element on #1 and #3. The other bands shouldn't be affected.

But I thought you had a high SWR problem, not a tuning problem?

Steve G3TXQ


Sun Apr 19, 2015 5:52 pm
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 Ma5b help 
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my mistake yes its a high swr 10 / 12 / 15 /17 seem to be ok ive adjusted bits all over the antenna checked sizes to the drawings on the instructions even tried a different radio the 756 pro 3 is the same as the 7600

when I press the tuner function it just goes to red and when u increase the power the swr goes off the scale


Sun Apr 19, 2015 6:17 pm
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 Ma5b help 
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2m0jmn wrote:
my mistake yes its a high swr 10 / 12 / 15 /17 seem to be ok ive adjusted bits all over the antenna checked sizes to the drawings on the instructions even tried a different radio the 756 pro 3 is the same as the 7600

when I press the tuner function it just goes to red and when u increase the power the swr goes off the scale


Couple of things come to mind. The screw connections inside the trap under the grey rubber seals are prone to corrosion. The the plastic inside the traps can get burned if you run high power or a poor SWR. And in my case the taps were full of dead spiders (honest).

A common mistake if SWR is all over the place is one or more traps are the wrong way round.

Len GM0ONX

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Sun Apr 19, 2015 8:56 pm
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 Ma5b help 
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what element does the 20 m band use the whole antenna seems to be working fine bar 20m


Sun Apr 19, 2015 9:19 pm
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 Ma5b help 
Silent Key

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2m0jmn wrote:
what element does the 20 m band use the whole antenna seems to be working fine bar 20m

See Post #2

Steve G3TXQ


Sun Apr 19, 2015 10:19 pm
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 Ma5b help 
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So if the trap was the issue it could be anyone of four on elements 1/3 ?


Mon Apr 20, 2015 5:39 am
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 Ma5b help 
Silent Key

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Any of the 4 traps on elements #1 and #3 will affect 20m; however they will also affect 15m and 10m. If you are confident that nothing has changed on 15m and 10m it's unlikely to be a trap. However, as Sherlock Holmes said: "...... when you have eliminated the impossible, whatever remains, however improbable, must be the truth?"

I guess it's possible that something inside the trap which connects to the outboard 20m tips may have become disconnected, causing a problem on 20m and leaving the other bands intact. I don't think it will be a very conclusive test, but you could check DC continuity between the two sides of each of those 4 traps.

Steve G3TXQ


Mon Apr 20, 2015 7:43 am
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 Ma5b help 
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So if i connect power on the outside of those traps at either tip if the traps ok power will pass thro ok ?


Mon Apr 20, 2015 8:52 am
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 Ma5b help 
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Would the crosshats not at correct angles affect the swr ?


Mon Apr 20, 2015 9:46 am
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 Ma5b help 
Silent Key

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2m0jmn wrote:
So if i connect power on the outside of those traps at either tip if the traps ok power will pass thro ok ?

Don't connect RF - just check the continuity at DC with a multimeter.

The angle of the capacity hat rods wont affect things much; but if one of the rods was not making good contact to the aluminium tubing it could give you the symptoms you're seeing. But I suggested that in Post #2, so I presume you've already checked?

Steve G3TXQ


Mon Apr 20, 2015 11:29 am
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